A Black Hole’s Lunch: Stellar Spaghetti

Astronomers call it “spaghettification,” and it’s not a pretty idea: It’s what happens when you venture too close to a black hole and fall in. Tidal forces stretch you and break you like a noodle, then your shreds circle the black hole until they collide and knock each other in.

On the upside, the energy released by your long fall and the crashing together of what used to be your atoms might produce a flash — a cosmic funeral pyre, if you will — that can be seen across the universe.

In a case reported last week, it was merely an anonymous star in a faraway galaxy that met its doom. Thanks to luck and ever-increasing vigilance of the heavens, the whole world was watching as the star went down.

“Indeed, it was quite a feast,” said Matt Nicholl, an astrophysicist at the University of Birmingham in England in an email. He led a team of astronomers that described this stellar apocalypse in the Monthly Notices of the Royal Astronomical Society on Monday.

“This black hole was a messy eater,” added Kate Alexander of Northwestern University and a member of Dr. Nicholl’s team, in an email. In the end, she said, only about half the star was consumed by the black hole. The rest of its disintegrated material was blown outward into space at a breakneck speed a few percent that of light.

The excitement began on Sept. 19, 2019, when the Zwicky Transient Facility, a telescope on Palomar Mountain in California, and other celestial surveillance networks detected a flare in the center of a galaxy 215 million light-years from Earth in the constellation Eridanus.

The flare had the hallmarks of a tidal disruption event, the technical name for when a black hole rips a star to shreds and eats it.

Astronomers rushed to their ground- and space-based telescopes to monitor AT2019qiz, as the flare was named. (“AT” stands for “astronomical transient.”)

Over the next few weeks the flare rapidly brightened. At its peak, it was blasting out about a billion times as much energy as our sun. In the subsequent five months the flare slowly faded.

The result was a unique and multidimensional look — based on radio emissions, X-rays and gamma rays as well as old-fashioned visible light observations — at the complexities of death by black hole.

ImageThe host galaxy, AT2019qiz, before the tidal disruption event.
Credit…M. Nicholl et al., Monthly Notices of the Royal Astronomical Society, 2020

Black holes are gravitational potholes in space-time predicted by general relativity, Albert Einstein’s theory of gravity. They are so deep and dense that nothing, not even light, can escape them. Our Milky Way galaxy, and presumably most galaxies, are littered with black holes produced when massive stars died and collapsed in on themselves. In addition, every galaxy seems to have at its core a supersize version of one of these monsters millions or billions of times as massive as the sun.

“We know that most galaxies have supermassive black hole at their centers,” Dr. Alexander wrote in an email. “But we still don’t understand exactly how these black holes grew to be as big as they are, or how they shape their host galaxies.” Studying stellar disruptions, she said, could help in understanding how these black holes eat, grow and interact with their environment.

The black hole in the Eridanus galaxy weighs in at about one million solar masses. As reconstructed by Dr. Nicholl and his team, a star about the size and mass of our own sun wandered into the center of the galaxy and came too close — about 100 million miles — to the black hole.

That’s roughly the distance from Earth to the sun. At that point, the gravitational pull from the black hole exceeded the gravitational pull from the star’s core, and the star was “spaghettified” into a long stream around the hole. Eventually the stream wrapped all the way around the black hole and collided with itself, “which is when the black hole began sucking it in,” Dr. Nicholl said.

He added, “If you were to picture the sun being stretched into a thin stream and rushing toward us, that’s what the black hole saw.”

Astronomers have documented other such black hole disruptions recently, but such events rarely occur so close to our own galaxy, and their internal dynamics are often obscured by dust and gas kicked up by the fatal collision. In this case, astronomers were able to see behind that curtain and observe that it was made of bits from the shredded star.

“Because we caught it early, we could actually see the curtain of dust and debris being drawn up as the black hole launched a powerful outflow of material,” Dr. Alexander said.

Most of the light that they saw was coming from this material, which was being blown into space at speeds of some 6,000 miles per second. Spectral studies indicated that the material flowing outward from the black hole was identical to what was falling in — evidence that it was crumbs from the clumsily eaten star.

The flare AT1910qiz could serve as a “Rosetta stone” for understanding other star-shredding events, Dr. Alexander said. AT2019qiz was special, she added, because the astronomers began observing it very early, right after the star was torn apart, and collected so much data from many different kinds of telescopes.

New telescopes like the Vera Rubin Observatory and the European Extremely Large Telescope, both under construction in Chile, should draw in even more of these cosmic-food Instagrams.

Bon appetit.

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