The world’s largest radio telescope captures the luminous aftermath of star collisions

On Wednesday, astronomers brought us a mysterious video: images of lime-green specks steadily evolving on a dark background. But right in the center of this shot, one speck isn’t like the others. It’s the brightest blob of neon of them all and gets better with every frame.

What you’re looking at is evidence that about 20 billion years ago, an ultra-strong neutron star collided with a fainter star, spewing out an explosive, short-lived burst of gamma-rays, rippling gravitational waves through the cosmos and spreading surrounding space with a powerful afterglow. It was a staggering merger that took place when the universe was only 40% of its current age, and our remarkable view of what happened is courtesy of the world’s largest radio telescope, the Atacama Large Millimeter/submillimeter Array in Chile.

More specifically, ALMA is a combination of 66 radio telescopes spread across the high Chilean Andes. And they work together to give us data on the violent side of our universe.

“Afterglow for short bursts is very hard to come by, so to see this event shine so brightly was spectacular,” Wen-fai Fong, an astronomer at Northwestern University and principal investigator on the ALMA program, said in a statement. “This surprising discovery opens up a new area of ​​research as it motivates us to observe much more of it with ALMA and other telescope arrays in the future.”

Details of Fong’s and other researchers’ findings will be published shortly in an upcoming issue of The Astrophysical Journal Letters. A preprint is currently available on arXiv.

An incomprehensible force of nature

Short-lived gamma-ray bursts, like this one officially dubbed GRB 211106A, are among the most intense, mind-bogglingly powerful explosions known to science. But unlike longer-lived ones, their fleeting nature meant they remained a mystery until NASA’s Neil Gehrel’s Swift Observatory first collected data on one in 2005.

In a matter of seconds, these cosmic thrusts can emit more energy than our sun will emit within itself entire Lifespan. Although such an extremity makes sense to them because these phenomena stem from binary collisions involving at least one neutron star, a hyperdense ball of gas that rivals even black holes in gravitational monstrosity.

Only one tablespoon of a neutron star would be roughly equivalent to the weight of Mount Everest.

“These mergers occur because of gravitational-wave radiation, which drains energy from the binary stars’ orbit, causing the stars to spiral toward each other,” said Tanmoy Laskar, lead author of the study and an astronomer at Radboud University, in a statement. “The resulting explosion is accompanied by jets traveling at nearly the speed of light. When one of these jets is aimed at Earth, we observe a short pulse of gamma rays, or a short-lived GRB.”

That’s the vivid green dot we see in the record of the last eruption.

ALMA know-how

The fact that the study team used ALMA to locate this particular burst marks the first-ever time such an event has been captured in millimeter wavelengths, the specialty of the Chilean “oscilloscope.”

Although this dramatic collision had already been studied by NASA’s Hubble Space Telescope, it was only seen under the guise of optical and infrared light wavelengths. With those wavelengths, Hubble was essentially only able to estimate information about the distant galaxy where that merger was occurring, but not too much about the afterglow that followed. Even if the agency’s groundbreaking James Webb Space Telescope one day embarks on a mission to study GRB 21106A, it will also be limited to infrared light wavelengths, albeit over a much broader spectrum.

ALMA, on the other hand, was able to see something different than Hubble with its millimeter wavelengths – it actually caught the afterglow of GRB 21106A. And after some deliberation, the team behind the new study realized that the afterglow from this brief gamma-ray burst is among the most luminous ever seen.

“What makes GRB 211106A so special is that not only is it the first short-duration GRB that we have detected in this wavelength, but we were also able to measure the aperture angle of the jet thanks to millimeter and radio detection,” says Rouco Escorial Co -author and astronomer at Northwestern University, said in a statement.

Down the line, such information could prove essential to infer the rates of such GRBs in our Universe and compare them to the rates of binary neutron star mergers and perhaps even black hole mergers.

“ALMA shakes the playing field in terms of its capabilities at millimeter wavelengths and has allowed us to see the faint, dynamic universe in this kind of light for the first time,” said Fong. “After a decade of observing short GRBs, it’s truly amazing to see how powerful these new technologies are in unwrapping surprising gifts from the universe.”