Scientists believe the gamma-ray emission, which lasted over 300 seconds, is the birth cry of a black hole, formed as the core of a massive and rapidly spinning star collapses under its own weight.
From: Harvard-Smithsonian Center for Astrophysics
March 28, 2023 -- 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
appears today in the Astrophysical Journal Letters, observations of
GRB 221009A spanning from radio waves to gamma-rays, including critical
millimeter-wave observations with the Center for Astrophysics | Harvard &
Smithsonian's Submillimeter Array (SMA) in Hawaii, 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.
"This burst, being
so bright, provided a unique opportunity to explore the detailed behavior and
evolution of an afterglow with unprecedented detail -- we did not want to miss
it!" says Edo Berger, professor of astronomy at Harvard University and the
CfA. "I have been studying these events for more than twenty years, and
this one was as exciting as the first GRB I ever observed."
"Thanks to its
rapid-response capability, we were able to quickly turn the SMA to the location
of GRB 221009A," says SMA project scientist and CfA researcher Garrett
Keating. "The team was excited to see just how bright the afterglow of
this GRB was, which we were able to continue to monitor for more than 10 days
as it faded."
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."
One possibility, says
Cendes, is that the powerful jet produced by GRB 221009A is more complex than
in most GRBs. "It is possible that the visible and X-ray light are
produced by one portion of the jet, while the early millimeter and radio waves
are produced by a different component."
"Luckily, this
afterglow is so bright that we will continue to study its radio emission for
months and maybe years to come," adds Berger. "With this much longer
time span we hope to decipher the mysterious origin of the early excess
emission."
Independent of the
exact details of this particular GRB, the ability to respond rapidly to GRBs
and similar events with millimeter-wave telescopes is an essential new
capability for astronomers.
"A key lesson from
this GRB is that without fast-acting radio and millimeter telescopes, such as
the SMA, we would miss out on potential discoveries about the most extreme
explosions in the universe," says Berger. "We never know in advance
when such events will occur, so we have to be as responsive as possible if
we're going to take advantage of these gifts from the cosmos."
https://www.sciencedaily.com/releases/2023/03/230328145539.htm
No comments:
Post a Comment