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Encyclopedia > Andromeda Galaxy
Andromeda Galaxy

A visible light image of the Andromeda Galaxy.
Credit: John Lanoue.
Observation data (J2000 epoch)
Constellation Andromeda
Right ascension 00h 42m 44.3s[1]
Declination +41° 16′ 9″[1]
Redshift −301 ± 1 km/s[2]
Distance 2.54 ± 0.06 Mly
(778 ± 17 kpc)[3][2][4][5][6][a]
Type SA(s)b[1]
Apparent dimensions (V) 190′ × 60′[1]
Apparent magnitude (V) 4.4[1]
Other designations
M31, NGC 224, UGC 454, PGC 2557[1]
See also: Galaxy, List of galaxies

The Andromeda Galaxy (IPA: /ænˈdrɒmədə/, also known as Messier 31, M31, or NGC 224; often referred to as the Great Andromeda Nebula in older texts) is a spiral galaxy approximately 2.5 million light-years away[4] in the constellation Andromeda. It is the nearest spiral galaxy to our own, the Milky Way, and is visible as a faint smudge on a moonless night to the naked eye. Image File history File links M31_Lanoue. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... The J2000. ... In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... This article is about the star grouping. ... Andromeda (IPA: ) is a constellation named for the princess Andromeda (which is Greek for Ruler over men), a character in Greek mythology. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... This article is about the physical phenomenon. ... “km” redirects here. ... This article is about the unit of time. ... (Redirected from 1 E22 m) Categories: Orders of magnitude (length) ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... 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. ... The Messier objects are a set of astronomical objects catalogued by Charles Messier in his catalogue of Nebulae and Star Clusters first published in 1774. ... The New General Catalogue (NGC) is the best-known catalogue of deep sky objects in amateur astronomy. ... The Uppsala General Catalogue of Galaxies (UGC) is a catalogue of 12921 galaxies visible from the northern hemisphere. ... The Principal Galaxies Catalogue (PGC) is an astronomical catalogue that contains all available primary information for each of the known galaxies: morphological type, major and minor axes, magnitude, radial velocity and position angle. ... For other uses, see Galaxy (disambiguation). ... List of galaxies: Abell 1835 IR1916 AM 0644-741 Andromeda Galaxy (M31/NGC 224) Andromeda I Andromeda II Andromeda III Aquarius Dwarf Barnards Galaxy (NGC 6822) Black Eye Galaxy (M64/NGC 4826) Bodes Galaxy (M81/NGC 3031) Canis Major Dwarf Galaxy Carina Dwarf Centaurus A Galaxy Draco Dwarf Fornax... The Triangulum Emission Nebula NGC 604 The Pillars of Creation from the Eagle Nebula For other uses, see Nebula (disambiguation). ... An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”[1] and, as... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... This article is about the star grouping. ... Andromeda (IPA: ) is a constellation named for the princess Andromeda (which is Greek for Ruler over men), a character in Greek mythology. ... An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”[1] and, as... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion...


Andromeda is the largest galaxy of the Local Group, which consists of the Andromeda Galaxy, the Milky Way Galaxy, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, it may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping.[7] However, recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars, greatly exceeding the number of stars in our own galaxy.[8] 2006 estimates put the mass of the Milky Way to be ~80% of the mass of Andromeda, which is estimated to be 7.1×1011 solar masses.[2] A member of the Local Group of galaxies, irregular galaxy Sextans A is 4. ... The Triangulum Galaxy (also known as Messier 33 or NGC 598) is a spiral galaxy about 3. ... For other uses, see Dark matter (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. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...


At an apparent magnitude of 4.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects,[9] making it easily visible to the naked eye even when viewed from areas with moderate light pollution. It appears quite small without a telescope because only the central part is bright enough to be visible, but the full angular diameter of the galaxy is seven times that of the full moon. 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. ... The Messier objects are a set of astronomical objects catalogued by Charles Messier in his catalogue of Nebulae and Star Clusters first published in 1774. ... The naked eye is a figure of speech referring to human visual perception that is unaided by enhancing equipment, such as a telescope or binoculars. ... This time exposure photo of New York City shows sky glow, one form of light pollution. ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... This article is about Earths moon. ...

