Smallest supermassive black hole may help us understand how they grow

Astronomers have identified the smallest supermassive black hole ever detected in the centre of a galaxy, which they hope will provide clues to how larger black holes formed along with their host galaxies billions of years ago.

When they small, everything is relative. The supermassive black hole in question is about 50,000 times the mass of the Sun. But that is less than half the mass of the previous smallest black hole at the centre of a galaxy.

It is is nearly 100 times less massive than the supermassive black hole found in the centre of our galaxy, the Milky Way and 200,000 times less massive than the heaviest black holes.

“It might sound contradictory, but finding such a small, large black hole is very important,” said Vivienne Baldassare of the University of Michigan in Ann Arbor, first author of a paper on these results published in The Astrophysical Journal Letters.

“We can use observations of the lightest supermassive black holes to better understand how black holes of different sizes grow.”

The black hole is in the centre of a dwarf disk galaxy, called RGG 118, about 340 million light years from Earth.

It was discovered using NASA’s Chandra X-ray Observatory and the 6.5-metre Clay Telescope in Chile.

“We found this little supermassive black hole behaves very much like its bigger, and in some cases much bigger, cousins,” said co-author Amy Reines of the University of Michigan.

“This tells us black holes grow in a similar way no matter what their size.”

The black hole in RGG 118. It’s also about found in the centers of other galaxies.

As NASA reports:

Astronomers think supermassive black holes may form when a large cloud of gas, with a mass of about 10,000 to 100,000 times that of the sun, collapses into a black hole. Many of these black hole seeds then merge to form much larger supermassive black holes. Alternately, a supermassive black hole seed could come from a giant star, about 100 times the sun’s mass, that ultimately forms into a black hole after it runs out of fuel and collapses.
“We have two main ideas for how these supermassive black holes are born,” said Elena Gallo of the University of Michigan. “This black hole in RGG 118 is serving as a proxy for those in the very early universe and ultimately may help us decide which of the two is right.”