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Size (left) and distance (right) of a few well-known galaxies put to scale. There are an estimated 100 billion galaxies in all of the observable universe. [1] On the order of 100,000 galaxies make up the Local Supercluster, and about 51 galaxies are in the Local Group (see list of nearest galaxies for a complete list).
The spiral galaxy NGC 4622 lies approximately 111 million light-years away from Earth in the constellation Centaurus. NGC 4622 is an example of a galaxy with leading spiral arms. [2] Each spiral arm winds away from the center of the galaxy and ends at an outermost tip that "points" in a certain direction (away from the arm).
The giant elliptical galaxy ESO 325-4. An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence and 1936 work The Realm of the Nebulae, [1] along with spiral and lenticular galaxies.
In Hubble's galaxy classification scheme, M87 is an E0 galaxy. In 1922, the American astronomer Edwin Hubble categorized M87 as one of the brighter globular nebulae, as it lacked any spiral structure, but like spiral nebulae, appeared to belong to the family of non-galactic nebulae. [ 20 ]
The NGC contains 7,840 objects, including galaxies, star clusters and emission nebulae. Dreyer published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues (abbreviated IC), describing a further 5,386 astronomical objects. Thousands of these objects are best known by their NGC or IC numbers, which remain in widespread use.
It differs from the “light travel distance” since the proper distance takes into account the expansion of the universe, i.e. the space expands as the light travels through it, resulting in numerical values which locate the most distant galaxies beyond the Hubble sphere and therefore with recession velocities greater than the speed of light c.
A brightest cluster galaxy (BCG) is defined as the brightest galaxy in a cluster of galaxies. BCGs include the most massive galaxies in the universe . They are generally elliptical galaxies which lie close to the geometric and kinematical center of their host galaxy cluster , hence at the bottom of the cluster potential well .
Six star systems have been found to have exoplanets. The Fornax Dwarf galaxy is a small faint satellite galaxy of the Milky Way. NGC 1316 is a relatively close radio galaxy. The Hubble's Ultra-Deep Field is located within the Fornax constellation. [1] It is the 41st largest constellation in the night-sky, occupying an area of 398 square degrees.