LIGO (Laser Interferometer Gravitational-Wave Observatory) has detected a second signal of gravitational waves from a merger of two black holes.
The first signal LIGO spied, recorded in September 2015 and unveiled to the world in February, emanated from surprisingly heavy black holes, with masses 36 and 29 times that of the sun. It lasted only 0.2 seconds, and physicists glimpsed only the last 10 cycles of the black holes’ spiraling motion before their collision. The December 2015 sighting involved smaller black holes, 14 and 7.5 times as heavy as the sun, as LIGO physicists explain in a paper published in Physical Review Letters. Physicists witnessed 55 cycles of the death spiral, a full second.
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[This] latest event yields new insights. For example, physicists determined that one of the black holes was spinning frenetically, at roughly 20% of the maximum spin rate allowed by general relativity. And because the new event includes many more cycles, it tests predictions of general relativity somewhat more stringently than the first event, González says. (Einstein’s theory passes the test.)
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Most important, the second observation shows that going forward, LIGO should reap a vast harvest of black hole mergers.