'Tsunami' of Gravitational Waves From Violent Cosmic Events Detected

Researchers from across the globe have revealed they have detected the largest collection of gravitational waves ever recorded. The gravitational waves, ripples in the very fabric of spacetime itself, come from powerful and violent cosmic events like the merger of black holes and collisions between neutron stars.

A study published by the team reveals 35 gravitational wave detections that were made using the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer between November 2019 and March 2020.

The gravitational waves come from 32 black hole collisions and mergers, and three suspected mixed collisions between a black hole and a neutron star. These latest detections bring the total number of detected gravitational waves to 90.

Australian National University distinguished professor Susan Scott described the detection as "a tsunami" of gravitational waves, adding that they constitute a "major leap forward in our quest to unlock the secrets of the Universe's evolution."

Gravitational waves were first predicted in Albert Einstein's theory of gravity, general relativity. This theory suggests that massive objects like black holes warp the very fabric of space and time, considered by Einstein to be a single entity "spacetime."

When these massive objects circle each other, collide, or even spin rapidly, they launch ripples through spacetime which get detected here on Earth by massive and sensitive laser interferometers.

One such device, the Laser Interferometer Gravitational-Wave Observatory (LIGO), detected the first gravitational wave signal in 2015 from a collision between two massive black holes, 1.3 billion light-years away.

Since then, scientists have built a catalog of gravitational-wave detections from events like further black hole collisions, neutron star mergers, and even a mixed impact involving a black hole and a neutron star.

"These discoveries represent a tenfold increase in the number of gravitational waves detected by LIGO and Virgo since they started observing," Scott said. "We've detected 35 events. That's massive! In contrast, we made three detections in our first observing run, which lasted four months in 2015-16."

Scott, who is also chief investigator of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), continued by explaining that the increasing volume of gravitational wave detections is revealing details of how black hole systems and neutron star systems come together and eventually merge.

"It also raises some really fascinating questions," Scott continued. "For example, did the system originally form with two stars that went through their life cycles together and eventually became black holes? Or were the two black holes thrust together in a very dense dynamical environment such as at the center of a galaxy?"

Scott pointed to the continuing improvement in the sensitivity of gravitational wave detection as being responsible for the increase in detection of the spacetime ripples, which Einstein once predicted would be too tiny to ever be detected.

"We are also probing the two black hole mass gap regions and providing more tests of Einstein's theory of general relativity," Scott concluded. "The other really exciting thing about the constant improvement of the sensitivity of the gravitational wave detectors is that this will then bring into play a whole new range of sources of gravitational waves, some of which will be unexpected.

"This really is a new era for gravitational wave detections and the growing population of discoveries is revealing so much information about the life and death of stars throughout the Universe."

Colliding Black Holes
An illustration of two black holes spiraling towards each other and merging, thus launching ripples through the very fabric of spacetime itself. Researchers have detected a wealth of gravitational waves from powerful cosmic events like this. NASA