Weird nearby gamma-ray burst defies expectations
This isn’t how they’re supposed to behave
Scientists have gotten their best look yet at a gamma-ray burst, the most dramatic type of explosion in the universe.
Astronomers think some of these explosions occur when a massive star – five or ten times the mass of our Sun – detonates, abruptly becoming a black hole. Gamma-ray bursts may also occur when two superdense stellar corpses called neutron stars collide, often forming a black hole. And, conveniently, a gamma-ray burst that scientists watched during a few nights in 2019 likely occurred only about 1 billion light years away from Earth, relatively close by for these dramatic events.
“We were really sitting in the front row when this gamma-ray burst happened,” said Andrew M. Taylor, a physicist at the Deutsches Elektronen-Synchrotron (German Electron Synchrotron, or DESY). “We could observe the afterglow for several days and to unprecedented gamma-ray energies.”
Two space-based NASA observatories, Fermi and Swift, first detected the event, which is known as GRB 190829A because it was detected on 29 August 2019. The fireworks came from the direction of the constellation Eridanus, a large swath of sky in the Southern Hemisphere.
When the scientists behind the new research heard about the gamma-ray burst detection, they mobilised a set of five gamma-ray telescopes in Namibia, called the High Energy Stereoscopic System (HESS). Over three nights, the telescopes observed the explosion for a total of 13 hours in an attempt to understand what took place.
With those observations, the scientists could analyse much higher energy photons than is possible in more distant gamma-ray bursts. “This is what’s so exceptional about this gamma-ray burst,” said Edna Ruiz-Velasco, an astrophysicist at the Max Planck Institute for Nuclear Physics in Heidelberg. “It happened in our cosmic backyard, where the very-high-energy photons were not absorbed in collisions with background light on their way to Earth, as happens over larger distances in the cosmos.”
During analyses, the team noticed that the patterns of X-rays and very-high-energy gamma rays matched – something scientists didn’t expect, since they believe different phenomena cause the two different types of radiation. But so far scientists have only observed four of these bright explosions from the surface of Earth, so they’re hoping that new instruments and additional observations give them more insight into the details of gamma-ray bursts.
“We could observe the afterglow for several days and to unprecedented gamma-ray energies”
Andrew M. Taylor