A black hole 10 billion light-years away suddenly 'switched on', becoming one of the brightest transient objects ever detected.
Scientists scouring the cosmos for signs of a rare explosion may have stumbled upon something even more remarkable: a gargantuan black hole "switching on" in the early universe, going from dim to tremendously bright in the cosmic blink of an eye.
The black
hole, dubbed J221951, is estimated to sit about 10 billion light-years from
Earth, meaning the cosmic monster turned up its lights when the universe was roughly
one-quarter of its current age. Despite this vast distance, the black hole brightened
so intensely that astronomers initially mistook it for a stellar explosion less
than 1 billion light-years away.
An illustration of a black hole "spaghettifying" a hapless star (Image credit: ESO/M. Kornmesser
The fact that the black hole appeared so bright from so far away makes it one of the single brightest transients — objects that brighten suddenly and then fade — ever detected, according to the authors of a study accepted for publication in the journal Monthly Notices of the Royal Astronomical Society and available as a preprint on arXiv.
"Our understanding of the different things that supermassive
black holes can do has greatly expanded in recent years," study co-author
Matt Nicholl, an astronomer at Queen's University Belfast, said in a statement. "J221951 is one of the most extreme examples yet of a black
hole taking us by surprise."
The first surprise came when the researchers tracked down the path
of a gravitational wave, a fast-moving ripple in space-time generated by the most massive cosmic
collisions. The team hypothesized that the wave was released during the
collision of two dense, dead stars known as neutron stars, which have been
known to go out in bright blasts called kilonova
explosions.
The ripple in space-time did indeed lead to a bright object. But
unlike a kilonova, which first appears blue before dimming to red over several days, this
spot in the sky remained bright and blue for months — far longer than a stellar
explosion should.
Follow-up observations with multiple telescopes, including NASA's
Hubble Space Telescope and Neil Gehrels Swift Observatory, revealed that the
mysterious object lines up with the center of a dim and distant galaxy,
suggesting that it could be a supermassive black hole, much like the one at the
center of the Milky Way. After 10 months of brightening, the object finally
began to fade again, proving that it wasn't a
galaxy itself but a transient object undergoing an intense, high-energy
outburst.
If J221951 is
indeed a supermassive black hole, its sudden burst of brightness has two possible
explanations, according to the researchers. First, the black hole could have pulled an
orbiting star into its clutches, stretching and tearing the star to shreds in a messy process called a tidal
disruption event or "spaghettification." The second, more mysterious
possibility is that the black hole could have shifted states from dormant to
actively feeding, as it suddenly began gorging on the fast-moving disk of gas
that surrounds it.
Figuring out precisely why the black hole "switched on"
will require further studies of the object's energy output. If the black hole
were to suddenly brighten again, it would mean it is probably
in feeding mode, the team concluded. But if it fades for good, it's more
likely that some unfortunate star was gobbled up in the most spectacular way
imaginable. May we all burn out so gloriously.
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