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Encyclopedia > Quasar
An artist's impression of a growing quasar.

A Quasar (contraction of QUASi-stellAR radio source) is an extremely bright and distant active galactic nucleus. They were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light that were point-like, similar to stars, rather than extended sources similar to galaxies. While there was initially some controversy over the nature of these objects, there is now a scientific consensus that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy. 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. ... This article is about the physical phenomenon. ... Electrical energy or Electromagnetic energy is a form of energy present in any electric field or magnetic field, or in any volume containing electromagnetic radiation. ... It has been suggested that this article or section be merged with Radio waves. ... Visible light redirects here. ... This article is about the astronomical object. ... Scientific consensus is the collective judgment, position, and opinion of the community of scientists in a particular field of science at a particular time. ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ... This article is about matter in physics and chemistry. ... Top: artists conception of a supermassive black hole tearing apart a star. ...

Contents

Overview

Quasars show a very high redshift which is an effect of the expansion of the universe between the quasar and the Earth. When combined with Hubble's law, the implication of the redshift is that the quasars are very distant. To be observable at that distance, the energy output of quasars dwarf every other astronomical event. Quasars may readily release energy in levels equal to the output of hundreds of average galaxies combined. The output of light is equivalent to one trillion suns. This article is about the physical phenomenon. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... For other uses, see Galaxy (disambiguation). ...


In optical telescopes, quasars look like single points of light (i.e. point source) although many have had their "host galaxies" identified.[1] The galaxies themselves are often too dim to be seen with any but the largest telescopes. Most quasars cannot be seen with small telescopes, but 3C 273, with an average apparent magnitude of 12.9, is an exception. At a distance of 2.44 billion light-years (lt-yr), it is one of the most distant objects directly observable with amateur equipment. This article does not cite any references or sources. ... Look up point source in Wiktionary, the free dictionary. ... 3C273 is a quasar located in the constellation Virgo. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ...


Some quasars display rapid changes in luminosity, which implies that they are small (an object cannot change faster than the time it takes light to travel from one end to the other; but see quasar J1819+3845 for another explanation). The highest redshift known for a quasar (as of December 2007) is 6.43,[2] which corresponds (assuming the currently-accepted value of 71 for the Hubble Constant) to a distance of approximately 28 billion light-years. (NB there are some subtleties in distance definitions in cosmology, so that distances greater than 13.7 billion lt-yr, or even greater than 27.4 = 2*13.7 lt-yr, can occur.) This article does not cite any references or sources. ... QSO J1819+3845 (Quasi-Stellar Object) is a quasar notable for being the most variable known extragalactic radio source. ... This article is about the physical phenomenon. ... Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe. ...


Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies. No other currently known mechanism appears able to explain the vast energy output and rapid variability. In astrophysics, the term accretion is used for at least two distinct processes. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ... 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. ...


Knowledge of quasars is advancing rapidly. As recently as the 1980s, there was no clear consensus as to their origin.


Properties of quasars

More than 100,000 quasars are known. All observed quasar spectra have redshifts between 0.06 and 6.4. Applying Hubble's law to these redshifts, it can be shown that they are between 780 million and 28 billion light-years away. Because of the great distances to the furthest quasars and the finite velocity of light, we see them and their surrounding space as they existed in the very early universe. This article is about the physical phenomenon. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ...


Most quasars are known to be farther than three billion light-years away. Although quasars appear faint when viewed from Earth, the fact that they are visible from so far away means that quasars are the most luminous objects in the known universe. The quasar that appears brightest in the sky is 3C 273 in the constellation of Virgo. It has an average apparent magnitude of 12.8 (bright enough to be seen through a small telescope), but it has an absolute magnitude of −26.7. From a distance of about 33 light-years, this object would shine in the sky about as brightly as our sun. This quasar's luminosity is, therefore, about 2 trillion (2 × 1012) times that of our sun, or about 100 times that of the total light of average giant galaxies like our Milky Way. 3C273 is a quasar located in the constellation Virgo. ... This article is about the star grouping. ... Virgo (pronounced , Latin: , symbol , ) is a constellation of the zodiac. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This article does not cite any references or sources. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... Sol redirects here. ... This article does not cite any references or sources. ... One million million (1,000,000,000,000) is the natural number following 999,999,999,999 and preceding 1,000,000,000,001. ... For other uses, see Milky Way (disambiguation). ...


