Gravitational Waves Reveal Lightest Black Hole Ever Observed

sciencehabit shares a report from Science Magazine: Gravitational wave detectors have spotted a cosmic collision in which a giant black hole swallowed up a mystery object seemingly too heavy to be a neutron star, but too light to be a black hole. Weighing in at 2.6 times the mass of the Sun, the object falls into a hypothetical “mass gap,” a desert between the heaviest neutron star and the lightest black hole that some theories predict — suggesting the gap doesn’t exist and that those theories need to be amended. The data come from physicists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of detectors in Louisiana and Washington state, and Virgo, a similar detector in Italy. It’s the 2.6-solar-mass object that raises eyebrows because it falls squarely in the mass gap, says Vicky Kalogera, an astrophysicist and LIGO team member from Northwestern University. “Now, for the first time, we have seen such an object,” she says. By sensing only the gravitational waves from the collision, LIGO and Virgo cannot tell for sure what the object is, she says. But nuclear physics suggests a neutron star heavier than about 2.2 solar masses cannot support its own weight, so the object is “almost certainly” a black hole, Miller says. The study has been published in The Astrophysical Journal Letters.