It’s not easy spotting black holes. By definition, they are black as nothing can escape them not even light. So astronomers have to find other ways to find them. Gravitational waves, when they merge are one way. Or by powerful x-ray emission when they feed. This means that finding the quiet ones, the so-called dormant black holes is extremely difficult. Now finding one in the galaxy next door is certainly cause for celebration then.
The team of astronomers looked at almost 1,000 stars in the Tarantula Nebula which is located in the Large Magellanic Cloud, the largest galactic companion of the Milky Way. Among those objects, there was VFTS 243 whose observations are consistent with a black hole of nine solar masses orbiting a hot blue star almost three times as heavy.
The finding, reported in Nature Astronomy, comes from a team that has spent several years disproving previous candidate dormant black holes. So they approached what they saw with a grain of salt. After all, there might be other explanations that fit the observations when you are around 160,000 light-years away.
“As a researcher who has debunked potential black holes in recent years, I was extremely skeptical regarding this discovery,” study leader Tomer Shenar from Amsterdam University, said in a statement.
“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,” explained co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian.
Stellar-mass black holes such as this one form at the end of a massive star’s life. Many will form after the star goes supernova, throwing some of the stellar material out into interstellar space. But not this one. The team believe that this one was a special kind of formation.
"The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no sign of a previous explosion," added 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 team is inviting other groups to check their results, as it is only fair after having spent so many years as the “black hole police”. They hope their approach, once VFTS 243 is confirmed, will lead to the discovery of many more of these objects.
“It is incredible that we hardly know of any dormant black holes, given how common astronomers believe them to be,” said co-author Pablo Marchant of KU Leuven.