The hyperluminous quasar APM 08279+5255 was, when discovered in 1998, given an absolute magnitude of −32.2, although high resolution imaging with the Hubble Space Telescope and the 10 m Keck Telescope revealed that this system is gravitationally lensed. A study of the gravitational lensing in this system suggests that it has been magnified by a factor of ~10. It is still substantially more luminous than nearby quasars such as 3C 273. This article or section is not written in the formal tone expected of an encyclopedia article. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... The Hubble Space Telescope (HST; also known colloquially as the Hubble or just Hubble) is a space telescope that was carried into Earth orbit by the Space Shuttle in April 1990. ... The Mauna Kea Observatory, an institute of the University of Hawaii, is considered one of the most important land-based observatories in the world for its isolated, unobstructed views of space without interference from man-made light sources. ... 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. ...


Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This evidence has allowed scientists to theorize that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across.


Quasars exhibit many of the same properties as active galaxies: Radiation is nonthermal and some are observed to have jets and lobes like those of radio galaxies. Quasars can be observed in many parts of the electromagnetic spectrum including radio, infrared, optical, ultraviolet, X-ray and even gamma rays. Most quasars are brightest in their rest-frame near-ultraviolet (near the 1216 angstrom (121.6 nm) Lyman-alpha emission line of hydrogen), but due to the tremendous redshifts of these sources, that peak luminosity has been observed as far to the red as 9000 angstroms (900 nm or 0.9 µm), in the near infrared. For other uses, see Radiation (disambiguation). ... 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. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ... For other uses, see Infrared (disambiguation). ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... For other uses, see Ultraviolet (disambiguation). ... 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... This article is about electromagnetic radiation. ... An angstrom, angström, or Ã¥ngström (symbol Ã…) is a unit of length. ... A nanometre (American spelling: nanometer) is 1. ... The Lyman series is the series of transitions and resulting emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1 (where n is the principal quantum number referring to the energy level of the electron). ...


Iron Quasars show strong emission lines resulting from ionized iron, such as IRAS 18508-7815. General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ...


Quasar emission generation

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.
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.

Since quasars exhibit properties common to all active galaxies, the emissions from quasars can be readily compared to those of small active galaxies powered by supermassive black holes. To create a luminosity of 1040 W (the typical brightness of a quasar), a super-massive black hole would have to consume the material equivalent of 10 stars per year. The brightest known quasars devour 1000 solar masses of material every year. The largest known is estimated to consume matter equivalent to 600 Earths per hour. Quasars 'turn on' and off depending on their surroundings, and since quasars cannot continue to feed at high rates for 10 billion years, after a quasar finishes accreting the surrounding gas and dust, it becomes an ordinary galaxy. Download high resolution version (700x700, 145 KB)Quasar Burst, source: http://www. ... Download high resolution version (700x700, 145 KB)Quasar Burst, source: http://www. ... In astronomy, starburst is a generic term to describe a region of space with a much higher than normal star formation. ... 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 tearing apart a star. ... For other uses, see Watt (disambiguation). ...


Quasars also provide some clues as to the end of the Big Bang's reionization. The oldest quasars (redshift > 4) display a Gunn-Peterson trough and have absorption regions in front of them indicating that the intergalactic medium at that time was neutral gas. More recent quasars show no absorption region but rather their spectra contain a spiky area known as the Lyman-alpha forest. This indicates that the intergalactic medium has undergone reionization into plasma, and that neutral gas exists only in small clouds. For other uses, see Big Bang (disambiguation). ... Schematic timeline of the universe, depicting reionizations place in cosmic history. ... This article is about the physical phenomenon. ... In Astronomical spectroscopy, the Gunn-Peterson trough is a feature of the spectra of quasars due to the presence of neutral hydrogen in the Intergalactic Medium (IGM). ... Intergalactic space is the physical space between galaxies. ... In astronomical spectroscopy, the Lyman alpha forest is the sum of absorption lines seen in spectra of distant galaxies and quasars, beginning from the Lyman alpha line at 121. ...


