Key takeaways

  • Researchers discovered a dormant stellar-mass black hole in the Large Magellanic Cloud, a galaxy near the Milky Way.
  • This is the first definitively found dormant stellar-mass black hole outside the Milky Way.
  • The discovery was made after six years of observations using ESO’s Very Large Telescope.
  • The star that formed the black hole collapsed without a massive explosion, supporting the ‘direct-collapse’ theory.
  • This finding could help uncover more black holes and deepen our understanding of black hole formation and mergers in the universe.

A team of worldwide researchers recognized for refuting black hole findings discovered a dormant stellar-mass black hole in the Milky Way’s neighboring galaxy, the Large Magellanic Cloud. The team comprises Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian, also known as the “black hole destroyer” by his colleagues.

“For the first time, our team got together to report on a black hole discovery, instead of rejecting one,” says research author Tomer Shenar, a Marie-Curie Fellow at Amsterdam University in the Netherlands.

The scientists discovered that the star that gave origin to the black hole disappeared without leaving any evidence of a tremendous explosion.

“We identified a needle in a haystack,” Shenar explains. Despite several comparable black hole possibilities being presented, the team says that this is the first “dormant” stellar-mass black hole to be definitively found outside of the Milky Way galaxy. The results were published today in the journal Nature Astronomy.

Stellar-mass black holes arise when large stars die and collapse due to their own gravity. This process results in a black hole in orbit with a brilliant companion star in a binary system, which is a system of two stars that revolve around one another. A black hole is considered “dormant” if it does not generate large quantities of X-ray radiation, which is generally used to discover such black holes.

The finding was found after six years of observations with ESO’s Very Large Telescope (VLT).

“It is incredible that we hardly know of any dormant black holes, given how common astronomers believe them to be,” says co-author Pablo Marchant of the KU Leuven. The newly discovered black hole has at least nine times the mass of the Sun and orbiting a bright, blue star that weighs 25 times the Sun’s mass.

Dormant black holes are especially difficult to detect since they do not interact much with their environment.

“We’ve been looking for such black-hole binary systems for over two years,” explains 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.”

To identify VFTS 243, the team looked for roughly 1,000 big stars in the Large Magellanic Cloud’s Tarantula Nebula area that may be accompanied by black holes. Identifying these partners as black holes is incredibly challenging since so many other options 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 CfA co-author El-Badry, whom Shenar calls the “black hole destroyer.” A recent Harvard Magazine story similarly calls El-Badry a “black hole debunker.”

“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 gives the researchers a unique perspective on the mechanisms involved in the development of black holes. Astronomers assume that a stellar-mass black hole originates when the core of a dying giant star collapses, but it is unclear if this is followed by a spectacular supernova explosion.

“The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion,” Shenar tells me. “Evidence for this ‘direct-collapse’ scenario has lately emerged, but our analysis may give one of the most direct indicators. This has huge ramifications for the formation of black hole mergers in the universe.”

The black hole in VFTS 243 was found using six years of observations of the Tarantula Nebula by the Fiber Large Array Multi Element Spectrograph (FLAMES) instrument on ESO’s VLT. FLAMES allows astronomers to observe more than a hundred objects at once, a significant saving of telescope time compared to studying each object one by one.

Despite the appellation “black hole police,” the team actively invites examination and hopes that their study may lead to the finding of more stellar-mass black holes surrounding big stars, hundreds of which are expected to exist in the Milky Way and Magellanic Clouds.

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

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