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Encyclopedia > Black hole
Simulated view of a black hole in front of the Milky Way. The hole has 10 solar masses and is viewed from a distance of 600 km. An acceleration of about 400 million g is necessary to sustain this distance constantly.[1]
 General relativity $G_{mu nu} = {8pi Gover c^4} T_{mu nu},$ Key topics Introduction to... Mathematical formulation of... Fundamental concepts Special relativity Equivalence principle World line · Riemannian geometry Phenomena Kepler problem · Lenses · Waves Frame-dragging · Geodetic effect Event horizon · Singularity Black hole A black hole is an object with sufficient density that the force of gravity prevents anything from escaping from it except through quantum tunneling behavior. ... Image File history File links Download high resolution version (2560x2048, 1172 KB) Summary Description: A Black Hole of ten solar masses as seen from a distance of 600km with the Milky Way in the background (horizontal camera opening angle: 90Â°) Source: Gallery of Tempolimit Lichtgeschwindigkeit Date: 14. ... Image File history File links Download high resolution version (2560x2048, 1172 KB) Summary Description: A Black Hole of ten solar masses as seen from a distance of 600km with the Milky Way in the background (horizontal camera opening angle: 90Â°) Source: Gallery of Tempolimit Lichtgeschwindigkeit Date: 14. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... Newtonâ€™s conception and quantification of gravitation held until the beginning of the 20th century, when Albert Einstein extended the special relativity to form the general relativity (GR) theory. ... For a less technical introduction to this topic, please see Introduction to mathematics of general relativity. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... In physics, the world line of an object is the unique path of that object as it travels through 4-dimensional spacetime. ... In differential geometry, Riemannian geometry is the study of smooth manifolds with Riemannian metrics, i. ... In general relativity, the Kepler problem involves solving for the motion of a particle of negligible mass in the external gravitational field of another body of mass M. This gravitational field is described by the Schwarzschild solution to the vacuum Einstein equations of general relativity, and particle motion is described... This article or section is in need of attention from an expert on the subject. ... In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ... According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ... The geodetic effect represents the effect of the curvature of spacetime, predicted by general relativity, on a spinning, moving body. ... For the science fiction film, see Event Horizon (film). ... A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ... Equations Linearized Gravity Post-Newtonian formalism Einstein field equations Advanced theories Kaluza-Klein Quantum gravity Solutions Schwarzschild Reissner-Nordström · Gödel Kerr · Kerr-Newman Kasner · Milne · Robertson-Walker It has been suggested that Weak-field approximation be merged into this article or section. ... The parameterized post-Newtonian formalism or PPN formalism is a tool used to compare classical theories of gravitation in the limit most important for everyday gravitational experiments: the limit in which the gravitational field is weak and generated by objects moving slowly compared to the speed of light. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ... This article does not cite any references or sources. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In physics and astronomy, a Reissner-NordstrÃ¶m black hole, discovered by Gunnar NordstrÃ¶m and Hans Reissner, is a black hole that carries electric charge , no angular momentum, and mass . ... The GÃ¶del solution is an exact solution of the Einstein field equation in which the stress-energy tensor contains two terms, the first representing the matter density of a homogeneous distribution of swirling dust particles, and the second associated with a nonzero cosmological constant (see lambdavacuum solution). ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... The Kerr-Newman metric is a solution of Einsteins general relativity field equation that describes the spacetime geometry around a charged (), rotating () black hole of mass m. ... The Kasner metric is an exact solution to Einsteins theory of general relativity. ... Milnes model follows the description from special relativity of an observable universes spacetime diagram containing past and future light cones along with elsewhere in spacetime. ... // The Friedmann-LemaÃ®tre-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... Scientists Einstein · Minkowski · Eddington Lemaître · Schwarzschild Robertson · Kerr · Friedman Chandrasekhar · Hawking · others â€œEinsteinâ€ redirects here. ... Hermann Minkowski. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... Father Georges-Henri LemaÃ®tre (July 17, 1894 â€“ June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer. ... Karl Schwarzschild (October 9, 1873 - May 11, 1916) was a noted German Jewish physicist and astronomer, father of astrophysicist Martin Schwarzschild. ... Howard Percy Robertson (January 27, 1903 - August 26, 1961) was a scientist known for contributions related to cosmology and the uncertainty principle. ... Roy Patrick Kerr (1934- ) is a New Zealand born mathematician who is best known for discovering the famous Kerr vacuum, an exact solution to the Einstein field equation of general relativity, which models the gravitational field outside an uncharged rotating massive object, or even a rotating black hole. ... Alexander Alexandrovich Friedman or Friedmann (ÐÐ»ÐµÐºÑÐ°Ð½Ð´Ñ€ ÐÐ»ÐµÐºÑÐ°Ð½Ð´Ñ€Ð¾Ð²Ð¸Ñ‡ Ð¤Ñ€Ð¸Ð´Ð¼Ð°Ð½) (June 16, 1888 â€“ September 16, 1925) was a Russian cosmologist and mathematician. ... Chandrasekhar redirects here. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... This is a partial list of persons who have made major contributions to the development of standard mainstream general relativity. ... This box: view • talk • edit

A black hole is a region of space whose gravitational field is so powerful that nothing can escape it once it has fallen past a certain point, called the event horizon. The name comes from the fact that even electromagnetic radiation (i.e. light) is unable to escape, rendering the interior invisible. However, black holes can be detected if they interact with matter outside the event horizon, for example by drawing in gas from an orbiting star. The gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation in the process.[2][3][4] A gravitational field is a model used within physics to explain how gravity exists in the universe. ... For the science fiction film, see Event Horizon (film). ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... This article does not cite any references or sources. ... Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ...

While the idea of an object with gravity strong enough to prevent light from escaping was proposed in the 18th century, black holes as presently understood are described by Einstein's theory of general relativity, developed in 1916. This theory predicts that when a large enough amount of mass is present within a sufficiently small region of space, all paths through space are warped inwards towards the center of the volume, forcing all matter and radiation to fall inwardly. Gravity is a force of attraction that acts between bodies that have mass. ... Einstein redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... This article or section is in need of attention from an expert on the subject. ... The hoop conjecture was proposed by Kip Thorne in 1972. ... In physics, the world line of an object is the unique path of that object as it travels through 4-dimensional spacetime. ...

While general relativity describes a black hole as a region of empty space with a pointlike singularity at the center and an event horizon at the outer edge, the description changes when the effects of quantum mechanics are taken into account. Research on this subject indicates that, rather than holding captured matter forever, black holes slowly leak a form of thermal energy called Hawking radiation.[5][6][7] However, the final, correct description of black holes, requiring a theory of quantum gravity, is unknown. A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ... Fig. ... In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ... This article does not cite any references or sources. ...

## Sizes of black holes

Black holes can have any mass. Since gravity increases in inverse proportion to volume, any quantity of matter that is sufficiently compressed will become a black hole. However, when black holes form naturally, only a few mass ranges are realistic. This article is about matter in physics and chemistry. ...

Black holes can be divided into several size categories:

• Supermassive black holes that contain millions to billions of times the mass of the sun are believed to exist in the center of most galaxies, including our own Milky Way.
• Intermediate-mass black holes, whose size is measured in thousands of solar masses, may exist. Intermediate-mass black holes have been proposed as a possible power source for ultra-luminous X ray sources.
• Stellar-mass black holes have masses ranging from about 1.5-3.0 solar masses (the Tolman-Oppenheimer-Volkoff limit) to 15 solar masses. These black holes are created by the collapse of individual stars. Stars above about 20 solar masses may collapse to form black holes; the cores of lighter stars form neutron stars or white dwarf stars. In all cases some of the star's material is lost (blown away during the red giant stage for stars that turn into white dwarfs, or lost in a supernova explosion for stars that turn into neutron stars or black holes). NB: Supernovae Can Only Occur With Red Supergiants
• Micro black holes, which have masses at which the effects of quantum mechanics are expected to become very important. This is usually assumed to be near the Planck mass. Alternatively, the term micro black hole or mini black hole may refer to any black hole with mass much less than that of a star. Black holes of this type have been proposed to have formed during the Big Bang (primordial black holes), but no such holes have been detected as of 2007.

Micro black holes might be produced by:

• The Big Bang, which produced pressures far larger than that of a supernova and therefore sufficient to produce primordial black holes without needing the powerful gravity fields of collapsing large stars.
• High-energy particle accelerators such as the Large Hadron Collider (LHC), if certain non-standard assumptions are correct (typically, an assumption of large extra dimensions). However, any black holes produced in such a manner will evaporate practically instantaneously, thus posing no danger to Earth.

## What makes it impossible to escape from black holes?

General relativity describes mass as changing the shape of spacetime, and the shape of spacetime as describing how matter moves through space. For objects much less dense than black holes, this results in something similar to Newton's laws of gravity: objects with mass attract each other, but it's possible to define an escape velocity which allows a test object to leave the gravitational field of any large object. For objects as dense as black holes, this stops being the case. The effort required to leave the hole becomes infinite, with no escape velocity defined. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... This article or section is in need of attention from an expert on the subject. ... For other uses of this term, see Spacetime (disambiguation). ... Isaac Newtons theory of universal gravitation (part of classical mechanics) states the following: Every single point mass attracts every other point mass by a force pointing along the line combining the two. ... Space Shuttle Atlantis launches on mission STS-71. ...