Contents

Observation history

The earliest recorded observation of the Andromeda Galaxy was in 964 CE by the Persian astronomer 'Abd Al-Rahman Al Sufi,[10] who described it as a "small cloud". Star charts of that period have it labeled as the Little Cloud.[10] The first description of the object based on telescopic observation was given by Simon Marius[10] in 1612. Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of the M31. He believed it to be the nearest of all the "great nebulae" and, based on the color and magnitude of the nebula, he estimated (incorrectly) that it was no more than 2,000 times the distance of Sirius.[11] BCE redirects here. ... Galileo is often referred to as the Father of Modern Astronomy. ... This article does not cite any references or sources. ... Simon Marius Simon Marius (January 10, 1573 – December 26, 1624) was a German astronomer. ... Charles Messier Charles Messier (June 26, 1730 – April 12, 1817) was a French astronomer who in 1774 published a catalogue of 45 deep sky objects such as nebulae and star clusters. ... For other persons named William Herschel, see William Herschel (disambiguation). ... This article is about the brightest star in the night sky of Earth. ...


William Huggins in 1864 observed the spectrum of M31 and noted that it differed from a gaseous nebula.[12] The spectra of M31 displayed a continuum of frequencies, superimposed with dark lines. This was very similar to the spectra of individual stars. From this it was deduced that M31 had a stellar nature. William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ... This article deals with the general meaning of spectrum and the history of its use. ... Look up continuum in Wiktionary, the free dictionary. ... For other uses, see Frequency (disambiguation). ... 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. ...


In 1885, a supernova (known as "S Andromedae") was seen in M31, the first and so far only one observed in that galaxy. At the time, since M31 was considered to be a "near by" object, it was thought to be a much less luminous and unrelated event called a nova, and was named accordingly Nova 1885. For other uses, see Supernova (disambiguation). ... S Andromedae (also SN 1885A) was a supernova in the Andromeda Galaxy, the only one seen in that galaxy so far by astronomers, and the first ever noted outside the Milky Way. ... Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ...

Great Andromeda Nebula by Isaac Roberts.
Great Andromeda Nebula by Isaac Roberts.

The first photographs of M31 were taken in 1887 by Isaac Roberts from his private observatory in Sussex. The long-duration exposure allowed the spiral structure of the galaxy to be seen for the first time.[13] However, at the time this object was commonly believed to be a nebula within our galaxy, and Roberts mistakenly believed that M31 and similar spiral nebulae were actually solar systems being formed, with the satellites nascent planets. Image File history File links Pic_iroberts1. ... Image File history File links Pic_iroberts1. ... Isaac Roberts Isaac Roberts (January 17/27 1829- July 17, 1904) was a British astronomer who was a pioneer in photography of nebulae. ... For other uses, see Photograph (disambiguation). ... Isaac Roberts Isaac Roberts (January 17/27 1829- July 17, 1904) was a British astronomer who was a pioneer in photography of nebulae. ... This article refers to the historic county in England. ...


The radial velocity of this object with respect to our solar system was measured in 1912 by Vesto Slipher at the Lowell Observatory, using spectroscopy. The result was the largest velocity recorded at that time, at 300 kilometres per second (186 miles/sec.), moving in the direction of the Sun.[14] Radial velocity is the velocity of an object in the direction of the line of sight. ... This article is about the Solar System. ... Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... Lowell Observatory Percival observing Mars from the Clark telescope at the Lowell Observatory. ... Animation of the dispersion of light as it travels through a triangular prism. ...


Island universe

In 1917, Heber Curtis had observed a nova within M31. Searching the photographic record, 11 more novae were discovered. Curtis noticed that these novae were, on average, 10 magnitudes fainter than those that occurred within our Galaxy. As a result he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the so-called "island universes" hypothesis, which held that spiral nebulae were actually independent galaxies.[15] Heber Doust Curtis (June 27, 1872 – January 9, 1942) was an American astronomer. ... In science, magnitude refers to the numerical size of something: see orders of magnitude. ... An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”[1] and, as...


