A supercluster is a large group of smaller galaxy clusters or galaxy groups; it is among the largest known structures of the universe. The Milky Way is part of the Local Group galaxy group, which in turn is part of the Virgo Supercluster, which is part of the Laniakea Supercluster. The large size and low density of superclusters means that they, unlike clusters, expand with the Hubble expansion. The number of superclusters in the observable universe is estimated to be 10 million.
An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly more than stellar black holes but less than the 105–109 solar mass supermassive black holes. Several IMBH candidate objects have been discovered in our galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.
The Sombrero Galaxy is a lenticular galaxy in the constellation borders of Virgo and Corvus, being about 9.55 megaparsecs from Earth. The galaxy has a diameter of approximately 15 kiloparsecs, 30% the size of the Milky Way. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero hat. Astronomers initially thought that the halo was small and light, indicative of a spiral galaxy, but the Spitzer Space Telescope found that the dust ring around the Sombrero Galaxy is larger and more massive than previously thought, indicative of a giant elliptical galaxy. The galaxy has an apparent magnitude of +8.0, making it easily visible with amateur telescopes, and it is considered by some authors to be the galaxy with the highest absolute magnitude within a radius of 10 megaparsecs of the Milky Way. Its large bulge, its central supermassive black hole, and its dust lane all attract the attention of professional astronomers.
Messier 32 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.
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.
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 elliptical 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.
A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.
NGC 3603 is a nebula situated in the Carina–Sagittarius arm of the Milky Way around 20,000 light-years away from the Solar System. It is a massive HII region containing a very compact open cluster HD 97950.
The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.
A hypercompact stellar system (HCSS) is a dense cluster of stars around a supermassive black hole that has been ejected from the center of its host galaxy. Stars that are close to the black hole at the time of the ejection will remain bound to the black hole after it leaves the galaxy, forming the HCSS.
M60-UCD1 is an ultracompact dwarf galaxy. It is 54 million light years from Earth, close to Messier 60 in the Virgo Cluster. Half of its stellar mass is in the central sphere 160 light years in diameter.
M85-HCC1 is an ultracompact dwarf galaxy with a star density 1,000,000 times that of the solar neighbourhood, lying near the galaxy Messier 85. As of 2015, it is the densest galaxy known.
NGC 1614 is the New General Catalogue identifier for a spiral galaxy in the equatorial constellation of Eridanus. It was discovered on December 29, 1885 by American astronomer Lewis Swift, who described it in a shorthand notation as: pretty faint, small, round, a little brighter middle. The nebula was then catalogued by Danish-Irish astronomer J. L. E. Drayer in 1888. When direct photography became available, it was noted that this galaxy displayed some conspicuous peculiarities. American astronomer Halton Arp included it in his 1966 Atlas of Peculiar Galaxies. In 1971, Swiss astronomer Fritz Zwicky described it as a "blue post-eruptive galaxy, compact patchy core, spiral plumes, long blue jet SSW".
NGC 5238 is an irregular galaxy in the constellation Canes Venatici. Located at a comoving distance of 4.51 Mpc, it is 64.4 arcseconds in diameter. It has sometimes been classified as a blue compact dwarf galaxy. Although some authors have hypothesized it to be a member of the M101 Group of galaxies, it is currently believed to be an isolated galaxy.
NGC 3311 is a supergiant elliptical galaxy located about 190 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 30, 1835. NGC 3311 is the brightest member of the Hydra Cluster and forms a pair with NGC 3309 which along with NGC 3311, dominate the central region of the Hydra Cluster.
NGC 1270 is an elliptical galaxy located about 250 million light-years away in the constellation Perseus. It was discovered by astronomer Heinrich d'Arrest on February 14, 1863. NGC 1270 is a member of the Perseus Cluster and has an estimated age of about 11 billion years. However, Greene et al. puts the age of NGC 1270 at about 15.0 ± 0.50 Gy.
NGC 1271 is a compact elliptical or lenticular galaxy located about 250 million light-years away in the constellation Perseus. The galaxy was discovered by astronomer Guillaume Bigourdan on November 14, 1884. NGC 1271 is a member of the Perseus Cluster and has a nuclear dust disk in its center. It also has an edge-on, intermediate-scale disk and has a central bulge. Like NGC 1277, NGC 1271 is a candidate "relic galaxy".
NGC 1281 is a compact elliptical galaxy located about 200 million light-years away in the constellation Perseus. NGC 1281 was discovered by astronomer John Dreyer on December 12, 1876. It is a member of the Perseus Cluster.
