When two black holes merge, they release gravitational waves. In the 10 years since then, scientists have detected hundreds of black holes coming together, as well as other extreme cosmic events like neutron stars colliding and black holes merging with a neutron star. On Jan. 14, detectors registered gravitational waves that came from two colliding black holes about 1.3 billion light-years away. Gravitational Waves: Unlocking The Secrets Of The Universe Science correspondent Nell Greenfieldboyce gives us the latest in gravitational waves and shares what scientists have learned (and heard) from these tiny ripples in spacetime. We are learning so much about them that sometimes I feel tempted to call this ‘black hole astronomy’ rather than ‘gravitational wave astronomy,'” she says.