Jacinta Bowler
Last October, a dying star released a giant gamma-ray burst, directed right towards Earth.
The burst – now called GRB 221009A – is the brightest in thousands of years, and has allowed astronomers a once in 10,000 year chance to study this astronomical phenomenon.
“The exceptional brightness of this gamma-ray burst meant astronomers were able to study it in unprecedented detail in real-time as the light arrived from that distant galaxy,” says University of Sydney astrophysicist James Leung.
“This gave us a golden opportunity to test intricate physical models that describe what happens before, during and after the death of a star.”
Two new sets of papers – one by NASA and another from an international team, analysed the gamma-ray burst in great detail, finding that the burst was 70 times brighter than any seen before.
GRB 221009A’s signal was traveling for about 1.9 billion years before we could see it from Earth. This makes it among the closest-known ‘long’ gamma-ray bursts. Long in this case meaning lasting longer than two seconds, while GRB 221009A lasted a whopping 10 hours.
Astronomers think these bursts are a type of black hole ‘cry’ which form when a huge star collapses. As it quickly ingests the surrounding matter, the black hole blasts out jets in opposite directions containing particles accelerated to near the speed of light.
Oxford and Sydney University researchers – looked at the ‘reverse shock’ after the initial blast. This is the implosion that occurs at the same time as the explosion. They could map this reverse shock in ‘unprecedented detail’ for variables such as time, length, size and energy.
“Our observations provide unmatched insights into the reverse shock model for gamma-ray burst emission, showing it is very difficult for existing models to replicate the slow evolution of the energy peaks that we observed,” said Leung.
“This means we have to refine and develop new theoretical models to understand these most extreme explosions in the Universe.”
The NASA research looked at a number of other parts of the burst, but one in particular highlights an interesting question – where is the supernova?
After an explosion like this, researchers expect to see a supernova which brightens over the first couple of weeks.
However, this hasn’t yet happened.
“We cannot say conclusively that there is a supernova, which is surprising given the burst’s brightness,” said Andrew Levan, a professor of astrophysics at Radboud University in Nijmegen, Netherlands. “If it’s there, it’s very faint. We plan to keep looking, but it’s possible the entire star collapsed straight into the black hole instead of exploding.”
This could be because of where the gamma-ray burst happened, as thick dust clouds are in the area and could obscure the view of any light from a supernova.
The team is planning to take more Webb and Hubble observations in infrared over the next few months to check.
With such a rare and well captured gamma-ray burst, there’s likely to be much more science we can learn about over the next few years.
The international research is available on preprint server arXiv and has been submitted for publication in Nature Astronomy. The NASA research is part of a focus issue in the The Astrophysical Journal Letters.