A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. This emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up because of friction and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Usually, quasars are categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.
In the fields of Big Bang theory and cosmology, reionization is the process that caused matter in the universe to reionize after the lapse of the "dark ages".
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.
A light echo is a physical phenomenon caused by light reflected off surfaces distant from the source, and arriving at the observer with a delay relative to this distance. The phenomenon is analogous to an echo of sound, but due to the much faster speed of light, it mostly only manifests itself over astronomical distances.
Galaxy Zoo is a crowdsourced astronomy project which invites people to assist in the morphological classification of large numbers of galaxies. It is an example of citizen science as it enlists the help of members of the public to help in scientific research.
Hanny's Voorwerp, is a rare type of astronomical object called a quasar ionization echo. It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel while she was participating as a volunteer in the Galaxy Zoo project, part of the Zooniverse group of citizen science websites. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor.
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).
9Spitch is a gravitationally lensed system of two galaxies. The nearer galaxy is approximately 2 billion light-years (610 Mpc) from Earth and is designated SDSS J020941.27+001558.4, while the lensed galaxy is 10 billion light-years (3.1 Gpc) distant and is designated ASW0009io9. It was discovered in January 2014 by Zbigniew "Zbish" Chetnik, an amateur astronomer from Northamptonshire, England, while classifying images on the website Spacewarps.org. The discovery was announced on the BBC television programme Stargazing Live.
The photon underproduction crisis is a cosmological discussion concerning the purported deficit between observed photons and predicted photons.
Tololo 1247-232 is a small galaxy at a distance of 652 million light-years. It is situated in the southern equatorial constellation of Hydra. Visually, Tol 1247 appears to be an irregular or possibly a barred spiral galaxy. Tol 1247 is named after the surveys that were carried at the Cerro Tololo Inter-American Observatory (CTIO), the first of which was in 1976. It is one of nine galaxies in the local universe known to emit Lyman continuum photons.
TON 618 is a hyperluminous, broad-absorption-line, radio-loud quasar and Lyman-alpha blob located near the border of the constellations Canes Venatici and Coma Berenices, with the projected comoving distance of approximately 18.2 billion light-years from Earth. It possesses one of the most massive black holes ever found, at 40 billion M☉.
The Teacup galaxy, also known as the Teacup AGN or SDSS J1430+1339 is a low redshift type 2 quasar, showing an extended loop of ionized gas resembling a handle of a teacup, which was discovered by volunteers of the Galaxy Zoo project and labeled as a Voorwerpje.
In astronomy, quenching is a process in which a galaxy loses cold gas, thus strongly suppressing star formation, because stars are formed from Nebulae and Nebulae are formed from accumulated Interstellar gas in the Interstellar medium (ISM). Evidence suggests that active supermassive black holes drive the process.
Direct collapse black holes are high-mass black hole seeds, putatively formed within the redshift range , when the Universe was about 100–250 million years old. Unlike seeds formed from the first population of stars (also known as Population III stars), direct collapse black hole seeds are formed by a direct, general relativistic instability. They are very massive, with a typical mass at formation of ~105 M☉. This category of black hole seeds was originally proposed theoretically to alleviate the challenge in building supermassive black holes already at redshift , as numerous observations to date have confirmed.
