Scientists Detect Biggest Collision of Black Holes Ever Observed

James Marshall
December 4, 2018

At a weekend workshop in Maryland, physicists from the LIGO and Virgo collaboration reported four previously unannounced detections of gravitational waves from merging black holes, including the biggest-known black-hole collision to date, roughly 5 billion years ago. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of nearly five solar masses was converted into gravitational radiation.

"The release of four additional binary black hole mergers further informs us of the nature of the population of these binary systems in the universe and better constrains the event rate for these types of events", said Albert Lazzarini, Deputy Director of the LIGO Laboratory at California Institute of Technology in the US.

In July 2017, the fusion of the black hole binary system was detected more than nine billion light years away and resulted in the largest black hole known, the ANU said in a statement.

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

The discovery brings the total number of black hole merger detections to 10, along with a neutron star collision, during the past three years. The waves appear as ripples in the fabric of spacetime, not unlike what you'd see after dropping a large object in water.

They can be produced, for instance, when black holes orbit each other or by the merging of galaxies.

USA scientists discovered the space-time ripples - officially known as gravitational waves - in a breakthrough in 2016, although their existence was predicted by Albert Einstein roughly a century ago. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

Susan Scott, a physicist at the Australian National University, said it was by far the most distant black-hole merger observed to date.

One day they hope to be able to reach back to the beginning of time just after the Big Bang, something which can not be done with light.

The newly announced gravitational-wave observations weren't found in new data - in fact, both LIGO and Virgo have been down for upgrades since August 2017.

"This should be the biggest announcement at the whole's a pinnacle of my career", she said.

Dr Karl Wette, a postdoctoral fellow in the group at ANU and a member of OzGrav, said scientists were not sure what was formed from the neutron-star merger that was detected in August previous year. That can tell scientists something about how black holes form and grow together, which can in turn yield insights into the evolution of stars.

One of the just-seen mergers (officially called GW170817) is believed to be a merger between two neutron stars.

The results of the discoveries will be published in Physical Review X.

They act as intense sources of gravity which hoover up dust and gas around them.

How they are formed is still poorly understood.

Astrophysicists now believe there are about 10,000 black holes at the centre of our own galaxy, the Milky Way, all of which surround a supermassive black hole at its core.

Astronomers believe they may form when a large cloud of gas up to 100,000 times bigger than the sun, collapses into a black hole. Among the things scientists have learned so far: all stellar black holes were formed from stars 45 times less than the mass of our Sun.

When these giant stars die, they also go "supernova", a huge explosion that expels the matter from the outer layers of the star into deep space.

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