In San Diego, California, at the American Astronomical Society meeting this week, Gabriela González, speaking for the LIGO team, reported that LIGO has confirmed a second gravitational wave in the data of their initial run (12 September 2015–19 January 2016) and identified a third candidate wave but has found no other evidence for black hole mergers with total masses below 100 M⊙. The new confirmed wave was spotted on 26 December 2015 Universal Time—Christmas Day in the US, where intrepid LIGO workers forewent their holiday celebrations to maintain the interferometer. The event, which lasted for about 1 second, is best explained as arising from a merger of black holes with 14 and 7.5 M⊙, with 1 M⊙ of energy liberated in gravitational waves. Although determining black hole spin is particularly challenging, the LIGO researchers established that at least one of the two merging black holes was spinning.
