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Most Massive Merger of Binary Black Holes Detected

An international collaboration of gravitational wave researchers has announced the detection of the most massive binary black hole merger yet witnessed in the universe. The black hole that resulted from this cataclysmic event is more than 80 times as massive as our Sun.

The discovery of GW170729 – along with evidence of nine other black hole mergers – comes just over a year since the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected, for the first time, the violent death spiral of two dense neutron stars via their gravitational waves.

Dr Meg Millhouse of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) and the University of Melbourne said the papers published by the LIGO Scientific Collaboration and The Virgo Collaboration (https://goo.gl/dgWnue; https://goo.gl/

fqcCGD) catalogue all gravitational wave signals “heard” by Advanced LIGO detectors in the past 3 years. “These signals are generated by some of the most violent events in the universe, when pairs of neutron stars and black holes – each with many times more mass than our Sun – come crashing together,” she said.

Dr Simon Stevenson of OzGrav and Swinburne University said that the additional information of the other nine binary black holes “means we are learning things about the population, such as how frequently binary black holes merge in the universe (once every few hundred seconds somewhere in the universe) and whether small or large black holes are more common. There are many more light black holes (5–10 times the mass of the Sun) in the universe than heavy black holes (around 30–40 times the mass of the Sun), but the heavy ones are ‘louder’ in gravitational waves and easier to ‘hear’ colliding.”

Dr Paul Altin of OzGrav and the Australian National University says Advanced LIGO will have even higher sensitivity this year due to the use of quantum squeezing, which “allows us to get around noise that comes from quantum mechanics, the fundamental theory that governs microscopic particles”. The Advanced LIGO squeezer was designed at ANU and is currently being installed in the USA.

Dr Dan Brown of OzGrav and the University of Adelaide says the next observation run aims to use squeezed light to reach the target sensitivity required to look for extreme events. “With OzGrav’s expertise in squeezed light and adaptive optics for compensating thermal effects from the increased laser power, we’re making significant contributions towards improving LIGO for the next run,” he said.