A team of astronomers known for exposing false black hole discoveries have found a dormant stellar-mass black hole in the Large Magellanic Cloud, the satellite galaxy of the Milky Way. The Large Magellanic Cloud floats in space 200,000 light years away from Earth.
The team includes Kareem El-Badry of the Center for Astrophysics, Harvard & Smithsonian, also known as the "black hole destroyer".
The team of astronomers is nicknamed "black hole police".
The star that gave rise to the black hole vanished without any sign of a powerful explosion, the astronomers found. The study describing the findings was recently published in the journal Nature Astronomy.
In a statement released by the Harvard Smithsonian Center for Astrophysics, Tomer Shenar, the lead author on the paper, said for the first time, the team got together to report on a black hole discovery, instead of rejecting one.
First ‘Dormant Stellar-Mass Black Hole To Be Detected Outside Milky Way
Shenar said the astronomers "identified a needle in a haystack". Similar black hole candidates have been proposed in the past. However, the astronomers claim this is the first "dormant" stellar-mass black hole to be unambiguously detected outside the Milky Way galaxy.
What Are Stellar-Mass Black Holes?
A stellar-mass black hole is a black hole formed by the gravitational collapse of a star, and weighs between a few and 100 times the mass of the Sun.
These black holes form when massive stars reach the end of their lives and collapse under their own gravity. A binary is a system in which two stars revolve around each other. As a result of this process, a black hole is left behind in orbit with a luminous companion star. If the black hole does not emit high levels of X-ray radiation, it is said to be "dormant". This is how black holes are typically detected.
How Was The Black Hole Discovered?
The astronomers made the discovery using six years of observations obtained with the European Southern Observatory's (ESO's) Very Large Telescope (VLT).
Pablo Marchant, a co-author on the paper, said it is "incredible" the researchers hardly know of any dormant black holes, given how common astronomers believe them to be. The black hole discovered in the Large Magellanic Cloud is at least nine times the mass of the Sun, and orbits a hot, blue star weighing 25 times the mass of the Sun, the study said.
Since dormant black holes do not interact much with their surroundings, they are hard to spot.
Julia Bodensteiner, another co-author on the paper, said that for more than two years now, the team has been looking for such black-hole-binary systems. She said she was very excited when she heard about VFTS 243, the binary system in the Large Magellanic Cloud which the black hole is a part of. Julia called the black hole the "most convincing candidate reported to date".
The astronomers observed nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, to find VFTS 243. The Tarantula Nebula is the most spectacular feature of the Large Magellanic Cloud, and glows brightly about 1,60,000 light years away. The team looked for stars that could have black holes as companions. Since many alternative possibilities exist, it is extremely difficult to identify the companions as black holes.
Shenar said that as a researcher who has "debunked potential black holes" in recent years, he was extremely sceptical regarding this discovery.
El-Badry, a co-author on the paper, was also sceptical about the discovery. He is also known as a "black hole debunker".
El-Badry explained that when Tomer asked him to double-check the findings, he had his doubts, but could not find a plausible explanation for the data that did not involve a black hole.
He said, "It's a very exciting project to be involved in".
Was The Formation Of The Black Hole Accompanied By A Supernova Explosion?
According to the Harvard Smithsonian Center for Astrophysics, the discovery of the black hole allows astronomers a unique view into the processes that accompany the formation of black holes. A stellar-mass black hole forms as the core of a dying star collapses, but it remains uncertain whether or not this is accompanied by a powerful supernova explosion, the statement said.
Shenar explained that the star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion. He added that evidence for this 'direct-collapse' scenario has been emerging recently, but the study provides one of the "most direct indications". He further said that this has enormous implications for the origin of black-hole mergers in the cosmos.
Six years of observations of the Tarantula Nebula by the Fiber Large Array Multi Element Spectrograph (FLAMES) instrument on the ESO's VLT culminated in the discovery of the black hole in VFTS 243, according to the study.
With the help of FLAMES, astronomers can observe more than a hundred objects at once. This saves telescope time as astronomers need not study each object one by one.
The "black hole police" hope that their work will enable the discovery of other stellar-mass black holes orbiting massive stars. Astronomers predict that thousands of stellar-mass black holes orbit massive stars in the Milky Way galaxy.