Discovery of record-breaking black hole collision surprises astronomers

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A team of international astronomers caught the merger of two unprecedented mass black holes, creating yet another massive black hole – a black hole that astronomers thought existed in theory but had never been detected.The two caught in the act were about 85 times and 66 times the mass of the sun (measured in solar masses). After the pair merged – producing a gravitational wave picked up by detectors – they created a black hole 142 times the mass of the sun.

“We’ve never seen anything like this before,” said Evan Goetz, associate researcher in the Department of Physics and Astronomy at the University of British Columbia and co-author of the article published Wednesday in the journals. Physical examination letters and astrophysical journal letters.

“This is the first time that a type of gravitational signal like this has been measured. ”

The discovery, called GW190521, was captured using Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the United States and the Virgo interferometer in Italy on May 21, 2019.

So far, gravitational waves – ripples in space-time caused by highly energetic processes in space, such as the fusion of pairs of black holes or neutron stars or a black hole and of a neutron star – usually create a sort of “chirp” on detectors.

This artist’s drawing illustrates a hierarchical pattern of black hole fusion. The LIGO and Virgo detectors recently observed a merger of black holes with a final mass 142 times that of the sun, making it the largest of its kind observed to date in gravitational waves. The event is believed to have occurred when two black holes of about 66 and 85 solar masses coiled into a spiral and merged. (LIGO / Caltech / MIT / R. Hurt IPAC])

But this one, the researchers say, instead created a short-lived “bang”, producing only about five or six waveforms – which can be thought of as actual oscillating waves. Comparatively, other gravitational wave detections produced hundreds of waveforms.

Partly because of its brief signal, astronomers had to make sure it wasn’t noise that was causing the alleged detection. Now that it’s been confirmed, it’s the first of its kind – and sheds light on an elusive member of the black hole family: intermediate-mass black holes.

Surprises are full of discoveries

There are two special parts to the findings: one, the size of the pair of black holes, especially the one which is 85 solar masses; and two, the final black hole itself.

Black holes are regions of space where gravity is so strong that nothing can escape them. But they are not all created the same.

According to the theory, stars that are about 10 times the mass of the sun can die in a massive explosion – a supernova – which can produce a black hole. It is believed that stars that are about 65 times more massive are destroying themselves. But stars with more than 120 solar masses are thought to collapse directly into a black hole at the end of their life.

So that means black holes between 65 and 120 solar masses shouldn’t even exist. Yet this new discovery contains two that fall within this range. The one with 85 solar masses is particularly intriguing because it is right in the middle.

WATCH | Simulation of the fusion of binary black holes:

Now let’s move on to the last black hole of 142 solar mass.

There are stellar mass black holes that astronomers say can be 10 to 100 times the mass of the sun. Then there are the supermassive black holes, which can be found at the center of most galaxies. These monsters can grow to millions or even billions of times the mass of the sun.

And while there have been theories about these black holes of 100 solar masses or more – called intermediate-mass black holes – none have been directly observed.

Until now.

“There was no observational evidence prior to this discovery,” Goetz said. “This is the first conclusive evidence of a black hole of intermediate mass. “

Some hypotheses

There are two main theories as to how these seemingly impossible things happened. The first is that two stars could have merged to produce a black hole in the range 65 to 85. The second is that several black holes could have merged into a dense star cluster, creating larger black holes of masses. different.

“It’s pretty exciting,” said Priya Natarajan, theoretical astrophysicist and professor of astronomy and physics at Yale University in New Haven, Connecticut, whose primary area of ​​study is black holes. She did not participate in the search.

In one 2014 article published in the journal Science, Natarajan and his colleague proposed that the creation of black holes similar to that of 142 solar masses discovered last year could have come in a dense star cluster, just as the new discovery was observed (although in his article , the black hole was bigger).

This graph compares the GW190521 fusion event to others observed by LIGO and Virgo. The black hole created by the fusion falls into a category known as an intermediate mass black hole – and is the first clear detection of a black hole of its kind. (LIGO / Caltech / MIT / R. Hurt [IPAC])

“The idea is that one of the stars becomes a little black hole, and it starts to wander and it is kind of fed by the gas fire hose. [from stars]; it grows really fast, “Natarajan said.” And then it gets massive, and it grows up to about 50 times, and then it sinks down to the center.

“The second guy would ride, but he wouldn’t grow that fast because there wouldn’t be so much gas left. And so we predict that if you make two that way, they can’t have the same mass, they’ll be different… and that’s what we’re seeing now, so it’s kind of exciting. ”

Although the discovery is a first, astronomers know they need to increase their sample size to adequately explain the existence of intermediate-mass black holes.

“We need more observations of this type of signal. So more mergers that produce intermediate mass black holes will help us understand… how they form, ”Goetz said. “Black holes play a key role in so many aspects of astrophysics that we are only just beginning to understand much more deeply with these observations. ”

And more importantly, they will help us understand how we got here, as black holes are essential to creating much of what exists.

“It’s part of the origin story of our universe,” Natarajan said. “We might not have been here if our Milky Way didn’t have black holes. “

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