There are several ways of describing the situation that causes escape to be impossible. The difference between these descriptions is how space and time coordinates are drawn on spacetime (the choice of coordinates depends on the choice of observation point and on additional definitions used). One common description, based on the Schwarzschild description of black holes, is to consider the time axis in spacetime to point inwards towards the center of the black hole once the horizon is crossed.[8] Under these conditions, falling further into the hole is as inevitable as moving forward in time. A related description is to consider the future light cone of a test object near the hole (all possible paths the object or anything emitted by it could take, limited by the speed of light). As the object approaches the event horizon at the boundary of the black hole, the future light cone tilts inwards towards the horizon. When the test object passes the horizon, the cone tilts completely inward, and all possible paths lead into the hole.[9] Space has been an interest for philosophers and scientists for much of human history. ... A pocket watch, a device used to tell time Look up time in Wiktionary, the free dictionary. ... For other uses of this term, see Spacetime (disambiguation). ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In special relativity, a light cone is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. ... â€œLightspeedâ€ redirects here. ... For the science fiction film, see Event Horizon (film). ...

## Do black holes have "no hair"?

Main article: No hair theorem

The "No hair" theorem states that black holes have only 3 independent internal properties: mass, angular momentum and electric charge. It is impossible to tell the difference between a black hole formed from a highly compressed mass of normal matter and one formed from, say, a highly compressed mass of anti-matter, in other words, any information about infalling matter or energy is destroyed. This is the black hole information paradox. In astrophysics, the no-hair theorem states that black holes are completely characterized only by three externally observable parameters: mass, electrical charge, and angular momentum. ... In astrophysics, the no-hair theorem states that black holes are completely characterized only by three externally observable parameters: mass, electrical charge, and angular momentum. ... This gyroscope remains upright while spinning due to its angular momentum. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Antimatter is matter that is composed of the antiparticles of those that constitute normal matter. ... This article or section cites very few or no references or sources. ...

The theorem only works in some of the types of universe which the equations of general relativity allow, but this includes four-dimensional spacetimes with a zero or positive cosmological constant, which describes our universe at the classical level. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Î›) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... Classical Physics refers to the ideas and laws developed before Relativity and Quantum Theory. ...

## Types of black holes

Despite the uncertainty about whether the "No Hair" theorem applies to our universe, astrophysicists currently classify black holes according to their angular momentum (non-zero angular momentum means the black hole is rotating) and electric charge: This gyroscope remains upright while spinning due to its angular momentum. ... Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ...

 Non-rotating Rotating Uncharged Schwarzschild Kerr Charged Reissner-Nordström Kerr-Newman

(All black holes have non-zero mass, so mass cannot be used for this type of "yes" / "no" classification) It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... In physics and astronomy, a Reissner-NordstrÃ¶m black hole, discovered by Gunnar NordstrÃ¶m and Hans Reissner, is a black hole that carries electric charge , no angular momentum, and mass . ... The Kerr-Newman metric is a solution of Einsteins general relativity field equation that describes the spacetime geometry around a charged (), rotating () black hole of mass m. ...

Physicists do not expect that black holes with a significant electric charge will be formed in nature, because the electromagnetic repulsion which resists the compression of an electrically charged mass is about 40 orders of magnitude greater (about 1040 times greater) than the gravitational attraction which compresses the mass. So this article does not cover charged black holes in detail, but the Reissner-Nordström black hole and Kerr-Newman metric articles provide more information. Coulombs torsion balance In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrostatic force that one stationary, electrically charged object of small dimensions (ideally, a point source) exerts on another. ... In physics and astronomy, a Reissner-NordstrÃ¶m black hole, discovered by Gunnar NordstrÃ¶m and Hans Reissner, is a black hole that carries mass , electric charge , and no angular momentum. ... The Kerr-Newman metric is a solution of Einsteins general relativity field equation that describes the spacetime geometry around a charged (), rotating () black hole of mass m. ...

On the other hand astrophysicists expect that almost all black holes will rotate, because the stars from which they are formed rotate. In fact most black holes are expected to spin very rapidly, because they retain most of the angular momentum of the stars from which they were formed but concentrated into a much smaller radius. The same laws of angular momentum make skaters spin faster if they pull their arms closer to their bodies. This gyroscope remains upright while spinning due to its angular momentum. ...

This article describes non-rotating, uncharged black holes first, because they are the simplest type.

## Major features of non-rotating, uncharged black holes

### Event horizon

This is the boundary of the region from which not even light can escape. An observer at a safe distance would see a dull black sphere if the black hole was in a pure vacuum but in front of a light background such as a bright nebula. The event horizon is not a solid surface, and does not obstruct or slow down matter or radiation which is traveling towards the region within the event horizon. Look up Vacuum in Wiktionary, the free dictionary. ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... For the science fiction film, see Event Horizon (film). ...

The event horizon is the defining feature of a black hole - it is black because no light or other radiation can escape from inside it. So the event horizon hides whatever happens inside it and we can only calculate what happens by using the best theory available, which at present is general relativity. For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ...

The gravitational field outside the event horizon is identical to the field produced by any other spherically symmetric object of the same mass. The popular conception of black holes as "sucking" things in is false: objects can maintain an orbit around black holes indefinitely provided they stay outside the photon sphere. (described below)

### Singularity at a single point

According to general relativity, a black hole's mass is entirely compressed into a region with zero volume, which means its density and gravitational pull are infinite, and so is the curvature of space-time which it causes. These infinite values cause most physical equations, including those of general relativity, to stop working at the center of a black hole. So physicists call the zero-volume, infinitely dense region at the center of a black hole a "singularity". The infinity symbol âˆž in several typefaces. ... A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ...

The singularity in a non-rotating, uncharged black hole is a point, in other words it has zero length, width and height.

But there is an important uncertainty about this description: quantum mechanics is as well-supported by mathematics and experimental evidence as general relativity, and does not allow objects to have zero size - so quantum mechanics says the center of a black hole is not a singularity but just a very large mass compressed into the smallest possible volume. At present we have no well-established theory which combines quantum mechanics and general relativity; and the most promising candidate, string theory, also does not allow objects to have zero size. Fig. ... This article or section is in need of attention from an expert on the subject. ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point...

The rest of this article will follow the predictions of general relativity, because quantum mechanics deals with very small-scale (sub-atomic) phenomena and general relativity is the best theory we have at present for explaining large-scale phenomena such as the behavior of masses similar to or larger than stars.

### A photon sphere

A non-rotating black hole's photon sphere is a spherical boundary of zero thickness such that photons moving along tangents to the sphere will be trapped in a circular orbit. For non-rotating black holes, the photon sphere has a radius 1.5 times larger than the radius of the event horizon. No photon is likely to stay in this orbit for long, for two reasons. First, it is likely to interact with any infalling matter in the vicinity (being absorbed or scattered). Second, the orbit is dynamically unstable; small deviations from a perfectly circular path will grow into larger deviations very quickly, causing the photon to either escape or fall into the hole. A photon sphere is a spherical region of space surrounding extremely massive objects such as black holes. ... For other uses, see tangent (disambiguation). ... Instability in systems is generally characterized by some of the outputs or internal states growing without bounds. ...

Other extremely compact objects such as neutron stars can also have photon spheres.[10] This follows from the fact that light "captured" by a photon sphere does not pass within the radius that would form the event horizon if the object were a black hole of the same mass, and therefore its behavior does not depend on the presence of an event horizon. This article is about the celestial body. ... The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. ...

### Accretion disk

Space is not a pure vacuum - even interstellar space contains a few atoms of hydrogen per cubic centimeter.[11] The powerful gravity field of a black hole pulls this towards and then into the black hole. The gas nearest the event horizon forms a disk and, at this short range, the black hole's gravity is strong enough to compress the gas to a relatively high density. The pressure, friction and other mechanisms within the disk generate enormous energy - in fact they convert matter to energy more efficiently than the nuclear fusion processes that power stars. As a result, the disk glows very brightly, although disks around black holes radiate mainly X-rays rather than visible light. Look up Vacuum in Wiktionary, the free dictionary. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...

Accretion disks are not proof of the presence of black holes, because other massive, ultra-dense objects such as neutron stars and white dwarfs cause accretion disks to form and to behave in the same ways as those around black holes. This article is about the celestial body. ... A white dwarf is an astronomical object which is produced when a low to medium mass star dies. ...

## Major features of rotating black holes

Main article: Rotating black hole
Two important surfaces around a rotating black hole. The inner sphere is the static limit (the event horizon). It is the inner boundary of a region called the ergosphere. The oval-shaped surface, touching the event horizon at the poles, is the outer boundary of the ergosphere. Within the ergosphere a particle is forced (dragging of space and time) to rotate and may gain energy at the cost of the rotational energy of the black hole (Penrose process).

Rotating black holes share many of the features of non-rotating black holes - inability of light or anything else to escape from within their event horizons, accretion disks, etc. But general relativity predicts that rapid rotation of a large mass produces further distortions of space-time in addition to those which a non-rotating large mass produces, and these additional effects make rotating black holes strikingly different from non-rotating ones. A rotating black hole (Kerr black hole or Kerr-Newman black hole) is a black hole that possesses angular momentum. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... A rotating black hole (Kerr black hole or Kerr-Newman black hole) is a black hole that possesses angular momentum. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ...

### Two event horizons

If two rotating black holes have the same mass but different rotation speeds, the inner event horizon of the faster-spinning black hole will have a larger radius and its outer event horizon will have a smaller radius than in the slower-spinning black hole. In the most extreme case the two event horizons have zero radius, the region hidden by them has zero size and therefore the object is not a black hole but a naked singularity. Many physicists think that some principle which has not yet been discovered prevents the existence of a naked singularity and therefore prevents a black hole from spinning fast enough to create one. blah blah blah, some people believe God made the universe and that is all there is. ... It has been suggested that Naked singularity be merged into this article or section. ...

### Two photon spheres

General relativity predicts that a rotating black hole has two photon spheres, one for each event horizon. A beam of light traveling in a direction opposite to the spin of the black hole will circularly orbit the hole at the outer photon sphere. A beam of light traveling in the same direction as the black hole's spin will circularly orbit at the inner photon sphere. This beam will then split itself in two and both pieces will move into the Hole.