One other interesting characteristic of quasars is that they show evidence of elements heavier than helium, indicating that galaxies underwent a massive phase of star formation, creating population III stars between the time of the Big Bang and the first observed quasars. Light from these stars may have been observed in 2005 using NASA's Spitzer Space Telescope,[3] although this observation remains to be confirmed. General Name, symbol, number helium, He, 2 Chemical series noble gases Group, period, block 18, 1, s Appearance colorless Standard atomic weight 4. ... Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ... For other uses, see Big Bang (disambiguation). ... For other uses, see NASA (disambiguation). ... The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility [SIRTF]) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ...


History of quasar observation

The first quasars were discovered with radio telescopes in the late 1950s. Many were recorded as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size.[4] Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for the optical counterparts. In 1960, radio source 3C 48 was finally tied to an optical object. Astronomers detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum. Containing many unknown broad emission lines, the anomalous spectrum defied interpretation — a claim by John Bolton of a large redshift was not generally accepted. The 1950s decade refers to the years 1950 to 1959 inclusive. ... The 76m Lovell Telescope at Jodrell Bank Observatory. ... Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. ... The Third Cambridge Catalogue of Radio Sources (3C) is an astronomical catalogue of celestial radio sources measured at 159-MHz. ... 3C48 was the first source in the Third Cambridge (3C) radio survey for which an optical identification was found (by Allan Sandage in 1960). ... John Gatenby Bolton (June 5, 1922 – July 6, 1993) was a British-Australian astronomer. ...


In 1962 a breakthrough was achieved. Another radio source, 3C 273, was predicted to undergo five occultations by the moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent. This discovery showed that 3C 273 was receding at a rate of 47,000 km/s.[5] This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources. As predicted earlier by Bolton, 3C 48 was found to have a redshift of 37% the speed of light. Year 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar) of the Gregorian calendar. ... 3C273 is a quasar located in the constellation Virgo. ... In Islam the occulation is the name given to the disappearance of the Twelfth Imam. ... This article is about Earths moon. ... The Parkes Observatory in New South Wales, Australia The Parkes Observatory is a radio telescope observatory, 20 kilometres north of the town of Parkes, New South Wales, Australia. ... Maarten Schmidt (born December 28, 1929) is a Dutch astronomer who measured the distances of astronomical objects called quasars. ... The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ... The Hale Telescope is the largest telescope at the Palomar Observatory. ...


The term quasar was coined by Chinese-born U.S. astrophysicist Hong-Yee Chiu in 1964, in Physics Today, to describe these puzzling objects: An astrophysicist is a person whose profession is astrophysics. ... Physics Today magazine, created in 1948, is the flagship publication of The American Institute of Physics. ...

So far, the clumsily long name 'quasi-stellar radio sources' is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form 'quasar' will be used throughout this paper.

Hong-Yee Chiu in Physics Today, May, 1964

Later it was found that not all (actually only 10% or so) quasars have strong radio emission (are 'radio-loud'). Hence the name 'QSO' (quasi-stellar object) is used (in addition to 'quasar') to refer to these objects, including the 'radio-loud' and the 'radio-quiet' classes.


One great topic of debate during the 1960s was whether quasars were nearby objects or distant objects as implied by their redshift. It was suggested, for example, that the redshift of quasars was not due to the expansion of space but rather to light escaping a deep gravitational well. However a star of sufficient mass to form such a well would be unstable and in excess of the Hayashi limit.[6] Quasars also show unusual spectral emission lines which were previously only seen in hot gaseous nebulae of low density, which would be too diffuse to both generate the observed power and fit within a deep gravitational well.[7] There were also serious concerns regarding the idea of cosmologically distant quasars. One strong argument against them was that they implied energies that were far in excess of known energy conversion processes, including nuclear fusion. At this time, there were some suggestions that quasars were made of some hitherto unknown form of stable antimatter and that this might account for their brightness. Others speculated that quasars were a white hole end of a wormhole. However, when accretion disc energy-production mechanisms were successfully modeled in the 1970s, the argument that quasars were too luminous became moot and today the cosmological distance of quasars is accepted by almost all researchers. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969. ... This article is about the physical phenomenon. ... This article is about the physical phenomenon. ... Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ... For other senses of this term, see antimatter (disambiguation). ... For the Red Dwarf episode, see White Hole (Red Dwarf episode). ... For other uses, see Wormhole (disambiguation). ... Artists conception of a binary star system with one black hole and one main sequence star Unsolved problems in physics: Accretion disc jets: Why do the discs surrounding certain objects, such as the nuclei of active galaxies, emit radiation jets along their polar axes? These jets are invoked by... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ...


