Elliptical galaxy

An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless image. Unlike flat spiral galaxies with organization and structure, elliptical galaxies are more three-dimensional, without much structure, and their stars are in somewhat random orbits around the center. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae,[1] along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies[2][3][4] with their intermediate scale disks, a subset of the "early-type" galaxy population.

Elliptical galaxies range in size from tens of millions to over one hundred trillion stars. Originally, Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false,[5] although the accretion of gas and smaller galaxies may build a disk around a pre-existing ellipsoidal structure.[6] [7] Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies.[5] Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium and minimal star formation activity, and they tend to be surrounded by large numbers of globular clusters. Elliptical galaxies are believed to make up approximately 10%–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall.[8] They are preferentially found close to the centers of galaxy clusters.[9]

Abell S740, cropped to ESO 325-G004
The giant elliptical galaxy ESO 325-G004

General characteristics

Elliptical galaxy IC 2006
Elliptical galaxy IC 2006.[10]

Elliptical galaxies are characterized by several properties that make them distinct from other classes of galaxy. They are spherical or ovoid masses of stars, starved of star-making gases. The smallest known elliptical galaxy is about one-tenth the size of the Milky Way. The motion of stars in elliptical galaxies is predominantly radial, unlike the disks of spiral galaxies, which are dominated by rotation. Furthermore, there is very little interstellar matter (neither gas nor dust), which results in low rates of star formation, few open star clusters, and few young stars; rather elliptical galaxies are dominated by old stellar populations, giving them red colors. Large elliptical galaxies typically have an extensive system of globular clusters.

The dynamical properties of elliptical galaxies and the bulges of disk galaxies are similar, suggesting that they may be formed by the same physical processes, although this remains controversial. The luminosity profiles of both elliptical galaxies and bulges are well fit by Sersic's law, and a range of scaling relations between the elliptical galaxies' structural parameters unify the population.[11]

Every massive elliptical galaxy contains a supermassive black hole at its center. Observations of 46 elliptical galaxies, 20 classical bulges, and 22 pseudobulges show that each contain a black hole at the center.[12] The mass of the black hole is tightly correlated with the mass of the galaxy,[13] evidenced through correlations such as the M–sigma relation which relates the velocity dispersion of the surrounding stars to the mass of the black hole at the center.

Elliptical galaxies are preferentially found in galaxy clusters and in compact groups of galaxies.

Star formation

The traditional portrait of elliptical galaxies paints them as galaxies where star formation finished after an initial burst at high-redshift, leaving them to shine with only their aging stars. Elliptical galaxies typically appear yellow-red, which is in contrast to the distinct blue tinge of most spiral galaxies. In spirals, this blue color emanates largely from the young, hot stars in their spiral arms. Very little star formation is thought to occur in elliptical galaxies, because of their lack of gas compared to spiral or irregular galaxies. However, in recent years, evidence has shown that a reasonable proportion (~25%) of early-type (E, ES and S0) galaxies have residual gas reservoirs[14] and low level star-formation.[15] Researchers with the Herschel Space Observatory have speculated that the central black holes in elliptical galaxies keep the gas from cooling enough for star formation.[16]

Sizes and shapes

Galactic fireflies
The central galaxy in this image is a gigantic elliptical galaxy designated 4C 73.08.[17]
MACSJ1423.8+2404
The brilliant central object is a supergiant elliptical galaxy, the dominant member of a galaxy cluster with the name MACSJ1423.8+2404. Note the gravitational lensing.

Elliptical galaxies vary greatly in both size and mass with diameters ranging from 3000 lightyears to more than 700,000 lightyears, and masses from 105 to nearly 1013 solar masses.[18] This range is much broader for this galaxy type than for any other. The smallest, the dwarf elliptical galaxies, may be no larger than a typical globular cluster, but contain a considerable amount of dark matter not present in clusters. Most of these small galaxies may not be related to other ellipticals.