In 1920 the Great Debate between Harlow Shapley and Heber Curtis took place, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that "Great Andromeda Nebula" (M31) was an external galaxy, Curtis also noted the appearance of dark lanes resembling the dust clouds in our own Galaxy, as well as the significant Doppler shift. Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars for the first time on astronomical photos of M31. These were made using a 2.5 metre (100 in) reflecting telescope, and they enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our Galaxy, but an entirely separate galaxy located a significant distance from our own.[16] The Andromeda Galaxy The Great Debate was an influential debate between the astronomers Harlow Shapley and Heber Curtis which concerned the nature of spiral nebulae and the size of the universe. ... Harlow Shapley in his earlier years. ... Heber Doust Curtis (June 27, 1872 – January 9, 1942) was an American astronomer. ... For other uses, see Milky Way (disambiguation). ... An example of a spiral galaxy, the Pinwheel Galaxy (also known as Messier 101 or NGC 5457) A spiral galaxy is a galaxy belonging to one of the three main classes of galaxy originally described by Edwin Hubble in his 1936 work “The Realm of the Nebulae”[1] and, as... For other uses, see Universe (disambiguation). ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Cepheid in the Spiral Galaxy M100 A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. ... This article or section contains a plot summary that is overly long or excessively detailed. ... This article is about the unit of length. ... 24 inch convertible Newtonian/Cassegrain reflecting telescope on display at the Franklin Institute. ...


This galaxy plays an important role in galactic studies, since it is the nearest giant spiral (although not the nearest galaxy). In 1943, Walter Baade was the first person to resolve stars in the central region of the Andromeda Galaxy. Based on his observations of this galaxy, he was able to discern two distinct populations of stars, naming the young, high velocity stars in the disk Type I and the older, red stars in the bulge Type II. This nomenclature was subsequently adopted for stars within the Milky Way, and elsewhere. (The existence of two distinct populations had been noted earlier by Jan Oort.)[17] Dr. Baade also discovered that there were two types of Cepheid variables, which resulted in a doubling of the distance estimate to M31, as well as the remainder of the Universe. The reader should be aware that there are certain unavoidable difficulties with this list. ... Wilhelm Heinrich Walter Baade (March 24, 1893 - June 25, 1960) was a German astronomer who emigrated to the USA in 1931. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... Jan Hendrik Oort (April 28, 1900 – November 5, 1992) was an internationally famous Dutch astronomer. ... Cepheid in the Spiral Galaxy M100 A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. ...


The first radio maps of the Andromeda Galaxy were made in the 1950s by John Baldwin and collaborators at the Cambridge Radio Astronomy Group. The core of the Andromeda Galaxy is called 2C 56 in the 2C radio astronomy catalogue. The Very Large Array, a radio interferometer in New Mexico, USA Radio astronomy is a subfield of astronomy that studies celestial objects in the radio frequency portion of the electromagnetic spectrum. ... Prof. ... The Cavendish Astrophysics Group (formerly the Radio Astronomy Group) is based at the Cavendish Laboratory at Cambridge University. ... The Second Cambridge Catalogue of Radio Sources (2C) was published in 1955 by J R Shakeshaft and colleagues. ...


General information

The Andromeda Galaxy is approaching the Sun at about 300 kilometers per second (186 miles/sec.), so it is one of the few blue shifted galaxies. Given the motion of the Solar System inside the Milky Way, one finds that the Andromeda Galaxy and the Milky Way are approaching one another at a speed of 100 to 140 kilometers per second (62–87 miles/sec.).[18] The impact is predicted to occur in about 2.5 billion years. In that case the two galaxies will likely merge to form a giant elliptical galaxy.[19] However, Andromeda's tangential velocity with respect to the Milky Way is only known to within about a factor of two, which creates uncertainty about the details of when the collision will take place and how it will proceed.[20] Such events are frequent among the galaxies in galaxy groups. Sol redirects here. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... This article is about the Solar System. ... The giant elliptical galaxy ESO 325-G004. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...


The measured distance to the Andromeda Galaxy was doubled in 1953 when it was discovered that there is another, dimmer type of Cepheid. In the 1990s, Hipparcos satellite measurements were used to calibrate the Cepheid distances. The corrected value gives the Andromeda Galaxy a distance of 2.9 million light-years. Unfortunately, all Cepheids lie further than Hipparcos could measure accurately, and it became clear that Hipparcos-calibrated values for Cepheids were not reliable.[citation needed] Hipparcos (for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. ...

