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 rapidly. Each kind has been linked to totally different cosmic occasions. But a couple of 12 months in the past, two NASA area 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 vision of the universe,” says astrophysicist Eleonora Troja of the Tor Vergata University of Rome. “This is the red flag that tells us, nope, it’s not. Surprise!”
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.
Prior to the invention of this burst, astronomers largely thought that there have been simply two methods to supply a GRB. The collapse of an enormous star simply earlier than it explodes in a supernova might make an extended 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 type a brand new black gap, releasing a brief gamma-ray burst of two seconds or much less.
But there had been some outliers. A surprisingly brief GRB in 2020 appeared to return from an enormous star’s implosion (SN: 8/2/21). And some long-duration GRBs courting again to 2006 lacked a supernova after the very fact, elevating questions on their origins.
“We always knew there was an overlap,” says astrophysicist Chryssa Kouveliotou of George Washington University in Washington, D.C., who wrote the 1993 paper that launched the 2 GRB classes, however was not concerned within the new work. “There were some outliers which we did not know how to 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 components being cast after a neutron star smashup.
This reveals the glow of a kilonova that adopted the oddball gamma-ray burst referred to as GRB 211211A, in photographs from the Gemini North telescope and the Hubble Space Telescope.M. Zamani/International Gemini Observatory/NOIRLab/NSF/AURA, NASA, ESA
“Although we suspected it was possible that extended emission GRBs were mergers … this is the first confirmation,” says astrophysicist Benjamin Gompertz of the University 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 area 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 long gamma-ray burst,” says astrophysicist Wen-fai Fong of Northwestern University in Evanston, Ill.
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It was comparatively shut by, as GRBs go. So 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.
As 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 mild than is typical for the supply of an extended GRB.
After ruling out different explanations, Troja and colleagues in contrast the burst’s aftereffects with the primary kilonova ever noticed in live performance with ripples in spacetime referred to as gravitational waves (SN: 10/16/17). The match was practically good. “That’s when many people got convinced we were talking about a kilonova,” she says.
In retrospect, it feels apparent that it was a kilonova, Troja says. But within the second, it felt as unattainable as seeing a lion within the Arctic. “It looks like a lion, it roars like a lion, but it shouldn’t be here, so it cannot be,” she says. “That’s exactly what we felt.”
Now the query is, what occurred? Typically, merging neutron stars collapse right into a black gap virtually 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 mild going for nearly a minute?
It’s potential 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.
Another risk 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 solely: a neutron star merging with a white dwarf, astrophysicist Bing Zhang of the University of Nevada, Las Vegas and colleagues counsel in Nature. “We suggest a third type of progenitor, something very different from the previous two types,” 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.
Whatever its origins, GRB 211211A is a giant deal for physics. “It is important because we wanted to understand, what on Earth are these events?” Kouveliotou says.
Figuring out what prompted it might illuminate how heavy components within the universe type. And some beforehand seen lengthy GRBs that scientists thought have been from supernovas may really be really from mergers.
To study extra, scientists want to seek 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 evidence,” Kouveliotou says. “Nature might be graceful and give us a couple of these events with gravitational wave counterparts, and maybe [help us] understand what’s going on.”