Black holes a few times the mass of the sun aren't just hard to spot: they may not exist. The finding offers a new twist in our idea of how black holes are born. Stars that are eight or more times the mass of the sun explode as supernovae at the end of their lives. If the core left behind weighs less than two or three suns, it will turn into a neutron star. If it weighs more, it will become a black hole. But there is a glaring lack of black holes observed at the lightest end of the spectrum, says Feryal Oezel of the University of Arizona in Tucson. Oezel and colleagues studied 16 systems in the Milky Way that contain a black hole and a stellar partner, and found that none of these black holes had a mass between two and five times that of the sun. This can't be explained by simple observational constraints, the team say. "These black holes really seem not to exist," Oezel says. The work will appear in The Astrophysical Journal.
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