Swift kick from a supernova could knock a black hole askew

Gravitational wave detection hints at unexpected power from star explosion

TILT THE BALANCE Black holes that orbit one another can have tilted spins (illustrated here, in an image of the third set of black holes LIGO detected). In LIGO’s second detection, the tilt of one black hole suggests it may have been kicked askew by the stellar explosion that created it.

AURORE SIMONNET/SONOMA STATE, MIT, CALTECH, LIGO

By Emily Conover

June 9, 2017 at 2:37 pm

Gravitational waves are providing new hints about how black holes get their kicks.

The Advanced Laser Interferometer Gravitational-Wave Observatory’s detection of spacetime ripples from two merging black holes on December 26, 2015, indicated that one black hole was spinning like a tilted top as it orbited with its companion (SN: 7/9/16, p. 8). That off-kilter spin could mean that the stellar explosion that produced the black hole gave it a strong kick, physicist Richard O’Shaughnessy and colleagues report in a paper in press in Physical Review Letters.

Scientists aren’t sure how black holes like those detected by LIGO pair up (SN Online: 6/19/16). Two neighboring stars may have obliterated themselves in a pair of explosions called supernovas, producing two black holes. But that scenario should lead to black holes that spin in the same plane as their orbit. It would take a sizeable jolt from the supernova, of about 50 kilometers per second, to account for the cockeyed spin, the researchers conclude.

Computer simulations of supernovas predict smaller black hole boosts, making for a cosmological conundrum. “This will be a serious challenge for supernova modelers to explain,” O’Shaughnessy, of the Rochester Institute of Technology in New York, said June 5 in a news conference in Austin, Texas, at a meeting of the American Astronomical Society.