NGC 6240, also known as the Starfish Galaxy, is a nearby ultraluminous infrared galaxy (ULIRG) in the constellation Ophiuchus. It was discovered by French astronomer Édouard Stephan on 12 July 1871.
The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area about 2.6 arcminutes on a side, about one 24-millionth of the whole sky, which is equivalent in angular size to a tennis ball at a distance of 100 metres. The image was assembled from 342 separate exposures taken with the Space Telescope's Wide Field and Planetary Camera 2 over ten consecutive days between December 18 and 28, 1995.
Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy approximately 12 million light-years away in the constellation Ursa Major. It is the second-largest member of the M81 Group, with the D25 isophotal diameter of 12.52 kiloparsecs (40,800 light-years). It is about five times more luminous than the Milky Way and its central region is about one hundred times more luminous. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As one of the closest starburst galaxies to Earth, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.
A starburst galaxy is one undergoing an exceptionally high rate of star formation, as compared to the long-term average rate of star formation in the galaxy, or the star formation rate observed in most other galaxies.
Centaurus A is a galaxy in the constellation of Centaurus. It was discovered in 1826 by Scottish astronomer James Dunlop from his home in Parramatta, in New South Wales, Australia. There is considerable debate in the literature regarding the galaxy's fundamental properties such as its Hubble type and distance. It is the closest radio galaxy to Earth, as well as the closest BL Lac object, so its active galactic nucleus has been extensively studied by professional astronomers. The galaxy is also the fifth-brightest in the sky, making it an ideal amateur astronomy target. It is only visible from the southern hemisphere and low northern latitudes.
Halton Christian "Chip" Arp was an American astronomer. He is remembered for his 1966 book Atlas of Peculiar Galaxies, which catalogued unusual looking galaxies and presented their images.
The Whirlpool Galaxy, also known as Messier 51a (M51a) or NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. It is 7.22 megaparsecs away and 23.58 kiloparsecs (76,900 ly) in diameter.
Messier 81 (also known as NGC 3031 or Bode's Galaxy) is a grand design spiral galaxy about 12 million light-years away in the constellation Ursa Major. It has a D25 isophotal diameter of 29.44 kiloparsecs (96,000 light-years). Because of its relative proximity to the Milky Way galaxy, large size, and active galactic nucleus (which harbors a 70 million M☉ supermassive black hole), Messier 81 has been studied extensively by professional astronomers. The galaxy's large size and relatively high brightness also makes it a popular target for amateur astronomers. In late February 2022, astronomers reported that M81 may be the source of FRB 20200120E, a repeating fast radio burst.
NGC 6946, sometimes referred to as the Fireworks Galaxy, is a face-on intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the northern constellations of Cepheus and Cygnus. Its distance from Earth is about 25.2 million light-years or 7.72 megaparsecs, similar to the distance of M101 in the constellation Ursa Major. Both were once considered to be part of the Local Group, but are now known to be among the dozen bright spiral galaxies near the Milky Way but beyond the confines of the Local Group. NGC 6946 lies within the Virgo Supercluster.
A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from other astrophysical masers by their large isotropic luminosity. Megamasers have typical luminosities of 103 solar luminosities (L☉), which is 100 million times brighter than masers in the Milky Way, hence the prefix mega. Likewise, the term kilomaser is used to describe masers outside the Milky Way that have luminosities of order L☉, or thousands of times stronger than the average maser in the Milky Way, gigamaser is used to describe masers billions of times stronger than the average maser in the Milky Way, and extragalactic maser encompasses all masers found outside the Milky Way. Most known extragalactic masers are megamasers, and the majority of megamasers are hydroxyl (OH) megamasers, meaning the spectral line being amplified is one due to a transition in the hydroxyl molecule. There are known megamasers for three other molecules: water (H2O), formaldehyde (H2CO), and methine (CH).
Luminous infrared galaxies or LIRGs are galaxies with luminosities, the measurement of brightness, above 1011 L☉. They are also referred to as submillimeter galaxies (SMGs) through their normal method of detection. LIRGs are more abundant than starburst galaxies, Seyfert galaxies and quasi-stellar objects at comparable luminosity. Infrared galaxies emit more energy in the infrared than at all other wavelengths combined. A LIRG's luminosity is 100 billion times that of the Sun.
APM 08279+5255 is a very distant, broad absorption line quasar located in the constellation Lynx. It is magnified and split into multiple images by the gravitational lensing effect of a foreground galaxy through which its light passes. It appears to be a giant elliptical galaxy with a supermassive black hole and associated accretion disk. It possesses large regions of hot dust and molecular gas, as well as regions with starburst activity.
NGC 1808 is a barred spiral galaxy located in the southern constellation of Columba, about two degrees to the south and east of Gamma Caeli. It was discovered on 10 May 1826 by Scottish astronomer James Dunlop, who described it as a "faint nebula". The galaxy is a member of the NGC 1808 group, which is part of the larger Dorado Group.
NGC 2276 is an intermediate spiral galaxy in the constellation Cepheus. The galaxy lies 120 million light-years away from Earth. NGC 2276 has an asymmetrical appearance, most likely caused by gravitational interactions with its neighbor, elliptical galaxy NGC 2300. NGC 2276 is traveling with an orbital velocity of about 968 km/s due to its neighbor. Trailing NGC 2276 is a long tail of interstellar medium about 300,000 light-years long, formed by ram pressure stripping.
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 2936, also known as the Penguin Galaxy or the Porpoise Galaxy, is an interacting spiral galaxy located at a distance of 326 million light years, in the constellation Hydra. NGC 2936 is interacting with elliptical galaxy NGC 2937, located just beneath it. They were both discovered by Albert Marth on Mar 3, 1864. To some astronomers, the galaxy looks like a penguin or a porpoise. NGC 2936, NGC 2937, and PGC 1237172 are included in the Atlas of Peculiar Galaxies as Arp 142 in the category "Galaxy triplet".
NGC 7469 is an intermediate spiral galaxy in the constellation of Pegasus. NGC 7469 is located about 200 million light-years away from Earth, which means, given its apparent dimensions, that NGC 7469 is approximately 90,000 light-years across. It was discovered by William Herschel on November 12, 1784.
Markarian 273 is a galaxy merger located in the constellation Ursa Major. It is located at a distance of about 500 million light years from Earth, which, given its apparent dimensions, means that Markarian 273 is about 130,000 light years across. It is an ultraluminous infrared galaxy and a Seyfert galaxy.
UGC 4653 known as Arp 195, is a trio of interacting galaxies located 763 million light-years away from the solar system in the Lynx constellation. The galaxies are being distorted through gravitational interactions with each other. The first known reference for this object, was in 1959 where B.A. Vorontsov-Vel'yaminov compiled it inside the Vorontsov-Vel'yaminov Interacting galaxies, as VV 243.
NGC 3509 known as Arp 335, is a barred spiral galaxy located in the constellation Leo. It is located 340 million light-years from the Solar System. NGC 3509 was discovered by astronomer William Herschel on December 30, 1786.
