Ultraluminous X-ray Source
An ultra-luminous X-ray source (ULX) is an astronomical source of X-rays that is less luminous than an active galactic nucleus but is more consistently luminous than any known stellar process (> 1039 erg/s, or 1032 watts), assuming that it radiates isotropically (the same in all directions). Typically there is about one ULX per galaxy in galaxies which host ULXs, but some galaxies contain many ULXs. The Milky Way does not contain a ULX. The main interest in ULXs stems from the fact that their luminosity exceeds the Eddington luminosity of neutron stars and even stellar black holes. It is not known what powers ULXs; models include beamed emission of stellar mass objects, accreting intermediate-mass black holes, and super-Eddington emission.
Read more about Ultraluminous X-ray Source: Observational Facts, Models, Notable ULXs
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