The winds of change blow, even around a black hole.
New Canadian-led research has peered into the strange world of black holes to discover they’re girded by electromagnetic winds that not only influence how the super-dense interstellar bodies gobble up anything that gets too close but also how they affect vast areas of space around them.
The insights, published Monday in the journal Nature, could ultimately help explain the formation of our own sun, our planetary neighbours and even our own galaxy.
“These winds are telling us two things,” said Greg Sivakoff, a physicist at the University of Alberta and a co-author of the paper.
“They’re changing our perception of how rapidly black holes might grow. The other is it’s going to be affecting the local environment.”
Black holes are the remnants of massive stars that have collapsed in on themselves to an unimaginably small point. That much concentrated mass creates attraction so intense that within a certain distance not even light can escape it — a distance known as the event horizon.
Outside that horizon, black holes are surrounded by giant spinning Frisbees called accretion discs. Those discs contain magnetic instabilities that force them to transfer rotational energy from the outside of the disc to the inside.
As particles fall toward the black hole, they gain energy — just as a figure skater’s spin speeds up as they pull their arms toward them. That energy causes the disc to heat up and emit X-rays.
“We use the X-rays to trace what’s going on,” Sivakoff said.
“We were watching how rapidly they decayed from their peak emission back down to when the disc is more stable. We were surprised to see that the discs were evolving more rapidly than we thought they should.
“The X-ray emissions were dropping too quickly.”
Sivakoff and his colleagues concluded that mass and energy were coming off the disc in some kind of wind.
He said the winds seem to be ongoing throughout the life of a black hole, which suggests that they “feed” much more slowly than we previously thought. Some models indicate that up to 80 per cent of the mass originally thought to be plunging into the black hole is instead blowing off in the wind.
That means black holes are contributing to and changing the interstellar environment, a hot topic among astrophysicists.
“Even though we had this idea of black holes as always taking things away, in this case the black hole may be actually affecting things around it.”
That has implications everywhere.
Accretion discs are common in space and are a feature in the growth of all stars and planets. Studying how black-hole discs work could teach more about the formation of all stars and planets.
And it gets bigger. At the centre of most galaxies lies a massive black hole. The one in our galaxy is about four million times the mass of our sun.
Scientists think the formation of galaxies is linked to the formation of these giant black holes. Sivakoff’s conclusion that black holes do affect their environment opens up new lines of inquiry into how galaxies are made.
“It may be that in some small way, the accretion disc around the black hole at the centre of our galaxy is why we’re here.”
Note to readers: This is a corrected story. An earlier version said the name of the journal the research appears in was Science