The Hubble classification of elliptical galaxies contains an integer that describes how elongated the galaxy image is. The classification is determined by the ratio of the major (a) to the minor (b) axes of the galaxy's isophotes:

Thus for a spherical galaxy with a equal to b, the number is 0, and the Hubble type is E0. While the limit in the literature is about E7, it has been known since 1966[2] that the E4 to E7 galaxies are misclassified lenticular galaxies with disks inclined at different angles to our line-of-sight. This has been confirmed through spectral observations revealing the rotation of their stellar disks. [19] [20] Hubble recognized that his shape classification depends both on the intrinsic shape of the galaxy, as well as the angle with which the galaxy is observed. Hence, some galaxies with Hubble type E0 are actually elongated.

It is sometimes said that there are two physical types of ellipticals: the giant ellipticals with slightly "boxy"-shaped isophotes, whose shapes result from random motion which is greater in some directions than in others (anisotropic random motion); and the "disky" normal and dwarf ellipticals, which contain disks. [21][22] This is, however, an abuse of the nomenclature, as there two types of early-type galaxy, those with disks and those without. Given the existence of ES galaxies with intermediate-scale disks, it is reasonable to expect that there is a continuity from E to ES, and onto the S0 galaxies with their large-scale stellar disks that dominate the light at large radii.

Dwarf spheroidal galaxies appear to be a distinct class: their properties are more similar to those of irregulars and late spiral-type galaxies.

At the large end of the elliptical spectrum, there is further division, beyond Hubble's classification. Beyond gE giant ellipticals, lies D-galaxies and cD-galaxies. These are similar to their smaller brethren, but more diffuse, with large haloes that may as much belong to the galaxy cluster within which they reside than the centrally-located giant galaxy.

Evolution

A galactic mega-merger
NGC 3597 is the product of a collision between two galaxies, and is slowly evolving to become a giant elliptical galaxy.

It is widely accepted that the evolution of elliptical galaxies is primarily composed of the merging of smaller galaxies. Many galaxies in the universe are gravitationally bound to other galaxies, which means that they will never escape the pull of the other galaxy. If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the two galaxies merging, but will instead be an elliptical galaxy.

Such major galactic mergers are thought to have been common at early times, but may occur less frequently today. Minor galactic mergers involve two galaxies of very different masses, and are not limited to giant ellipticals. The Milky Way galaxy is, depending upon an unknown tangential component, on a collision course in 4–5 billion years with the Andromeda Galaxy.[23] It has been theorized that an elliptical galaxy will result from a merger of the two spirals.

It is believed that black holes may play an important role in limiting the growth of elliptical galaxies in the early universe by inhibiting star formation.

