Astronomers using the Hubble orbital telescope found a "supermassive" black hole lurking at the heart of the only dwarf galaxy ever observed to host one, they reported Wednesday. The surprise was discovered at the core of a tiny but incredibly dense galaxy, M60-UCD1, about 50 million light years from Earth, the team reported in the journal Nature.
M60-UCD1 is packed with some 140 million stars but is only 300 light years across - 1/500th of the diameter of our Milky Way. Black holes are enigmatic phenomena whose gravitational force is so extreme that not even light can escape their clutch. Supermassive versions of these beasts have until now only been seen at the centre of large galaxies, including our own, but never one so small. The astronomers were especially taken aback when they calculated that the hole accounts for a whopping 15 percent of the galactic mass.
The hole has the mass of 20 million Suns, making it five times heavier than the black hole at the centre of the Milky Way. One explanation could be that M60-UCD1 was once part of a much larger galaxy, which split and left one section with the black hole. If this theory is wrong and further sky-gazing shows that ultra-compact dwarf galaxies do typically harbour a supermassive black hole, the time could be nigh for a rethink. It would mean there could be twice as many black holes in our region of the Universe than previously estimated, the journal said.