A team of astrophysicists known for debunking past putative black holes announced a discovery of their own on Monday: the first “dormant” stellar-mass black hole orbiting a star in a nearby galaxy.
Although thought to be widespread throughout the universe, these black holes have proven difficult to find, and they themselves have rejected several possible candidates in recent years.
Now the international team has found a “needle in a haystack,” said Tomer Shenar, an astrophysicist at the University of Amsterdam and lead author of a new study in the journal Nature Astronomy.
The team scanned the sky for what could eventually become a binary black hole, in which two black holes orbit each other after swallowing their stars in a supernova explosion.
“We found a fairly massive star that weighs 25 times our Sun and orbits something we don’t see,” Shenar told AFP.
They believe the blue star, located in the Large Magellanic Cloud galaxy neighboring our Milky Way, is caught in a dance of death with a black hole nine times the mass of our Sun.
These types of black holes are usually detected by the X-rays they emit as they collect material from their companion star.
But this binary system, known as VFTS 243, is said to be dormant because it’s not emitting X-rays — it’s not close enough to suck matter from its star.
– ‘Black Hole Destroyer’ –
Hugues Sana, an astrophysicist at KU Leuven University in Belgium, said there are estimated to be around 100 million stellar-mass black holes in the Milky Way alone, much smaller than their supermassive big brothers.
However, only 10 were found, said Sana, a co-author of the study.
This could be because many are dormant, biding their time to eventually swallow their companion star.
Sana said watching her is like watching two people dance in a dark room, one in white and the other in black. You may only see one dancer, but you know the other is there.
“We’ve never really discovered such systems,” Shenar told AFP. “There have been a few claims in recent years, but they’ve all been more or less disproved,” Shenar told AFP.
In fact, members of his team were among those who dismissed previous discoveries by offering alternatives for what the data might indicate.
Because of that, Shenar said they expected an additional scrutiny.
So they set about meticulously ruling out all other possibilities, Shenar said, until they were satisfied that “it’s either a fat, invisible alien — or a black hole.”
Then they called the most famous black hole debunker they knew.
Kareem El-Badry of the Harvard-Smithsonian Center for Astrophysics has been “debunking black holes one after the other” for the past several years, Tomer said, calling him the “black hole destroyer.”
“I sent him the data and told him, listen, we found this object – prove me wrong,” Tomer said.
“I had my doubts,” said El-Badry, who joined the team and ran his own simulations.
“But I couldn’t find a plausible explanation for the data that didn’t include a black hole.”
– Not with a bang, but a whimper –
The discovery could also provide insight into the formation of black holes.
Stellar-mass black holes are believed to be born during the death of a large star in a massive supernova explosion.
The force of the explosion throws black holes in a binary system into an elliptical instead of a circular orbit.
However, VFTS 243 has an orbit that is also perfectly circular.
“That means the star immediately disappeared into the black hole,” Shenar said.
“This has many implications for how these black hole pairs form,” he said, adding that VFTS 243’s star could eventually collapse in a similar fashion.
Andrew Norton, an astrophysicist at the UK Open University who was not involved in the study, said: “This is important evidence that all these stars may not end their lives in supernovae explosions.”
Shenar said he welcomes other scientists trying to debunk the debunkers.
“If someone comes along and debunks this as well, I’m sure they’ll have a pretty fantastic explanation – like the fat alien.”
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