An international team of experts, known for making several black hole discoveries, has found a stellar-mass black hole in the Large Magellanic Cloud, a galaxy neighboring our own. “For the first time, our team came together to report a black hole discovery instead of rejecting one,” says study leader Tomer Shenar. In addition, they found that the star that gave birth to the black hole disappeared without any sign of a powerful explosion. The discovery was made thanks to six years of observations obtained with the European Southern Observatory’s (ESO) Very Large Telescope (VLT).We have identified a ‘needle in a haystack,'” says Shenar, who started the study at KU Leuven in Belgium and is now a Marie-Curie Fellow at the University of Amsterdam in the Netherlands. Although other similar black hole candidates [were] – proposed , the team claims is the first “dormant” stellar-mass black hole that has been unequivocally detected outside our galaxy.
Stellar-mass black holes form when massive stars reach the end of their lives and collapse under their own gravity. In a binary star, a system of two stars orbiting each other, this process leaves a black hole with a luminous companion star in orbit. A black hole is “dormant” if it is not emitting high levels of X-rays, which is how such black holes are usually detected. “It’s incredible that we hardly know any dormant black holes, given what ordinary astronomers believe they are,” explains co-author Pablo Marchant from KU Leuven. The newly found 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 the Sun.
Dormant black holes are particularly hard to detect because they don’t interact much with their surroundings. “We have been looking for such binary systems with black holes for more than two years,” says co-author Julia Bodensteiner, a researcher at ESO in Germany. “I was very excited to hear about VFTS 243, which I believe is the most compelling candidate yet reported.” In the search for VFTS 243, the collaboration searched nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud for those that might have black hole companions. Identifying these companions as black holes is extremely difficult because there are so many alternative possibilities.
“As a researcher who has discovered potential black holes in recent years, I was extremely skeptical about this discovery,” says Shenar. Co-author Kareem El-Badry of the Center for Astrophysics shared this skepticism Harvard & Smithsonian in the US, which Shenar calls a “black hole destroyer”. “When Tomer asked me to double-check his findings, I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t involve a black hole,” explains El-Badry.
The discovery also gives the team a unique insight into the processes that accompany the formation of black holes. Astronomers believe that a stellar-mass black hole is formed when the core of a dying massive star collapses, but it remains uncertain whether this is accompanied by a powerful supernova explosion.”The star that created the black hole in VFTS 243 appears to have completely collapsed, with no signs of a previous explosion,” explains Shenar. “Evidence for this ‘direct collapse’ scenario has emerged recently, but our study probably provides one of the most direct indications. This has huge implications for the origin of merging black holes in the universe.”
The black hole in VFTS 243 was found using six years of observations of the Tarantula Nebula by ESO’s Fiber Large Array Multi Element Spectrograph [VLT]. Despite being nicknamed the “black hole shelf,” the team is actively promoting research and hopes that their work, published today in Nature Astronomy, will lead to the discovery of other stellar black holes orbiting massive stars, of which thousands are thought to exist in the Milky Way and in the Magellanic Clouds.
Source Journal Reference: Tomer Shenar, et al. An X-ray-quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud. Nature Astronomy, 2022; DOI: 10.1038/s41550-022-01730-y
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