The Andromeda Galaxy pictured in ultraviolet light by GALEX
The Andromeda Galaxy pictured in ultraviolet light by GALEX
See also: Andromeda-Milky Way collision

Download high resolution version (6200x6200, 4227 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (6200x6200, 4227 KB) Wikipedia does not have an article with this exact name. ... For other uses, see Ultraviolet (disambiguation). ... The Galaxy Evolution Explorer is an orbiting space telescope that was launched on April 28, 2003. ... It has been suggested that this article or section be merged into Milky Way. ...

Recent distance estimates

At least four distinct techniques have been used to measure distances to M31.


In 2003, using the infrared surface brightness fluctuations (I-SBF) and adjusting for the new period-luminosity value of Freedman et al. 2001 and using a metallicity correction of -0.2 mag dex-1 in (O/H), an estimate of 2.57 ± 0.06 Mly (787 ± 18 kpc) was derived. Surface brightness fluctuation (SBF) is a secondary distance indicator used to estimate distances to galaxies. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ...


Using the Cepheid variable method, an estimate of 2.51 ± 0.13 Mly (770 ± 40 kpc) was achieved in 2004.[3][2] Cepheid in the Spiral Galaxy M100 A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. ...


In 2005, a group of astronomers consisting of Ignasi Ribas (CSIC, IEEC) and his colleagues announced the discovery of an eclipsing binary star in the Andromeda Galaxy. The binary star, designated M31VJ00443799+4129236,[c] has two luminous and hot blue stars of types O and B. By studying the eclipses of the stars, which occur every 3.54969 days, the astronomers were able to measure their sizes. Knowing the sizes and temperatures of the stars they were able to measure the absolute magnitude of the stars. When the visual and absolute magnitudes are known, the distance to the star can be measured. The stars lie at the distance of 2.52 ± 0.14 Mly (770 ± 40 kpc) and the whole Andromeda Galaxy at about 2.5 Mly.[4] This new value is in excellent agreement with the previous, independent Cepheid-based distance value. Animation showing how an eclipsing binary stars light intensity changes as they orbit An eclipsing binary star is a binary star in which the orbit plane of the two stars lies so nearly in the line of sight of the observer that the components undergo mutual eclipses. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... 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 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. ...


Andromeda is close enough that the Tip of the Red Giant Branch (TRGB) method may also be used to estimate its distance. The estimated distance to M31 using this technique in 2005 yielded 2.56 ± 0.08 Mly (785 ± 25 kpc).[5] Tip of the Red Giant Branch (TRGB) is a primary distance indicator used in astronomy. ...


Averaged together, all these distance measurements give a combined distance estimate of 2.54 ± 0.06 Mly (778 ± 17 kpc).[a] Based upon the above distance, the diameter of M31 at the widest point is estimated to be 141 ± 3 kly.[d]


Mass estimates

Mass estimates for the Andromeda halo (including dark matter) give a value of approximately 1.23×1012 M[21] (or 1.2 million million solar masses) compared to 1.9×1012 M for the Milky Way. Thus M31 may be less massive than our own galaxy, although the error range is still too large to say for certain. M31 does contain many more stars than our own galaxy and has a much larger size. For other uses, see Dark matter (disambiguation). ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... One million million (1,000,000,000,000) is the natural number following 999,999,999,999 and preceding 1,000,000,000,001. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...


In particular, M31 appears to have significantly more common stars than the Milky Way, and the estimated luminosity of M31 is double that of our own galaxy.[22] However the rate of star formation in the Milky Way is much higher, with M31 only producing about one solar mass per year compared to 3–5 solar masses for the Milky Way. The rate of novae in the Milky Way is also double that of M31.[23] This suggests that M31 has experienced a great star formation phase in its past, while the Milky Way is in the middle of a current star formation phase. This could mean that in the future, the number of stars in the Milky Way will match the number observed in M31. Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ...


Structure

Based on its appearance in visible light, the Andromeda galaxy is classified as an SA(s)b galaxy in the de Vaucouleurs-Sandage extended classification system of spiral galaxies.[1] However, data from the 2MASS survey showed that the bulge of M31 has a box-like appearance, which implies that the galaxy is actually a barred galaxy with the bar viewed almost directly along its long axis.[24] Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... Observations for the Two Micron All-Sky Survey (2MASS) began in 1997 and were completed in 2001 at two telescopes located one each in the northern and southern hemispheres (Mt. ...