### Ergosphere

A large, ultra-dense rotating mass creates an effect called frame-dragging, so that space-time is dragged around it in the direction of the rotation. According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ...

Rotating black holes have an ergosphere, a region bounded by: A rotating black hole (Kerr black hole or Kerr-Newman black hole) is a black hole that possesses angular momentum. ...

• on the outside, an oblate spheroid which coincides with the event horizon at the poles and is noticeably wider around the "equator". This boundary is sometimes called the "ergosurface", but it is just a boundary and has no more solidity than the event horizon. At points exactly on the ergosurface, space-time is dragged around at the speed of light.
• on the inside, the outer event horizon.

Within the ergosphere space-time is dragged around faster than light - general relativity forbids material objects to travel faster than light (so does special relativity), but allows regions of space-time to move faster than light relative to other regions of space-time. An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ...

Objects and radiation (including light) can stay in orbit within the ergosphere without falling to the center. But they cannot hover (remain stationary as seen by an external observer) because that would require them to move backwards faster than light relative to their own regions of space-time, which are moving faster than light relative to an external observer.

Objects and radiation can also escape from the ergosphere. In fact the Penrose process predicts that objects will sometimes fly out of the ergosphere, obtaining the energy for this by "stealing" some of the black hole's rotational energy. If a large total mass of objects escapes in this way the black hole will spin more slowly and may even stop spinning eventually. To meet Wikipedias quality standards, this article or section may require cleanup. ...

### Ring-shaped singularity

General relativity predicts that a rotating black hole will have a ring singularity which lies in the plane of the "equator" and has zero width and thickness - but remember that quantum mechanics does not allow objects to have zero size in any dimension (their wavefunction must spread), so general relativity's prediction is only the best idea we have until someone devises a theory which combines general relativity and quantum mechanics. In general relativity the gravitational singularity at the centre of a rotating black hole (a Kerr black hole) is supposed to form a circle rather than a point. ... Fig. ... This article discusses the concept of a wavefunction as it relates to quantum mechanics. ... This article or section is in need of attention from an expert on the subject. ...

### Possibility of escaping from a rotating black hole

Penrose diagrams of various Schwarzschild solutions. Time is the vertical dimension, space is horizontal, and light travels at 45° angles. Paths less than 45° to the horizontal are forbidden by special relativity, but rotating black holes allow for travel to future "universes"

Kerr's solution for the equations of general relativity predicts that: Image File history File links Size of this preview: 685 Ã— 599 pixelsFull resolution (695 Ã— 608 pixel, file size: 31 KB, MIME type: image/png) Penrose Diagrams of various Schwarzschild solutions I, the creator of this work, hereby release it into the public domain. ... Image File history File links Size of this preview: 685 Ã— 599 pixelsFull resolution (695 Ã— 608 pixel, file size: 31 KB, MIME type: image/png) Penrose Diagrams of various Schwarzschild solutions I, the creator of this work, hereby release it into the public domain. ... In theoretical physics, a Penrose diagram (named after Roger Penrose who invented them) is usually a two-dimensional diagram that captures the causal relations between different points in spacetime. ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ...

• The properties of space-time between the two event horizons allow objects to move only towards the singularity.
• But the properties of space-time within the inner event horizon allow objects to move away from the singularity, pass through another set of inner and outer event horizons, and emerge out of the black hole into another universe or another part of this universe without traveling faster than the speed of light.
• Passing through the ring shaped singularity may allow entry to a negative gravity universe.[12]

If this is true, rotating black holes could theoretically provide the wormholes which often appear in science fiction. Unfortunately, it is unlikely that the internal properties of a rotating black hole are exactly as described by Kerr's solution[13] and it is not currently known whether the actual properties of a rotating black hole would provide a similar escape route for an object via the inner event horizon. In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... For other uses, see Universe (disambiguation). ... â€œLightspeedâ€ redirects here. ... A wormhole, also known as an Einstein-Rosen bridge, is a hypothetical topological feature of spacetime that is essentially a shortcut from one point in the universe to another point in the universe, allowing travel between them that is faster than it would take light to make the journey through... Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ...

Even if this escape route is possible, it is unlikely to be useful because a spacecraft which followed that path would probably be distorted beyond recognition by spaghettification. Click here for animated version Spaghettification is caused by the gravitational forces acting on the four objects. ...

## What happens when something falls into a black hole?

This section describes what happens when something falls into a non-rotating, uncharged black hole. The effects of rotating and charged black holes are more complicated but the final result is much the same - the falling object is absorbed (unless rotating black holes really can act as wormholes). A wormhole, also known as an Einstein-Rosen bridge, is a hypothetical topological feature of spacetime that is essentially a shortcut from one point in the universe to another point in the universe, allowing travel between them that is faster than it would take light to make the journey through...

### Spaghettification

An object in any very strong gravitational field feels a tidal force stretching it in the direction of the object generating the gravitational field. This is because the inverse square law causes nearer parts of the stretched object to feel a stronger attraction than farther parts. Near black holes, the tidal force is expected to be strong enough to deform any object falling into it; this is called spaghettification. Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... In physics, an inverse-square law is any physical law stating that some quantity is inversely proportional to the square of the distance from a point. ... Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... Click here for animated version Spaghettification is caused by the gravitational forces acting on the four objects. ...

The strength of the tidal force depends on how gravitational attraction changes with distance, rather than on the absolute force being felt. This means that small black holes cause spaghettification while infalling objects are still outside their event horizons, whereas objects falling into large, supermassive black holes may not be deformed or otherwise feel excessively large forces before passing the event horizon. Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... For the science fiction film, see Event Horizon (film). ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ...

### Before the falling object crosses the event horizon

An object in a gravitational field experiences a slowing down of time, called gravitational time dilation, relative to observers outside the field. The observer will see that physical processes in the object, including clocks, appear to run slowly. As a test object approaches the event horizon, its gravitational time dilation (as measured by an observer far from the hole) would approach infinity. A pocket watch, a device used to tell time Look up time in Wiktionary, the free dictionary. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ...

From the viewpoint of a distant observer, an object falling into a black hole appears to slow down, approaching but never quite reaching the event horizon: and it appears to become redder and dimmer, because of the extreme gravitational red shift caused by the gravity of the black hole. Eventually, the falling object becomes so dim that it can no longer be seen, at a point just before it reaches the event horizon. All of this is a consequence of time dilation: the object's movement is one of the processes that appear to run slower and slower, and the time dilation effect is more significant than the acceleration due to gravity; the frequency of light from the object appears to decrease, making it look redder, because the light appears to complete fewer cycles per "tick" of the observer's clock; lower-frequency light has less energy and therefore appears dimmer. For other topics related to Einstein see Einstein (disambig) In the general theory of relativity by Albert Einstein, the gravitational redshift or Einstein shift is the effect that clocks in a gravitational field tick slower when observed by a distant observer. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...

From the viewpoint of the falling object, distant objects may appear either blue-shifted or red-shifted, depending on the falling object's trajectory. Light is blue-shifted by the gravity of the black hole, but is red-shifted by the velocity of the infalling object. Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ...

### As the object passes through the event horizon

From the viewpoint of the falling object, nothing particularly special happens at the event horizon (apart from spaghettification due to tidal forces, if the black hole has relatively low mass). An infalling object takes a finite proper time to fall past the event horizon. Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ...

An outside observer, however, will never see an infalling object cross this surface. The object appears to halt just above the horizon, due to gravitational redshift, fading from view as its light is red-shifted and the rate at which it emits photons drops to approach zero. This doesn't mean that the object never crosses the horizon; instead, it means that light from the horizon-crossing event is delayed by a time that approaches infinity as the object approaches the horizon. The time of crossing depends on how the outside observer chooses to define space and time axes on spacetime near the horizon. This article or section is in need of attention from an expert on the subject. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... For other uses of this term, see Spacetime (disambiguation). ...

### Inside the event horizon

The object reaches the singularity at the center within a finite amount of proper time, as measured by the falling object. An observer on the falling object would continue to see objects outside the event horizon, blue-shifted or red-shifted depending on the falling object's trajectory. Objects closer to the singularity aren't seen, as all paths light could take from objects farther in point inwards towards the singularity. In relativity, proper time is time measured by a single clock between events that occur at the same place as the clock. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ...

The amount of proper time a faller experiences below the event horizon depends upon where they started from rest, with the maximum being for someone who starts from rest at the event horizon. A study in 2007 examined the effect of firing a rocket pack with the black hole, showing that this can only reduce the proper time of a person who starts from rest at the event horizon. However, for anyone else, a judicial burst of the rocket can extend the life time of the faller, but over doing it will again reduce the proper time experienced. However, this cannot prevent the inevitable collision with the central singularity.[14]

### Hitting the singularity

As an infalling object approaches the singularity, tidal forces acting on it approach infinity. All components of the object, including atoms and subatomic particles, are torn away from each other before striking the singularity. At the singularity itself, effects are unknown; a theory of quantum gravity is needed to accurately describe events near it. Regardless, as soon as an object passes within the hole's event horizon, it is lost to the outside universe. An observer far from the hole simply sees the hole's mass, charge, and angular momentum change to reflect the addition of the new object's matter. After the event horizon all is unknown. Anything that passes this point cannot be retrieved to study. Many people believe that the matter is extremely compacted. Stephen Hawking made a theory that the matter disappeared into the universe, defying the laws of physics. He later revised this theory to say that the disappearing matter was compensated by parallel universes without black holes, saying, in the end, the matter was not lost. Comet Shoemaker-Levy 9 after breaking up under the influence of Jupiters tidal forces. ... For other uses, see Atom (disambiguation). ... Helium atom (not to scale) Showing two protons (red), two neutrons (green) and a probability cloud (gray) of two electrons (yellow). ... This article does not cite any references or sources. ... ...

