An ultra diffuse galaxy (UDG), or dark galaxy,[1] is an extremely low luminosity galaxy, the first example of which was discovered in the nearby Virgo Cluster by Allan Sandage and Bruno Binggeli in 1984.[a] These galaxies have been studied for many years prior to their renaming in 2015. Their lack of luminosity is due to the lack of star-forming gas, which results in these galaxies being reservoirs of very old stellar populations.[3][4]
Based on discoveries confirmed in 2018, this class of galaxies includes both extremes of dark matter content: Some UDGs consist almost entirely of dark matter (such a galaxy may have the same size and mass as the Milky Way but a visible star count of only 1%),[5] while other UDGs appear to be almost entirely free of dark matter.[6]
- ^ Overbye, Dennis (26 January 2024). "What Do You Call a Galaxy Without Stars? - To dark matter and dark energy, add dark galaxies — collections of stars so sparse and faint that they are all but invisible". The New York Times. Archived from the original on 26 January 2024.
- ^ Conselice, Christopher J. (March 2018). "Ultra-diffuse galaxies are a subset of cluster dwarf elliptical/spheroidal galaxies". Research Notes of the AAS. 2 (1): 43. arXiv:1803.06927. Bibcode:2018RNAAS...2...43C. doi:10.3847/2515-5172/aab7f6. ISSN 2515-5172. S2CID 55462455.
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