Elliptical galaxy

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 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 with lenticular galaxies (S0) with their large-scale disks, and ES galaxies[2][3][4] with their intermediate scale disks, a subset of the "early-type" galaxy population.

Most elliptical galaxies are composed of older, low-mass stars, with a sparse interstellar medium, and they tend to be surrounded by large numbers of globular clusters. Star formation activity in elliptical galaxies is typically minimal; they may, however, undergo brief periods of star formation when merging with other galaxies.[5] Elliptical galaxies are believed to make up approximately 10–15% of galaxies in the Virgo Supercluster, and they are not the dominant type of galaxy in the universe overall.[6] They are preferentially found close to the centers of galaxy clusters.[7]

Elliptical galaxies range in size from dwarf ellipticals with tens of millions of stars, to supergiants of over one hundred trillion stars that dominate their galaxy clusters. Originally, Edwin Hubble hypothesized that elliptical galaxies evolved into spiral galaxies, which was later discovered to be false,[8] although the accretion of gas and smaller galaxies may build a disk around a pre-existing ellipsoidal structure.[9][10] Stars found inside of elliptical galaxies are on average much older than stars found in spiral galaxies.[8]

  1. ^ Hubble, E.P. (1936). The realm of the nebulae. Mrs. Hepsa Ely Silliman Memorial Lectures, 25. New Haven: Yale University Press. ISBN 9780300025002. OCLC 611263346. Alt URL(pp. 124–151)
  2. ^ Liller, M.H. (1966), The Distribution of Intensity in Elliptical Galaxies of the Virgo Cluster. II
  3. ^ Nieto, J.-L. et al. (1988), More isotropic oblate rotators in elliptical galaxies
  4. ^ Graham, A.W. et al. (2016), Disky Elliptical Galaxies and the Allegedly Over-massive Black Hole in the Compact “ES“ Galaxy NGC 1271 (see their Fig.7).
  5. ^ Pearson, W. J.; Wang, L.; Alpaslan, M.; Baldry, I.; Bilicki, M.; Brown, M. J. I.; Grootes, M. W.; Holwerda, B. W.; Kitching, T. D.; Kruk, S.; van der Tak, F. F. S. (November 2019). "Effect of galaxy mergers on star-formation rates". Astronomy & Astrophysics. 631: A51. arXiv:1908.10115. Bibcode:2019A&A...631A..51P. doi:10.1051/0004-6361/201936337.
  6. ^ Loveday, J. (February 1996). "The APM Bright Galaxy Catalogue". Monthly Notices of the Royal Astronomical Society. 278 (4): 1025–1048. arXiv:astro-ph/9603040. Bibcode:1996MNRAS.278.1025L. doi:10.1093/mnras/278.4.1025.
  7. ^ Dressler, A. (March 1980). "Galaxy morphology in rich clusters – Implications for the formation and evolution of galaxies". The Astrophysical Journal. 236: 351–365. Bibcode:1980ApJ...236..351D. doi:10.1086/157753.
  8. ^ a b John, D. (2006). Astronomy: The definitive guide to the universe. Bath, UK: Parragon Publishing., p. 224-225
  9. ^ Dekel, A., et al. (2009), Cold streams in early massive hot haloes as the main mode of galaxy formation
  10. ^ Stewart, Kyle R., et al. (2013), Angular Momentum Acquisition in Galaxy Halos