## Formation and evaporation

### Formation of stellar-mass black holes

Stellar-mass black holes are formed in two ways: A stellar black hole is a black hole formed by the gravitational collapse of a massive star (3 or more solar masses) at the end of its lifetime. ...

• As a direct result of the gravitational collapse of a star.
• By collisions between neutron stars.[15] Although neutron stars are fairly common, collisions appear to be very rare. Neutron stars are also formed by gravitational collapse, which is therefore ultimately responsible for all stellar-mass black holes.

Stars undergo gravitational collapse when they can no longer resist the pressure of their own gravity. This usually occurs either because a star has too little "fuel" left to maintain its temperature, or because a star which would have been stable receives a lot of extra matter in a way which does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight (Charles's law explains the connection between temperature and volume). This article or section does not cite its references or sources. ... STARS can mean: Shock Trauma Air Rescue Society Special Tactics And Rescue Service, a fictional task force that appears in Capcoms Resident Evil video game franchise. ... This article or section does not cite its references or sources. ... Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ... Wikibooks has more about this subject: Constructing school science lab equipment/Making Charles law tubes AARON IS SO COOL!!!!! Charles law (sometimes called the Law of Charles) is one of the gas laws. ...

The collapse transforms the matter in the star's core into a denser state which forms one of the types of compact star. Which type of compact star is formed depends on the mass of the remnant, i.e. of the matter left to be compressed after the supernova (if one happened - see below) triggered by the collapse has blown away the outer layers. Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure arises from the Pauli exclusion principle. ... In astronomy, the term compact star (sometimes compact object) is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ...

Only the largest remnants, those exceeding 1.4 solar masses (known as the Chandrasekhar limit), generate enough pressure to produce black holes, because singularities are the most radically transformed state of matter known to physics (if you can still call it matter) and the force which resists this level of compression, neutron degeneracy pressure, is extremely strong. Remnants exceeding 5 solar masses are produced by stars which were over 20 solar masses before the collapse (the rest of the mass is usually blown into space by the supernova triggered by the collapse). The Chandrasekhar limit, is the maximum mass possible for a white dwarf (one of the end stages of stars when they cool down) and is approximately 3 Ã— 1030 kg, around 1. ... Degenerate matter is matter which has sufficiently high density that the dominant contribution to its pressure arises from the Pauli exclusion principle. ...

In stars which are too large to form white dwarfs, the collapse releases energy which usually produces a supernova, blowing the star's outer layers into space so that they form a spectacular nebula. But the supernova is a side-effect and does not directly contribute to producing a compact star. For example a few gamma ray bursts were expected to be followed by evidence of supernovae but this evidence did not appear,[16][17] and one explanation is that some very large stars can form black holes fast enough to swallow the whole star before the supernova blast can reach the surface. This article or section does not adequately cite its references or sources. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ...

### Formation of larger black holes

There are two main ways in which black holes of larger than stellar mass can be formed:

• Stellar-mass black holes may act as "seeds" which grow by absorbing mass from interstellar gas and dust, stars and planets or smaller black holes.
• Star clusters of large total mass may be merged into single bodies by their members' gravitational attraction. This will usually produce a supergiant or hypergiant star which runs short of "fuel" in a few million years and then undergoes gravitational collapse, produces a supernova or hypernova and spends the rest of its existence as a black hole.

Supergiants are the most massive stars. ... This article does not cite its references or sources. ... Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ... This article needs additional references or sources for verification. ...

### Formation of smaller black holes

No known process currently active in the universe can form black holes of less than stellar mass. This is because all present black hole formation is through gravitational collapse, and the smallest mass which can collapse to form a black hole produces a hole approximately 1.5-3.0 times the mass of the sun (the Tolman-Oppenheimer-Volkoff limit). Smaller masses collapse to form white dwarf stars or neutron stars. Sol redirects here. ... This article is in need of attention from an expert on the subject. ... This article or section does not adequately cite its references or sources. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ...

There are still a few ways in which smaller black holes might be formed, or might have formed in the past:

• By evaporation of larger black holes. If the initial mass of the hole was stellar mass, the time required for it to lose most of its mass via Hawking evaporation is much longer than the age of the universe, so small black holes are not expected to have formed by this method yet.
• By the Big Bang, which produced sufficient pressure to form smaller black holes without the need for anything resembling a star. None of these hypothesized primordial black holes have been detected.
• By very powerful particle accelerators. In principle, a sufficiently energetic collision within a particle accelerator could produce a micro black hole. In practice, this is expected to require energies comparable to the Planck energy, which is vastly beyond the capability of any present, planned, or expected future particle accelerator to produce. Some variant models of the unification of the four fundamental forces allow the formation of black holes at much lower energies. This would allow production of extremely short-lived black holes in terrestrial particle accelerators. No conclusive evidence of this type of black hole production has been presented as of 2007.

In physics, Hawking radiation is thermal radiation emitted by black holes due to quantum effects. ... The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... For other uses, see Big Bang (disambiguation). ... A black hole concept drawing by NASA A primordial black hole is a hypothetical type of black hole that is formed not by the gravitational collapse of a star but by the extreme density of matter present during the universes early expansion. ... A particle accelerator uses electric fields to propel charged particles to great energies. ... This article or section is in need of attention from an expert on the subject. ... The Planck energy is the natural unit of energy, denoted by EP. 1. ... This article or section is in need of attention from an expert on the subject. ... A fundamental interaction or fundamental force is a mechanism by which particles interact with each other, and which cannot be explained in terms of another interaction. ... 2007 is a common year starting on Monday of the Gregorian calendar. ...

### Evaporation

Hawking radiation is a theoretical process by which black holes can evaporate into nothing. As there is no experimental evidence to corroborate it and there are still some major questions about the theoretical basis of the process, there is still debate about whether Hawking radiation can enable black holes to evaporate. In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ...

Quantum mechanics says that even the purest vacuum is not completely empty but is instead a "sea" of energy (known as zero-point energy) which has wave-like fluctuations. We cannot observe this "sea" of energy directly because there is no lower energy level with which we can compare it. The Heisenberg uncertainty principle dictates that it is impossible to know the exact value of the mass-energy and position pairings. The fluctuations in this sea produce pairs of particles in which one is made of normal matter and the other is the corresponding antiparticle (special relativity proves mass-energy equivalence, i.e. that mass can be converted into energy and vice versa). Normally each would soon meet another instance of its antiparticle and the two would be totally converted into energy, restoring the overall matter-energy balance as it was before the pair of particles was created. The Hawking radiation theory suggests that, if such a pair of particles is created just outside the event horizon of a black hole, one of the two particles may fall into the black hole while the other escapes, because the two particles move in slightly different directions after their creation. From the point of view of an outside observer, the black hole has just emitted a particle and therefore the black hole has lost a minute amount of its mass. Fig. ... In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may possess and is the energy of the ground state of the system. ... This page is a candidate for speedy deletion. ... In quantum physics, the Heisenberg uncertainty principle is a mathematical property of a pair of canonical conjugate quantities - usually stated in a form of reciprocity of spans of their spectra. ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... Corresponding to most kinds of particle, there is an associated antiparticle with the same mass and opposite charges. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... 15ft sculpture of Einsteins 1905 E = mcÂ² formula at the 2006 Walk of Ideas, Germany In physics, mass-energy equivalence is the concept that all mass has an energy equivalence, and all energy has a mass equivalence. ...

If the Hawking radiation theory is correct, only the very smallest black holes are likely to evaporate in this way. For example a black hole with the mass of our Moon would gain as much energy (and therefore mass - mass-energy equivalence again) from cosmic microwave background radiation as it emits by Hawking radiation, and larger black holes will gain more energy (and mass) than they emit. To put this in perspective, the smallest black hole which can be created naturally at present is about 5 times the mass of our sun, so most black holes have much greater mass than our Moon. 15ft sculpture of Einsteins 1905 E = mcÂ² formula at the 2006 Walk of Ideas, Germany In physics, mass-energy equivalence is the concept that all mass has an energy equivalence, and all energy has a mass equivalence. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ...

Over time the cosmic microwave background radiation becomes weaker. Eventually it will be weak enough so that more Hawking radiation will be emitted than the energy of the background radiation being absorbed by the black hole. Through this process, even the largest black holes will eventually evaporate. However, this process may take nearly a googol years to complete. A googol is the large number 10100, that is, the digit 1 followed by one hundred zeros (in decimal representation). ...

## Techniques for finding black holes

### Accretion disks and gas jets

Formation of extragalactic jets from a black hole's accretion disk

Most accretion disks and gas jets are not clear proof that a stellar-mass black hole is present, because other massive, ultra-dense objects such as neutron stars and white dwarfs cause accretion disks and gas jets to form and to behave in the same ways as those around black holes. But they can often help by telling astronomers where it might be worth looking for a black hole. Download high resolution version (792x700, 322 KB)Black hole jet diagram. ... Download high resolution version (792x700, 322 KB)Black hole jet diagram. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Relativistic Jet. ... A stellar black hole is a black hole formed by the gravitational collapse of a massive star (3 or more solar masses) at the end of its lifetime. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ... This article or section does not adequately cite its references or sources. ...

On the other hand, extremely large accretion disks and gas jets may be good evidence for the presence of supermassive black holes, because as far as we know any mass large enough to power these phenomena must be a black hole.
Top: artists conception of a supermassive black hole drawing material from a nearby star. ...

