A black hole emits strange belches that baffle scientists

Astronomers have published an important finding: a black hole is “belching” energy from a small star observed to be shredding in 2018, after two years without ejecting such material.

How unusual is that?

“Super unusual,” Yvette Cendes, an astronomer at the Center for Astrophysics, Harvard and Smithsonian and the paper’s lead author, tells NPR. “We’ve never seen it on this scale before.”

Researchers made the discovery when they used a powerful radio telescope facility – the Very Large Array in New Mexico – to study about two dozen black holes in which stars were shredded after getting too close. That is, the material in the star has been pulled apart, or “spaghettified.” Such events are called tidal disturbance events or TDEs.

What they found was that one of the TDEs (the one named AT2018hyz, in case you’re curious) was emitting energy at an unusual rate and at a very surprising time: more than two years after the event.

This behavior differs from what has previously been observed for black holes in two ways. First, timing: it’s more common to see radio emissions from black holes in the first few months after a star has been swallowed up. And second, the energy emitted in this case doesn’t quite match what astronomers have seen so far.

In most cases where black holes swallow stars, perhaps 99%, the outflow is lower in energy. And 1% of the time, that outflow is much larger — “an extremely ejected event,” says Cendes, a very rare event.

But in this case? It’s in between – about half the speed of light.

This is “the first instance where we’ve seen this type of velocity associated with this event or this type of outflow,” explains Cendes. “But also that it happened — the best guess we have is about two years after the star was eaten by this black hole, when this outflow started — and that’s really exciting.” This has never been seen before.”

And scientists aren’t sure why that’s happening.

Cendes says that while the research team was good at ruling out what is not they cause, they still have no answer to what is.

You might be wondering: hey, I thought nothing can escape from a black hole?

“There’s a point at which you get too close to a black hole, where you can’t escape the black hole – that’s called the event horizon. But this material has never crossed that limit, to our best estimate,” explains Cendes.

In other words, the star got close enough to the black hole to be shredded — but not to fall to this point of no return.

The team’s discovery opens up fascinating new avenues for research.

“It’s really exciting for theorists because suddenly it really opens up a new dimension in our understanding of physics and the possibilities. … You absolutely have to get to work and tell me what’s going on because I’m also very curious,” laughs Cendes.

And, she says, there are other star-eating black holes to study in more detail. Such occurrences may occur are more common than astronomers previously thought.

For Cendes, the discovery is what she and her fellow astronomers hope to find — something big.

“I’ve wanted to be an astronomer since I was 13,” she says. “Making this discovery has truly been the excitement of my life. … It was definitely a lot of work and I definitely had a lot of good collaborators to help me get this out, but it was very, very rewarding and it’s what I wanted. So that was pretty awesome. ”

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