Black holes eject matter as well as feed off it

Black holes are well known to be voracious feeders, but in the rush to consume all around them, some of the material gets flung far into space.

A paper published in Nature Astronomy describes how magnetic fields around the black holes govern both actions. They drive turbulent winds that blows gas and stellar particles away as well as creating a vortex that both pulls matter into the black hole.

“A good fraction of the mass actually gets kicked out of the black hole,” says astrophysicist Keigo Fukumura, who led the study. “If it didn’t get thrown off, we wouldn’t see it.”

The research could also explain why some galaxies stop forming stars with the outflows heating up and stripping away the gas reservoirs of host galaxies.

The model of disk accretion and ejection has previously been used to describe the architecture of supermassive black holes millions of times the mass of the Sun. This study suggests that it holds true for black hole of all sizes, even relatively small ones. 

It was first suggested in the 1970s that magnetic fields might be driving the winds around black holes, but the winds were not directly observable. They have been detected using a black hole’s X-ray spectrum.

The study bases its findings on observations of GRO J1655-40, a small black hole 11,000 light-years away in the constellation Scorpius and just seven times the mass of the Sun, with a companion star twice the size of the Sun.

While scientists agreed that GRO J1655-40’s X-rays revealed its turbulent winds, astronomers fell into two camps when deciding what drove them. Some argued that powerful magnetic fields fuelled the winds, while other believed they were the result of extremely hot swirling gases.

The Fukumura model developed appears to clear up the controversy, showing dense winds matching models of magnetically fuelled wind blowing close to the black hole.