On October 9, 2022, an intense pulse of gamma-ray radiation swept through our solar system, overwhelming gamma-ray detectors on numerous orbiting satellites, and sending astronomers on a chase to study the event using the most powerful telescopes in the world.
The new source, dubbed GRB 221009A for its discovery date, turned out to be the brightest gamma-ray burst (GRB) ever recorded.
In a new study that appeared in March, in The Astrophysical Journal Letters, has shed new light on the decades-long quest to understand the origin of these extreme cosmic explosions.
The gamma-ray emission from GRB 221009A lasted over 300 seconds. Astronomers think that such “long-duration” GRBs are the birth cry of a black hole, formed as the core of a massive and rapidly spinning star collapses under its own weight. The newborn black hole launches powerful jets of plasma at near the speed of light, which pierce through the collapsing star and shine in gamma-rays.
With GRB 221009A being the brightest burst ever recorded, a real mystery lay in what would come after the initial burst of gamma-rays. “As the jets slam into gas surrounding the dying star, they produce a bright ‘afterglow’ of light across the entire spectrum,” says Tanmoy Laskar, assistant professor of physics and astronomy at the University of Utah, and lead author of the study. “The afterglow fades quite rapidly, which means we have to be quick and nimble in capturing the light before it disappears, taking its secrets with it.”
As part of a campaign to use the world’s best radio and millimeter telescopes to study the afterglow of GRB 221009A, astronomers Edo Berger and Yvette Cendes of the Center for Astrophysics (CfA) rapidly gathered data with the SMA.
After analyzing and combining the data from the SMA and other telescopes all over the world, the astronomers were flummoxed: the millimeter and radio wave measurements were much brighter than expected based on the visible and X-ray light.
“This is one of the most detailed datasets we have ever collected, and it is clear that the millimeter and radio data just don’t behave as expected,” says CfA research associate Yvette Cendes. “A few GRBs in the past have shown a brief excess of millimeter and radio emission that is thought to be the signature of a shockwave in the jet itself, but in GRB 221009A the excess emission behaves quite differently than in these past cases.”
She adds, “It is likely that we have discovered a completely new mechanism to produce excess millimeter and radio waves.”
In 2005 an explosion 50,000 light years away, on the other side of the galaxy, was characterized at the time as the largest of it kind ever seen on Earth. If it had been just 10 light years away it could have caused mass extinctions and severely damaged our atmosphere. As it was, the blast was more than 100 times more powerful than any previous explosion ever recorded. The exploding neutron star is called a magnestar for its intense magnetic fields. No bigger than a large Earth city, the explosion was said to produce more energy in a tenth of a second than our own sun turns out in 100,000 years.
Fortunately, scientists say, there are no such magnestars within 4,000 light years of Earth. Some scientists, like astrophysicist Paul LaViolette (whose work has been outlined in Atlantis Rising Magazine) have argued that catastrophic events in Earth’s history may have been the result of of just such stellar explosions (https://www.cambridge.org/core/journals/radiocarbon/article/evidence-for-a-solar-flare-cause-of-the-pleistocene-mass-extinction/799A4720B75245B4627AFE412661B3B6).
AR #114
Is Anybody Home
by Martin Ruggles
