Starbust galaxies are either young or rejuvenated galaxies, with a star formation activity significantly larger than in our own Milky Way. These galaxies typically contain very luminous X-ray sources, including the Ultra-luminous X-ray sources (ULXs) that may harbor massive black holes (see X-ray sources in galaxies). A nearby example of starburst galaxy is M82, which hosts a number of variable ULXs; the most luminous of these ULXs reaches a peak luminosity in the range of 1041 erg s-1 and is the best and most discussed candidate for a black hole of mass higher than 100 solar masses. Hot X-ray emitting interstellar matter is also found in starburst galaxies. In M82 this hot gas appears to be escaping the nuclear region as a wind, visible above and below the stellar disk of this galaxy. Galaxy interaction or merging is frequently the trigger of a starburst episode (see Interacting galaxies and mergers).