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An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the four main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together with lenticular galaxies (S0) with their large-scale disks, and ES galaxies with their intermediate scale disks, a subset of the "early-type" galaxy population.
During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926.
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.
A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are companions to the Andromeda Galaxy (M31). While similar to dwarf elliptical galaxies in appearance and properties such as little to no gas or dust or recent star formation, they are approximately spheroidal in shape and generally have lower luminosity.
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word "metals" as a convenient short term for "all elements except hydrogen and helium". This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting solid. Stars and nebulae with relatively high abundances of heavier elements are called "metal-rich" in astrophysical terms, even though many of those elements are nonmetals in chemistry.
The Sculptor Dwarf Galaxy is a dwarf spheroidal galaxy that is a satellite of the Milky Way. The galaxy lies within the constellation Sculptor. It was discovered in 1937 by American astronomer Harlow Shapley using the 24-inch Bruce refractor at Boyden Observatory. The galaxy is located about 290,000 light-years away from the Solar System. The Sculptor Dwarf contains only 4 percent of the carbon and other heavy elements in our own galaxy, the Milky Way, making it similar to primitive galaxies seen at the edge of the universe.
NGC 3109 is a small barred Magellanic type spiral or irregular galaxy around 4.34 Mly away in the direction of the constellation of Hydra. NGC 3109 is believed to be tidally interacting with the dwarf elliptical galaxy Antlia Dwarf. It was discovered by John Herschel on March 24, 1835 while he was in what is now South Africa.
A dark galaxy is a hypothesized galaxy with no, or very few, stars. They received their name because they have no visible stars, but may be detectable if they contain significant amounts of gas. Astronomers have long theorized the existence of dark galaxies, but there are no confirmed examples to date. Dark galaxies are distinct from intergalactic gas clouds caused by galactic tidal interactions, since these gas clouds do not contain dark matter, so they do not technically qualify as galaxies. Distinguishing between intergalactic gas clouds and galaxies is difficult; most candidate dark galaxies turn out to be tidal gas clouds. The best candidate dark galaxies to date include HI1225+01, AGC229385, and numerous gas clouds detected in studies of quasars.
The Pisces Dwarf, also known as Pisces I, is an irregular dwarf galaxy that is part of the Local Group. The galaxy, taking its name from the constellation Pisces where it appears, is suspected of being a satellite galaxy of the Triangulum Galaxy (M33). It displays a blueshift, as it is approaching the Milky Way at 287 km/s. It may be transition-type galaxy, somewhere between dwarf spheroidal and dwarf irregular. Alternatively, it may be a rare, but statistically acceptable, version of one of the two types.
The Boötes Dwarf Galaxy is a galaxy discovered in 2006, which appears faint, with a luminosity of 100,000 L☉ and an absolute magnitude of –5.8. It lies about 197,000 light-years away in the constellation Boötes. This dwarf spheroidal galaxy appears to be tidally disrupted by the Milky Way Galaxy, which it orbits, and has two stellar tails that cross over to form a cross. Tidally disrupted galaxies usually only form one tail.
Gary Alan Wegner is an American astronomer, the endowed Leede '49 Professor of Physics and Astronomy at Dartmouth College, and recipient of the Alexander Von Humboldt Prize. Wegner was also a member of a famous group of seven astronomers called the Seven Samurai who, in the 1980s, discovered the location of the Great Attractor. He has co-authored and authored over 320 articles in astronomy and astrophysics.
A Pea galaxy, also referred to as a Pea or Green Pea, might be a type of luminous blue compact galaxy that is undergoing very high rates of star formation. Pea galaxies are so-named because of their small size and greenish appearance in the images taken by the Sloan Digital Sky Survey (SDSS).
The Pisces Overdensity is a clump of stars in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy. It is situated in the Pisces constellation and was discovered in 2009 by analysis of distribution of RR Lyrae stars in the data obtained by the Sloan Digital Sky Survey's data. The galaxy is located at the distance of about 80 kpc from the Sun and moves towards it with a speed of about 75 km/s.
NGC 5053 is the New General Catalogue designation for a globular cluster in the northern constellation of Coma Berenices. It was discovered by German-British astronomer William Herschel on March 14, 1784 and cataloged as VI-7. In his abbreviated notation, he described it as, "an extremely faint cluster of extremely small stars with resolvable nebula 8 or 10′ diameter, verified by a power of 240, beyond doubt". Danish-Irish astronomer John Louis Emil Dreyer reported in 1888 that the cluster appeared, "very faint, pretty large, irregular round shape, growing very gradually brighter at the middle".
The Antlia-Sextans Group is a small grouping of galaxies in the constellations Hydra, Sextans, Antlia and Leo. It is generally considered to be at the very edge of the Local Group and thus part of it. However, other researchers indicate it is an independent group, and thus the nearest group to the Local Group. It is, on average, approximately 4.3 million light-years away from the Milky Way.
PHL 293B, also known as Kinman's dwarf, is a low-metallicity blue compact dwarf galaxy about 22.6 Mpc from the Earth in the constellation Aquarius.
Evan David Skillman is an American astronomer and astrophysicist.
The Peekaboo Galaxy is an irregular compact blue dwarf galaxy in the constellation Hydra. The galaxy is relatively small, at about 1,200 light-years across; and nearby, at a distance of about 22 million light-years from Earth. The Peekaboo Galaxy is considered one of the most metal-poor, least chemically enriched, and seemingly primordial, galaxies known.
References
- 1 2 Aver, Erik; Berg, Danielle A.; Hirschauer, Alec S.; Olive, Keith A.; Pogge, Richard W.; Rogers, Noah S J.; Salzer, John J.; Skillman, Evan D. (2021). "A comprehensive chemical abundance analysis of the extremely metal poor Leoncino Dwarf galaxy (AGC 198691)". Monthly Notices of the Royal Astronomical Society. 510: 373–382. arXiv: 2109.00178 . doi:10.1093/mnras/stab3226.
- ↑ Aron, Jacob (21 May 2016). "The galaxy that time forgot". New Scientist. 230 (3074): 12.
- ↑ Nowakowski, Tomasz (16 March 2016). "Astronomers discover the most metal-poor galaxy in the local universe". phys.org. Retrieved 8 June 2016.
- ↑ Hirschauer, Alec S.; Salzer, John Joseph; Cannon, John M.; Skillman, Evan D. (1 January 2016). "The Extremely Metal-Poor Dwarf Galaxy AGC 198691". American Astronomical Society. 227: 136.06. Bibcode:2016AAS...22713606H.
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