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Arizona researchers work to solve mysteries of ‘brightest of all time’ gamma burst

By Nicholas Gerbis
Published: Thursday, March 30, 2023 - 4:27pm
Updated: Friday, April 7, 2023 - 11:08am

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NASA/Swift/Cruz deWilde.
As a star explodes, the narrow beam (white) of gamma rays is emitted first, followed by the wider beam (purple).

On Oct. 9, an unusually narrow and staggeringly bright jet of energy swept through our solar system.

The Astrophysical Journal Letters this month published a series of research papers focused on the event, a gamma ray burst called GRB 221009A and nicknamed the BOAT, or “brightest of all time.”

Researchers say it’s a once-in-10,000-year event — the brightest in the history of human civilization. For GRBs, which already top the list as the most energetic explosions since the Big Bang, that’s saying something.

“It was so energetic that some of our detectors got saturated, so we couldn't really get the data,” said co-author Manisha Shrestha, a postdoc at UA’s Steward Observatory.

The observatory’s Large Binocular Telescope on Mount Graham contributed to the observations, as did the MMT on Mount Hopkins.

Hear Manisha Shrestha discuss the gamma ray burst with host Lauren Gilger on The Show

Located 1.9 billion light years away, the BOAT is raising many questions.

“It is changing a lot of ways we theoretically explain these objects in general,” said Shrestha.

GRBs flash brightly then quickly dim, lasting ten milliseconds to several hours, with 2 seconds marking the division between long and short GRBs.

Long-lived bursts typically spawn from cataclysmic star explosions that birth black holes. Energy from such supernovae also heat and ionize gas and dust in the interstellar medium, creating a longer-lasting afterglow that spans the electromagnetic spectrum, from gamma to radio waves.

Yet scientists so far have found no evidence of such a supernova — or of the neutral subatomic particles called neutrinos that typically carry away much of the explosion’s energy.

“We cannot say for sure that there was no supernova, because it could be hidden under this bright afterglow,” said Shrestha. “But we definitely don't see a very clear sign of supernova that we have seen previously in other long gamma ray bursts.”

NASA's Goddard Space Flight Center.
In the most common type of gamma-ray burst, the core of a massive star collapses, forming a black hole that sends a jet out into space at near the speed of light, where radiation across the spectrum arises from hot ionized gas, forming an afterglow.

Short-duration GRBs form when neutron stars collide. Such mergers also produce gravitational waves like the ones detected in August 2017 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer.

Having the GRB occur nearby (in astronomical terms) and swing through our solar neighborhood gives scientist an unprecedented chance to better understand such phenomena, build better models and solve lingering and emerging mysteries. This also marks the first time the James Webb Space Telescope has observed a GRB.

“It being so bright and so energetic, but also it being so close to us, gives us very good laboratory to study these objects,” said Shrestha.

Research continues, but the BOAT could help answer key questions about the structure of stars and the origins of heavy elements in the universe.

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