The Laser Interferometer Gravitational-Wave Observatory (LIGO) has announced the third detection of gravitational waves. The detection points to merging black holes that are twice as far away from Earth as the two earlier pairs – about 3 billion light-years away. The two black holes were unequal in size, one significantly lighter than the other. They merged into a black hole whose size is in the middle of the other two merged black hole pairs. The finding solidifies the case for a new class of black hole pairs, or binary black holes, with masses that are larger than researchers believed possible. The newfound black hole, formed by the pair's merger, has a mass about 49 times that of the sun. "Our handful of detections so far is revealing an intriguing black hole population we did not know existed until now," said Vicky Kalogera at Northwestern University, a senior astrophysicist with the LIGO Scientific Collaboration, which conducts research related to the twin LIGO detectors. "Now we have three pairs of black holes, each pair ending their death spiral dance over millions or billions of years in some of the most powerful explosions in the universe. In astronomy, we say with three objects of the same type you have a class. We have a population and we can do analysis." The new detection, called GW170104, occurred during LIGO's current observing run, which began in November and will continue through this summer. LIGO's observations are carried out by twin detectors in Hanford, Wash., and Livingston, La.
