A small supermassive black hole might sound like an oxymoron, but it’s not, as observations made using NASA’s Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile have now shown. Astronomers have discovered the tiniest supermassive black hole ever detected at the center of a galaxy.
“It might sound contradictory, but finding such a small, large black hole is very important,” Vivienne Baldassare of the University of Michigan in Ann Arbor, the lead author of a study detailing the findings, said in a statement. “We can use observations of the lightest supermassive black holes to better understand how black holes of different sizes grow.”
The tiny supermassive black hole -- located at a distance of about 340 million light-years in the dwarf galaxy RGG 118 -- is nearly 100 times less massive than the supermassive black hole found in the center of the Milky Way.
The mass of black holes is measured relative to the mass of our sun. These celestial bodies -- regions of space-time where the gravitational force is so strong that not even light can escape -- come in two varieties. The “stellar mass” black holes, which are formed by the gravitational collapse of a massive star and typically have masses ranging between 5 and 10 solar masses, and the “supermassive” black holes found at the center of almost all galaxies.
Supermassive black holes can have masses ranging from anywhere between a few million and a few billion solar masses. The Milky Way’s supermassive black hole is believed to hold nearly 4 million times the mass of our sun.
“We found this little supermassive black hole [RGG 118] behaves very much like its bigger, and in some cases much bigger, cousins,” co-author Amy Reines from the University of Michigan, said in the statement. “This tells us black holes grow in a similar way no matter what their size.”
Observations suggest that supermassive black holes are formed either due to the merger of smaller black hole seeds, or a supermassive black hole seed 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.
Scientists believe that the latest discovery might help them decide which of the theories is more accurate. “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,” co-author Elena Gallo from the University of Michigan, said in the statement.