The Andromeda Galaxy seen in infrared by the Spitzer Space Telescope, one of NASA's four Great Space Observatories
The Andromeda Galaxy seen in infrared by the Spitzer Space Telescope, one of NASA's four Great Space Observatories

In 2005, astronomers used the Keck telescopes to show that the tenuous sprinkle of stars extending outward from the galaxy is actually part of the main disk itself.[25] This means that the spiral disk of stars in Andromeda is three times larger in diameter than previously estimated. This constitutes evidence that there is a vast, extended stellar disk that makes the galaxy more than 220,000 light-years in diameter. Previously, estimates of Andromeda's size ranged from 70,000 to 120,000 light-years across. Image File history File linksMetadata Download high resolution version (3600x1294, 4337 KB) Summary Image of Adromeda Galaxy in infrared. ... Image File history File linksMetadata Download high resolution version (3600x1294, 4337 KB) Summary Image of Adromeda Galaxy in infrared. ... For other uses, see Infrared (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. ... For other uses, see NASA (disambiguation). ... NASAs series of Great Observatories satellites were four large, powerful space-based telescopes. ... The W. M. Keck Observatory is home to the two largest optical/near-infrared telescopes at the 4,145 meter (13,600 ft) summit of Mauna Kea in Hawaii. ...


The galaxy is inclined an estimated 77° relative to the Earth (where an angle of 90° would be viewed directly from the side). Analysis of the cross-sectional shape of the galaxy appears to demonstrate a pronounced, S-shaped warp, rather than just a flat disk.[26] A possible cause of such a warp could be gravitational interaction with the satellite galaxies near M31. It also should be noted that the galaxy M33 could be responsible for some warp in M31's arms, though more precise distances and radial velocities are required. Messier Object 33, the Triangulum Galaxy. ...


Spectroscopic studies have provided detailed measurements of the rotational velocity of this galaxy at various radii from the core. In the vicinity of the core, the rotational velocity climbs to a peak of 225 kilometres per second (140 miles/sec.) at a radius of 1,300 light-years, then descends to a minimum at 7,000 light-years where the rotation velocity may be as low as 50 kilometres per second (31 miles/sec.). Thereafter the velocity steadily climbs again out to a radius of 33,000 light-years, where it reaches a peak of 250 kilometres per second (155 miles/sec.). The velocities slowly decline beyond that distance, dropping to around 200 kilometres per second (124 miles/sec.) at 80,000 light-years. These velocity measurements imply a concentrated mass of about 6×109 M in the nucleus. The total mass of the galaxy increases linearly out to 45,000 light-years, then more slowly beyond that radius.[27] Rotation curve of a typical spiral galaxy: predicted (A) and observed (B). ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... The nucleus of a galaxy is a large feature, most easily observed in spiral galaxies. ... For other uses, see Linear (disambiguation). ...


The spiral arms of Andromeda are outlined by a series of H II regions that Baade described as resembling "beads on a string". They appear to be tightly wound, although they are more widely spaced than in our galaxy.[28] Rectified images of the galaxy show a fairly normal spiral galaxy with the arms wound up in a clockwise direction. There are two continuous trailing arms that are separated from each other by a minimum of about 13,000 light-years. These can be followed outward from a distance of roughly 1,600 light-years from the core. The most likely cause of the spiral pattern is thought to be interaction with M32. This can be seen by the displacement of the neutral hydrogen clouds from the stars.[29] A spiral galaxy presents a face-on view of its spiral arms. ... NGC 604, a giant H II region in the Triangulum Galaxy. ... 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. ... An H I region (pronounced aitch one region) is an interstellar cloud composed of neutral atomic hydrogen (H1). ...

