In the Milky Way, researchers say, a black hole (one illustrated) with a mass equal to around 68 suns was found. The dark mass is much heavier than other black holes like that.
The object is locked in orbit with a star about 13,800 light years away from Earth
It is heftier than other stellar-mass black holes (those with masses below about 100 suns) in and around the Milky Way with a mass of about 68 suns, scientists say.
It’s not just a record, it’s also a conundrum. Black holes in our galaxy, according to theory, that form from the explosive deaths of massive stars as this one probably did shouldn’t be heavier than about 25 suns.
The black hole is locked into orbit with a young blue star called LB-1, in the constellation Gemini, researchers found, about 13,800 light-years away.
Combining data from China’s LAMOST telescope, Jifeng Liu, an astrophysicist at Beijing’s Chinese Academy of Sciences, and colleagues realized that LB-1 is moving repeatedly at high speed to and from Earth a sign that the star orbits something massive.
With additional observations from telescopes in Hawaii and the Canary Islands, the team sketched out the orbit and deduced that the star is about 68 times as massive as the sun whipped around by a dark mass. The team reports in Nature on November 27 that only a black hole fits that description.
“I never thought in my wildest dreams you could form a black hole this big “Milky Way” black hole,” explains Michael Zevin, an astrophysicist at Northwestern University in Evanston, Ill. “If the observations pan out to be correct, this is really going to have people scratching their heads.”
This black hole is not the heaviest in the Milky Way. The title goes to the behemoth in the center of the galaxy, a supermassive black hole with a mass of over 4 million suns in a class all of its own.
Nevertheless, the mass of the black hole of LB-1 is on par with some of the black holes recently discovered by gravitational wave detectors, which detects ripples from (among other things) black holes merging pairs (SN: 2/17/16).
But those black holes were formed in far-off galaxies, likely in environments with a relative dearth of heavier elements than helium. The star LB-1 has a richer inventory of those elements, and the star that formed its partner black hole probably had a similar stock.
Stars with a greater abundance of heavy elements lose to stellar winds more of their mass, as these elements present a larger target to the radiation that drives those winds. During the supernova explosions that end their lives, massive stars that form black holes also expel a lot of their mass.
“These two processes make very small black holes even out of very massive stars,” stated. But the black hole near LB-1 apparently didn’t get that memo.
To create a black hole of 68 solar masses requires a factor of five to reduce the mass lost to stellar winds, Liu added. “We don’t know whether this is possible theoretically.”


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