Intense but one-time gamma ray bursts (GRBs) may signal the birth of "new" black holes, because astrophysicists think that GRBs are caused either by the gravitational collapse of giant stars[18] or by collisions between neutron stars,[19] and both types of event involve sufficient mass and pressure to produce black holes. But it appears that a collision between a neutron star and a black hole can also cause a GRB,[20] so a GRB is not proof that a "new" black hole has been formed. All known GRBs come from outside our own galaxy, and most come from billions of light years away[21] so the black holes associated with them are actually billions of years old. The image above shows the optical afterglow of gamma ray burst GRB-990123 taken on January 23, 1999. ... This article or section does not cite its references or sources. ... A light-year or lightyear (symbol: ly) is a unit of measurement of length, specifically the distance light travels in vacuum in one year. ...

Some astrophysicists believe that some ultraluminous X-ray sources may be the accretion disks of intermediate-mass black holes.[22] An ultra-luminous X-ray source (ULX) is an astronomical source of X-rays that is not in the nucleus of a galaxy, and is more luminous than erg/s, assuming that it radiates isotropically. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... An Intermediate-mass black hole (IMBH) is a black hole whose mass is significantly more than stellar black holes (a few tens of the mass of Sun) yet far less than supermassive black holes (a few millions of the mass of Sun). ...

Quasars are thought to be caused by the accretion disks of supermassive black holes, since we know of nothing else which is powerful enough to produce such strong emissions. While X-rays and gamma rays have much higher frequencies and shorter wavelengths than visible light, quasars radiate mainly radio waves, which have lower frequencies and longer wavelengths than visible light. This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... The wavelength is the distance between repeating units of a wave pattern. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ...

### Gravitational lensing

Gravitational lensing distorts the image around a black hole in front of the Large Magellanic Cloud (artistic interpretation)

Gravitational lensing is another phenomenon which can have other causes besides the presence of a black hole, because any very strong gravitational field bends light rays. The most spectacular examples produce multiple images of very distant objects by bending towards our telescopes light rays which would otherwise have gone in different directions. But these multiple-image effects are probably produced by distant galaxies. [Does not explain fully] Image File history File links Download high-resolution version (2560x2048, 9143 KB) Gravitational distortions caused by a black hole in front of the Large Magellanic cloud File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Black hole ... Image File history File links Download high-resolution version (2560x2048, 9143 KB) Gravitational distortions caused by a black hole in front of the Large Magellanic cloud File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Black hole ... A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ... The Large Magellanic Cloud (LMC for short) is a dwarf galaxy that orbits our own galaxy, the Milky Way. ... A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...

### Objects orbiting possible black holes

Some large celestial objects are almost certainly orbiting around black holes, and the principles behind this conclusion are surprisingly simple if we consider a circular orbit first (although all known astronomical orbits are elliptical): Elliptical may refer to: Ellipse: a shape and mathematical construct Elliptical trainer: an exercise machine This is a disambiguation page &#8212; a navigational aid which lists other pages that might otherwise share the same title. ...

• The radius of the central object round which the observed object is orbiting must be less than the radius of the orbit, otherwise the two objects would collide.
• The orbital period and the radius of the orbit make it easy to calculate the centrifugal force created by the orbiting object. Strictly speaking the centrifugal force also depends on the orbiting object's mass, but the next two steps show why we can get away with pretending this is a fixed number, e.g. 1.
• The gravitational attraction between the central object and the orbiting object must be exactly equal to the centrifugal force, otherwise the orbiting body would either spiral into the central object or drift away.
• The required gravitational attraction depends on the mass of the central object, the mass of the orbiting object and the radius of the orbit. But we can simplify the calculation of both the centrifugal force and the gravitational attraction by pretending that the mass of the orbiting object is the same fixed number, e.g. 1. This makes it very easy to calculate the mass of the central object.
• If the Schwarzschild radius for a body with the mass of the central object is greater than the maximum radius of the central object, the central object must be a black hole whose event horizon's radius is equal to the Schwarzschild radius.

Unfortunately, since the time of Johannes Kepler, astronomers have had to deal with the complications of real astronomy: Remote Authentication Dial In User Service (RADIUS) is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... Centrifugal force (from Latin centrum centre and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. ... For the science fiction film, see Event Horizon (film). ... Johannes Kepler (December 27, 1571 â€“ November 15, 1630) was a German mathematician, astronomer and astrologer, and a key figure in the 17th century astronomical revolution. ...

• Astronomical orbits are elliptical. This complicates the calculation of the centrifugal force, the gravitational attraction and the maximum radius of the central body. But Kepler could handle this without needing a computer.
• The orbital periods in this type of situation are several years, so several years' worth of observations are needed to determine the actual orbit accurately. The "possibly a black hole" indicators (accretion disks, gas jets, radiation emissions, etc.) help "black hole hunters" to decide which orbits are worth observing for such long periods.
• If there are other large bodies within a few light years, their gravity fields will perturb the orbit. Adjusting the calculations to filter out the effects of perturbation can be difficult, but astronomers are used to doing it.

Elliptical may refer to: Ellipse: a shape and mathematical construct Elliptical trainer: an exercise machine This is a disambiguation page &#8212; a navigational aid which lists other pages that might otherwise share the same title. ... Perturbation is a term used in astronomy to describe alterations to an objects orbit caused by gravitational interactions with other bodies. ...

## Black hole candidates

Although black holes cannot be detected directly, many observational studies have provided substantial evidence for black holes. Black holes may be divided into three classes of objects:

Further details are given below. A stellar black hole is a black hole formed by the gravitational collapse of a massive star (3 or more solar masses) at the end of its lifetime. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... An Intermediate-mass black hole (IMBH) is a black hole whose mass is significantly more than stellar black holes (a few tens of the mass of Sun) yet far less than supermassive black holes (a few millions of the mass of Sun). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ...

### Supermassive black holes at the centers of galaxies

The jet originating from the center of M87 in this image comes from an active galactic nucleus that may contain a supermassive black hole. Credit: Hubble Space Telescope/NASA/ESA.

For decades, astronomers have used the term "active galaxy" to describe galaxies with unusual characteristics, such as unusual spectral line emission and very strong radio emission.[24][25] However, theoretical and observational studies have shown that the active galactic nuclei (AGN) in these galaxies may contain supermassive black holes.[24][25] The models of these AGN consist of a central black hole that may be millions or billions of times more massive than the Sun; a disk of gas and dust called an accretion disk; and two jets that are perpendicular to the accretion disk.[25] An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ... Sol redirects here. ... The interstellar medium (or ISM) is a term used in astronomy to describe the rarefied gas and dust that exists between the stars (or their immediate circumstellar environment) within a galaxy. ... Interstellar cloud is the generic name given to accumulations of gas and dust in our galaxy. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Relativistic Jet. ...

Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the Andromeda Galaxy, M32, M87, NGC 3115, NGC 3377, NGC 4258, and the Sombrero Galaxy.[23] JASON YOU SUCK!!!!!!! The Andromeda Galaxy (IPA: , also known as Messier 31, M31, or NGC 224; older texts often called it the Great Andromeda Nebula) is a spiral galaxy approximately 2. ... Elliptical Galaxy M32 (also known as Messier Object 32, Messier 32, M32, or NGC 221) is a dwarf elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ... M87 (also known as Virgo A, Messier 87 or NGC 4486) is a giant elliptical galaxy. ... NGC 3115, also called the Spindle Galaxy or the Spindle Galaxy in Sextans, was discovered by William Herschel on February 22, 1787. ... The Spiral Galaxy M106 (also known as Messier Object 106, Messier 106, M106, or NGC 4258) is a spiral galaxy in the Canes Venatici constellation. ... The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. ...

Astronomers are confident that our own Milky Way galaxy has a supermassive black hole at its center, in a region called Sagittarius A*: For the confectionery, see Milky Way bar. ... Sagittarius A* (pronounced A-star) is a bright and very compact source of radio emission at the center of the Milky Way Galaxy, part of a larger astronomical feature at that location (Sagittarius A). ...

• A star called S2 (star) follows an elliptical orbit with a period of 15.2 years and a pericenter (closest) distance of 17 light hours from the central object.
• The first estimates indicated that the central object contains 2.6M (2.6 million) solar masses and has a radius of less than 17 light hours. Only a black hole can contain such a vast mass in such a small volume.
• Further observations[26] strengthened the case for a black hole by showing that the central object's mass is about 3.7M solar masses and its radius no more than 6.25 light-hours.

S2 is a star that is located close to the radio source Sagittarius A*, orbiting it with an orbital period of 15. ... Elliptical may refer to: Ellipse: a shape and mathematical construct Elliptical trainer: an exercise machine This is a disambiguation page &#8212; a navigational aid which lists other pages that might otherwise share the same title. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... A light hour (also written light-hour) is a unit of length. ...

### Intermediate-mass black holes in globular clusters

In 2002, the Hubble Space Telescope produced observations indicating that globular clusters named M15 and G1 may contain intermediate-mass black holes. [citation needed] This interpretation is based on the sizes and periods of the orbits of the stars in the globular clusters. But the Hubble evidence is not conclusive, since a group of neutron stars could cause similar observations. Until recent discoveries, many astronomers thought that the complex gravitational interactions in globular clusters would eject newly-formed black holes. A globular cluster is a spherical bundle of stars (star cluster) that orbits a galaxy as a satellite. ... The central square arcminute of M15 imaged using the lucky imaging technique Globular Cluster M15 (also known as Messier Object 15 or NGC 7078) is a globular cluster in the constellation Pegasus. ... Mayall II, G1, SKHB 1, or HBK 0-1 is a globular cluster in M31, the Andromeda Galaxy. ... An Intermediate-mass black hole (IMBH) is a black hole whose mass is significantly more than stellar black holes (a few tens of the mass of Sun) yet far less than supermassive black holes (a few millions of the mass of Sun). ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ...