Examples

See also

References

  1. ^ Hubble, E.P. (1936). The realm of the nebulae. Mrs. Hepsa Ely Silliman Memorial Lectures, 25. New Haven: Yale University Press. ISBN 9780300025002. OCLC 611263346. Archived from the original on 29 September 2012.(pp. 124–151)
  2. ^ a b Liller, M.H. (1966), The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster. II
  3. ^ Nieto, J.-L. et al. (1988), More isotropic oblate rotators in elliptical galaxies
  4. ^ Graham, A.W. et al. (2016), Disky Elliptical Galaxies and the Allegedly Over-massive Black Hole in the Compact “ES“ Galaxy NGC 1271 (see their Fig.7).
  5. ^ a b John, D. (2006). Astronomy: The definitive guide to the universe. Bath, UK: Parragon Publishing., p. 224-225
  6. ^ Dekel, A., et al. (2009), Cold streams in early massive hot haloes as the main mode of galaxy formation
  7. ^ Stewart, Kyle R., et al. (2013), Angular Momentum Acquisition in Galaxy Halos
  8. ^ Loveday, J. (February 1996). "The APM Bright Galaxy Catalogue". Monthly Notices of the Royal Astronomical Society. 278 (4): 1025–1048. arXiv:astro-ph/9603040. Bibcode:1996MNRAS.278.1025L. doi:10.1093/mnras/278.4.1025.
  9. ^ Dressler, A. (March 1980). "Galaxy morphology in rich clusters – Implications for the formation and evolution of galaxies". The Astrophysical Journal. 236: 351–365. Bibcode:1980ApJ...236..351D. doi:10.1086/157753.
  10. ^ "Elliptical galaxy IC 2006". www.spacetelescope.org. ESA/Hubble. Retrieved 21 April 2015.
  11. ^ Graham, A.W. (2013), Elliptical and Disk Galaxy Structure and Modern Scaling Laws
  12. ^ Kormendy, John; Ho, Luis C. (2013-08-18). "Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies". Annual Review of Astronomy and Astrophysics. 51 (1): 511–653. arXiv:1304.7762. Bibcode:2013ARA&A..51..511K. doi:10.1146/annurev-astro-082708-101811. ISSN 0066-4146.
  13. ^ Graham, A.W. (2016), Galaxy Bulges and Their Massive Black Holes: A Review
  14. ^ Young, L. M.; et al. (June 2011). "The Atlas3D project – IV: the molecular gas content of early-type galaxies". Monthly Notices of the Royal Astronomical Society. 414 (2): 940–967. arXiv:1102.4633. Bibcode:2011MNRAS.414..940Y. doi:10.1111/j.1365-2966.2011.18561.x.
  15. ^ Crocker, A. F.; et al. (January 2011). "Molecular gas and star formation in early-type galaxies". Monthly Notices of the Royal Astronomical Society. 410 (2): 1197–1222. arXiv:1007.4147. Bibcode:2011MNRAS.410.1197C. doi:10.1111/j.1365-2966.2010.17537.x.
  16. ^ "Red And Dead Galaxies Have Beating Black Hole 'Hearts', Preventing Star Formation."
  17. ^ "Galactic fireflies". ESA/Hubble Picture of the Week. Retrieved 13 February 2013.
  18. ^ Fraknoi, Andrew; Morrison, David; Wolf, Sidney C. (13 January 2017). Open Stax Astronomy. Retrieved 2 February 2017.
  19. ^ Graham, A.W. et al. (1998), Extended stellar kinematics of elliptical galaxies in the Fornax cluster
  20. ^ Emsellem, E. (2011), The ATLAS3D project - III. A census of the stellar angular momentum within the effective radius of early-type galaxies: unveiling the distribution of fast and slow rotators
  21. ^ Pedraz, S. et al. (2002), Evidence of fast rotation in dwarf elliptical galaxies
  22. ^ Toloba, E. et al. (2015), Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. III. Angular Momentum and Constraints on Formation Scenarios
  23. ^ Nagamine, Kentaro; Loeb, Abraham (2003), Future evolution of nearby large-scale structures in a universe dominated by a cosmological constant

Further reading

External links

Dwarf elliptical galaxy

Dwarf elliptical galaxies, or dEs, are elliptical galaxies that are smaller than ordinary elliptical galaxies. They are quite common in galaxy groups and clusters, and are usually companions to other galaxies.

List of NGC objects (1–1000)

This is a list of NGC objects 1–1000 from the New General Catalogue (NGC). The astronomical catalogue is composed mainly of star clusters, nebulae, and galaxies. Other objects in the catalogue can be found in the other subpages of the list of NGC objects.

The constellation information in these tables is from The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J. L. E. Dreyer, which was accessed using the VizieR Service. Galaxy morphological types and objects that are members of the Small Magellanic Cloud are identified using the NASA/IPAC Extragalactic Database. The other data of these tables are from the SIMBAD Astronomical Database unless otherwise stated.