In 1979 the gravitational lens effect predicted by Einstein's General Theory of Relativity was confirmed observationally for the first time with images of the double quasar 0957+561.[8] Also: 1979 by Smashing Pumpkins. ... This article or section is in need of attention from an expert on the subject. ... Einstein redirects here. ... General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... The Twin Quasar (Double Quasar) or Old Faithful is also known as Q0957+561, or QSO 0957+561. ...


In the 1980s, unified models were developed in which quasars were classified as a particular kind of active galaxy, and a general consensus emerged that in many cases it is simply the viewing angle that distinguishes them from other classes, such as blazars and radio galaxies. The huge luminosity of quasars results from the accretion discs of central supermassive black holes, which can convert on the order of 10% of the mass of an object into energy as compared to 0.7% for the p-p chain nuclear fusion process that dominates the energy production in sun-like stars. The 1980s refers to the years from 1980 to 1989. ... A blazar is a very compact and highly variable energy source associated with a supermassive black hole at the center of a host galaxy. ... 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. ... Artists conception of a binary star system with one black hole and one main sequence star Unsolved problems in physics: Accretion disc jets: Why do the discs surrounding certain objects, such as the nuclei of active galaxies, emit radiation jets along their polar axes? These jets are invoked by... For other uses, see Mass (disambiguation). ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ...


This mechanism also explains why quasars were more common in the early universe, as this energy production ends when the supermassive black hole consumes all of the gas and dust near it. This means that it is possible that most galaxies, including our own Milky Way, have gone through an active stage (appearing as a quasar or some other class of active galaxy depending on black hole mass and accretion rate) and are now quiescent because they lack a supply of matter to feed into their central black holes to generate radiation.


Further reading

This article does not cite its references or sources. ... The headquarters of the Cambridge University Press, in Trumpington Street, Cambridge. ...

See also

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 blazar is a very compact and highly variable energy source associated with a supermassive black hole at the center of a host galaxy. ... Proper naming of quasars are by Catalogue Entry, Qxxxx±yy using B1950 coordinates, or QSO Jxxxx±yyyy using J2000 coordinates. ... An OVV Quasar, or an Optically Visually Violent Quasar, is a type of highly variable quasar. ... Top: artists conception of a supermassive black hole tearing apart a star. ... Microquasars are smaller cousins of quasars. ...

References

  1. ^ Hubble Surveys the "Homes" of Quasars Hubblesite News Archive, 1996-35
  2. ^ Chris J. Willott et al. (2007). "Four Quasars above Redshift 6 Discovered by the Canada-France High-z Quasar Survey". The Astronomical Journal 134: 2435-2450. 
  3. ^ NASA Goddard Space Flight Center: News of light that may be from population III stars
  4. ^ The MKI and the discovery of Quasars. Jodrell Bank Observatory. Retrieved on 2006-11-23.
  5. ^ Schmidt Maarten (1963). "3C 273: a star-like object with large red-shift". Nature 197: 1040-1040. 
  6. ^ S. Chandrasekhar (1964). "The Dynamic Instability of Gaseous Masses Approaching the Schwarzschild Limit in General Relativity". Astrophysical Journal 140 (2): 417–433. 
  7. ^ J. Greenstein and M. Schmidt (1964). "The Quasi-Stellar Radio Sources 3C 48 and 3C ". Astrophysical Journal 140 (1): 1–34. 
  8. ^ Active Galaxies and Quasars - Double Quasar 0957+561
  • Complete Cosmos - Discovery Science Channel

The 76m Lovell Telescope at Jodrell Bank Observatory. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 327th day of the year (328th in leap years) in the Gregorian calendar. ...

External links

is the 207th day of the year (208th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ...

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