Earth has been hit by an intense, unusual blast of light that could change our understanding of the universe, scientists have said.
Late last year, scientists spotted a 50-second-long blast of energy coming towards Earth, known as a gamma-ray burst or GRB, which are the most powerful explosions in the universe. Immediately, researchers started looking for the afterglow that such blasts leave behind, with that visible light being useful to find where the blast has come from.
But those researchers instead found something else entirely: that the blast appeared to have come from a kilonova. Those rare events only happen when a neutron star merges with another very compact object – either another neutron star or a black hole.
The study challenges our understanding of where such long-lasting GRBs come from. But it could also provide an exciting way to answer other questions about the universe, such as where its heaviest elements come from, which still remains a mystery.
And the galaxy from which the GRB came from is also strange. It is young and still forming stars – the opposite of the only other known nearby galaxy that has played host to such an event.
“This event looks unlike anything else we have seen before from a long gamma-ray burst,” said Jillian Rastinejad, from Northwestern University, who led the study. “Its gamma rays resemble those of bursts produced by the collapse of massive stars.
Given that all other confirmed neutron star mergers we have observed have been accompanied by bursts lasting less than two seconds, we had every reason to expect this 50-second GRB was created by the collapse of a massive star. This event represents an exciting paradigm shift for gamma-ray burst astronomy.”
A paper describing the findings, ‘A kilonova following a long-duration gamma-ray burst at 350 Mpc’, is published in the journal Nature today.
The blast was first spotted in December 2021, by Nasa’s Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope. Since then, researchers have been looking to categorise the explosion, and understand where it might have come from.
Among other findings, they showed that the one event produced heavy elements that amounted to roughly 1,000 times the mass of our Earth. That suggests that kilonovae are the main place that gold is produced in the universe.
And because the galaxy from which the GRB came from is relatively nearby, scientists were able to get an unusually good look at it. What’s more, that could help explain other gamma-ray bursts that do not seem to fit with our understanding of where they come from.
“This was a remarkable GRB,” said Benjamin Gompertz. “We don’t expect mergers to last more than about two seconds. Somehow, this one powered a jet for almost a full minute. It’s possible the behaviour could be explained by a long-lasting neutron star, but we can’t rule out that what we saw was a neutron star being ripped apart by a black hole.
“Studying more of these events will help us determine which is the right answer and the detailed information we gained from GRB 211211A will be invaluable for this interpretation.”
And scientists hope that the switch-on of the James Webb Space Telescope will get an even better view of kilonovae. That telescope is able to capture images of distant astronomical objects, and “sniff” their atmosphere, allowing it to see exactly what elements are present through a process known as spectroscopy.
“Unfortunately, even the best ground-based telescopes are not sensitive enough to perform spectroscopy,” Rastinejad said. “With the JWST, we could have obtained a spectrum of the kilonova. Those spectral lines provide direct evidence that you have detected the heaviest elements.”
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