Image of Andromeda Galaxy (M31) taken by Spitzer in infrared, 24 micrometres (Credit:NASA/JPL-Caltech/K. Gordon (University of Arizona)

In 1998, images from the European Space Agency's Infrared Space Observatory demonstrated that the overall form of the Andromeda galaxy may be transitioning into a ring galaxy. The gas and dust within Andromeda is generally formed into several overlapping rings, with a particularly prominent ring formed at a radius of 32,000 light-years from the core.[30] This ring is hidden from visible light images of the galaxy because it is composed primarily of cold dust. ImageMetadata File history File links Download high resolution version (4097x1205, 1014 KB) Summary Andromeda Galaxy (M31) 2. ... ImageMetadata File history File links Download high resolution version (4097x1205, 1014 KB) Summary Andromeda Galaxy (M31) 2. ... The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility [SIRTF]) is an infrared space observatory, the fourth and final of NASAs Great Observatories. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... For other uses, see NASA (disambiguation). ... The JPL complex in Pasadena, Ca. ... California Institute of Technology The California Institute of Technology (commonly known as Caltech) is a private, coeducational university located in Pasadena, California, in the United States. ... The University of Arizona (UA or U of A) is a land-grant and space-grant public institution of higher education and research located in Tucson, Arizona, United States. ... ESA redirects here. ... The Infrared Space Observatory (ISO)is a space telescope for infrared light designed and operated by the European Space Agency (ESA). ... A ring galaxy is a galaxy with a ring-like appearance. ...


Close examination of the inner region of Andromeda showed a smaller dust ring that is believed to have been caused by the interaction with M32 more than 200 million years ago. Simulations show that the smaller galaxy passed through the disk of Andromeda along the latter's polar axis. This collision stripped more than half the mass from the smaller M32 and created the ring structures in Andromeda.[31]


Studies of the extended halo of M31 show that it is roughly comparable to that of the Milky Way, with stars in the halo being generally "metal"-poor, and increasingly so with greater distance.[32] This evidence indicates that the two galaxies have followed similar evolutionary paths. They are likely to have accreted and assimilated about 1–200 low-mass galaxies during the past 12 billion years.[33] The stars in the extended halos of M31 and the Milky Way may extend nearly one-third the distance separating the two galaxies.


Nucleus

HST image of Andromeda galaxy core showing possible double structure. NASA/ESA photo.
HST image of Andromeda galaxy core showing possible double structure. NASA/ESA photo.
Artist's concept of Andromeda galaxy core showing a view across a mysterious disk of young, blue stars encircling a supermassive black hole. NASA/ESA photo.
Artist's concept of Andromeda galaxy core showing a view across a mysterious disk of young, blue stars encircling a supermassive black hole. NASA/ESA photo.

M31 is known to harbor a dense and compact star cluster at its very center. In a large telescope it creates a visual impression of a star embedded in the more diffuse surrounding bulge. The luminosity of the nucleus is in excess of the most luminous globular clusters. Image File history File links 1993-18-a-web. ... Image File history File links 1993-18-a-web. ... For other uses, see NASA (disambiguation). ... This article is about the European Space Agency. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (4800 × 3600 pixel, file size: 18. ... Image File history File links Metadata Size of this preview: 800 × 600 pixelsFull resolution (4800 × 3600 pixel, file size: 18. ... For other uses, see NASA (disambiguation). ... This article is about the European Space Agency. ...


In 1991 Tod R. Lauer used WFPC, then on board the Hubble Space Telescope, to image Andromeda's inner nucleus. The nucleus is double, consisting of two concentrations separated by 1.5 parsecs. The brighter concentration, designated as P1, is offset from the center of the galaxy. The dimmer concentration, P2, falls at the true center of the galaxy and contains a 108 M black hole. Tod R. Lauer is an associate astronomer on the research staff of the National Optical Astronomy Observatory. ... The Wide Field and Planetary Camera (WFPC) was a camera installed on the Hubble Space Telescope. ... 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. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ... For other uses, see Black hole (disambiguation). ...


Scott Tremaine has proposed the following explanation of the double nucleus: P1 is the projection of a disk of stars in an eccentric orbit around the central black hole. The eccentricity is such that stars "linger" longer at the orbital apocenter, creating a concentration of stars. P2 also contains a compact disk of hot, spectral class A-stars. The A-stars are not evident in redder filters, but in blue and ultraviolet light they dominate the nucleus, causing P2 to appear more prominent than P1.[34] Scott Tremaine is a Canadian-born Astrophysicist. ... (This page refers to eccitricity in astrodynamics. ... A diagram of Keplerian orbital elements. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ...


