Size of newfound black hole defies scientific theories
Before now, scientists did not think it was possible for a stellar black hole to have a mass larger than 20 times that of the sun, an approximation based on their understanding of the way stars evolve and die in the Milky Way.
But that assumption was metaphorically crushed in the gravity of a “monster” black hole that a group of Chinese-led international scientists discovered inside our own solar system. The hole has a mass 70 times greater than the sun, the researchers said in a study in the journal Nature — much larger than what astronomers previously thought could exist.
“No one has ever seen a 70-solar-mass stellar black hole anywhere,” said Joel Bregman, one of the study authors and a professor of astronomy at the University of Michigan. “This is the first.”
Black holes form when a star runs out of fuel and collapses on itself, creating a strong gravitational pull that prevents anything — even light — from escaping. In the process, those stars lose much of their mass, producing black holes that reflect their diminished size.
The newly discovered black hole, named LB-1, is 15,000 light-years from Earth, according to a news release. And it is huge.
“Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution,” Liu Jifeng, a professor at the National Astronomical Observatory of China, said in a news release from the Chinese Academy of Sciences. “Now theorists will have to take up the challenge of explaining its formation.”
LB-1 was discovered by China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), which has provided scientists with a new way to find the estimated 100 million black holes in the Milky Way. LAMOST enables researchers to detect black holes by first tracking stars that are orbiting something invisible to more than the naked eye, such as a black hole.
“Is this object extremely unusual? Or is it more common than we thought?” Bregman said. “If we look at 20 (black holes) and find two of three of these things, that would be truly amazing. It would change ideas of how massive stars evolve and die.”
The study suggests some potential explanations, including the “exciting possibility” that LB-1 might actually consist of two black holes orbiting each other, though Bregman said that would be rare. The study also points to a phenomenon known as fallback supernova, which means that during the supernova stage of a star’s evolution — when it explodes — it loses only a fraction of its mass and the rest falls back into the black hole, increasing its size.
Another option, one Bregman thinks is most likely, is that a very large star did not shed its normal amount of matter as it evolved and before it became a black hole.
“This has big implications for the evolution, the final days, of massive stars,” Bregman said.