“Last year, a team of astronomers made a blockbuster claim, saying they had captured the most distant cosmic explosion ever — a gamma ray burst in a galaxy called GN-z11,” reports Science magazine.
“But that flash of light — supposedly from the most distant galaxy known — has a far more prosaic explanation: It was a glinting reflection from a tumbling, spent Russian rocket that happened to photobomb observers at just the right moment, two new studies claim…”
Although they happen all the time, the chances of catching one when a telescope is pointed at a particular galaxy are quite slim. So it was even more surprising when astronomer Linhua Jiang of Peking University and colleagues claimed — using data from the W. M. Keck Observatory in Hawaii — to find a burst coming from GN-z11, a galaxy dating back to a mere 420 million years after the big bang. Indeed, the team itself reported in December 2020 that the odds of catching such a burst were one in 10 billion.
Those odds raised red flags for Charles Steinhardt, an astronomer at the University of Copenhagen. “You start asking,” he says, “‘Are there any other causes that are more likely?'”
That’s where the Russian rocket comes in. Humans have launched and left behind large numbers of objects in orbit around Earth, including satellites, rocket boosters, and even screwdrivers gone missing during spacewalks. Up to half a million bits of metal larger than 1 centimeter are thought to be tumbling around our planet. Glints of sunlight reflecting off this debris could be responsible for as many as 10,000 flashes of light per hour throughout the night sky, estimates Eran Ofek, an astrophysicist at the Weizmann Institute of Science who has published independent analyses of this phenomenon. The vast majority are invisible to the naked eye, he says, but they can be discernable to astronomical observatories.
Given such potential light pollution, the possibility of finding a debris glint in a random telescope image is somewhere between one in 1000 and one in 10,000, Steinhardt and his collaborators calculate in one of the new studies, published today in Nature Astronomy. That seems more likely than the one-in-10-billion chance of a gamma ray burst, Steinhardt says. “If you have to pick between the two answers, yes they’re both unlikely, but one of them is millions of times more likely.”
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