Astronomers see the first flare of light from two distant black holes colliding

At a whopping 7.5 billion light-years from Earth, two black holes, each the size of Long Island, spun rapidly several times per second before crashing into a cataclysmic explosion that sent shock waves through the Universe. Typically, violent junctions like this are dark events, but astronomers think they saw a flash of light emerge from this celestial dance, potentially the first time light has been seen since the merger of black holes.

It is a unique discovery since black holes are known to not produce any light. These super dense objects are so massive that nothing can escape their gravitational pull, not even light. So how exactly did the researchers see a flare of two black holes that aren’t supposed to glow?

Well, black holes may have been in the right place at the right time, according to a new study published in the journal. Physical Review Letters. When they spun together, they settled into a giant disk of gas and dust. This disk of material spans light years and actually surrounds a third black hole, a supermassive one at the center of a galaxy. Since the dueling black holes were within this dusty environment, their fusion and eventual fusion created something like a shock wave that crashed into the surrounding earth and gas. That heated the nearby material, making it glow brighter than normal and allowing Earth researchers to detect it.

“If two black holes merge, you don’t expect to see anything,” says Matt Graham, a professor of astronomy research at Caltech and lead author of the study. The edge. “But because black holes are surrounded by these things, by this accretion disk, that’s different.”

The researchers identified this strange event with the help of the LIGO-Virgo collaboration, an international scientific association that has become increasingly adept at detecting cataclysmic events such as black hole fusion. More specifically, LIGO and Virgo search for small waves in the structure of the Universe, known as gravitational waves, that come from distant celestial events. Whenever two massive objects in the distant Universe merge, they create rippling waves in the structure of space and time that travel outward at the speed of light. When they reach Earth, such waves are very small, but the two LIGO observatories in the US USA And the Virgo Observatory in Italy are sensitive enough to collect them.

LIGO made history in 2015 when the collaboration first detected gravitational waves from the merger of two black holes. Since then, LIGO and now Virgo, which went online in 2017, have been beefing up their resumes, detecting a host of mergers across the Universe, including those of black holes, neutron stars, and perhaps even a black hole. colliding with a neutron. star. When neutron stars collide, fusions can sometimes be picked up by observatories that measure their light, even though the objects are really faint. When black holes collide, it’s not something we can see, until perhaps now. “It is a strange and wonderful event, and we don’t actually know how rare they are,” says Chiara Mingarelli, an assistant professor at the University of Connecticut who studies gravitational waves, who was not involved in the study. The edge.

One of the LIGO observatories in Livingston, Louisiana.
Image: LIGO

To find this flare, Graham and his colleagues capitalized on LIGO’s triumph by finding mergers across space to help them solve a puzzle. Graham and his team study really active supermassive black holes in galaxies, known as quasars, and noticed a strange trend. Sometimes these quasars ignited unexpectedly, glowing super bright without warning, and they wanted to know why. “And we said, ‘Well, I wonder what would happen if you had black holes in that environment,'” says Graham.

Two of Graham’s colleagues, Saavik Ford and Barry McKernan, published a document that theorizes that black holes merging into these gaseous disks could cause the mysterious outbreaks. “The idea that there could be black holes at the centers of galaxies, very close to a supermassive black hole, is actually quite controversial,” says Ford. The edge, adding, “[We] we sat down to think what the consequences of that might be, and we began to develop a theory that we have been pursuing for the past decade. “

Then they decided to put that theory to the test. In 2019, LIGO conducted a third observation race, looking for a new crop of mergers in space. Meanwhile, Graham and his colleagues were working at Caltech’s Zwicky Transitional Facility, which inspects the entire night sky, looking for strange behaviors, such as flares in distant galaxies. Astronomers decided to wait about six months after LIGO’s observations had ended to see how many mergers the collaboration detected. Then they tried to combine those fusions with the flashes they had detected with ZTF, to see if any of them corresponded.

Once they got all the potential LIGO and Virgo fusions, it was just a matter of narrowing everything down. They combined all the flares they had seen with ZTF with the fusions LIGO had detected, making sure they matched the right side of the sky, at the correct distance from Earth. The team also looked at time; They predicted that a meltdown eruption would occur 60 to 100 days after the collision, as it would take time for things to heat up and cause that glow. They then made sure that the flares they found matched the correct profile they expected, and it didn’t appear that they had been caused by an exploding star or some other explanation.

Ultimately, that led Graham and his team to the merger of the black hole they found. And actually finding something they had theorized about was quite exciting. “It’s the kind of thing you dream of as a scientist,” says Ford, “to say, ‘I think the universe is going to do that. I’m going to call my shot. And make the Universe say,’ Yes, here you go! ‘ ”

However, things are still not fully confirmed yet. The LIGO-Virgo-detected black hole fusion remains only one candidate; It has not been officially named as a merger, and LIGO has not released detailed detection data. But the good news is that Graham’s team could get additional verification in the future that the flare they recorded was actually coming from whirlpools of black holes. When the black holes merged, it is likely that the resulting black hole that formed was ejected from the surrounding dusty disk. However, that hole is still orbiting the supermassive black hole at the center of the galaxy, and will likely intersect with the hot gas disk in a year or two, heating up the material and causing another bright flare. So if the team sees another glow in the same galaxy, they’ll be pretty sure their findings were correct.

When that happens, the eruption measurement could help the team learn more about this galaxy and better restrict how massive the supermassive black hole is at the center. “It will actually allow us to directly probe these discs around supermassive black holes in ways we couldn’t do before,” says Mingarelli.

This discovery also gives astronomers another clue as to how some distant galaxies form. It tells them that there may be strange objects doing strange things on the discs surrounding supermassive black holes. “It is not just a large disk of gas falling into a supermassive black hole,” says Graham. “There are also stars and black holes doing things there.”

Also, this strange dance of black holes within a giant gaseous disk may be the only way we can really “see” black holes merging in deep space. And that’s even more information that researchers can use to study the cosmos. “We actually now have this probe, both the electromagnetic signature and the gravitational wave, that provide information,” says Ford. “It is a new and totally different tool to study how galaxies came to be the way they are.”