While at the initial time of its discovery it was hypothesized that the brighter portion of the double nucleus was the remnant of a small galaxy 'cannibalized' by Andromeda,[35] this is no longer considered to be a viable explanation. Such a nucleus would have an exceedingly short lifetime to tidal disruption by the central black hole, nor does it have its own black hole to stabilize it. Further the clump does not resemble a galactic nucleus, nor is there any evidence of a merger at larger radii in the bulge.


Discrete sources

Multiple X-ray sources have been detected in the Andromeda Galaxy, using observations from the ESA's XMM-Newton orbiting observatory. Dr. Robin Barnard et al hypothesized that these are candidate black holes or neutron stars, which are heating incoming gas to millions of kelvins and emitting X-rays. The spectrum of the neutron stars is the same as the hypothesized black holes, but can be distinguished by their masses.[36] ESA redirects here. ... This article is about XMM-Newton. ... This article is about the celestial body. ...


There are approximately 460 globular clusters associated with the Andromeda galaxy.[37] The most massive of these clusters, identified as Mayall II, nicknamed Globular One, has a greater luminosity than any other known globular cluster in the local group of galaxies.[38] It contains several million stars, and is about twice as luminous as Omega Centauri, the brightest known globular cluster in the Milky Way. Globular One (or G1) has several stellar populations and a structure too massive for an ordinary globular. As a result, some consider G1 to be the remnant core of a dwarf galaxy that was consumed by M31 in the distant past.[39] The globular with the greatest apparent brightness is G76 which is located in the south-west arm's eastern half.[10] The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ... Mayall II, G1, SKHB 1, or HBK 0-1 is a globular cluster in M31, the Andromeda Galaxy. ... A member of the Local Group of galaxies, irregular galaxy Sextans A is 4. ... A small region at the heart of Omega Centauri, containing some 50,000 stars (NASA/STScI) Omega Centauri or NGC 5139 is a globular cluster of stars orbiting our galaxy, the Milky Way. ... For other uses, see Milky Way (disambiguation). ... A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Ways 200-400 billion stars. ...


In 2005, astronomers discovered a completely new type of star cluster in M31. The new-found clusters contain hundreds of thousands of stars, a similar number of stars that can be found in globular clusters. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across – and hundreds of times less dense. The distances between the stars are, therefore, much greater within the newly discovered extended clusters.[40]


Satellites

Like the Milky Way, Andromeda Galaxy has satellite galaxies, consisting of 14 known dwarf galaxies. The best known and most readily observed satellite galaxies are M32 and M110. Plane of the Andromeda Galaxys satellites The Andromeda Galaxy has satellite galaxies just like the Milky Way Galaxy. ... For other uses, see Milky Way (disambiguation). ... A satellite galaxy orbits a larger galaxy, due to gravitational attraction. ... A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Ways 200-400 billion stars. ... 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. ... The Elliptical Galaxy M110 (also known as Messier Object 110, Messier 110, M110, or NGC 205) is an elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ...


Based on current evidence, it appears that M32 underwent a close encounter with M31 (Andromeda) in the past. M32 may once have been a larger galaxy that had its stellar disk removed by M31, and underwent a sharp increase of star formation in the core region, which lasted until the relative recent past.[41]


M110 also appears to be interacting with M31, and astronomers have found a stream of metal-rich stars in the halo of M31 that appears to have been stripped from these satellite galaxies.[42] M110 does contain a dusty lane, which is a hint for recent or ongoing star formation. This is unusual in elliptical galaxies, which are usually fairly low in dust and gas. Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are much smaller than others, classified as dE. They are quite common in galaxy groups and clusters, and are usually companions to other galaxies. ...


In 2006 it was discovered that nine of these galaxies lay along a plane that intersects the core of the Andromeda Galaxy, rather than being randomly arranged as would be expected from independent interactions. This may indicate a common tidal origin for the satellites.[43]

Andromeda's satellites discovered before 1900
Name Type Distance
from Sun
(Mly)
Magnitude Discovered by Year
discovered
M32 cE2 2.65 ± 0.10 +9.0 Guillaume Le Gentil 1749
M110 E5 pec 2.69 ± 0.09 +8.9 Charles Messier 1773
NGC 185 dSph/dE3 2.08 ± 0.15 +10.1 William Herschel 1787
NGC 147 dSph/dE5 2.67 ± 0.18 +10.5 John Herschel 1829

