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.
A lenticular galaxy is a type of galaxy intermediate between an elliptical and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have very little ongoing star formation. They may, however, retain significant dust in their disks. As a result, they consist mainly of aging stars. Despite the morphological differences, lenticular and elliptical galaxies share common properties like spectral features and scaling relations. Both can be considered early-type galaxies that are passively evolving, at least in the local part of the Universe. Connecting the E galaxies with the S0 galaxies are the ES galaxies with intermediate-scale discs.
Dwarf elliptical galaxies (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.
In astronomy, a galactic bulge is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies. Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.
A mass deficit is the amount of mass that has been removed from the center of a galaxy, presumably by the action of a binary supermassive black hole.
A satellite galaxy is a smaller companion galaxy that travels on bound orbits within the gravitational potential of a more massive and luminous host galaxy. Satellite galaxies and their constituents are bound to their host galaxy, in the same way that planets within the Solar System are gravitationally bound to the Sun. While most satellite galaxies are dwarf galaxies, satellite galaxies of large galaxy clusters can be much more massive. The Milky Way is orbited by about fifty satellite galaxies, the largest of which is the Large Magellanic Cloud.
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.
IC 1101 is a class S0 supergiant (cD) lenticular galaxy at the center of the Abell 2029 galaxy cluster. It has an isophotal diameter at about 123.65 to 169.61 kiloparsecs. It possesses a diffuse core which is the largest known core of any galaxy to date, and contains a supermassive black hole, one of the largest discovered. IC 1101 is located at 354.0 megaparsecs from Earth. It was discovered on 19 June 1790, by the British astronomer William Herschel.
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved, but the exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution and also provides astronomers with clues about how galaxies grew into their current forms over long stretches of time.
The Sérsic profile is a mathematical function that describes how the intensity of a galaxy varies with distance from its center. It is a generalization of de Vaucouleurs' law. José Luis Sérsic first published his law in 1963.
Galactic clusters are gravitationally bound large-scale structures of multiple galaxies. The evolution of these aggregates is determined by time and manner of formation and the process of how their structures and constituents have been changing with time. Gamow (1952) and Weizscker (1951) showed that the observed rotations of galaxies are important for cosmology. They postulated that the rotation of galaxies might be a clue of physical conditions under which these systems formed. Thus, understanding the distribution of spatial orientations of the spin vectors of galaxies is critical to understanding the origin of the angular momenta of galaxies.
The type-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.
Abell 1413 is a massive and rich type I galaxy cluster straddling the border between the constellations Leo and Coma Berenices, with the projected comoving distance of approximately 640 Mpc (2.1 billion ly). The cluster is especially notable due to the presence of its very large brightest cluster galaxy (BCG), one of the most extreme examples of its type, as well as one of the largest galaxies known. The cluster was first noted by George O. Abell in 1958.
A2261-BCG is a huge elliptical galaxy in the cluster Abell 2261. One of the largest galaxies known, A2261-BCG is estimated to have a diameter of a million light-years, some 10 times larger than the Milky Way. It is the brightest and the most massive galaxy in the cluster, and has one of the largest galactic cores ever observed, spanning more than 10,000 light-years. Yet, unusually, its center does not contain a supermassive black hole.
NGC 3311 is a super-giant 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.
Abell 2219 BCG, also known as LEDA 2285869, is a massive type-cD elliptical galaxy residing as the brightest cluster galaxy (BCG) in the Abell 2219 galaxy cluster located in constellation Hercules. At the redshift of 0.224, the galaxy is around 2.7 billion light-years from Earth.
Abell 1942 BCG, also known as PGC 1256558, is a massive elliptical galaxy of type-cD residing as the brightest cluster galaxy of the Abell 1942 galaxy cluster, located in the constellation Virgo. With a redshift of 0.224, the galaxy is located nearly 2.7 billion light-years away from Earth.
Abell 697 BCG, also known as LEDA 2079433, is a massive type-cD elliptical galaxy residing as the brightest cluster galaxy in Abell 697 galaxy cluster. It is located in the constellation of Lynx and has a redshift of 0.28, meaning the galaxy is located 3.5 billion light-years away from Earth.
Abell 68 is massive and rich galaxy cluster located in the constellation of Pisces with a projected co-moving distance of approximately 1124.6 Mpc or 3.668 billion light-years away from Earth. The cluster is especially notable for its gravitational lensing and was first discovered by George O. Abell in 1958.
4C +26.42 is an elliptical galaxy located in the constellation of Boötes. It has a redshift of 0.063, estimating the galaxy to be located 863 million light-years from Earth. It has an active galactic nucleus and is the brightest cluster galaxy (BCG) in Abell 1795, an X-ray luminous rich cluster (LX 1045 ergs s-1), with an estimated cooling-flow rate of 300 M yr-1.