In November 2004 a team of astronomers reported the discovery of the first well-confirmed intermediate-mass black hole in our Galaxy, orbiting three light-years from Sagittarius A*. This black hole of 1,300 solar masses is within a cluster of seven stars, possibly the remnant of a massive star cluster that has been stripped down by the Galactic Centre.[27][28] This observation may add support to the idea that supermassive black holes grow by absorbing nearby smaller black holes and stars. An Intermediate-mass black hole (IMBH) is a black hole whose mass is significantly more than stellar black holes (a few tens of the mass of Sun) yet far less than supermassive black holes (a few millions of the mass of Sun). ...

In January 2007, researchers at the University of Southampton in the United Kingdom reported finding a black hole, possibly of about 400 solar masses, in a globular cluster associated with a galaxy named NGC 4472, some 55 million light-years away.[29]

### Stellar-mass black holes in the Milky Way

Artist's impression of a binary system consisting of a black hole and a main sequence ("normal") star. The black hole is drawing matter from the main sequence star via an accretion disk around it, and some of this matter forms a gas jet.

Our Milky Way galaxy contains several probable stellar-mass black holes which are closer to us than the supermassive black hole in the Sagittarius A* region. These candidates are all members of X-ray binary systems in which the denser object draws matter from its partner via an accretion disk. The probable black holes in these pairs range from three to more than a dozen solar masses.[30][31] Download high resolution version (3000x2400, 111 KB) [1] File links The following pages link to this file: Black hole Accretion disc Categories: NASA images ... Download high resolution version (3000x2400, 111 KB) [1] File links The following pages link to this file: Black hole Accretion disc Categories: NASA images ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Relativistic Jet. ... A stellar black hole is a black hole formed by the gravitational collapse of a massive star (3 or more solar masses) at the end of its lifetime. ... Sagittarius A* (pronounced A-star) is a bright and very compact source of radio emission at the center of the Milky Way Galaxy, part of a larger astronomical feature at that location (Sagittarius A). ... X-ray binaries are a class of binary stars that are very luminous in X-rays. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

### Micro black holes

The formation of micro black holes on Earth in particle accelerators has been tentatively reported,[32] but not yet confirmed. So far there are no observed candidates for primordial black holes. This article or section is in need of attention from an expert on the subject. ... A particle accelerator uses electric fields to propel charged particles to great energies. ... A black hole concept drawing by NASA A primordial black hole is a hypothetical type of black hole that is formed not by the gravitational collapse of a star but by the extreme density of matter present during the universes early expansion. ...

## History of the black hole concept

The Newtonian conceptions of Michell and Laplace are often referred to as "dark stars" to distinguish them from the "black holes" of general relativity. The terms Dark Star or Darkstar may refer to: Dark star, a theoretical star whose gravity is strong enough to trap light, mostly superseded by the concept of black holes. RQ-3 Dark Star, a military drone developed by the United States Dark Star (band), an English rock band Dark...

### Newtonian theories (before Einstein)

The concept of a body so massive that even light could not escape was put forward by the geologist John Michell in a 1784 paper sent to Henry Cavendish and published by the Royal Society.[33] The Geologist by Carl Spitzweg A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system (see planetary geology). ... John Michell (1724 â€“ April 29, 1793) was an English natural philosopher and geologist, whose work was rediscovered in the 1970s. ... For other persons named Henry Cavendish, see Henry Cavendish (disambiguation). ... The premises of The Royal Society in London (first four properties only). ...

 “ If the semi-diameter of a sphere of the same density as the Sun were to exceed that of the Sun in the proportion of 500 to 1, a body falling from an infinite height towards it would have acquired at its surface greater velocity than that of light, and consequently supposing light to be attracted by the same force in proportion to its vis inertiae, with other bodies, all light emitted from such a body would be made to return towards it by its own proper gravity. ”

Michell's analysis is based on the concept of escape velocity, which can be deduced from Newton's Law of Gravitation. But Newton's Law of Gravitation assumes a pair of masses, not a single mass. So any analysis based on escape velocity assumes that photons have a non-zero rest mass (vis inertiae in the quote from Michell), but we now know that this is not true. The concept of escape velocity also allows an object to rise for an indefinite distance before falling back, and therefore does not predict event horizons around black holes. Space Shuttle Atlantis launches on mission STS-71. ... The law of universal gravitation states that gravitational force between masses decreases with the distance between them, according to an inverse-square law. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... The term mass in special relativity is used in a couple of different ways, occasionally leading to a great deal of confusion. ... For the science fiction film, see Event Horizon (film). ...

In 1796, the mathematician Pierre-Simon Laplace promoted the same idea in the first and second editions of his book Exposition du système du Monde (it was removed from later editions). To meet Wikipedias quality standards, this article or section may require cleanup. ...

The idea of black holes was largely ignored in the nineteenth century, since light was then thought to be a massless wave and therefore not influenced by gravity.

Note: before quantum mechanics was developed, physicists had been perplexed since about 1600 by the problem of wave-particle duality - some thought of light as a stream of particles, others thought of it as a series of waves, and the two different views went in and out of fashion alternately. Fig. ... In physics, wave-particle duality holds that light and matter exhibit properties of both waves and of particles. ...

### Theories based on Einstein's general relativity

In 1915, Albert Einstein developed the theory of gravity called general relativity, having earlier shown that gravity does influence light (although light has zero rest mass, its path follows any curvature of space-time, and gravity is curvature of space-time). A few months later, Karl Schwarzschild gave the solution for the gravitational field of a point mass and a spherical mass,[34][35] showing that a black hole could theoretically exist. The Schwarzschild radius is now known to be the radius of the event horizon of a non-rotating black hole, but this was not well understood at that time, for example Schwarzschild himself thought it was not physical. Johannes Droste, a student of Lorentz, independently gave the same solution for the point mass a few months after Schwarzschild and wrote more extensively about its properties. â€œEinsteinâ€ redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... The term mass in special relativity is used in a couple of different ways, occasionally leading to a great deal of confusion. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... Karl Schwarzschild (October 9, 1873 - May 11, 1916) was a noted German Jewish physicist and astronomer, father of astrophysicist Martin Schwarzschild. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. ... For the science fiction film, see Event Horizon (film). ... Hendrik Antoon Lorentz (July 18, 1853, Arnhem â€“ February 4, 1928, Haarlem) was a Dutch physicist who shared the 1902 Nobel Prize in Physics with Pieter Zeeman for the discovery and elucidation of the Zeeman effect. ...

In 1930, the astrophysicist Subrahmanyan Chandrasekhar argued that, according to special relativity, a non-rotating body above 1.44 solar masses (the Chandrasekhar limit), would collapse since there was nothing known at that time could stop it from doing so. His arguments were opposed by Arthur Eddington, who believed that something would inevitably stop the collapse. Eddington was partly right: a white dwarf slightly more massive than the Chandrasekhar limit will collapse into a neutron star. But in 1939, Robert Oppenheimer published papers (with various co-authors) which predicted that stars above about three solar masses (the Tolman-Oppenheimer-Volkoff limit) would collapse into black holes for the reasons presented by Chandrasekhar.[36] An astrophysicist is a person whose profession is astrophysics. ... Chandrasekhar redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... The Chandrasekhar limit, is the maximum mass possible for a white dwarf (one of the end stages of stars when they cool down) and is approximately 3 Ã— 1030 kg, around 1. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... This article or section does not adequately cite its references or sources. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ... J. Robert Oppenheimer[1] (April 22, 1904 â€“ February 18, 1967) was an American theoretical physicist, best known for his role as the director of the Manhattan Project, the World War II effort to develop the first nuclear weapons, at the secret Los Alamos laboratory in New Mexico. ... This article is in need of attention from an expert on the subject. ...

Oppenheimer and his co-authors used Schwarzschild's system of coordinates (the only coordinates available in 1939), which produced mathematical singularities at the Schwarzschild radius, in other words the equations broke down at the Schwarzschild radius because some of the terms were infinite. This was interpreted as indicating that the Schwarzschild radius was the boundary of a "bubble" in which time "stopped". For a few years the collapsed stars were known as "frozen stars" because the calculations indicated that an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it inside the Schwarzschild radius. But many physicists could not accept the idea of time standing still inside the Schwarzschild radius, and there was little interest in the subject for over 20 years. It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In mathematics, a singularity is in general a point at which a given mathematical object is not defined, or a point of an exceptional set where it fails to be well-behaved in some particular way, such as differentiability. ... The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. ... The infinity symbol âˆž in several typefaces. ...

In 1958 David Finkelstein broke the deadlock over "stopped time" and introduced the concept of the event horizon by presenting the Eddington-Finkelstein coordinates, which enabled him to show that "The Schwarzschild surface r = 2m is not a singularity but acts as a perfect unidirectional membrane: causal influences can cross it but only in one direction".[37] Note that at this stage all theories, including Finkelstein's, covered only non-rotating, uncharged black holes. David Finkelstein (born July 19, 1929, New York City) is currently professor of physics at the Georgia Institute of Technology. ... For the science fiction film, see Event Horizon (film). ... In general relativity, Eddington-Finkelstein coordinates are a pair of coordinate systems for a Schwarzschild geometry which are adapted to radial null geodesics (i. ...

In 1963 Roy Kerr extended Finkelstein's analysis by presenting the Kerr metric (coordinates) and showing how this made it possible to predict the properties of rotating black holes.[38] In addition to its theoretical interest, Kerr's work made black holes more believable for astronomers, since black holes are formed from stars and all known stars rotate. Roy Patrick Kerr (1934- ) is a New Zealand born mathematician who is best known for discovering the famous Kerr vacuum, an exact solution to the Einstein field equation of general relativity, which models the gravitational field outside an uncharged rotating massive object, or even a rotating black hole. ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... A rotating black hole (Kerr black hole or Kerr-Newman black hole) is a black hole that possesses angular momentum. ...