Astronomers classify galaxies based on their overall shape (elliptical, spiral or barred spiral) and further by the specific properties of the individual galaxy (for example degree of ellipse, number of spirals or definition of bar). ... Sol redirects here. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... 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. ... 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. ... Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière (September 12, 1725 – October 22, 1792) was a French astronomer. ... The Elliptical Galaxy M110 (also known as Messier Object 110, Messier 110, M110, or NGC 205) is an elliptical galaxy in the Andromeda constellation, a satellite of the Andromeda Galaxy, and a member of the Local Group galaxies. ... Charles Messier Charles Messier (June 26, 1730 – April 12, 1817) was a French astronomer who in 1774 published a catalogue of 45 deep sky objects such as nebulae and star clusters. ... NGC 185 is a dwarf elliptical galaxy about 2. ... For other persons named William Herschel, see William Herschel (disambiguation). ... Dwarf spheroidal galaxy NGC 147 is a member of the Local Group of galaxies. ... John Herschel Sir John Frederick William Herschel (7 March 1792 – 11 May 1871) was an English mathematician and astronomer. ...

See also

Galaxies other than the Milky Way are popular settings for creators of science fiction, particularly those working with broad-scale space opera settings. ... Mayall II, G1, SKHB 1, or HBK 0-1 is a globular cluster in M31, the Andromeda Galaxy. ... The Globular Cluster M80 in the constellation Scorpius is located about 28,000 light years from the Sun and contains hundreds of thousands of stars. ... NGC 206 is a bright star cloud in the Andromeda Galaxy. ... A star cloud is a group of stars that appear to be in the same position in the sky. ... Table of images of all 110 Messier objects. ... The New General Catalogue (NGC) is the best-known catalogue of deep sky objects in amateur astronomy. ...

Notes

  1. ^ average(787 ± 18, 770 ± 40, 772 ± 44, 783 ± 25) = ((787 + 770 + 772 + 783) / 4) ± ((182 + 402 + 442 + 252)0.5 / 4) = 778 ± 17
  2. ^ Apparent Magnitude of 4.36 - distance modulus of 24.4 = −20.0
  3. ^ J00443799+4129236 is at celestial coordinates R.A. 00h 44m 37.99s, Dec. +41° 29′ 23.6″.
  4. ^ distance × tan( diameter_angle = 190′ ) = 141 ± 3 kly diameter

The distance modulus is a way of expressing distances which is often used in astronomy to express the distance to galaxies and clusters of galaxies. ... In astronomy, a celestial coordinate system is a coordinate system for mapping positions in the sky. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ...

References

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A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... is the 36th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 144th day of the year (145th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 157th day of the year (158th in leap years) in the Gregorian calendar. ... 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Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Wilhelm Heinrich Walter Baade (March 24, 1893 - June 25, 1960) was a German astronomer who emigrated to the USA in 1931. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Also see: 2002 (number). ... is the 127th day of the year (128th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 144th day of the year (145th in leap years) in the Gregorian calendar. ... 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  Results from FactBites:
 
Andromeda Galaxy: Definition and Much More from Answers.com (3983 words)
Andromeda was believed to be the largest galaxy of the Local Group of galaxies, which consists of the Andromeda Galaxy, the Milky Way Galaxy, and the Triangulum Galaxy, and about 30 other smaller galaxies.
The Andromeda Galaxy is easily visible to the naked eye in a moderately dark sky, though such a sky is available only in smaller towns and isolated areas reasonably far from population centers and sources of light pollution.
The spiral arms of Andromeda are outlined by a series of H II regions that Baade described as resembling "beads on a string".
Andromedia Galaxy & Constellation - Crystalinks (1405 words)
The Andromeda Galaxy (also known as Messier Object 31, M31, or NGC 224; older texts often call it the Andromeda Nebula) is a giant spiral galaxy in the Local Group, together with the Milky Way galaxy.
The Andromeda Galaxy is easily visible to the naked eye in a truly dark sky; however, such a truly dark sky is available only in relatively few, isolated areas very far from population centers and sources of light pollution.
In Greek mythology, Andromeda was the daughter of Cepheus and Cassiopeia, king and queen of Ethiopia.
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