NGC 4414, a teepical spiral galaxy in the constellation Coma Berenices, is about 55,000 licht-years in diameter an approximately 60 million licht-years away frae Yird

A galaxy is a gravitationally boond seestem o starns, stellar remnants, interstellar gas, dust, an dark matter.[1][2] The wird galaxy is derived frae the Greek galaxias (γαλαξίας), leeterally "milky", a reference tae the Milky Way. Galaxies range in size frae dwarfs wi juist a few billion (109) starns tae giants wi ane hunder trillion (1014) starns,[3] each orbitin its galaxy's centre o mass. Galaxies are categorised accordin tae thair veesual morphology as elliptical,[4] spiral an irraiglar.[5] Mony galaxies are thocht tae hae black holes at thair active centres. The Milky Way's central black hole, kent as Sagittarius A*, haes a mass fower million times greater nor the Sun.[6] As o Mairch 2016, GN-z11 is the auldest an maist distant observed galaxy wi a comovin distance o 32 billion licht-years frae Yird, an observed as it exeestit juist 400 million years efter the Big Bang, accordin tae scientists.

Recent estimates o the nummer o galaxies in the observable universe range frae 200 billion (2×1011)[7] tae 2 trillion (2×1012) or mair,[8][9] conteenin mair starns nor aw the grains o saund on planet Yird.[10] Maist o the galaxies are 1,000 tae 100,000 parsecs in diameter an separatit bi distances on the order o millions o parsecs (or megaparsecs). The space atween galaxies is filled wi a tenuous gas haein an average density o less nor ane atom per cubic metre. The majority o galaxies are gravitationally organised intae groups, clusters, an superclusters. At the lairgest scale, thir associations are generally arranged intae sheets an filaments surroondit bi immense voids.[11] The lairgest structur o galaxies yet recognised is a cluster o superclusters, that haes been named Laniakea[12]


  1. Sparke & Gallagher III 2000, p. i
  2. Hupp, E.; Roy, S.; Watzke, M. (August 12, 2006). "NASA Finds Direct Proof of Dark Matter". NASA. Retrieved April 17, 2007.
  3. Uson, J. M.; Boughn, S. P.; Kuhn, J. R. (1990). "The central galaxy in Abell 2029 – An old supergiant". Science. 250 (4980): 539–540. Bibcode:1990Sci...250..539U. doi:10.1126/science.250.4980.539. PMID 17751483.
  4. Hoover, A. (June 16, 2003). "UF Astronomers: Universe Slightly Simpler Than Expected". Hubble News Desk. Retrieved March 4, 2011. Based upon:
  5. Jarrett, T. H. "Near-Infrared Galaxy Morphology Atlas". California Institute of Technology. Retrieved January 9, 2007.
  6. Finley, D.; Aguilar, D. (November 2, 2005). "Astronomers Get Closest Look Yet At Milky Way's Mysterious Core". National Radio Astronomy Observatory. Retrieved August 10, 2006.
  7. Gott III, J. R.; et al. (2005). "A Map of the Universe". The Astrophysical Journal. 624 (2): 463–484. arXiv:astro-ph/0310571. Bibcode:2005ApJ...624..463G. doi:10.1086/428890.
  8. Christopher J. Conselice; et al. (2016). "The Evolution of Galaxy Number Density at z < 8 and its Implications". The Astrophysical Journal. 830 (2): 83. arXiv:1607.03909v2. doi:10.3847/0004-637X/830/2/83. Explicit use of et al. in: |author= (help)
  9. Fountain, Henry (17 October 2016). "Two Trillion Galaxies, at the Very Least". The New York Times. Retrieved 17 October 2016.
  10. Mackie, Glen (1 February 2002). "To see the Universe in a Grain of Taranaki Saund". Centre for Astrophysics and Supercomputing. Retrieved 28 January 2017.
  11. "Galaxy Clusters and Large-Scale Structure". University of Cambridge. Retrieved January 15, 2007.
  12. Gibney, Elizabeth (2014). "Earth's new address: 'Solar System, Milky Way, Laniakea'". Nature. doi:10.1038/nature.2014.15819.