 |
| Gamma ray burst. |
The James Webb Space Telescope has discovered the
cause of the most powerful cosmic explosion since the Big Bang.
The explosion (nicknamed the BOAT or "brightest
of all time") is a gamma-ray burst (GRB) that spat photons at Earth with
more energy than those found inside the Large Hadron Collider. This light was
detected by telescopes in orbit and on the ground on October 9, 2022, and came
from 2.4 billion light-years away in the constellation Sagitta.
Now, a team of scientists have tracked down BOAT's
likely origins to a gigantic supernova that came after the collapse of a giant
star.
Yet their research reveals a new mystery —
supernovas such as the one behind the BOAT are supposed to be cosmic factories
for heavy elements such as platinum and gold, but when the researchers looked,
they found no evidence for them. The scientists published their findings April
12 in the journal Nature Astronomy.
"When we confirmed that the GRB was generated
by the collapse of a massive star, that gave us the opportunity to test a
hypothesis for how some of the heaviest elements in the universe are
formed," lead study author Peter Blanchard, an astrophysicist at
Northwestern University, said in a statement. "We did not see signatures
of these heavy elements, suggesting that extremely energetic GRBs like the BOAT
do not produce these elements.
“That doesn't mean that all GRBs do not produce
them,” Blanchard added, “but it's a key piece of information as we continue to
understand where these heavy elements come from."
When a massive star runs out of fuel, it collapses
before exploding outward in a gigantic supernova explosion, leaving behind an
ultra-dense neutron star or a black hole. It is these stellar explosions — and
occasionally even collisions between two neutron stars — that produce powerful
bursts of gamma rays that can be picked up by observatories in space and even
on Earth.
 |
| How the Swift observatory saw the gamma-ray burst GRB221009A, which may be the most energetic emission of this kind ever seen by astronomers. |
The first gamma-ray bursts were detected
accidentally by US military satellites in the 1960s. Since then, they have
continued to ping up on equipment that is able to detect their high-energy
light. But when the BOAT appeared, it was at least 10 times brighter than any
other cosmic explosion ever witnessed.
"The event produced some of the highest-energy
photons ever recorded by satellites designed to detect gamma rays,"
Blanchard said. "This was an event that Earth sees only once every 10,000
years.”
The burst was so bright, in fact, that the
astronomers had to wait six months for it to die down before they could use the
James Webb Space Telescope to look at it directly.
"The GRB was so bright that it obscured any
potential supernova signature in the first weeks and months after the
burst," Blanchard said. "At these times, the so-called afterglow of
the GRB was like the headlights of a car coming straight at you, preventing you
from seeing the car itself. So, we had to wait for it to fade significantly to
give us a chance of seeing the supernova."
After pointing the JWST's Near Infrared Spectrograph
(NIRSpec) instrument towards the source of the explosion, the researchers found
signatures of elements such as oxygen and calcium, which are commonly found within
supernovas. But they didn't find any elements heavier than iron among the
debris, potentially ruling out bright explosions such as the BOAT as heavy
metal producers.
And surprisingly, despite the extreme brightness of
the gamma-ray burst, the supernova it came from was of fairly average
brightness. It's possible, according to the researchers, that the BOAT acquired
its extraordinary intensity from the exploding star's material being funneled
along an unusually narrow relativistic jet — a near-light-speed stream of
charged matter.
"It's like focusing a flashlight's beam into a
narrow column, as opposed to a broad beam that washes across a whole
wall," co-author Tanmoy Laskar, an assistant professor of physics at the
University of Utah, said in the statement. "In fact, this was one of the
narrowest jets seen for a gamma-ray burst so far, which gives us a hint as to
why the afterglow appeared as bright as it did. There may be other factors
responsible as well, a question that researchers will be studying for years to
come."
The researchers say their next steps will be to use
the JWST to look at other supernovas. Contrasting their different brightnesses,
jets, chemical elements and host galaxy characteristics could help them figure
out just how unusual the BOAT was, and the conditions under which the
universe's heavy elements are made.
0 Comments