Biggest stellar-mass black hole discovered

An international team of scientists led by China has discovered a king-size, stellar-mass black hole in Earth's "cosmic backyard" containing the mass of 70 suns. It is the biggest known of its kind and roughly three times bigger than what scientists previously thought was possible, researchers said on Thursday.

The discovery challenged astronomers' understanding of the formation models for black holes of its class, and provided a new way to find similar black holes in the Milky Way galaxy that may lead to new theories for black hole astrophysics and stellar evolution.

The black hole, named LB-1, was found slowly devouring gas from a nearby star more than 13,800 light-years from Earth, relatively nearby, considering the estimated 105,700 light-year diameter of Earth's galaxy.

"It is like a 'little emperor' of a black hole in our cosmic backyard," said Liu Jifeng, deputy director of the National Astronomical Observatory of China and lead researcher for the discovery.

Scientists believed that stellar-mass black holes were created when massive stars died and collapsed, but current theoretical calculations show that no matter how big the star initially was, the mass of the final black hole cannot exceed 25 solar masses if the star is rich in metals like the newly discovered one.

"When a giant star born in our galaxy approaches the end of its life, it must shed most of its gas in powerful stellar winds," Liu said. "Therefore, it should not leave such a massive remnant like LB-1. It is an extraordinary find and we may have to revamp our models to explain its formation."

One hypothesis is that LB-1 was created when two smaller black holes merged, he said. The merging of black holes is one of the most energetic events in the universe, capable of creating ripples in space-time known as gravitational waves, which were first detected in 2015.

"This discovery forces us to reexamine our models of how stellar-mass black holes form," said David Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatory Laboratory.

"This remarkable result, along with the … detections of binary black hole collisions during the past four years, really points toward a renaissance in our understanding of black hole astrophysics," he said in a scientific review.