Messier 105

Messier 105 or M105, also known as NGC 3379, is an elliptical galaxy located 36.6 million light years away in the equatorial constellation of Leo. It was discovered by Pierre Méchain on 24 March 1781, just a few days after he discovered the nearby galaxies Messier 95 and Messier 96. This galaxy is one of several that were not originally included in the original Messier Catalogue compiled by Charles Messier. Messier 105 was included in the catalog only when Helen S. Hogg found a letter by Méchain describing Messier 105 and when the object described by Méchain was identified as a galaxy previously named NGC 3379.This galaxy has a morphological classification of E1, indicating a standard elliptical galaxy with a flattening of 10%. The major axis is aligned along a position angle of 71°. Isophotes of the galaxy are near perfect ellipses, twisting no more than 5° out of alignment, with changes in ellipticity of no more than 0.06. There is no fine structure apparent in the isophotes, such as ripples. Observation of giant stars in the halo indicate there are two general populations: a dominant metal-rich subpopulation and a weaker metal-poor group.Messier 105 is known to have a supermassive black hole at its core whose mass is estimated to be between 1.4×108 and 2×108 M☉. The galaxy has a weak active galactic nucleus of the LINER type with a spectral class of L2/T2, meaning no broad Hα line and intermediate emission line ratios between a LINER and a H II region. The galaxy also contains a few young stars and stellar clusters, suggesting some elliptical galaxies still form new stars, but very slowly.This galaxy, along with its companion the barred lenticular galaxy NGC 3384, is surrounded by an enormous ring of neutral hydrogen with a radius of 200 kiloparsecs (650 kilolight-years) and a mass of 1.8×109 M☉ where star formation has been detected. Messier 105 is one of several galaxies within the M96 Group (also known as the Leo I Group), a group of galaxies in the constellation Leo. The group also includes the Messier objects M95 and M96.

Messier 110

Messier 110 or M110, also known as NGC 205, is a dwarf elliptical galaxy that is a satellite of the Andromeda Galaxy. Although Charles Messier never included the galaxy in his list, it was depicted by him, together with M32, on a drawing of the Andromeda galaxy; a label on the drawing indicates that Messier first observed NGC 205 on August 10, 1773. The galaxy was independently discovered by Caroline Herschel on August 27, 1783; her brother William Herschel described her discovery in 1785. The suggestion to assign the galaxy a Messier number was made by Kenneth Glyn Jones in 1967.This galaxy has a morphological classification of pec dE5, indicating a dwarf elliptical galaxy with a flattening of 50%. M110 is designated peculiar because there are patches of dust and young blue stars located near the center. This is unusual for dwarf elliptical galaxies in general, and the reason for this peculiarity is unclear. Unlike M32, NGC 205 does not (as of 2005) show evidence for a supermassive black hole at its center.The interstellar dust in M110 has a mass of (1.1–1.8)×104 M☉ with a temperature of 18–22 K, and the interstellar gas has (4–7)×106 M☉. The inner regions of M110 show a deficiency in the interstellar medium (IM) materials, which most likely were ejected by supernova explosions. Tidal interactions with M31 may have stripped away a significant fraction of the expelled gas and dust, leaving the galaxy as a whole deficient in its IM density.A few novae have been detected in this galaxy, including one discovered

in 1999 by Johnson and Modjaz, and another detected in 2002, by Nakano and Sumoto. The latter, designated EQ J004015.8+414420, had also been captured in images taken by the Sloan Digital Sky Survey (SDSS) in October, 2002.About half of the Andromeda's satellite galaxies are orbiting the host galaxy along a highly flattened plane, with 14 out of 16 following the same sense of rotation. One theory proposes that these objects once belonged to a subhalo surrounding NGC 205, then the group was broken up by tidal forces during a close encounter with Andromeda.

Messier 32

Messier 32 (also known as M32 and NGC 221) is a dwarf "early-type" galaxy located about 2.65 million light-years from Earth, appearing in the constellation Andromeda. M32 is a satellite galaxy of the Andromeda Galaxy (M31) and was discovered by Guillaume Le Gentil in 1749. M32 measures 6.5 ± 0.2 thousand light-years in diameter at the widest point.The galaxy is a prototype of the relatively rare, compact elliptical (cE) galaxy class.

Half the stars concentrate within an effective radius of only 100 parsecs.

Densities in the central stellar cusp increase steeply, exceeding 3×107 M⊙ pc−3 at the smallest radii resolved by HST, and the half-light radius of this central star cluster is around 6 parsec.

Like more ordinary elliptical galaxies, M32 contains mostly older faint red and yellow stars with practically no dust or gas and consequently no current star formation. It does, however, show hints of star formation in the relatively recent past.

Messier 49

Messier 49 (also known as M 49 or NGC 4472) is an elliptical galaxy located about 56 million light-years away in the equatorial constellation of Virgo. This galaxy was discovered by French astronomer Charles Messier on February 16, 1777.

