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Record haul of 35 gravitational waves provides insight into how universe formed: astronomers

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Almost all the newly detected gravitational waves were created when black holes collided. (Supplied: Mark Myers/OzGrav)

Almost all the newly detected gravitational waves were created when black holes collided. 

Astronomers have bagged more than a third of gravitational waves ever discovered in just five months.

Gravitational waves were first discovered in 2015, with the Nobel Prize-winning detection of two merging black holes by the Laser Interferometer Gravitational-wave Observatory (LIGO).

Since then, astronomers have detected gravitational waves created by the collision of two neutron stars – the dense remnants of massive stars that died – producing a fireball known as a kilonova.

They've also detected waves created by black holes swallowing a  neutron star.

The addition of 35 new confirmed observations of these tiny ripples in the fabric of space-time, published on ArXiv, takes the tally of detections to 90.

"Our first observing run [in 2015] went for four months and we got three events [including the initial detection," said astrophysicist Susan Scott of the Australian National University and a member of the international Advanced LIGO team.

"This run is only one month long and we've got 35."

The gravitational waves were detected between November 2019 and March 2020 after the Advanced LIGO and Virgo observatories had been upgraded.

Professor Scott said the new detections were very exciting.

"Information from the black hole masses and spins … gives us a lot of information about how the structure of the universe formed."

A bag of black holes and neutron stars

Like the initial detections, 32 of the new gravitational waves were created in the moments leading up to the collision of two black holes.

One of these collisions, known as GW200220_061928, was created by a massive pair of black holes orbiting each other, with a combined mass 145 times heavier than the Sun.

While not the largest merger seen to date, this merger created another black hole in a range only recently discovered, Professor Scott said.

Another two detections involved the gobbling up of a neutron star by a black hole.

The final one, dubbed GW200210_092254, created between an object that is 24 times the mass of our Sun and a lighter object that is 2.83 solar masses, is a bit "ambiguous", Professor Scott said.

It could be created by two black holes, or a black hole and a neutron star.

"People do feel it could be a big neutron star, but it's bigger than our models predict a neutron star can be.

"Our theories to get one that big [2.83 solar masses] are not thick on the ground.

"My own personal feeling is it's probably a black hole which has been formed in an earlier life by two neutron stars smashing together," Professor Scott said.

What's next for gravitational wave discoveries?

Each time the Advanced LIGO and Virgo detectors are upgraded, they can see further out into the universe and capture more events.

The next observing run will start in August 2022.

"We are expecting to get a lot of gravitational wave events in that observing run and hopefully some new things too," Professor Scott said.

The team is now on the hunt for gravitational waves created by supernova explosions.

"In the past, they've been too weak for us to detect them, but we are getting into that realm where that should be possible," she said.

Another big one the team would like to spot is gravitational waves created by a single misshapen neutron star.

"Neutron stars are the mystery objects of the universe," Professor Scott said.

"They are the densest type of matter in the universe and we can't study that kind of matter in laboratories on Earth because the conditions are just too extreme."

According to Einstein's theory of relativity, a single object needs to be asymmetric to create gravitational waves.

"So if a neutron star was a bit more like an AFL football, it should produce gravitational waves," she said.

 

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