Astronomers detect a hidden black hole in the galactic center

Artist's impression of a cloud of gas swirling around a black hole.

Astronomers have detected a stealth black hole of its effects on a cloud of interstellar gas. This intermediate mass black hole is one of the more than 100 million quiet black holes that should be hiding in our galaxy. These results provide a new method for searching for other hidden black holes and help us understand the growth and evolution of black holes.

Black holes are objects of such gravity that everything, including light, is sucked in and can not escape. Since black holes do not emit light, astronomers must deduce their existence from the effects of gravity on other objects. The mass of black holes varies from about 5 times that of the Sun to supermassive black holes, millions of times greater than that of the Sun. Astronomers believe that small black holes merge and develop gradually, but no one has ever found a black hole of intermediate mass, hundreds or thousands of times the mass of the Sun.

A research team led by Shunya Takekawa at the National Astronomical Observatory of Japan noticed HCN – 0.009-0.044, a gas cloud moving strangely near the center of the galaxy 25,000 light-years from Earth in the constellation of Sagittarius. They have used ALMA (Atacama Large Millimeter / submillimeter Array) to perform high resolution cloud observations and found that it was swirling around an invisible massive object.

Takekawa explains, "The detailed kinematic analyzes revealed that a huge mass, 30,000 times greater than the Sun's, was concentrated in a region much smaller than our solar system. This and the lack of object observed at this location strongly suggest a black hole of intermediate mass. By analyzing other abnormal clouds, we hope to expose other silent black holes. "

Tomoharu Oka, a professor at Keio University and co-leader of the team, adds, "It is significant that this mid-mass black hole was discovered only 20 light-years away from the supermassive black hole of the galactic center. In the future, he will fall into the supermassive black hole; a bit like gas is falling into it right now. This supports the merging model of black hole growth. "

These results were published in Takekawa et al. "Indication of another black hole of intermediate mass in the galactic center" in The Astrophysical Journal Letters of January 20, 2019.