A bizarre gamma-ray burst breaks the rules for these cosmic eruptions

Astronomers have noticed a vibrant gamma-ray burst that upends earlier theories of how these energetic cosmic eruptions happen.

For many years, astronomers thought that GRBs got here in two flavors, lengthy and brief — that’s, lasting longer than two seconds or winking out extra shortly. Every sort has been linked to totally different cosmic occasions. However a couple of yr in the past, two NASA house telescopes caught a brief GRB in lengthy GRB’s clothes: It lasted a very long time however originated from a brief GRB supply.

“We had this black-and-white imaginative and prescient of the universe,” says astrophysicist Eleonora Troja of the Tor Vergata College of Rome. “That is the purple flag that tells us, nope, it’s not. Shock!”

This burst, referred to as GRB 211211A, is the primary that unambiguously breaks the binary, Troja and others report December 7 in 5 papers in Nature and Nature Astronomy.

Previous to the invention of this burst, astronomers principally thought that there have been simply two methods to supply a GRB. The collapse of a massive star simply earlier than it explodes in a supernova might make a protracted gamma-ray burst, lasting greater than two seconds (SN: 10/28/22). Or a pair of dense stellar corpses referred to as neutron stars might collide, merge and kind a brand new black gap, releasing a brief gamma-ray burst of two seconds or much less.

However there had been some outliers. A surprisingly brief GRB in 2020 appeared to return from a massive star’s implosion (SN: 8/2/21). And a few long-duration GRBs courting again to 2006 lacked a supernova after the very fact, elevating questions on their origins.

“We at all times knew there was an overlap,” says astrophysicist Chryssa Kouveliotou of George Washington College in Washington, D.C., who wrote the 1993 paper that introduced the two GRB categories, however was not concerned within the new work. “There have been some outliers which we didn’t know how you can interpret.”

There’s no such thriller about GRB 211211A: The burst lasted greater than 50 seconds and was clearly accompanied by a kilonova, the attribute glow of recent parts being solid after a neutron star smashup.

“Though we suspected it was attainable that prolonged emission GRBs have been mergers … that is the primary affirmation,” says astrophysicist Benjamin Gompertz of the College of Birmingham in England, who describes observations of the burst in Nature Astronomy. “It has the kilonova, which is the smoking gun.”

NASA’s Swift and Fermi house telescopes detected the explosion on December 11, 2021, in a galaxy about 1.1 billion light-years away. “We thought it was a run-of-the-mill lengthy gamma-ray burst,” says astrophysicist Wen-fai Fong of Northwestern College in Evanston, Ailing.

It was comparatively shut by, as GRBs go. In order that allowed Fong’s and Troja’s analysis teams to independently proceed intently observing the burst in nice element utilizing telescopes on the bottom, the groups report in Nature.

Because the weeks wore on and no supernova appeared, the researchers grew confused. Their observations revealed that no matter had made the GRB had additionally emitted way more optical and infrared gentle than is typical for the supply of a protracted GRB.

After ruling out different explanations, Troja and colleagues in contrast the burst’s aftereffects with the first kilonova ever observed in concert with ripples in spacetime called gravitational waves (SN: 10/16/17). The match was practically good. “That’s when many individuals acquired satisfied we have been speaking a couple of kilonova,” she says.

On reflection, it feels apparent that it was a kilonova, Troja says. However within the second, it felt as unimaginable as seeing a lion within the Arctic. “It appears to be like like a lion, it roars like a lion, but it surely shouldn’t be right here, so it can’t be,” she says. “That’s precisely what we felt.”

Now the query is, what occurred? Usually, merging neutron stars collapse right into a black gap nearly instantly. The gamma rays come from materials that’s superheated because it falls into the black gap, however the materials is scant, and the black gap gobbles it up inside two seconds. So how did GRB 211211A preserve its gentle going for nearly a minute?

It’s attainable that the neutron stars first merged right into a single, bigger neutron star, which briefly resisted the stress to break down right into a black gap. That has implications for the basic physics that describes how tough it’s to crush neutrons right into a black gap, Gompertz says.

One other chance is {that a} neutron star collided with a small black gap, about 5 instances the mass of the solar, as an alternative of one other neutron star. And the method of the black gap consuming the neutron star took longer.

Or it might have been one thing else fully: a neutron star merging with a white dwarf, astrophysicist Bing Zhang of the College of Nevada, Las Vegas and colleagues counsel in Nature. “We recommend a 3rd sort of progenitor, one thing very totally different from the earlier two varieties,” he says.

White dwarfs are the remnants of smaller stars just like the solar, and usually are not as dense or compact as neutron stars. A collision between a white dwarf and a neutron star might nonetheless produce a kilonova if the white dwarf may be very heavy.

The ensuing object could possibly be a extremely magnetized neutron star referred to as a magnetar (SN: 12/1/20). The magnetar might have continued pumping vitality into gamma rays and different wavelengths of sunshine, extending the lifetime of the burst, Zhang says.

No matter its origins, GRB 211211A is an enormous deal for physics. “It can be crucial as a result of we wished to know, what on Earth are these occasions?” Kouveliotou says.

Determining what triggered it might illuminate how heavy parts within the universe kind. And a few beforehand seen lengthy GRBs that scientists thought have been from supernovas would possibly really be really from mergers.

To be taught extra, scientists want to search out extra of those binary-busting GRBs, plus observations of gravitational waves on the similar time. Trejo thinks they’ll be capable to get that when the Laser Interferometer Gravitational-Wave Observatory, or LIGO, comes again on-line in 2023.

“I hope that LIGO will produce some proof,” Kouveliotou says. “Nature is likely to be sleek and provides us a few these occasions with gravitational wave counterparts, and possibly [help us] perceive what’s occurring.”