How feasting black holes time their burps

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This week on Two Blocks from the White House.

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Hi, I'm Bob McDonald. Welcome to Quirks and Quarks. On this week's show, tracking elusive wolverines in the mountains of Western Canada.

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And then we hung frozen beavers between trees. And that's enough to attract wolverines.

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And figuring out why and when black holes burp.

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So we can just watch one star go in, the black hole will swallow the material, eject out some things, and then at some point, eventually will burp.

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Plus reconstructing the insect soundscape of the Jurassic, hints of hidden chambers in King Tutankhamen's tomb, and blurring the line between native and introduced species. All this today on Quirks and Quarks.

Burping after a big meal is in many cultures considered to be quite rude. But you try telling that to a black hole. Black holes are voracious eaters, but they're also quite messy. And after devouring a star, they'll often let out a big burp, launching jets of high-energy particles tremendous distances through space.

And while we humans might not want to be around for a huge post-dinner belch, astrophysicists often do want to see black holes spewing out this matter. But it's a big challenge for them to know when a burp is coming. Well, now in a recent study, a team of astrophysicists, including Dr. Adele Goodwin, has figured out the timing of these burps in the hopes of being able to catch them in action. Dr. Goodwin is with Curtin University in Australia. Hello, and welcome to our program.

Adele Goodwin (2:18)

Hi, thanks so much for having me.

Bob McDonald (2:20)

First of all, describe a black hole burp. What's actually going on there?

Adele Goodwin (2:25)

Yeah. So it sounds a bit strange to think that a black hole might be able to burp, but what we refer to them as jets or outflows. And it's actually when the black hole is swallowing material, it forms an accretion disk, and that accretion disk can actually have very strong magnetic fields. Particles can get chanted along those magnetic field lines and can get ejected out at really high speeds. And so this is what we would refer to as a burp, is this ejected material because we see it moving through the host galaxy of the black hole.

Bob McDonald (2:59)

Ah, so the accretion disk, that's the sort of a ring of material around the black hole before it falls in.

Adele Goodwin (3:06)

Yeah. So as like material doesn't just fall in from all directions, it kind of forms a sort of flat structure that's swirling into the black hole. So kind of like how water swirls down a bathpug, but it's gas swirling into a black hole.

Bob McDonald (3:21)

Well, we usually think of black holes as having voracious appetites, that everything falls into a black hole, nothing gets out. So what's launching these jets?

Adele Goodwin (3:30)

Yeah, this is I think quite a common misconception, is that people always assume that black holes are these like giant sucking machines in space and that all this like anything close to a black hole will just be immediately swallowed. And that is true if it makes it within the event horizon, which is kind of like the point of no return for a black hole, where gravity is so strong that nothing can escape, not even light. But that's quite close to the black hole. And a lot of the interesting physics that happens around a black hole happens outside of the event horizon, in my opinion.

And this is where we see these jets and outflows being launched from.

Bob McDonald (4:04)

Wow. It's sort of like, as you say, water going down a drain, it would be as though your bathtub is draining out, but some of the water is shooting up into the air.

Adele Goodwin (4:13)

Yes, exactly. So, yeah, when you're watching water go down the bath plug, it doesn't usually come out, but occasionally for a black hole, because there are magnetic fields and other things involved, particles can get really ejected out and at really high speed. So we're talking close to the speed of light sometimes, so highly relativistic ejections.