How black holes can spaghetti up stars that come too close

This is exactly what astronomers around the world observed over a six-month period when a black hole stretched and tore apart a star that was sucked into its intense gravity grip at a distance of 215 million light years from Earth, as per the Royal Astronomical Society released . It was the most accurate observation of such an event to date, and a particularly revealing one to investigate what happens to the parts of stars that are not consumed immediately and are instead thrown back from black holes.

Matt Nicholl, author of the most recent study, assistant professor at the Harvard and Smithsonian Center for Astrophysics, and research fellow at the Royal Astronomical Society, said these star-wrecking “tidal disruption events” are quite rare, especially in the vicinity, and researchers have made some really nice observations from this one .

“Thanks to the proximity and the good data, we were able to get an amazing insight into the feeding process and see how messy an eater this black hole was,” he explained. “Much of the star debris was actually driven out of the system by the energy released when the black hole was fed.”

The observation may have solved a longstanding question as to why flares from these events are 100 times colder than predicted.

“The expectation is that the energy will be generated in a very compact region around the bra that needs to get very hot,” said Nicholl. “In this case, we found that the runoff allowed it to cool, which explains the lower temperatures observed.”

This animation, created by the European Southern Observatory, shows this type of star festival and how star material is flung outwards.

Of course, a black hole doesn’t “eat” or “suck” the way we traditionally imagine it to be eating food or sucking a drink through a straw, but Nicholl said these terms give a pretty good idea of ​​what’s going on.

“Falling is good because that’s gravity,” he said. “The scientific term would be to say that the destroyed star is the black hole” accreted “- the gravitational pull brings them together and the black hole increases its mass by adding the mass of the star.”

The term spaghettification describes, more viscerally, what is happening to the star at the beginning of the tidal disruption event. It works pretty much the way it sounds.

“An object’s attraction decreases the further away you are,” said Nicholl. “In an extreme gravitational field like that around a black hole, this gradient becomes so pronounced that the side of the object (in this case a star, but it could be anything!) Facing the black hole can experience a much stronger pull than the side that is further away. ”

“I think you would literally start to look like a string of spaghetti.”

This is where things start to get spaghetti-like.

“This difference in forces between the near and far sides stretches the object like a spaghetti string the closer it gets to the black hole,” said Nicholl.

If you, as a person, fell feet first on a black hole, you too would be spaghettified.

“Because your feet are a little closer to the black hole than your head, they experience a much stronger pull and that gets worse the closer and closer you get,” said Nicholl. “You just get out and out and out and I think you’d literally look like a string of spaghetti if you fell on the black hole itself, so I think it’s really quite a fitting terminology.”

The spaghettified star in this case was actually at a similar distance from its black hole as Earth was from the sun, Nicholl said. So if you imagine that the sun in the sky is stretched towards us like spaghetti, it is similar to what I saw in the black hole. ”

The distance at which spaghettification occurs is relative to both the size of the black hole and the size of the object falling on it. That’s because a disruption occurs when the gravity of a black hole overwhelms the cohesive forces that hold an object together.

“The star is held together by gravity, and even though it’s a whole star there is a lot of gravity there, but gravity is still very, very weak, while your body is held together by electromagnetic forces between atoms, which is much, much stronger is than gravity, “said Nicholl,” so I think you wouldn’t be bothered at the same distance as the star. I think you’d have to get a lot closer but I haven’t calculated that distance yet so I don’t know what would be the difference but I think it’s safe to say that the star will be disturbed first if you fall for it. ”

For a black hole like the one at the center of this recently observed tidal disruption event, about 1 million times the size of the Sun’s mass, the star outside the black hole was torn apart and stretched like spaghetti around the black hole, it collided with itself and formed one hot accretion disk. As it swirls around, the disc heats up due to friction that creates the observable light, Nicholl said.

A hot accretion disk is what appears in the very first image of the Messier 87 black hole, captured by the Event Horizon Telescope collaboration in April 2019. That particular accretion disk is a persistent one that is always around this black hole, Nicholl said. while it is being re-formed here.

It looks a little different with larger black holes. Or rather, we can’t look at them at all.

“For a black hole larger than 100 million times the mass of the Sun, stars cross the event horizon where no light can escape (you can think of this as the ‘surface’ of the black hole, but there is no actual barrier ). “Before they are shredded,” said Nicholl.

By observing what happens to objects around a black hole, we can better understand the effects of these supermassive regions and the effects on the cosmos around them.

“Seeing how matter behaves so close to a black hole is a great test of general relativity,” he said. “The energy released and all material drains help us understand how massive black holes shape the galaxies in which they live. One big mystery is how black holes in the centers of galaxies had to get so massive very early in the life of galaxies, studying how they accumulate stars could be key to this question. ”