As an elliptical galaxy, Messier 49 has the physical form of a radio galaxy, but it only has the radio emission of a normal galaxy. From the detected radio emission, the core region has roughly 1053 erg (1046 J or 1022 YJ) of synchrotron energy. The nucleus of this galaxy is emitting X-rays, suggesting the likely presence of a supermassive black hole with an estimated mass of 5.65 × 108 solar masses, or 565 million times the mass of the Sun. X-ray emissions shows a structure to the north of Messier 49 that resembles a bow shock. To the southwest of the core, the luminous outline of the galaxy can be traced out to a distance of 260 kpc. The only supernova event observed within this galaxy is SN 1969Q, discovered in June 1969.This galaxy has a large collection of globular clusters, estimated at about 5,900. However, this count is far exceeded by the 13,450 globular clusters orbiting the supergiant elliptical galaxy Messier 87. On average, the globular clusters of M 49 are about 10 billion years old. Between 2000 and 2009, strong evidence for a stellar mass black hole was discovered in an M 49 cluster. A second candidate was announced in 2011.Messier 49 was the first member of the Virgo Cluster of galaxies to be discovered. It is the most luminous member of that cluster and more luminous than any galaxy closer to the Earth. This galaxy forms part of the smaller Virgo B subcluster located 4.5° away from the dynamic center of the Virgo Cluster, centered on Messier 87. Messier 49 is gravitationally interacting with the dwarf irregular galaxy UGC 7636. The dwarf shows a trail of debris spanning roughly 1 × 5 arcminutes, which corresponds to a physical dimension of 6 × 30 kpc.

Messier 59

Messier 59 or M59, also known as NGC 4621, is an elliptical galaxy in the equatorial constellation of Virgo. M59 is a member of the Virgo Cluster, with the nearest component being separated from M59 by 8′ and around 5 magnitudes fainter. The nearest cluster member of comparable brightness is the lenticular galaxy NGC 4638, which is around 17′ away. Messier 59 and the nearby elliptical galaxy Messier 60 were both discovered by Johann Gottfried Koehler in April 1779 during observations of a comet in the same part of the sky. Charles Messier listed both in the Messier Catalogue about three days after Koehler's discovery.This is an elliptical galaxy of type E5 with a position angle of 163.3°, indicating the overall shape shows a flattening of 50%. However, isophotes for this galaxy deviate from a perfect ellipticity, showing pointed shapes instead. These can be decomposed mathematically into a three component model, with each part having a different eccentricity. The main elliptical component appears to be superimposed upon a flatter, disk-like feature, with the entirety embedded within a circular halo. The luminosity contribution of the components is 62% for the pure elliptical part, 22% for the halo, and the remainder coming from the disk. The light ratio of the disk to the main elliptical body is 0.25, whereas it is typically closer to 0.5 in a lenticular galaxy.The core contains a supermassive black hole (SMBH), with a mass that has been estimated to be 270 million times the mass of the Sun, and counter-rotates with respect of the rest of the galaxy, being bluer. The SMBH is quiescent, but is detectable as an X-ray and radio source that indicates an outflow. The nucleus contains an embedded stellar disk that is bluer (younger) than the bulge region, with a blue component stretching along a position angle of around 150°. This extended disk feature may be the result of a galactic merger followed by a starburst event.Messier 59 is very rich in globular clusters, with a population of them that has been estimated to be around 2,200. It has a satellite, the Ultra Compact Dwarf galaxy M59-UCD3.One supernova (1939B) has been recorded in M59; it reached a peak magnitude of 11.9. The region where this supernova occurred shows no trace of star formation, which suggests this was a type Ia supernova.

