The relatively nearby dwarf galaxy M60-UCD1 may house a supermassive black hole at its heart equal in mass to ~ 21 million suns.
It lies ~ 54 million ly away from Earth and orbits M60, one of the largest galaxies near the Milky Way, at a distance of only ~ 22000 ly from the larger galaxy's center, closer than the sun is to the center of the Milky Way!
The scientists calculated the size of the supermassive black hole that may lurk inside M60-UCD1 by analyzing the motions of the stars in that galaxy, which helped the researchers deduce the amount of mass needed to exert the gravitational field seen pulling on those stars. The stars at the center of M60-UCD1 zip at speeds of ~ 370000 km/h, much faster than stars would be expected to move in the absence of such a black hole.
The supermassive black hole at the
core of the Milky Way has a mass of ~ 4 million suns, taking up less than 0.01% of the galaxy's estimated total mass, which is ~ 50 billion suns. In comparison, the supermassive black hole that may lie in the core of M60-UCD1 appears five times larger than the one in the Milky Way, and also
seems to make up about 15% of the dwarf galaxy's mass, which is ~ 140 million suns. That's pretty amazing, given that the Milky Way is 500 times larger and more than 1000 times heavier than M60-UCD1.
The researchers suggest M60-UCD1 was once a very large galaxy, with maybe 10 billion stars, but then it passed very close to the center of an even larger galaxy, M60, and in that process, all the stars and dark matter in the outer part of the galaxy got torn away and became part of M60. That was maybe as much as 10 billion years ago.
Eventually, M60-UCD1 may merge with the center of M60, which has a monster black hole in it, with 4.5 billion solar masses (>1000 times bigger than the supermassive black hole in our galaxy!). When that happens, the
black hole in M60-UCD1 will merge with that monster black hole.
The astronomers suggest the way stars move in many other ultra-compact dwarf galaxies hints that they may host supermassive black holes, as well. All in all, the scientists suggest that ultra-compact dwarf galaxies could double the number of supermassive black holes known in the nearby regions of the universe. The researchers are participating in ongoing projects that may provide conclusive evidence for supermassive black holes in 4 other ultra-compact dwarfs.
