Black holes do something strange after eating them
It would be very unpleasant if you fell into a black hole. The forces of gravity will be so intense that – assuming you fall feet first – the drag on your feet will be much stronger than the drag on your head, just because it’s a bit closer to the center of gravity. It won’t be “a little bit” closer for very long. At some point, a few hundred or thousands of miles away depending on the size of the black hole, the gravitational gradient will be so steep that tidal forces will pull the parts closest inward, warping your body into a ridiculously long and thin spaghetti. This process is appropriately called spaghetti. It’s the same process by which the Moon creates tides on Earth, to the extreme.
No one’s been recruited yet, though if we get enough subscription renewals we’ll consider building a ship to send Chris Thompson straight to Sagittarius A*. But spaghetti isn’t just for unlucky astronauts and death-wishing bloggers. It’s also how black holes “eat” stars, in a way that isn’t wise enough to wander close enough to them. Tidal forces tear the hapless star apart, and the black hole’s rotation wraps the strands of the former star around it like spaghetti around a fork. (If you enjoy the spaghetti analogy, there’s still another to come.) This is pretty violent action, and about half of the star’s matter is ejected outward, visible to us as radio emissions. But the other half, called the accretion disk, was thought to be relatively stable, gradually spiraling inward, allowing the black hole to feed leisurely long after its initial capture. This was supposed to be the end of the show.
Until very recently, all of this was determined by mathematical models; It wasn’t until 2018 that a black hole was imaged while turning a star into spaghetti. In the following years, scientists paid more attention to these tidal disturbance events, or TDEs. In a new paper submitted to Astrophysical Journal And the researchers say they’ve discovered something completely unexpected and hitherto inexplicable: Black holes have been “burping up” their food for years after eating.
“Black holes are chaotic eaters,” Yvette Sindis, the study’s lead author and researcher at the Harvard-Smithsonian Center for Astrophysics, said in a Reddit post describing the paper. Scientists have spent years looking at recently feeding black holes, and have found that many of them mysteriously begin emitting radio emissions months and years later, often rising to second and even third highs long after the initial TDE has subsided.
“There was a second peak, where the two black holes re-brightened, and that’s completely new and unexpected,” Sendis told Live Science. “People thought you’d have one outflow, and then it kind of went away. So this observation means these black holes can ‘turn on’ and then ‘turn on’ again.”
And that doesn’t seem to be a rarity either: Ten of the 24 TDEs the group has subsequently spotted have collected stellar objects. Black holes seem to eat a bit like a toddler with a bowl of spaghetti in sauce (here it is): many of them will end up somewhere else.
Why haven’t we noticed this before? Well, oftentimes we don’t find what we don’t expect to see, and in this case we weren’t even looking. As Sindis noted, “radio telescope time is precious,” and it was not a good idea to use the time or money to point the telescopes in the aftermath of Stars Day, when the fireworks were supposed to be over. But this team continued to monitor black holes, and found them spewing out six years later. It is not known how common this process is or how long it takes; Only more notes will tell. But it’s surprising if this happens at all, because there is no currently known mechanism that helps matter escape from a black hole’s accretion disk.
To be clear, we are not talking about things that have fallen inside The emergence of a black hole. Once you pass the event horizon, you will not leave it, even if you are literally light. We’re also not talking about coaxial planes; The paper’s authors were able to note this as well, and they are completely separate forms and sources of radio emissions. What we’re talking about is something theoretically sound but mechanically inconspicuous, a way to allow matter to escape what we thought was a relentless downward spiral. The study, reasonably, doesn’t even pretend to try to answer. But Cendes got even more pensive in her Reddit post. I note that the only computational models that explain these observations are those in which, contrary to current and accepted theory, the accretion disk does not form long after TDE. In this scenario, all those chewed up stellar bits might be banging around chaotically for a while, occasionally sending chunks blasting off into space, before settling into a stable disk.
That’s all guesswork for now. We can’t know more until more observations are made, or until we hurl Chris into a black hole and recover some of his atoms.