New kilonova has astronomers rethinking what we learn about gamma-ray bursts

A yr in the past, astronomers found a strong gamma-ray burst (GRB) lasting almost two minutes, dubbed GRB 211211A. Now that uncommon occasion is upending the long-standing assumption that longer GRBs are the distinctive signature of an enormous star going supernova. Instead, two impartial groups of scientists recognized the supply as a so-called “kilonova,” triggered by the merger of two neutron stars, in keeping with a new paper printed within the journal Nature. Because neutron star mergers have been assumed to solely produce brief GRBs, the invention of a hybrid occasion involving a kilonova with an extended GBR is sort of shocking.

“This detection breaks our standard idea of gamma-ray bursts,” mentioned co-author Eve Chase, a postdoc at Los Alamos National Laboratory. “We can no longer assume that all short-duration bursts come from neutron-star mergers, while long-duration bursts come from supernovae. We now realize that gamma-ray bursts are much harder to classify. This detection pushes our understanding of gamma-ray bursts to the limits.”

As we have reported beforehand, gamma-ray bursts are extraordinarily high-energy explosions in distant galaxies lasting between mere milliseconds to a number of hours. The first gamma-ray bursts have been noticed within the late Nineteen Sixties, because of the launching of the Vela satellites by the US. They have been meant to detect telltale gamma-ray signatures of nuclear weapons checks within the wake of the 1963 Nuclear Test Ban Treaty with the Soviet Union. The US feared that the Soviets have been conducting secret nuclear checks, violating the treaty. In July 1967, two of these satellites picked up a flash of gamma radiation that was clearly not the signature of a nuclear weapons take a look at.

Just a few months in the past, a number of space-based detectors picked up a highly effective gamma-ray burst passing by way of our photo voltaic system, sending astronomers worldwide scrambling to coach their telescopes on that a part of the sky to gather very important knowledge on the occasion and its afterglow. Dubbed GRB 221009A, it was essentially the most highly effective gamma-ray burst but recorded and sure could possibly be the “beginning cry” of a brand new black gap.

There are two forms of gamma-ray bursts: brief and lengthy. Classic short-term GRBs final lower than two seconds, they usually have been beforehand thought to solely happen from the merging of two ultra-dense objects, like binary neutron stars, producing an accompanying kilonova. Long GRBs can final anyplace from a couple of minutes to a number of hours and are thought to happen when an enormous star goes supernova.

Astronomers on the Fermi and Swift telescopes concurrently detected this newest gamma-ray burst final December and pinpointed the placement within the constellation Boötes. That fast identification allowed different telescopes world wide to show their consideration to that sector, enabling them to catch the kilonova in its earliest levels. And it was remarkably close by for a gamma-ray burst: about 1 billion light-years from Earth, in comparison with round 6 billion years for the typical gamma-ray burst detected so far. (Light from essentially the most distant GRB but recorded traveled for some 13 billion years.)

“It was something we had never seen before,” mentioned co-author Simone Dichiara, an astronomer at Penn State University and a member of the Swift crew. “We knew it wasn’t associated with a supernova, the death of a massive star, because it was too close. It was a completely different kind of optical signal, one that we associate with a kilonova, the explosion triggered by colliding neutron stars.”

As two binary neutron stars start circling into their demise spiral, they ship out highly effective gravitational waves and strip neutron-rich matter from one another. Then the celebrities collide and merge, producing a sizzling cloud of particles that glows with mild of a number of wavelengths. It’s the neutron-rich particles that astronomers imagine creates a kilonova’s seen and infrared mild—the glow is brighter within the infrared than within the seen spectrum, a particular signature of such an occasion that outcomes from heavy components within the ejecta which block seen mild however lets the infrared by way of.

That signature is what subsequent evaluation of GRB211211A revealed. And since the following decay of a neutron star merger produces heavy components like gold and platinum, astronomers now have a brand new technique of learning how these heavy components type in our universe.

Several years in the past, the late astrophysicist Neil Gehrels recommended that longer gamma-ray bursts could possibly be produced by neutron star mergers. It appears solely becoming that NASA’s Swift Observatory, which is called in his honor, performed a key function within the discovery of GRB 211211A and the primary direct proof for that connection.

“This discovery is a clear reminder that the Universe is never fully figured out,” mentioned co-author Jillian Rastinejad, a Ph.D. pupil at Northwestern University. “Astronomers often take it for granted that the origins of GRBs can be identified by how long the GRBs are, but this discovery shows us there’s still much more to understand about these amazing events.”

DOI: Nature, 2022. 10.1038/s41550-022-01819-4  (About DOIs).