A team of international experts known for debunking several black hole discoveries has discovered a stellar-mass black hole in the Large Magellanic Cloud, our neighbor galaxy. “For the first time, our team came together to report on a black hole discovery rather than reject one,” study leader Tomer Shenar says. Furthermore, they discovered that the star that gave rise to the black hole vanished with no trace of a powerful explosion. Six years of observations with the European Southern Observatory’s (ESO) Very Large Telescope resulted in the discovery (VLT).
“We found a ‘needle in a haystack,'” says Shenar, who began the research at KU Leuven in Belgium and is now a Marie-Curie Fellow at Amsterdam University in the Netherlands. Despite the fact that other similar black hole candidates have been proposed, the team claims that this is the first ‘dormant’ stellar-mass black hole to be unequivocally detected outside our galaxy.
When massive stars reach the end of their lives and collapse under their own gravity, stellar-mass black holes form. This process leaves a black hole in orbit with a luminous companion star in a binary, a system of two stars revolving around each other. If a black hole does not emit high levels of X-ray radiation, which is how such black holes are typically detected, it is said to be ‘dormant.’ “It’s incredible that we don’t know of any dormant black holes, given how common astronomers believe them to be,” says KU Leuven co-author Pablo Marchant. The newly discovered black hole has at least nine times the mass of our Sun and orbits a hot, blue star with a mass 25 times that of our Sun.
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.
Tomer Shenar
Dormant black holes are particularly hard to spot since they do not interact much with their surroundings. “For more than two years now, we have been looking for such black-hole-binary systems,” says co-author Julia Bodensteiner, a research fellow at ESO in Germany. “I was very excited when I heard about VFTS 243, which in my opinion is the most convincing candidate reported to date.”
Despite their well-documented existence, black holes remain enigmatic. And they’re not exactly easy to come by. Some reported discoveries are not black holes at all. One international group of astronomers is well-known for debunking “discoveries” of black holes. Other astronomers have begun to refer to them as the “black hole police.” This group, however, has now announced its own first verified discovery. They discovered a stellar-mass black hole in the Tarantula Nebula, a small companion galaxy to our Milky Way.
To find VFTS 243, the collaboration searched nearly 1000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, looking for the ones that could have black holes as companions. Identifying these companions as black holes is extremely difficult, as so many alternative possibilities exist.
“As a researcher who has [debunked] – potential black holes in recent years, I was extremely skeptical regarding this discovery,” says Shenar. The skepticism was shared by co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian in the USA, whom Shenar calls the “black hole destroyer.” “When Tomer asked me to double check his findings, I had my doubts. But I could not find a plausible explanation for the data that did not involve a black hole,” explains El-Badry.
The discovery also provides the team with a unique perspective on the processes that lead to the formation of black holes. Astronomers believe a stellar-mass black hole forms when the core of a dying massive star collapses, but whether or not this is accompanied by a powerful supernova explosion is unknown.
“The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion,” explains Shenar. “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.”
The black hole in VFTS 243 was discovered after six years of observations of the Tarantula Nebula by ESO’s[VLTFibre ]’s Large Array Multi Element Spectrograph ([FLAMES]).
Despite the moniker “black hole cops,” the team actively encourages scrutiny and hopes that their findings, which were published today in Nature Astronomy, will lead to the discovery of other stellar-mass black holes orbiting massive stars, thousands of which are predicted to exist in the Milky Way and the Magellanic Clouds.
“Of course, I expect others in the field to carefully examine our analysis and try to concoct alternative models,” El-Badry concludes. “It’s a very exciting project to be a part of.”