In 1967 astronomers discovered pulsars, and within a few years could show that the known pulsars were rapidly rotating neutron stars. Until that time, neutron stars were also regarded as just theoretical curiosities. So the discovery of pulsars awakened interest in all types of ultra-dense objects that might be formed by gravitational collapse. Composite Optical/X-ray image of the Crab Nebula pulsar, showing surrounding nebular gases stirred by the pulsars magnetic field and radiation. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ...

In December 1967 the theoretical physicist John Wheeler coined the expression "black hole" in his public lecture Our Universe: the Known and Unknown, and this mysterious, slightly menacing phrase attracted more attention than the static-sounding "frozen star". John Archibald Wheeler (born July 9, 1911) is an eminent American theoretical physicist. ...

In 1970, Stephen Hawking and Roger Penrose proved that black holes are a feature of all solutions to Einstein's equations of gravity, not just of Schwarzschild's, and therefore black holes cannot be avoided in some collapsing objects.[39] Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Sir Roger Penrose, OM, FRS (born 8 August 1931) is an English mathematical physicist and Emeritus Rouse Ball Professor of Mathematics at the Mathematical Institute, University of Oxford and Emeritus Fellow of Wadham College. ...

## Black holes and Earth

Black holes are sometimes listed among the most serious potential threats to Earth and humanity,[40][41] on the grounds that:

• A naturally-produced black hole could pass through our Solar System.
• A large particle accelerator might produce a micro black hole, and if this escaped it could gradually eat the whole of the Earth. The micro black hole could also be defined as a strangelet which can absorb other particles despite the Earth's gravity and eventually accumulate enough mass to become an averaged sized black hole.

For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ... This article or section is in need of attention from an expert on the subject. ... A strangelet or strange nugget is a hypothetical object, consisting of a bound state of roughly equal numbers of up, down, and strange quarks. ...

### Black hole wandering through our Solar System

Stellar-mass black holes travel through the Milky Way just like stars. Consequently, they may collide with the Solar System or another planetary system in the galaxy, although the probability of this happening is very small. Significant gravitational interactions between the Sun and any other star in the Milky Way (including a black hole) are expected to occur approximately once every 1019 years.[42] For comparison, the Sun has an age of only 5 × 109 years, and is expected to become a red giant about 5 × 109 years from now, incinerating the surface of the Earth.[25] Hence it is extremely unlikely that a black hole will pass through the Solar System before the Sun exterminates life on Earth. Sol redirects here. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... Sol redirects here. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...

### Micro black hole escaping from a particle accelerator

There is a theoretical possibility that a micro black hole might be created inside a particle accelerator.[43] Formation of black holes under these conditions (below the Planck energy) requires non-standard assumptions, such as large extra dimensions. This article or section is in need of attention from an expert on the subject. ... For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ... The Planck energy is the natural unit of energy, denoted by EP. 1. ... In particle physics, the ADD model, also known as the model with old large dimensions, is a scenario inspired by string theory to explain the weakness of gravity relatively to other forces in which the fields of the Standard Model are confined to a higher-dimensional membrane but gravity can... Kaluza-Klein theory (or KK theory, for short) is a model which sought to unify classical gravity and electromagnetism. ...

However, many particle collisions that naturally occur as the cosmic rays hit the edge of our atmosphere are often far more energetic than any collisions created by man. If micro black holes can be created by current or next-generation particle accelerators, they have probably been created by cosmic rays every day throughout most of Earth's history, i.e. for billions of years, evidently without earth-destroying effects. Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ...

Even if, say, two protons at the Large Hadron Collider could merge to create a micro black hole, this black hole would be extremely unstable, and it would evaporate due to Hawking radiation before it had a chance to propagate. For a 14 TeV black hole (the center-of-mass energy at the Large Hadron Collider), direct computation of its lifetime by the Hawking radiation formula indicates that it would evaporate in 10-100 seconds. For alternative meanings see proton (disambiguation). ... The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland (). Currently under construction, the LHC is scheduled to begin operation in May 2008. ... In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ... A TeV is a teraelectronvolt, i. ...

CERN conducted a study assessing the risk of producing dangerous objects such as black holes at the Large Hadron Collider, and concluded that there is "no basis for any conceivable threat."[44] CERN logo The European Organization for Nuclear Research (French: ), commonly known as CERN (see Naming), pronounced (or in French), is the worlds largest particle physics laboratory, situated just northwest of Geneva on the border between France and Switzerland. ... The Large Hadron Collider (LHC) is a particle accelerator and collider located at CERN, near Geneva, Switzerland (). Currently under construction, the LHC is scheduled to begin operation in May 2008. ...

## Alternative models

Several alternative models, which behave like a black hole but avoid the singularity, have been proposed. However, most researchers judge these concepts artificial, as they are more complicated but do not give near term observable differences from black holes (see Occam's razor). The most prominent alternative theory is the Gravastar. For the House episode, see Occams Razor (House episode) Occams razor (sometimes spelled Ockhams razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham. ... In astrophysics, the Gravastar theory is a proposal by Emil Mottola and Pawel Mazur to replace the black hole. ...

In March 2005, physicist George Chapline at the Lawrence Livermore National Laboratory in California proposed that black holes do not exist, and that objects currently thought to be black holes are actually dark-energy stars. He draws this conclusion from some quantum mechanical analyses. Although his proposal currently has little support in the physics community, it was widely reported by the media.[45][46] A similar theory about the non-existence of black holes was later developed by a group of physicists at Case Western Reserve University in June 2007.[47] George Chapline is a condensed matter physicist at Lawrence Livermore National Laboratory. ... Aerial view of the lab and surrounding area. ... Official language(s) English Capital Sacramento Largest city Los Angeles Largest metro area Greater Los Angeles Area  Ranked 3rd  - Total 158,302 sq mi (410,000 kmÂ²)  - Width 250 miles (400 km)  - Length 770 miles (1,240 km)  - % water 4. ... This article is in need of attention. ... Case Western Reserve University is a private research university located in Cleveland, Ohio, United States, with some residence halls on the south end of campus located in Cleveland Heights. ...

Among the alternate models are magnetospheric eternally collapsing objects, clusters of elementary particles[48] (e.g., boson stars[49]), fermion balls,[50] self-gravitating, degenerate heavy neutrinos[51] and even clusters of very low mass (~0.04 solar mass) black holes.[48] A Magnetospheric Eternally Collapsing Object or MECO is an alternative to a black hole. ... In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not made up of smaller particles. ... In particle physics, bosons, named after Satyendra Nath Bose, are particles having integer spin. ... In particle physics, fermions are particles with half-integer spin, such as protons and electrons. ... Neutrinos are elementary particles denoted by the symbol Î½. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ...

If ultra-high-energy collisions of particles in a particle accelerator can create microscopic black holes, it is expected that all types of particles will be emitted by black hole evaporation, providing key evidence for any grand unified theory. Above are the high energy particles produced in a gold ion collision on the RHIC.

### Black hole unitarity

An open question in fundamental physics is the so-called information loss paradox, or black hole unitarity paradox. Classically, the laws of physics are the same run forward or in reverse. That is, if the position and velocity of every particle in the universe were measured, we could (disregarding chaos) work backwards to discover the history of the universe arbitrarily far in the past. In quantum mechanics, this corresponds to a vital property called unitarity which has to do with the conservation of probability.[53] This article or section cites very few or no references or sources. ... For other uses, see Chaos Theory (disambiguation). ... In mathematics and physics, unitarity is the property of an operator (or a matrix) that is unitary. ...

Black holes, however, might violate this rule. The position under classical general relativity is subtle but straightforward: because of the classical no hair theorem, we can never determine what went into the black hole. However, as seen from the outside, information is never actually destroyed, as matter falling into the black hole takes an infinite time to reach the event horizon. In astrophysics, the no-hair theorem states that black holes are completely characterized only by three externally observable parameters: mass, electrical charge, and angular momentum. ...

Ideas about quantum gravity, on the other hand, suggest that there can only be a limited finite entropy (i.e. a maximum finite amount of information) associated with the space near the horizon; but the change in the entropy of the horizon plus the entropy of the Hawking radiation is always sufficient to take up all of the entropy of matter and energy falling into the black hole. In physics, the Bekenstein bound imposes a limit on the entropy S or information that can be contained within a three-dimensional volume. ...

Many physicists are concerned however that this is still not sufficiently well understood. In particular, at a quantum level, is the quantum state of the Hawking radiation uniquely determined by the history of what has fallen into the black hole; and is the history of what has fallen into the black hole uniquely determined by the quantum state of the black hole and the radiation? This is what determinism, and unitarity, would require.

## Mathematical theory

Further information: Schwarzschild metric  and Deriving the Schwarzschild solution

Black holes are predictions of Albert Einstein's theory of general relativity. There are many known solutions to the Einstein field equations which describe black holes, and they are also thought to be an inevitable part of the evolution of any star of a certain size. In particular, they occur in the Schwarzschild metric, one of the earliest and simplest solutions to Einstein's equations, found by Karl Schwarzschild in 1915. This solution describes the curvature of spacetime in the vicinity of a static and spherically symmetric object, where the metric is, It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... It has been suggested that this article or section be merged into Schwarzschild solution. ... â€œEinsteinâ€ redirects here. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... Karl Schwarzschild (October 9, 1873 - May 11, 1916) was a noted German Jewish physicist and astronomer, father of astrophysicist Martin Schwarzschild. ... In mathematics, curvature refers to a number of loosely related concepts in different areas of geometry. ... For other uses of this term, see Spacetime (disambiguation). ... A sphere is a symmetrical geometrical object. ... Sphere symmetry group o. ... In mathematics, a metric space is a set where a notion of distance between elements of the set is defined. ...

