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| NGC 4889 | |
|---|---|
 The elliptical galaxy NGC 4889 Credit:Hubble Space Telescope | |
| Observation data (J2000.0epoch) | |
| Constellation | Coma Berenices |
| Right ascension | 13h 00m 08.1s[1] |
| Declination | +27° 58′ 37″[1] |
| Redshift | 0.021502±0.000010[1] |
| Heliocentric radial velocity | 6495±13 km/s[1] |
| Galactocentric velocity | 6509±13 km/s[1] |
| Apparent magnitude (V) | 12.9[1] |
| Characteristics | |
| Type | cD; E4; Dd[1] |
| Size | 86.976 to 90.9 kpc (283,680 to 296,480 ly) (diameter; D25.0 B-band and2MASS K-band total isophotes)[1] |
| Apparent size (V) | 2.9 × 1.9moa[1] |
| Other designations | |
| ZWG 160.241, DRCG 27-148,Caldwell 35,NGC 4884,UGC 8110,MCG +5-31-77,PGC 44715[2] | |
NGC 4889 (also known asCaldwell 35) is an E4 supergiantelliptical galaxy.[3] It was discovered in 1785 by the British astronomerFrederick William Herschel I, who catalogued it as a bright, nebulous patch. The brightest galaxy within the northernComa Cluster, it is located at a median distance of 94 millionparsecs (308 millionlight years) from Earth. At the core of the galaxy is asupermassive black hole that heats the intracluster medium through the action of friction from infalling gases and dust. Thegamma ray bursts from the galaxy extend out to several million light years of the cluster.
As with other similar elliptical galaxies, only a fraction of the mass of NGC 4889 is in the form of stars. They have a flattened, unequal distribution that bulges within its edge. Between the stars is a denseinterstellar medium full of heavy elements emitted by evolved stars. The diffusestellar halo extends out to one million light years in diameter. Orbiting the galaxy is a very large population ofglobular clusters. NGC 4889 is also a strong source of soft X-ray, ultraviolet, and radio frequency radiation.
As the largest and the most massive galaxy easily visible to Earth, NGC 4889 has played an important role in both amateur and professional astronomy, and has become a prototype in studying the dynamical evolution of othersupergiant elliptical galaxies in the more distant universe.
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NGC 4889 was not included by theastronomerCharles Messier in his famousMessier catalogue despite being an intrinsically bright object quite close to some Messier objects. The first known observation of NGC 4889 was that of Frederick William Herschel I, assisted by his sister,Caroline Lucretia Herschel, in 1785, who included it in theCatalogue of Nebulae and Clusters of Stars published a year later. In 1864, Herschel's son,John Frederick William Herschel, published theGeneral Catalogue of Nebulae and Clusters of Stars. He included the objects catalogued by his father, including the one later to be called NGC 4889, plus others he found that were somehow missed by his father.
In 1888 the astronomerJohn Louis Emil Dreyer published theNew General Catalogue of Nebulae and Clusters of Stars (NGC), with a total of 7,840 objects, but he erroneously duplicated the galaxy in two designations,NGC 4884 andNGC 4889. Within the following century, several projects aimed to revise the NGC catalogue, such as The NGC/IC Project, Revised New General Catalogue of Nebulae and Clusters of Stars, and the NGC 2000.0 projects, discovered the duplication. It was then decided that the object would be called by its latter designation, NGC 4889, which is in use today.
In December 1995,Patrick Caldwell Moore compiled theCaldwell catalogue, a list of 109 persistent, bright objects that were somehow missed by Messier in his catalogue. The list also includes NGC 4889, which is given the designationCaldwell 35.
NGC 4889 is located along the high declination region of Coma Berenices, south of the constellationCanes Venatici. It can be traced by following the line fromBeta Comae Berenices toGamma Comae Berenices. With an apparent magnitude of 11.4, it can be seen by telescopes with 12 inch aperture, but its visibility is greatly affected by light pollution due to glare of the light from Beta Comae Berenices. However, under very dark, moonless skies, it can be seen by small telescopes as a faint smudge, but larger telescopes are needed in order to see the galaxy's halo.
