Black holes are inherently mysterious objects. Just when we think we understand how big they can get under various circumstances, we go and find new ones that bend the rules. Now, astronomers have found a stellar black hole in our galaxy that’s so big it defies explanation.
The newly-discovered black hole has been dubbed LB-1, and it’s located about 15,000 light-years from Earth. It belongs to a class of objects known as stellar black holes, which usually have masses between five and 15 times that of the Sun. But LB-1 is a monster – it has a mass equal to 70 Suns, making it by far the biggest of its class.
In fact, it might even be too big. Stellar mass black holes usually form as the leftovers after a star explodes as a supernova. The problem is, LB-1 is way too massive for that story to work, leaving astronomers scratching their heads.
“(The) LB-1 black hole seems impossible to explain,” says Chris Belczynski, an author of the study. “Stars massive enough to form a 70-solar-mass black hole monster should be totally destroyed by powerful pair-instability supernova explosions that leave only scattered gas and dust behind, and not black holes!”
As notoriously dark objects, stellar black holes can be hard to find, and normally only show themselves when they start snacking on dust or stars. But LB-1 was discovered through a different method, known as radial-velocity.
Using the LAMOST telescope in China, the astronomers watched for stars that seemed to have weird wobbles in their movements. This can suggest they’re locked in a binary orbit with a massive, virtually invisible object – a black hole. LB-1 was found using this method, alongside a star measuring eight solar masses in a 79-day orbit.
Interestingly, this isn’t the first time huge stellar black holes have been discovered through unconventional means. For the last few years, LIGO and other facilities have been detecting gravitational waves – ripples in spacetime created by collisions of massive objects, including black holes.
Calculations from an event detected in 2015 suggest that the two black holes that collided had masses of 29 and 36 solar masses, creating a new black hole of 62 solar masses (three solar masses’ worth was lost as gravitational waves). Not only were the original 29- and 36-solar-mass black holes pretty big for their type, but the resulting black hole is pretty close to the mass of LB-1. This may seem like a possible explanation, but the environment around LB-1 doesn’t seem conducive to this kind of collision.
Instead, the researchers say we might need to adjust our models of black hole evolution, in the face of a growing body of evidence of these monsters.
The research was published in the journal Nature.
