Researchers have discovered the smallest supermassive black hole known to science, and the finding could provide clues as to how these larger black holes develop.
The "oxymoronic" black hole is about 50,000 times the mass of the sun, which is less than half the mass of the previously smallest-known black hole at the center of a galaxy, the Chandra X-ray Observatory reported. The object exists at the center of a dwarf disk galaxy, dubbed RGG 118, which is located about 340 million light years from Earth.
"It might sound contradictory, but finding such a small, large black hole is very important," said Vivienne Baldassare of the University of Michigan. "We can use observations of the lightest supermassive black holes to better understand how black holes of different sizes grow."
The researchers were able to calculate the mass of the unusual black hole by studying the motion of cool gas near the center of the galaxy from visible light data picked up with the 6.5-meter Clay Telescope in Chile. The data allowed them to determine the X-ray brightness of hot gas moving towards the black hole. The observations revealed the outward push of radiation pressure from the gas is about 1 percent of the black hole's inward pull of gravity, which is a characteristic of supermassive black holes.
"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."
Scientists believe supermassive black holes may form when a cloud of gas between 10,000 to 100,000 times the mass of the Sun collapses into a black hole. These black hole "seeds" could merge to form even larger black holes. Another theory suggests black hole seeds could come from giant stars that are about 100 times the sun's mass and form these objects after they run out of fuel and collapse.
"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."
The findings were published in a recent edition of the Astrophysical Journal Letters.