In the updatedHubble sequencegalaxy morphological classification scheme by the French astronomerGérard de Vaucouleurs in 1959, NGC 4889 is classified as an E4 type galaxy, which means it has a flat distribution of stars within its width. It is also classified as a cD galaxy, a giant type of D galaxy, a classification devised by theAmerican astronomerWilliam Wilson Morgan in 1958 for galaxies with an elliptical-shaped nucleus surrounded by an immense, diffuse, dustless, extended halo.
NGC 4889 is far enough that its distance can be measured usingredshift. With the redshift of 0.0266 as derived from theSloan Digital Sky Survey, and theHubble constant as determined in 2013 by theESACOBRAS/SAMBA/Planck Surveyor translates its distance of 94 Mpc (308 million light years) from Earth.
NGC 4889 is probably the largest and the most massive galaxy out to the radius of 100 Mpc (326 million light years) of the Milky Way. The galaxy has an effective radius which extends at 2.9 arcminutes of the sky, translating to a diameter of 239,000 light years, about the size of theAndromeda Galaxy. In addition it has an immense diffuse light halo extending to 17.8 arcminutes, roughly half the angular diameter of theSun, translating to 1.3 million light years in diameter.
Along with its large size, NGC 4889 may also be extremely massive. If we take the Milky Way as the standard of mass, it may be close to 8 trillion solar masses. However, as NGC 4889 is a spheroid, and not a flat spiral, it has a three-dimensional profile, so it may be as high as 15 trillion solar masses. However, as usual for elliptical galaxies, only a small fraction of the mass of NGC 4889 is in the form of stars that radiate energy.
Giant elliptical galaxies like NGC 4889 are believed to be the result of multiplemergers of smaller galaxies. There is now little dust remaining to form the diffuse nebulae where new stars are created, so the stellar population is dominated by old, population II stars that contain relatively low abundances of elements other than hydrogen and helium. The egg-like shape of this galaxy is maintained by random orbital motions of its member stars, in contrast to the more orderly rotational motions found in a spiral galaxy such as the Milky Way. NGC 4889 has 15,800 globular clusters, more thanMessier 87, which has 12,000. This is half ofNGC 4874's collection of globular clusters, which has 30,000 globular clusters.
The space between the stars in the galaxy is filled with a diffuse interstellar medium of gas, which has been filled by the elements ejected from stars as they passed beyond the end of their main sequence lifetime. Carbon and nitrogen are being continuously supplied by intermediate mass stars as they pass through the asymptotic giant branch. The heavier elements from oxygen to iron are primarily produced by supernova explosions within the galaxy. The interstellar medium is continuously heated by the emission of in-falling gases towards its central SMBH.
On December 5, 2011, astronomers measured the velocity dispersion of the central regions of two massive galaxies, NGC 4889, and the other beingNGC 3842 in theLeo Cluster. According to the data of the study, they found out the centralsupermassive black hole of NGC 4889 is 5,200 times more massive than the central black hole of the Milky Way, or equivalent to 2.1×1010 (21 billion) solar masses (best fit of data; possible range is from 6 billion to 37 billion solar masses).[5] This makes it one of themost massive black holes on record. The diameter of the black hole's immense event horizon is about 20 to 124 billion kilometers, 2 to 12 times the diameter ofPluto's orbit. The ionized medium detected around the black hole suggests that NGC 4889 may have been a quasar in the past. It is quiescent, presumably because it has already absorbed all readily available matter.[6]
NGC 4889 lies at the center of the component A of theComa Cluster, a giant cluster of 2,000 galaxies which it shares withNGC 4874, although NGC 4889 is sometimes referred as the cluster center, and it has been called by its other designationA1656-BCG. The total mass of the cluster is estimated to be on the order of 4×1015M☉.
The Coma Cluster is located at exactly the center of theComa Supercluster, which is one of the nearest superclusters to theLaniakea Supercluster. The Coma Supercluster itself is within the CfA Homunculus, the center of theCfA2 Great Wall, the nearest galaxy filament to Earth and one of the largest structures in the known universe.
