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Astronomers think that they have found the ultimate mismatched fight: a supermassive black hole versus a tiny white dwarf. But it’s not a simple David and Goliath story: the white dwarf may be winning — for now — but the ultimate outcome is not in doubt. It’s a supermassive black hole. It’s gonna win.

The black hole is called 1ES 1927+654 (the name is alphanumeric salad, but it comes from the fact that it was found in a survey taken by the old Einstein X-ray observatory, and the numbers are its coordinates on the sky). It’s sitting in the center of a galaxy about 270 million light-years from Earth, and has a mass equal to about 1.4 million times that of the Sun. That’s a lightweight as far as these kinds of beasts go — the black hole in the center of our Milky Way is 4 million solar masses and is considered somewhat small — but still not something you want to fool around with.

The black hole is actively eating material falling in from the galaxy around it. This material forms a flat disk well out from the black hole called an accretion disk. The material in it heats up considerably, getting extremely luminous. It shines with the light of several billion times the Sun’s.

A few years ago scientists noticed it acting weirdly. Black holes like this are surrounded by extremely hot ionized gas — material so hot electrons have been stripped off, called a plasma — that emits X-rays, very high-energy light. This halo, called a corona, of material around 1ES 1927+654 suddenly stopped emitting X-rays in 2018, something that had never been seen before.

So astronomers kept a close eye on it, hoping to see something that might explain why it went dark. Maybe something disrupted the corona, stirred the material up somehow, so it stopped emitting.

What they found was something even more weird [link to journal paper]. In mid-2022 the black hole was emitting flashes of X-ray light, pulses, every 18 minutes. When they observed it again in February 2023 the pulses had quickened to one every 10 minutes. By August they were one every 7.5 minutes, and finally by March 2024 there was one every 7.1 minutes^*.

So something was pulsing, but the pulse rate was increasing over time. Even weirder, the rate at which it increased was slowing. In 2022 – 2023 the time between pulses dropped rapidly from 18 to 10 minutes in less than a year, but by 2024 it dropped from 7.5 to only 7.1 in roughly the same amount of time. What could do this?

It’s possible the corona of hot material around the black hole is oscillating somehow; the physics of that isn’t well understood. But the astronomers came up with another idea, and it’s extremely cool.

Sometimes stars fall into toward a supermassive black hole. If the star is old, it might have already “died”, using up all its core fuel and blowing away its outer layers. When that happens all that’s left is a tiny, superdense object called a white dwarf, the leftover core of the star (I cover white dwarfs in an episode of my Crash Course Astronomy videos). It’s possible the white dwarf is orbiting the black hole, causing the X-ray flashes. In 2022 it was orbiting once every 18 minutes, but over time it’s moved in closer to the black hole and is now orbiting once every 7.1 minutes. That would explain the change in the pulse periods!

The reason the change in the pulse rate is slowing is because as it gets closer, the black hole’s immense gravity is enough to start pulling material off the white dwarf. Mind you, the surface gravity of a typical white dwarf can be 100,000 times Earth’s gravity! If I stood on a white dwarf I’d weigh over 8,000 tons, nearly as heavy as the Eiffel Tower. So, yikes.

But as the white dwarf gets closer to the black hole, material on its surface can get stripped off, falling into the black hole. But as it leaves the white dwarf it can add to the white dwarf’s angular momentum, which means it acts a bit like a rocket slowing its descent toward The Point of No Return. It might even be able to stop the dead star’s descent and start it moving away a little bit.

But not much. The white dwarf, if this idea is correct, has already lost most of its mass, and has little left to give. Eventually it’ll lose so much that it can’t stop the black hole’s implacable grasp, and will fall toward it once again. When you’re that close to a supermassive black hole — only about 40 million kilometers, the closest object we’ve ever seen to one — there’s only one way this is going to end. And that’s down.

Again, it’s not certain this is what’s going on; there could be other mechanisms causing these pulses and their slowdown. But this does fit all the facts, and we know such things can happen. In fact, there’s some evidence the corona of the black hole was disrupted by a star getting close to it, so it’s possible the white dwarf was involved in that.

And if this idea is true, well, at some point that black hole will tidally disrupt the white dwarf, tearing it apart. I suspect that would cause a considerable amount of energy to be released (that is, a very large cosmic KA-BLAMMO) that would be easily seen in X-rays. That would be amazing, and would certainly confirm the idea.

The Universe is a weird place, where immense objects casually toss around monumentally fierce forces. In this case, while it’s super cool, I’m glad it’s so far away.

^* Correction (Jan. 21, 2025): I made a confusing mistake originally, getting mixed up describing the rate of the pulses with the time between them. It’s one of those cases of knowing what I meant in my head so I didn’t notice the problem in the text. Arg. Anyway, thanks to the folks who sent me emails who were correctly baffled by my error.

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