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Size (left) and distance (right) of a few well-known galaxies put to scale. The following is a list of notable galaxies.. There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in the Local Supercluster, and an estimated 100 billion in all of the observable universe.
The Milky Way is an example of a spiral galaxy. It is estimated that there are between 200 billion [7] (2 × 10 11) to 2 trillion [8] galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances in the order of millions of parsecs (or ...
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31 , M31 , and NGC 224 . Andromeda has a D 25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years ) [ 8 ] and is approximately 765 kpc (2.5 million light-years ...
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to ...
Active galactic nucleus. An active galactic nucleus ( AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such excess, non-stellar emissions have been observed in the radio, microwave ...
1995 — First detection of small-scale structure in the cosmic microwave background. 1995 — Hubble Deep Field survey of galaxies in field 144 arc seconds across. 1998 — The 2dF Galaxy Redshift Survey maps the large-scale structure in a section of the Universe close to the Milky Way. 1998 — The Hubble Deep Field South is compiled.
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, [ 1] along with spiral and lenticular galaxies. Elliptical (E) galaxies are, together ...
The Circinus Galaxy, a Type II Seyfert galaxy. Seyfert galaxies are one of the two largest groups of active galaxies, along with quasar host galaxies. They have quasar-like nuclei (very luminous sources of electromagnetic radiation that are outside of our own galaxy) with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, [1] but unlike quasars, their ...