Jul 23, 2022 I Paul Seaburn

The 'Black Hole Police' Find a Mysterious Black Hole Not Formed From a Dying Star

Black holes don’t need any help being mysterious. After all, we can’t see them – we can only see what they do to things around them. They come in various sizes -- some galaxies have supermassive ones at their center but other don’t. At the other end of the size spectrum there may be micro black holes and the Large Hadron Collider could conceivably create them. If a black hole is “stellar mass” – of a size up to around 50 times that of our Sun – it has long been accepted that it was formed when a star died in a supernova explosion and collapsed upon itself. That assumption changed recently with the discovery in a neighboring galaxy of a mysterious black hole that is dormant – not emitting any X-ray energy due to digesting everything around it – and doesn’t appear to have been born in a stellar supernova. If that isn’t mysterious enough, it was discovered by a group known as the “Black Hole Police” and they describe its rarity as “a needle in a haystack” because it had no telltale “black-hole kick.”

Black-hole kick? Black hole police? When did astronomy terminology collide with law enforcement and martial arts jargon? Let’s start with the “black hole police” – a term proudly proclaimed in the headline of a press release and study from the European Southern Observatory (ESO). “'Black hole police' discover a dormant black hole outside our galaxy” announced the publication of the study “An X-ray-quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud” in the journal Nature Astronomy. The paper was co-authored by Tomer Shenar, a Marie-Curie Fellow at Amsterdam University and a team of team of international experts known for debunking the black hole discoveries of other astronomers – hence the moniker “Black hole police.”

Call the Black Hole Police! 

"For the first time, our team got together to report on a black hole discovery, instead of rejecting one."

Perhaps out of guilt, Shenar reveals that when the “black hole police” aren’t debunking them, they are themselves looking for black holes. In this case, the team has spent six years using the ESO’s Very Large Telescope (VLT) to scan nearly 1000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud – a satellite galaxy positioned right next to the Milky Way. Since many black holes in the Milky Way are paired with stars, this seemed like a way to determine if such a binary pairing existed in other galaxies. Besides helping to find the black hole, the orbiting star or stars can aid in calculating the black hole's mass and location. All of this depends on the black hole being active – ejecting X-rays as it consumes space objects, including pieces of its companion star or stars. Two years ago, they believed they found one – but this black hole was like none they had ever observed.

“No other X-ray-quiet black hole is unambiguously known outside our Galaxy. The (near-) circular orbit and kinematics of VFTS 243 imply that the collapse of the progenitor into a black hole was associated with little or no ejected material or black-hole kick.”

Named VFTS 243, the black hole was discovered using gravitational lensing which revealed it orbiting a hot, blue star with 25 times the Sun’s mass. The black hole itself is nine times the mass of the Sun. (An illustration of the pair can be seen here.) it was fortunate that the lensing effect showed VFTS 243 because it was emitting no X-rays – a sign that this was an extremely rare discovery of a dormant black hole. Shenar explains why the team referred to this as finding “a needle in a haystack.”

"The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion. Evidence for this ‘direct-collapse’ scenario has been emerging recently, but our study arguably provides one of the most direct indications. This has enormous implications for the origin of black-hole mergers in the cosmos."

Being an upstanding member of the “black hole police,” Shenar knew what he had to do – have VFTS 243 verified by another black hole police officer. For this, he chose co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian – better known as the “black hole destroyer”. El-Badry says he did his best to debunk it, but “I could not find a plausible explanation for the data that did not involve a black hole.”

VFTS 243 and its massive blue-white O-type companion star are around 160,000 light-years away. While the star has 25 times the mass of the Sun, VFTS 243 only has 9 times its mass, putting its event horizon at a minuscule 27 kilometers (17 miles) across. The pair is in the Tarantula Nebula or 30 Doradus, a large region of ionized interstellar atomic hydrogen in the southeast corner of the Large Magellanic Cloud. The name comes from its spider shape (let’s hope the James Webb Space Telescope can give us a better view) and this is the place astronomers look for views of young stars, since the Tarantula Nebula is considered to be a nursery for extremely massive young stars.

Tarantula Nebula (credit: NASA)

Astronomers believe that dormant black holes are very common, but that is extremely difficult to prove because of their lack of X-ray emissions. The fact that VFTS 243 is in the Tarantula Nebula makes it even more rare because it means the dormant black hole was created by the non-explosive death of a young star in this stellar nursery. Why would this happen to a stellar mass star? The black hole police have no idea, but their seemingly unbelievable discovery of this dormant back hole ‘needle’ means their debunking may take a back seat to an energized search for more of them, both in the Large Magellanic Cloud and the Milky Way. Kareem El-Badry – the “black hole destroyer” – knows what this means:

“Of course I expect others in the field to pore over our analysis carefully, and to try to cook up alternative models. It's a very exciting project to be involved in.”

Which makes a better band name – Black Hole Police or Black Hole Destroyer?

Paul Seaburn

Paul Seaburn is the editor at Mysterious Universe and its most prolific writer. He’s written for TV shows such as "The Tonight Show", "Politically Incorrect" and an award-winning children’s program. He's been published in “The New York Times" and "Huffington Post” and has co-authored numerous collections of trivia, puzzles and humor. His “What in the World!” podcast is a fun look at the latest weird and paranormal news, strange sports stories and odd trivia. Paul likes to add a bit of humor to each MU post he crafts. After all, the mysterious doesn't always have to be serious.

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