by Using the James Webb Space Telescope (JWST), scientists have finally solved the mysterious origin of the “BOAT”, possibly the biggest cosmic explosion since the Big Bang.
A supernova explosion appears to have launched the brightest gamma-ray burst ever (hence the acronym The Brightest Of All Time), or the BOAT, which was accompanied by the death and collapse of a massive star some 2.4 million light years away. taking place. This event probably also gave birth to a black hole.
By solving this cosmic mystery, however, the team of astrophysicists has opened up another celestial puzzle. That’s because traces of heavy elements like gold and platinum, traces that would be expected to linger around a supernova of this type, are nowhere to be found.
“This was an event that Earth only sees once every 10,000 years,” Peter Blanchard, team leader and Northwestern University scientist, said in a statement. “The event produced some of the highest energy photons ever recorded by satellites designed to detect gamma rays.”
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“Once we confirmed that the GRB was generated by the collapse of a massive star, it allowed us to test a hypothesis about how some of the heaviest elements in the universe are formed,” said Blanchard. “We did not see signatures of these heavy elements, suggesting that highly energetic GRBs like the BOAT do not produce these elements.”
The scientists did not miss the BOAT
The BOAT, officially designated GRB 221009A, was first observed on October 9, 2022, and immediately stood out from other GRBs due to its extreme nature. Astronomers saw it as an extremely bright flash of high-energy gamma-rays followed by an after-glass decay over many wavelengths of light.
The powerful GRB was first observed by gamma-ray and X-ray telescopes, including NASA’s Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. After the BOAT was first detected, horrified astronomers raced to find its possible source. They pointed their telescopes towards the constellation Sagitta, believing that’s where the answer must be.
“As far as we have been able to detect GRBs, there is no question that this GRB is the brightest we have ever seen by a factor of 10 or more,” one of the discoveries of the BOAT Wen-fai Fong, professor associate of physics and astronomy and head of the Fong Group at Northwestern, around the time of the discovery.
Blanchard and his colleagues were in no rush to chase after BOAT, however.
Instead, they wanted to see the BOAT as it evolved, and track it during the later stages. So, they trained the JWST on the gamma-ray burst about six months after it was first observed.
“The GRB was so bright that it hid any possible 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 slow down a lot to give us a chance to see the supernova.”
Using JWST’s Near-Infrared Spectrograph (NIRSpec) instrument, Blanchard and his colleagues observed BOAT’s post-infrared glass. This revealed the signature of elements such as calcium and oxygen, all of which are characteristic of supernovas.
Surprisingly, however, even though the BOAT was the most powerful cosmic eruption of its kind ever seen, the supernova that created it actually appeared to be the average starburst death.
“It’s not brighter than previous supernovas. It looks fairly normal in the context of other supernovae associated with less energetic GRBs,” said Blanchard. “You might expect that the same collapsing star that produces a very energetic and bright GRB would also have an extremely energetic and bright supernova. But it turns out that’s not the case. This GRB is incredibly bright us, just a normal supernova.”
The team is currently unsure how a “normal” supernova could create such a massive energy explosion as the BOAT.
Team member and University of Utah assistant professor of physics, Tammoy Laskar, thinks that the extreme GRB could be the result of the shape and structure of near-light velocity jets sent by collapsing massive stars to form black holes. If a massive star is spinning rapidly when it collapses, then the beams it bursts out are narrow, more focused, and therefore brighter.
“It’s like focusing a flashlight beam into a narrow column, as opposed to washing a wide beam across an entire wall,” Laskar said. “In fact, this was one of the narrowest jets seen for a gamma-ray burst to date, which gives us a clue as to why the halo appeared so bright.
“Other factors may also be responsible, a question researchers will be studying for years to come.”
Furthermore, it is not another aspect of this supernova that will require much deeper investigation than what it has, but those things that seem to be missing.
The missing elements
The cores of stars are like stellar furnaces that combine light elements together to form progressively heavier elements. This process creates elements up to iron, but after that, even the biggest stars struggle to fuse heavier elements like gold and platinum.
For many years, scientists have suspected that these relatively heavier elements are created when very close dead stars, known as neutron stars, collide, and JWST has recently played a key role in such a theory to confirm.
But the researchers also thought that the extreme environments created around supernovae capable of launching GRBs could facilitate the “rapid capture” of neutrons, or the “e-process,” which creates elements like gold. The reason for this speculation is that neutron star collisions alone are too rare to create amounts of elements heavier than lead scientists see in the early universe.
“There is probably another source. It takes a very long time for binary neutron stars to merge. Two stars in a binary system must first explode to leave neutron stars behind. Then, it can take billions and billions of years to take for both neutrons. stars to slowly come closer and closer and finally merge,” said Blanchard. “But observations of very old stars show that parts of the universe were enriched with heavy metals before most binary neutron stars had time to merge.
“That’s telling us another channel.”
That other channel had theorized that a rapidly spinning giant star had collapsed, the exact type of event scientists have confirmed was the BOAT’s launch.
Using the JWST, the team was able to peer into the deep layers of this supernova, where elements heavier than iron should have formed. “Early starburst material is opaque, so you can only see the outer layers,” Blanchard said. “But when it expands and cools, it becomes transparent. Then, you can see the photons coming from the inner layer of the supernova. Moreover, different elements absorb and emit photons at different wavelengths, depending on their structure atomic, giving each element its unique spectral signature.”
That means looking at the spectrum of an object can tell astronomers what elements are present.
“When we examined the BOAT spectrum, we saw no signature of heavy elements, suggesting that extreme events like GRB 221009A are not primary sources,” Blanchard said. “This is critical information as we continue to try to figure out where the heaviest elements form.”
Blanchard adds that this does not mean that scientists should not give up studying the GRB channel of heavy element production just yet if heavy elements are not detected around the BOAT supernova source.
“That doesn’t mean all GRBs don’t produce them, but it’s a key piece of information as we continue to understand where these heavy elements come from,” he said. “Future observations with JWST will determine whether these features are produced by BOAT’s ‘normal’ cousins.”
In addition to learning more about the BOAT and confirming its origin with the JWST, the team was also able to detect the signature of an intense bout of star formation in the event’s host galaxy. This indicated that the star that died before the birth of the BOAT may have formed in a different environment than other supernova stars.
One aspect of this galaxy that may help further unravel the mysteries of the BOAT is that it appears to have a low concentration of elements heavier than hydrogen or helium, which astronomers have called “metals”.
“This is another unique feature of BOAT that may help explain its properties,” team member and Penn State University graduate student Yijia Li said in the statement.
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“We are fortunate to live in a time when we have the technology to detect these explosions that are happening around the globe,” Blanchard concluded. “It is so exciting to observe such a rare astronomical phenomenon as the BOAT and to work to understand the physics behind this exceptional event.”
The research was published on Friday (April 12) in the journal Nature Astronomy.
