A mysterious “dormant” black hole has been discovered in outer space

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Scientists have discovered a stellar-mass black hole with the Very Large Telescope in the Large Magellanic Cloud, a nearby galaxy. This discovery was made after six years of observations with the Very Large Telescope (VLT) of the European Southern Observatory (ESO).

The Large Magellanic Cloud, a neighboring galaxy to the Milky Way, is home to a dormant stellar-mass black hole, according to a group of researchers known for disproving past black hole discoveries.

“For the first time, our team came together to report the discovery of a black hole, rather than rejecting it,” says study leader Tomer Shenar, a Marie Curie fellow at the University of Amsterdam, the Netherlands.

Scientists from the Center for Astrophysics/Harvard and the Smithsonian (CfA) in the United States, including Kareem El-Badry, found that the star that gave birth to the black hole most likely disappeared without any signs of an explosion.

“We identified a needle in a haystack,” Mr. Shenar said. Although other similar candidates have been proposed, this is the first stellar-mass black hole unambiguously detected outside the Milky Way.

Massive stars collapse under their own gravity when they reach the end of their lives and form stellar-mass black holes. When two stars orbit each other, they create a binary system with a black hole orbiting the bright companion star. If a black hole is not emitting high levels of X-rays, which is how they are usually detected, it is considered “dormant”.

A six-year observation campaign led by the European Southern Observatory (ESO) led to this discovery.

“It’s amazing that we know of virtually no dormant black holes, given how often astronomers believe they are present,” admits co-author Pablo Marchant, of the University of Leuven (KU Leuven) in Belgium.

In fact, the newly discovered black hole has a mass about nine times that of the Sun and orbits a hot, blue star with a mass about 25 times that of our Sun. In other words, the star around which the “dormant” black hole orbits is about 200,000 times larger than the black hole itself.

The collaboration found VFTS 243 by searching for nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud. This research aimed to determine if these stars were accompanied by a black hole. Unfortunately, many other possibilities may be present, making it difficult to identify these companions as black holes.

The first image of the supermassive black hole at the center of the Milky Way – Sagittarius A*. Credit: ESA

“As a researcher who has debunked possible black holes in recent years, I was extremely skeptical of this finding,” admits Shenar.

“When Tomer asked me to verify his conclusions, I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t involve a black hole,” says El-Badry.

Furthermore, this discovery sheds unique light on the processes associated with the formation of black holes. Stellar-mass black holes are thought to form when the core of a dying-mass star collapses. However, it is unknown whether a powerful supernova explosion may accompany this collapse.

VFTS 243’s black hole is believed to have formed following the star’s collapse, although there is no sign of an earlier explosion, according to 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 black hole mergers in the cosmos. »

ESO’s VLT, which uses the Fiber Large Array Multi Element Spectrograph (FLAMES) instrument , discovered the black hole VFTS 243 after six years of observing the Tarantula Nebula. FLAMES allows astronomers to study many objects at the same time, saving them valuable time at the telescope.

The team, though dubbed the “black hole police,” actively encourages scrutiny and hopes their work, published in Nature Astronomy (July 18, 2022), will uncover other stellar-mass black holes orbiting around massive stars, the number of which is estimated at several thousand in the Milky Way and in the Magellanic clouds.

“Of course, I hope other experts will seriously consider our analysis and try to come up with alternative models,” says El-Badry. “It’s a very exciting project to get involved in.”

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