Media ReleaseFrom: OzGRav
An international group of scientists, including dozens of Australians, this weekend 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 one year since scientists announced they had witnessed, for the first time, the violent death spiral of two dense neutron stars via gravitational waves, another set of major astrophysical discoveries have been announced in the US.
The series of papers including the work of the Australians, all from the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), present the full catalogue of observations of binary black hole and binary neutron star mergers from the first two observing runs (2015, 2016-17) of the Advanced LIGO (US) and Advanced Virgo (Italy) gravitational-wave detectors.
According to Dr Meg Millhouse, from OzGrav and the University of Melbourne, the papers outline a catalogue of all gravitational wave signals "heard" by the Advanced LIGO detectors in the last three 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, from 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 (low mass) or large (high mass) black holes are more common -- there are many more light black holes (around 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,” he said.
“With each new detection we learn something more about how these extraordinary objects came to be. The detections also help to answer questions about the theory of gravity, the formation of galaxies, and how heavy elements (including gold and platinum) are produced”, said co-author Dr Xu (Sundae) Chen from OzGrav and the University of Western Australia.
Another author, student Colm Talbot from OzGrav and Monash University, in a separate paper describes how the detection of these new black holes will assist in understanding the Universe’s entire population of black holes. “Each of these black holes formed from huge stars which died in violent explosions called supernovae. By studying these black holes, we act as black hole archaeologists to learn how these cosmic giants die,” he said.
Last year Dr Paul Altin from OzGrav and the Australian National University was part of LIGO's "rapid response team", whose job it is to be ready to receive a detection alert at any time, day or night, in order to quickly analyse the data and decide whether the event is significant enough for an alert to be sent to our partner astronomers for follow-up observations. According to Dr Altin, in 2019 Advanced LIGO comes back online with even higher sensitivity, in part due to the use of quantum squeezing. “Squeezing allows us to get around noise that comes from quantum mechanics, the fundamental theory that governs microscopic particles,” he said. The Advanced LIGO squeezer was designed at ANU and is currently being installed in the US.
Several OzGrav members are currently in the US at LIGO Hanford installing upgrades to the detector. According to Dr Dan Brown, from OzGrav and the University of Adelaide, the next observation run aims to use squeezed light to reach the target sensitivity 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.
Papers available on the arXiv and the LIGO DCC, https://dcc.ligo.org/