Three gas clouds nearly grazed the edge of the Milky Way’s black hole

As far as close shaves with a black hole go, it doesn’t get much closer than this.

Scientists have spotted clouds of gas hurtling around the monster black hole at the center of the Milky Way, not far from the behemoth’s edge. Observed on three separate occasions, the gas clouds careened along at unimaginably fast speeds — 30 percent of the speed of light, researchers report October 31 in Astronomy & Astrophysics. 

The gas seemed to be near a boundary known as the innermost stable circular orbit — the closest matter can circle the black hole without falling in. The clumps, which researchers observed when the gas caused flares of infrared light, orbited at a distance just a few times the radius of the black hole’s event horizon, the boundary from beyond which nothing, not even light, can return (SN: 5/31/14, p. 16). That’s equivalent to about a quarter of the distance from Earth to the sun.

Previously, scientists had tracked the motion of a star orbiting close to the black hole (SN: 8/18/18, p. 12). But that star was hundreds of times farther away than the gas.

“What’s exciting now is that we can get closer to the black hole,” says study coauthor Jason Dexter, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. The researchers observed the clouds using the Very Large Telescope array in the Atacama Desert of Chile.

These up-close encounters strengthen scientists’ belief that the Milky Way has a bona fide black hole lurking at its center. Harvard University astrophysicist Avi Loeb helped predict the existence of such flares 13 years ago, and the results match expectations.  Such measurements could also help physicists test Einstein’s theory of gravity, general relativity, Loeb says.