The scene involves three players: the ultracompact dwarf galaxy which harbors a supermassive black hole, a giant galaxy, and a third normal galaxy which is heading towards a collision with the giant.
The ultracompact galaxy, named M60-UCD1, is one of its kind because it is the smallest galaxy known to contain such a massive light-sucking black hole at its centre.
"It is the smallest and lightest object that we know of that has a supermassive black hole," says Seth, lead author of the study published in Thursday's issue of the journal Nature. "It's also one of the most black hole-dominated galaxies known."
The black hole has a mass equal to 21 million suns small galaxy. Compare this to the supermassive black hole at the center of our Milky Way galaxy: its mass is a mere 4 million suns, making up less than 0.01 percent of the Milky Way's total mass, estimated at some 50 billion solar masses. The newly discovered unltracompact dwarf galaxy's black hole is a stunning 15 percent of the galaxy's total mass of 140 million suns. These dwarf galaxies are less than a few hundred light years across compared with our Milky Way's 100,000-light-year diameter."That is pretty amazing, given that the Milky Way is 500 times larger and more than 1,000 times heavier than the dwarf galaxy M60-UCD1," Seth says.
"We believe this once was a very big galaxy with maybe 10 billion stars in it, 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," he says. "That was maybe as much as 10 billion years ago. We don't know."
Their finding suggests plenty of other ultracompact dwarf galaxies likely also contain supermassive black holes - and those dwarfs may be the stripped remnants of larger galaxies that were torn apart during collisions with yet other galaxies.
Seth says ultracompact dwarf galaxy M60-UCD1 may be doomed, although he cannot say when because the dwarf galaxy's orbit around M60 isn't known. "Eventually, this thing may merge with the center of M60, which has a monster black hole in it, with 4.5 billion solar masses - more than 1,000 times bigger than the supermassive black hole in our galaxy. When that happens, the black hole we found in M60-UCD1 will merge with that monster black hole."
Meanwhile, M60 is also pulling in another galaxy, named NGC4647. M60 is about 25 times more massive than NGC4647. Ultimately, these two will also collide.
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