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An unusual bright burst of light detected by multiple telescopes in December 2021 was the result of a rare cosmic explosion that created a wealth of heavy elements such as gold and platinum.
The gamma-ray burst, called GRB 211211A, lasted about a minute. Gamma-ray bursts are considered among the strongest and brightest explosions in the universe and can last from milliseconds to several hours.
The duration of the burst hinted that it was caused by the explosion of a massive star as it died in a supernova. But the aftermath of the gamma-ray burst was weak and faded faster than those created by supernovae, and astronomers analyzing the event also saw excess infrared light.
“There are a lot of objects in our night sky that are rapidly fading,” said Wen-fai Fong, assistant professor of physics and astronomy at Northwestern University’s Weinberg College of Arts and Sciences and lead author and co-author of one of four studies published on the event Wednesday in the journal Nature Astronomy.
“We imagine a source in different filters to get color information, which helps us determine the identity of the source. In this case, the red color prevailed and bluer colors faded faster. This color shift is a telltale signature of a kilonova, and kilonovae can only come from neutron star mergers.
Kilonovas are rare, massive explosions caused by the catastrophic collisions between neutron stars, which are the incredibly dense remnants of exploded stars., or collisions between neutron stars and black holes.
After determining that a kilonova created infrared light, astronomers became even more perplexed by gamma-ray bursts duration. The gamma-ray bursts caused by these rare explosions have only ever been observed for less than two seconds, but this signal lasted for at least a minute.
“When we tracked this long gamma-ray burst, we expected it to lead to evidence of a massive star collapse,” Fong said. “Instead, what we found was very different. When I entered the field 15 years ago, it was set in stone that long gamma-ray bursts originated from massive star collapses. This unexpected discovery not only represents a major shift in our understanding, but also opens up an exciting new window of discovery.
Neutron stars are compact cosmic objects, so researchers didn’t expect them to contain enough matter to create a gamma-ray burst that could last nearly a minute.
The explosion occurred in a galaxy about 1 billion light-years from Earth. Since the event happened relatively close, astronomically speaking, astronomers used multiple telescopes to glean unprecedented detail.
“We found that this single event produced about 1,000 times the mass of Earth in very heavy elements. This supports the idea that these kilonovae are the main gold factories in the Universe,” said Dr Matt Nicholl, associate professor at the University of Birmingham in the UK and co-author of one of the studies on the astronomy of nature, in a press release.
The newly observed features of this event change the way astronomers understand gamma-ray bursts, or GRBs.
“Such a peculiar GRB was the first of its kind ever detected,” said Bing Zhang, professor of astrophysics at the University of Nevada, Las Vegas and co-author of one of the nature astronomy studies. in a report. “This finding has not only challenged our understanding of the origins of GRBs, (but) it also forces us to consider a new model for how certain GRBs form.”
Zhang’s team believe the unique nature of the burst may have resulted from a likely collision between a neutron star and a white dwarf, or the size of Earth. remnant that emerges when low-mass stars die.
The event also helped answer some questions about the creation of the heaviest elements in the universe.
“Kilonovae are fueled by the radioactive decay of some of the heaviest elements in the universe,” said Jillian Rastinejad, a doctoral student in astronomy at Northwestern and first author of one of the nature astronomy studies. “But kilonovae are very difficult to observe and fade very quickly. Now we know that we can also use long gamma-ray bursts to look for more kilonovae.
The James Webb Space Telescope will allow astronomers to search for emissions from kilonovae using spectroscopy or by measuring different wavelengths of light.
“Unfortunately, even the best ground-based telescopes aren’t sensitive enough to perform spectroscopy,” Rastinejad said. “With the (Webb telescope), we could have obtained a spectrum of the kilonova. These spectral lines provide direct evidence that you have detected the heaviest elements.
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