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 a 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.
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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.