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A More Perfect Union

17 June 2016

This illustration depicts the view from outside of a rapidly-accreting black hole. NRAO/AUI/NSF and Dana Berry/SkyWorks
This illustration depicts the view from outside of a rapidly-accreting black hole.

On 26 December 2015 the LIGO observatory saw another merger of two black holes. This time the black holes were smaller, with masses of about 8 and 14 Suns. As a result, we captured the inspiraling of the black holes for a longer time. Gravitational wave astronomy is now fully under way.1

The cleaned up observation of the black hole merger. LIGO
The cleaned up observation of the black hole merger.

Because of the size and distance of this merger (about 1.4 billion light years) this particular merger is fainter than the first. It was seen a periodic fluctuation buried within the LIGO noise, so the data has to be matched to computer simulations to really determine its properties. It’s statistical validity dances around the usual five sigma range, so there is no doubt the signal is real.

More than the first merger, this is a textbook example of a merger. We captured nearly thirty orbits of the two black holes as they danced ever closer to each other. We can see not only the steady gravitational waves of their orbits, we can also see how their orbital periods get shorter, orbiting ever faster as they approach the merger. This is textbook behavior. It is exactly the type of event we expected to see. The merging of stellar-mass binaries.

Overall this new observation is further confirmation not only of general relativity, but of central aspects of astrophysics. Black holes are real, they occasionally merge just as we predicted, and we can now start using gravitational waves as an astronomical tool.

  1. Abbott, Benjamin P., et al. “GW151226: observation of gravitational waves from a 22-solar-mass binary black hole coalescence.” Physical review letters 116.24 (2016): 241103. ↩︎