Messier 60

Messier 60 or M60, also known as NGC 4649, is an elliptical galaxy approximately 57 million light-years away in the equatorial constellation of Virgo. Together with NGC 4647, it forms a pair known as Arp 116. Messier 60 and the nearby spiral galaxy Messier 59 were both discovered by Johann Gottfried Koehler in April 1779 during observations of a comet in the same part of the sky. Charles Messier added both to his catalogue about three days after Koehler's discovery.This is an elliptical galaxy of type E1/2 (E1.5), although some sources class it as S0 – a lenticular galaxy. An E2 class indicates a flattening of 20%, which has a nearly round appearance. The isophotes of the galaxy are boxy in shape, rather than simple ellipses. The mass-to-light ratio is a near constant 9.5 in the V (visual) band of the UBV system. The galaxy has an effective radius of 128″ (about 10 kpc), with an estimated mass of ~1012 M☉ within three times that radii, of which nearly half is dark matter. The mass estimated from X-ray emission is (1.0±0.1)×1012 M☉ within 5 effective radii.At the center of M60 is a supermassive black hole (SMBH) of 4.5±1.0 billion solar masses, one of the largest ever found. It is currently inactive. X-ray emission from the galaxy shows a cavity created by jets emitted by the hole during past active periods, which correspond to weak radio lobes. The power needed to generate these features is in the range (6–7)×1041 erg·s−1.In 2004, supernova SN 2004W was observed in Messier 60. It was a type 1a supernova located 51.6″ west and 78.7″ south of the nucleus.M60 is the third-brightest giant elliptical galaxy of the Virgo cluster of galaxies, and is the dominant member of a subcluster of four galaxies, the M60 group, which is the closest-known isolated compact group of galaxies. It has several satellite galaxies, one of them being the ultracompact dwarf galaxy M60-UCD1. The motion of M60 through the intercluster medium is resulting in ram-pressure stripping of gas from the galaxy's outer halo, beyond a radius of 12 kpc.NGC 4647 appears approximately 2′.5 from Messier 60; the optical disks of the two galaxies overlap. Although this overlap suggests that the galaxies are interacting, photographic images of the two galaxies do not reveal any evidence for gravitational interactions between the two galaxies as would be suggested if the two galaxies were physically close to each other. This suggests that the galaxies are at different distances and are only weakly interacting if at all. However, studies with the Hubble Space Telescope show indications that a tidal interaction may have just begun.Messier 60 was the fastest-moving galaxy included in Edwin Hubble's landmark 1929 paper concerning the relationship between recession speed and distance. He used a value of 1090 km/s for the recession speed, quite close to the more recent value of about 1110 km/s (based on a redshift of 0.003726). But he estimated the distance of Messier 60, as well as of the other three nebulas of the Virgo Cluster which he included (Messier 85, 49, and 87), to be only two million parsecs, rather than the accepted value today of around 16 million parsecs. These errors in distance led him to propose a "Hubble constant" of 500 km/s/Mpc, whereas the present estimate is around 70 km/s/Mpc.

Messier 87

Messier 87 (also known as Virgo A or NGC 4486, generally abbreviated to M87) is a supergiant elliptical galaxy in the constellation Virgo. One of the most massive galaxies in the local Universe, it is notable for its large population of globular clusters—about 12,000 compared to the 150–200 orbiting the Milky Way—and its jet of energetic plasma that originates at the core and extends at least 1,500 parsecs (4,900 light-years), traveling at relativistic speed. It is one of the brightest radio sources in the sky, and a popular target for both amateur and professional astronomers.

The French astronomer Charles Messier discovered M87 in 1781, and catalogued it as a nebulous feature while searching for objects that would otherwise confuse comet hunters. M87 is located about 16.4 million parsecs (53 million light-years) from Earth and is the second-brightest galaxy within the northern Virgo Cluster, having many satellite galaxies. Unlike a disk-shaped spiral galaxy, M87 has no distinctive dust lanes. Instead, it has an almost featureless, ellipsoidal shape typical of most giant elliptical galaxies, diminishing in luminosity with distance from the center. Forming around one sixth of its mass, M87's stars have a nearly spherically symmetric distribution. Their population density decreases with increasing distance from the core. It has an active supermassive black hole at its core, which forms the primary component of an active galactic nucleus.

The galaxy is a strong source of multiwavelength radiation, particularly radio waves. Its galactic envelope extends to a radius of about 150 kiloparsecs (490 thousand light-years), where it is truncated—possibly by an encounter with another galaxy. Its interstellar medium consists of diffuse gas enriched by elements emitted from evolved stars.

