Irregular galaxy

An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an elliptical galaxy.^[1] Irregular galaxies do not fall into any of the regular classes of the Hubble sequence, and they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arm structure.^[2]

Collectively they are thought to make up about a quarter of all galaxies. Some irregular galaxies were once spiral or elliptical galaxies but were deformed by an uneven external gravitational force. Irregular galaxies may contain abundant amounts of gas and dust.^[3] This is not necessarily true for dwarf irregulars.^[4]

Irregular galaxies are commonly small, about one tenth the mass of the Milky Way galaxy. Due to their small sizes, they are prone to environmental effects like colliding with large galaxies and intergalactic clouds.^[5]

^ Butz, Stephen D. (2002). Science of Earth Systems. Cengage Learning. p. 107. ISBN 978-0-7668-3391-3.
^ Morgan, W. W. & Mayall, N. U. (1957). "A Spectral Classification of Galaxies." Publications of the Astronomical Society of the Pacific. 69 (409): 291–303.
^ Faulkes Telescope Educational Guide – Galaxies – Irregulars
^ Walter, F. et al. Astophys J 661, 102 - 114, 2007
^ Elmegreen, Debra Meloy, and Bruce G. Elmegreen. "Galaxies." Space Sciences, edited by Pat Dasch, vol. 2: Planetary Science and Astronomy, Macmillan Reference USA, 2002, pp. 50-56. Gale Virtual Reference Library, go.galegroup.com/ps/i.do?p=GVRL&sw=w&u=mcc_pv&v=2.1&it=r&id=GALE%7CCX3408800138&asid=f1f899f2eb1f500bc3341c4f13abb896. Accessed 25 September 2017.

[1] Butz, Stephen D. (2002). Science of Earth Systems. Cengage Learning. p. 107. ISBN 978-0-7668-3391-3.

[2] Morgan, W. W. & Mayall, N. U. (1957). "A Spectral Classification of Galaxies." Publications of the Astronomical Society of the Pacific. 69 (409): 291–303.

[3] Faulkes Telescope Educational Guide – Galaxies – Irregulars

[4] Walter, F. et al. Astophys J 661, 102 - 114, 2007

[5] Elmegreen, Debra Meloy, and Bruce G. Elmegreen. "Galaxies." Space Sciences, edited by Pat Dasch, vol. 2: Planetary Science and Astronomy, Macmillan Reference USA, 2002, pp. 50-56. Gale Virtual Reference Library, go.galegroup.com/ps/i.do?p=GVRL&sw=w&u=mcc_pv&v=2.1&it=r&id=GALE%7CCX3408800138&asid=f1f899f2eb1f500bc3341c4f13abb896. Accessed 25 September 2017.

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