Huge Black Hole 'That Shouldn't Exist in Our Galaxy' Discovered by Scientists

A large black hole that "should not exist" in the Milky Way has been discovered. The black hole, named LB-1, was detected after researchers found a star with an orbit that could only be explained if it had a "dark companion." This companion, they found, was a black hole with a mass 70 times that of the sun—far bigger than current models of stellar evolution allow for.

Researchers led by Liu Jifeng, from the Chinese Academy of Sciences' National Astronomical Observatory of China (NAOC), had been looking to identify more of the estimated 100 million stellar black holes that are believed to populate the Milky Way. So far only a few dozen of these black holes have been found. This is because normally, they only become visible when they consume gas from nearby stars—a process that produces powerful X-ray emissions that can be detected with Earth-based telescopes. While they are fasting—which is a lot of the time—they are hidden from view.

However, using China's Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), researchers have now been able to look for black holes by searching for stars that are orbiting invisible objects—black holes. With LAMOST, the team noticed a star 15,000 light years from Earth that appeared to be orbiting a black hole, but after examining their data, something did not add up. The star orbiting the black hole was about eight times heavier than the sun and orbited the black hole once every 79 days. But more intriguingly, the black hole was far, far bigger than it should be.

"We were surprised and shocked," Liu told Newsweek. "[It] took a year to examine the data [...] analysis, again and again, and to discuss the results with many people in pursuit of explanations." They performed follow up observations using the Gran Telescopio Canarias in Spain and the Keck Telescope in the U.S. In total, they performed 26 observations, involving 3,000 targets to find the black hole. Their findings are published in Nature.

Stellar black holes in the Milky Way form when stars die. When this happens, Liu explained, the star loses a substantial amount of mass. "Only a small part of its initial mass is left to become a black hole," he said. "Theoretical calculations show that no matter how massive the star initially was, the mass of the final black hole cannot exceed 25 solar masses if the star is rich of metals like the one discovered in this paper."

At 70 solar masses, LB-1 is almost triple what models predict is possible. "Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution," Liu said in a statement. LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation." The team is now planning to search for more black holes, to monitor the black hole and make a more refined estimate of its mass.

David Reitze, the director of the gravitational wave detector LIGO, who was not involved in the study, commented on the findings. "This discovery forces us to re-examine our models of how stellar-mass black holes form," he said in a statement. "This remarkable result, along with the LIGO-Virgo detections of binary black hole collisions during the past four years, really points towards a renaissance in our understanding of black hole astrophysics."