Science First Look

Slow food? Black hole taking entire decade to gobble star.

A study published Monday in the journal Nature Astronomy describes a black hole that's taken a whole decade to devour a star, some 1.8 billion light-years from Earth. 

This artist rendering provided by NASA shows a star being swallowed by a black hole, and emitting an X-ray flare, shown in red, in the process.
NASA/Chandra X-ray Observatory/M.Weiss/AP
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Astronomers have discovered evidence that a distant black hole took a massive bite out of a nearby star more than a decade ago and has continued to devour it ever since.

The 11-year feeding frenzy is far and away the longest scientists have observed, said University of New Hampshire research scientist Dacheng Lin.

“We have witnessed a star’s spectacular and prolonged demise,” said Dr. Lin in a statement. “Dozens of these so-called tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”

The discovery by Lin and his colleagues, reported in a paper published Monday in the journal Nature Astronomy, adds to our understanding of supermassive black holes and their origins in the early days of the universe.  

The star’s death in a small galaxy 1.8 billion light years away was observed starting in 2005 by three orbiting X-ray telescopes — NASA’s Chandra X-Ray Observatory and Swift satellite and the European Space Agency’s XMM-Newton.

The three telescopes found evidence of a tidal disruption event, in which tidal forces from the intense gravitational pull of a black hole can destroy an object that wanders too close to it, in this case a star. During this feeding frenzy, the black hole flings stellar debris outward at high speeds. The rest of the star falls into the black hole, which cooks it to millions of degrees. The temperature spike then generates a distinct X-ray flare observable by satellites.

Scientists have found evidence of these X-ray flares before. But these events have been short-lived, typically lasting only a year, according to a statement. This flare has remained bright for nearly a decade, meaning it’s either the most massive star to ever be torn apart during one of these tidal events, or it is the first where a smaller star was completely torn apart.

The researchers also found evidence that the material surrounding the black hole has consistently surpassed the so-called Eddington limit, the balance between the outward pressure of radiation from hot gas and the inward pull of the gravity of the black hole.

“For most of the time we’ve been looking at this object, it has been growing rapidly,” said co-author of the study James Guillochon of the Harvard-Smithsonian Center for Astrophysics. “This tells us something unusual – like a star twice as heavy as our Sun – is being fed into the black hole.”

While the researchers expect the event to die down over the next decade, the discovery is not only a newly observed phenomenon, but it might also help explain how supermassive black holes can reach masses about a billion times higher than the Sun when the universe was only about a billion years old.

This is the second discovery on this subject this year, as a study published in January detailed how NASA’s Chandra X-Ray Observatory also found a minefield of black holes 12 billion to 13 billion light years away.

“It turned up a patch featuring the highest concentration of supermassive black holes ever observed, according to the observatory – equivalent to about 5,000 being stuffed into an area as big as that of the moon. And they grew not by slow accumulation, say researchers, but in bursts,” wrote David Iaconangelo for The Christian Science Monitor. “The work might nudge scientists closer toward understanding how supermassive black holes got so big, so fast in the early days of the universe – the images contain hints that the "seeds" of those black holes are much heavier than previously thought – and highlights the importance of X-ray imaging in efforts to understand black holes.”

Another NASA mission scheduled for 2020 includes plans to launch a spacecraft equipped with X-ray detectors from the Italian Space Agency that can measure polarization levels of radiation in the extreme environments bordering black holes.

This report includes material from the Associated Press.

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