$mathrm{d}s^2 = - c^2 left( 1 - {2Gm over c^2 r} right) mathrm{d}t^2 + left( 1 - {2Gm over c^2 r} right)^{-1} mathrm{d}r^2 + r^2 mathrm{d}Omega^2$,

where $mathrm{d}Omega^2 = mathrm{d}theta^2 + sin^2theta; mathrm{d}phi^2$ is a standard element of solid angle.

The Schwarzschild radius is given by

$r_{rm S} = {2,Gm over c^2}$

where G is the gravitational constant, m is the mass of the object, and c is the speed of light. For an object with the mass of the Earth, the Schwarzschild radius is a mere 9 millimeters — about the size of a marble. According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... This article or section is in need of attention from an expert on the subject. ... â€œLightspeedâ€ redirects here. ... This article is about Earth as a planet. ... Categories: Game stubs | Games | National Toy Hall of Fame ...

The mean density inside the Schwarzschild radius decreases as the mass of the black hole increases, so while an earth-mass black hole would have a density of 2 × 1030 kg/m³, a supermassive black hole of 109 solar masses has a density of around 20 kg/m³, less than water! The mean density is given by In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

$rho=frac{3,c^6}{32pi m^2G^3}.$

Since the Earth has a mean radius of 6371 km, its volume would have to be reduced 4 × 1026 times to collapse into a black hole. For an object with the mass of the Sun, the Schwarzschild radius is approximately 3 km, much smaller than the Sun's current radius of about 696,000 km. It is also significantly smaller than the radius to which the Sun will ultimately shrink after exhausting its nuclear fuel, which is several thousand kilometers. More massive stars can collapse into black holes at the end of their lifetimes. Sol redirects here. ...

The formula also implies that any object with a given mean density is a black hole if its radius is large enough. The same formula applies for white holes as well. For example, if the observable universe has a mean density equal to the critical density, then it is a white hole, since its singularity is in the past and not in the future as should be for a black hole. In astrophysics, a white hole is a postulated celestial body that spews out matter, in essence an anti-black hole, or the time reversal of a black hole. ... See universe for a general discussion of the universe. ... In cosmology, the Big Crunch is a hypothesis that states the universe will stop expanding and start to collapse upon itself; a counterpart to the Big Bang. ... This article or section is in need of attention from an expert on the subject. ... Singularity has several different meanings: mathematical singularity - a point where a mathematical function goes to infinity or is in certain other ways ill-behaved. ...

More general black holes are also predicted by other solutions to Einstein's equations, such as the Kerr metric for a rotating black hole, which possesses a ring singularity. Then we have the Reissner-Nordström metric for charged black holes. Last the Kerr-Newman metric is for the case of a charged and rotating black hole. In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... In general relativity the gravitational singularity at the centre of a rotating black hole (a Kerr black hole) is supposed to form a circle rather than a point. ... In physics and astronomy, a Reissner-NordstrÃ¶m black hole, discovered by Gunnar NordstrÃ¶m and Hans Reissner, is a black hole that carries electric charge , no angular momentum, and mass . ... The Kerr-Newman metric is a solution of Einsteins general relativity field equation that describes the spacetime geometry around a charged (), rotating () black hole of mass m. ...

There is also the Black Hole Entropy formula:

$S = frac{Akc^3}{4hbar G}.$

Where A is the area of the event horizon of the black hole, $hbar$ is Dirac's constant (the "reduced Planck constant"), k is the Boltzmann constant, G is the gravitational constant, c is the speed of light and S is the entropy. Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ... Plancks constant, denoted h, is a physical constant that is used to describe the sizes of quanta. ... Ludwig Boltzmann The Boltzmann constant (k or kB) is the physical constant relating temperature to energy. ... According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... â€œLightspeedâ€ redirects here. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...

A convenient length scale to measure black hole processes is the "gravitational radius", which is equal to

$r_{rm G} = {Gm over c^2} .$

When expressed in terms of this length scale, many phenomena appear at integer radii. For example, the radius of a Schwarzschild black hole is two gravitational radii and the radius of a maximally rotating Kerr black hole is one gravitational radius. The location of the light circularization radius around a Schwarzschild black hole (where light may orbit the hole in an unstable circular orbit) is 3rG. The location of the marginally stable orbit, thought to be close to the inner edge of an accretion disk, is at 6rG for a Schwarzschild black hole.

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Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 192nd day of the year (193rd in leap years) in the Gregorian calendar. ... arXiv (pronounced archive, as if the X were the Greek letter Ï‡) is an archive for electronic preprints of scientific papers in the fields of physics, mathematics, computer science and quantitative biology which can be accessed via the Internet. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 7th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 7th day of the year in the Gregorian calendar. ... is the 76th day of the year (77th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... is the 46th day of the year in the Gregorian calendar. ... Year 1939 (MCMXXXIX) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar. ... is the 27th day of the year in the Gregorian calendar. ... Year 1970 (MCMLXX) was a common year starting on Thursday (link shows full calendar) of the Gregorian calendar. ... is the 312th day of the year (313th in leap years) in the Gregorian calendar. ... is the 7th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 171st day of the year (172nd in leap years) in the Gregorian calendar. ... Case Western Reserve University is a private research university located in Cleveland, Ohio, United States, with some residence halls on the south end of campus located in Cleveland Heights. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 183rd day of the year (184th in leap years) in the Gregorian calendar. ... is the 51st day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Cover of A Brief History of Time A Brief History of Time is a popular science book written by Professor Stephen Hawking and first published in 1988. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 250th day of the year (251st in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ...

• Ferguson, Kitty (1991). Black Holes in Space-Time. Watts Franklin. ISBN 0-531-12524-6.
• Hawking, Stephen (1998). A Brief History of Time. Bantam Books, Inc. ISBN 0-553-38016-8.
• Melia, Fulvio (2003). The Black Hole at the Center of Our Galaxy. Princeton U Press. ISBN 978-0-691-09505-9.
• Melia, Fulvio (2003). The Edge of Infinity. Supermassive Black Holes in the Universe. Cambridge U Press. ISBN 978-0-521-81405-8.
• Pickover, Clifford (1998). Black Holes: A Traveler's Guide. Wiley, John & Sons, Inc. ISBN 0-471-19704-1.
• Thorne, Kip S. (1994). Black Holes and Time Warps. Norton, W. W. & Company, Inc. ISBN 0-393-31276-3.

Cover of A Brief History of Time A Brief History of Time is a popular science book written by Professor Stephen Hawking and first published in 1988. ... This article does not cite its references or sources. ... This article does not cite its references or sources. ... This page is a candidate for speedy deletion. ...

### University textbooks and monographs

• Carter, B. (1973). Black hole equilibrium states, in Black Holes, eds. DeWitt B. S. and DeWitt C.
• Chandrasekhar, Subrahmanyan (1999). Mathematical Theory of Black Holes. Oxford University Press. ISBN 0-19-850370-9.
• Frolov, V. P. and Novikov, I. D. (1998), Black hole physics.
• Hawking, S. W. and Ellis, G. F. R. (1973), The large-scale structure of space-time, Cambridge University Press.
• Melia, Fulvio (2007). The Galactic Supermassive Black Hole. Princeton U Press. ISBN 978-0-691-13129-0.
• Taylor, Edwin F.; Wheeler, John Archibald (2000). Exploring Black Holes. Addison Wesley Longman. ISBN 0-201-38423-X.
• Thorne, Kip S.; Misner, Charles; Wheeler, John (1973). Gravitation. W. H. Freeman and Company. ISBN 0-7167-0344-0.
• Wald, Robert M. (1992). Space, Time, and Gravity: The Theory of the Big Bang and Black Holes. University of Chicago Press. ISBN 0-226-87029-4.

### Research papers

• Hawking, S. W. (July 2005), Information Loss in Black Holes, arxiv:hep-th/0507171. Stephen Hawking's purported solution to the black hole unitarity paradox, first reported at a conference in July 2004.
• Ghez, A.M. et al. Stellar orbits around the Galactic Center black hole, Astrophysics J. 620 (2005). arXiv:astro-ph/0306130 More accurate mass and position for the black hole at the centre of the Milky Way.
• Hughes, S. A. Trust but verify: the case for astrophysical black holes, arXiv:hep-ph/0511217. Lecture notes from 2005 SLAC Summer Institute.

In mathematics and physics, unitarity is the property of an operator (or a matrix) that is unitary. ... The Stanford Linear Accelerator Center (SLAC) is a U.S. national laboratory operated by Stanford University for the U.S. Department of Energy. ...

Results from FactBites:

 Black Holes (1902 words) The event horizon is the point outside the fl hole where the gravitational attraction becomes so strong that the escape velocity (the velocity at which an object would have to go to escape the gravitational field) equals the speed of light. Black holes almost certainly exist, and one of their basic properties is that they trap light. In fact, the theoretical prediction of fl holes is due to the General Theory of Relativity, which is built on the principle that the speed of light in a vacuum is constant.
 Black hole - Wikipedia, the free encyclopedia (5465 words) Intermediate-mass fl holes have been proposed as a possible power source for ultra-luminous X ray sources, and in 2004 detection was claimed of an intermediate-mass fl hole orbiting the Sagittarius A* supermassive fl hole candidate at the core of the Milky Way galaxy. Black holes require the general relativistic concept of a curved spacetime: their most striking properties rely on a distortion of the geometry of the space surrounding them. The "surface" of a fl hole is the so-called event horizon, an imaginary surface surrounding the mass of the fl hole.
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