List of largest galaxies

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This is a list of largest galaxies known, sorted by order of increasing major axis diameters. The unit of measurement used is the light-year (approximately 9.46×1012 kilometers).

A Hubble Space Telescope image of the supergiant elliptical galaxy ESO 306-17. Supergiant elliptical galaxies are some of the largest galaxies known.
The Condor Galaxy is a colossal spiral galaxy disturbed by the smaller IC 4970. It is the largest known spiral galaxy with the isophotal diameter of over 717,000 light-years (220 kiloparsecs).[1]

Overview

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Galaxies are vast collections of stars, planets, nebulae and other objects that are surrounded by an interstellar medium and held together by gravity. They do not have a definite boundary by nature, and are characterized with gradually decreasing stellar density as a function of increasing distance from its center. Because of this, measuring the sizes of galaxies can often be difficult and have a wide range of results depending on the sensitivity of the detection equipment and the methodology being used. Some galaxies emit more strongly in wavelengths outside the visible spectrum, depending on its stellar population, whose stars may emit more strongly in other wavelengths that are beyond the detection range. It is also important to consider the morphology of the galaxy when attempting to measure its size – an issue that has been raised by the Russian astrophysicist B.A. Vorontsov-Vel'Yaminov in 1961, which considers separate determination methods in measuring the sizes of spiral and elliptical galaxies.[2]

For a full context about how the diameters of galaxies are measured, including the estimation methods stated in this list, see section Galaxy#Physical diameters.

List

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Listed below are galaxies with diameters greater than 700,000 light-years. This list uses the mean cosmological parameters of the Lambda-CDM model based on results from the 2015 Planck collaboration, where H0 = 67.74 km/s/Mpc, ΩΛ = 0.6911, and Ωm = 0.3089.[3] Due to different techniques, each figure listed on the galaxies has varying degrees of confidence in them. The reference to those sizes plus further additional details can be accessed by clicking the link for the NASA/IPAC Extragalactic Database (NED) on the right-hand side of the table.

Listed below are some notable galaxies under 700,000 light-years in diameter, for the purpose of comparison. All links to NED are available, except for the Milky Way, which is linked to the relevant paper detailing its size.

See also

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Notes

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  1. ^ a b c d e f g h i j k l m n o p q r s t u The physical diameters given by NED for this object are based on the mean of one or more redshift-independent distance techniques, which are subject to errors and sensitivity to extreme values. The diameters given for this object in this list was based on NED's provided scale "Virgo + GA + Shapley" multiplied with the values for the angular diameter of the cited estimation method.
  2. ^ a b c d e f g h i j k l m n o Morphology unlisted; images show an elliptical galaxy.
  3. ^ The larger galaxy in the Antennae Galaxies pair.
  4. ^ Starburst galaxy
  5. ^ A blazar.
  6. ^ Major axis refers to the visible stellar axis of the host galaxy. Radio lobes are 15 million light-years across, though not considered a part of the main galaxy.
  7. ^ This is the diameter as measured through the 25.0 mag/arcsec−2 isophote at the B-band. The diffuse stellar halo of this galaxy extends up to 300 kiloparsecs (980,000 light-years) across.
  8. ^ This is the diameter measured through the quoted estimation method. This galaxy has an immense, diffuse low-surface brightness spiral extending up to 200 kiloparsecs (650,000 light-years) across.
  9. ^ No stated minor axis
  10. ^ No stated minor axis

References

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  1. ^ "Your NED Search Results". ned.ipac.caltech.edu.
  2. ^ Vorontsov-Vel'Yaminov, B. A. (1961). "The Comparison of Galaxy Diameters". Soviet Astronomy. 4: 735. Bibcode:1961SvA.....4..735V.
  3. ^ Ade, P. A. R.; et al. (2016). "Planck2015 results". Astronomy & Astrophysics. 594: A13. arXiv:1502.01589. Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830. S2CID 119262962.
  4. ^ Goodwin, S. P.; Gribbin, J.; Hendry, M. A. (22 April 1997). "The Milky Way is just an average spiral". arXiv:astro-ph/9704216.
  5. ^ Goodwin, S. P.; Gribbin, J.; Hendry, M. A. (August 1998). "The relative size of the Milky Way". The Observatory. 118: 201–208. Bibcode:1998Obs...118..201G.

Further reading

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