Messier 89

Messier 89 (M89 for short, also known as NGC 4552) is an elliptical galaxy in the constellation Virgo. It was discovered by Charles Messier on March 18, 1781. M89 is a member of the Virgo Cluster of galaxies.

NGC 163

NGC 163 is an elliptical galaxy in the constellation Cetus. It was discovered by William Herschel since 1890. It has been found in a faint object but when seeing using an optical telescope was an elliptical galaxy that ranges up to 13 magnitude.

NGC 185

NGC 185 (also known as Caldwell 18) is a dwarf spheroidal galaxy located 2.08 million light-years from Earth, appearing in the constellation Cassiopeia. It is a member of the Local Group, and is a satellite of the Andromeda Galaxy (M31). NGC 185 was discovered by William Herschel on November 30, 1787, and he cataloged it "H II.707". John Herschel observed the object again in 1833 when he cataloged it as "h 35", and then in 1864 when he cataloged it as "GC 90" within his General Catalogue of Nebulae and Clusters. NGC 185 was first photographed between 1898 and 1900 by James Edward Keeler with the Crossley Reflector of Lick Observatory. Unlike most dwarf elliptical galaxies, NGC 185 contains young stellar clusters, and star formation proceeded at a low rate until the recent past. NGC 185 has an active galactic nucleus (AGN) and is usually classified as a type 2 Seyfert galaxy, though its status as a Seyfert is questioned. It is possibly the closest Seyfert galaxy to Earth, and is the only known Seyfert in the Local Group.

NGC 194

NGC 194 is an elliptical galaxy located in the constellation Pisces. It was discovered on December 25, 1790 by William Herschel.

NGC 233

NGC 233 is an elliptical galaxy located in the constellation Andromeda. It was discovered on September 11, 1784 by William Herschel.

NGC 28

NGC 28 is an elliptical galaxy located in the Phoenix constellation. It was discovered on the 28th October 1834 by John Herschel

NGC 28 2MASS (near-infrared)

NGC 4881

NGC 4881 is an elliptical galaxy about 102 megaparsecs away in the Coma cluster of galaxies. NGC 4881 was discovered by Heinrich Louis d'Arrest in 1865.

In 1994, the Hubble Space Telescope examined the Coma cluster and NGC 4881.

NGC 7318

NGC 7318 (also known as UGC 12099/UGC 12100 or HCG 92d/b) are a pair of colliding galaxies about 300 million light-years from Earth. They appear in the Constellation Pegasus and are members of the Stephan's Quintet.

The Spitzer Space Telescope revealed the presence of a huge intergalactic shock wave, shown by a green arc produced by one galaxy falling into another at millions of kilometers per hour. As NGC 7318B collides with NGC 7318A, gas spread throughout the cluster, atoms of hydrogen are heated in the shock wave, producing the green glow. The molecular hydrogen visible in the collision is one of the most turbulent forms known. This phenomenon was discovered by an international team of scientists of the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg. This collision can help provide a view into what happened in the early universe, around 10 billion years ago.

Sagittarius Dwarf Spheroidal Galaxy

The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph), also known as the Sagittarius Dwarf Elliptical Galaxy (Sgr dE or Sag DEG), is an elliptical loop-shaped satellite galaxy of the Milky Way. It consists of four globular clusters, the main cluster having been discovered in 1994. Sgr dSph is roughly 10,000 light-years in diameter, and is currently about 70,000 light-years from Earth, travelling in a polar orbit (i.e. an orbit passing over the Milky Way’s galactic poles) at a distance of about 50,000 light-years from the core of the Milky Way (about 1/3 the distance of the Large Magellanic Cloud). In its looping, spiraling path, it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core, causing unexpected rippling movements of the stars triggered when it sailed past the Milky Way between 300 and 900 million years ago.

Type-cD galaxy

The type-cD galaxy (also cD-type galaxy, cD galaxy) is a galaxy morphology classification, a subtype of type-D giant elliptical galaxy. Characterized by a large halo of stars, they can be found near the centres of some rich galaxy clusters. They are also known as supergiant ellipticals or central dominant galaxies.

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