Black holes tend to get a bad rap, often as giant, cosmic vacuum cleaners sucking up everything in range. But as researchers at the University of Colorado Boulder recently found, they’re actually a lot like toddlers.
CU astrophysicist Julie Comerford says black holes nap after meals. They’re also messy and somewhat picky eaters.
“You're trying to feed a kid dinner and the kid is pushing away some of the food, so some of the food gets eaten and then some of it gets thrown onto the floor,” she says. Well, black holes do that too, says Comerford. They slurp up stars and gas that come their way, but they also shove a bunch away in the form of big bursts of energy and gas. Here's what it looks like:
And if humans could hear X-rays, this is an approximation of what a black hole feast would sound like.
In a galaxy far, far away, Comerford and her colleagues recently found something special: a supermassive black hole that ate two big meals of stars and gas -- tossing some out along the way -- and then went quiet after each one, like it was taking a nap. As the scientists wrote in the Astrophysical Journal, the meals happened just 100,000 years apart.
“A hundred thousand years is a long time for us, but in a cosmological context that's really fast,” says Comerford. “So what that tells us is that black holes have these feeding episodes that are actually pretty fast.”
Scientists had predicted that black holes could gorge themselves fairly often, but hadn’t observed it happening repeatedly. It took five big research telescopes to spot these meals, indicated by bursts of energy making their way away from the black hole. The galaxy where the black hole resides is officially called SDSS J1354+1327, but unofficially Comerford and her colleagues started calling it "the galaxy that will haunt our dreams."
“Black holes growing in the centers of galaxies are really interesting beasts, really important for the evolution of universe. And one thing we don't know about them at all is: On what time scales are the black holes growing?” says Meg Urry, an astrophysicist at Yale University who wasn't involved in the study. “These things could be turning on and off every few decades. Or they could have steady accretion for millions of years and then turn off. And those two scenarios have a very different profile for how energy is being transferred to the galaxy.”
Urry says this kind of study helps clarify the story of how the universe came to be what it is today.
“We're really good at observing what the universe looks like today and what it looked like in the past. And we're trying to fill in all the physics of how it got from there to here,” she says.
The study could also help explain patterns of star formation.
Brooke Simmons, an astrophysicist at the University of California San Diego who wasn’t involved with the study, says that when a black hole tosses out part of its starry meal, it also tosses out a lot of energy with it. Those bursts of energy can heat up the galactic neighborhood in two ways: One can create a spurt of brand new stars, the other can prevent them from forming.
“You can get both new stars forming and then they sort of quench afterwards. You get a burst of star formation and then a quenching that happens that follows along right behind,” she says. And it’s likely that there are black holes all over the universe doing the same thing, altering their galaxies as they do.
“We actually think that every galaxy -- or almost every galaxy -- will go through phases like this as well,” says Simmons.
In fact, our own galaxy has a supermassive black hole called Sagittarius A*. It’s a very light eater, occasionally grazing on a cloud of gas or a single star every so often. It's pretty calm.
“Thank goodness, because it's dangerous when all that energy gets released,” says Urry.
But in about 4 billion years, big things are expected to happen in the Milky Way.
“The Andromeda galaxy is headed straight for us and we're headed straight for them and in 4 billion years we're going to collide,” says Julie Comerford. They’ll squish together into a new galaxy that Comerford refers to as “Mandromeda galaxy.” In the process, a lot of gas will head towards our supermassive black hole.
“And I'm positive our black hole is going to have a big feeding outburst even then in four billion years. I wish I could be around to see it,” says Comerford.
No one knows what the Earth will look like then, or if it will be around at all. Researchers predict that around the same time, the sun will swell up and swallow our piece of the solar system whole.
