Dying stars can emit a powerful stream of radiation, as seen in an artist’s impression
StockTrek Images, Inc./ Alamy
Astronomers believe they have seen for the first time a type of explosion produced by a dying star called a dirty fireball, and it could help us understand how massive stars die.
When a massive star runs out of fuel, it can collapse and explode in a number of ways. If a black hole is produced in the collapse, an extremely powerful jet of radiation can burst through the star, producing a flash of high-energy light called a gamma ray burst.
These explosions are among the most powerful in the universe and can emit energy equal to the total lifetime of small stars like the Sun in a single beam. But astronomers still don’t know exactly how this process works or how variations between different giant stars affect the jet.
Physicists have hypothesized that if the jet somehow becomes contaminated with the star’s heavier matter, such as protons and neutrons, we might see something different. These particles would act as a sponge, slowing down the jet and emitting X-rays instead of gamma rays. But until now, this “dirty fireball” scenario had not been seen.
Jiang-Yu Wang He and his colleagues at Nanjing University in China have now picked up a flash of X-rays called EP241113A that fits the picture of a dirty fireball, using a new space telescope called the Einstein Probe.
Wang and his team detected a flash of light from a galaxy about 9 billion light years away, with as much energy as a gamma ray burst, but in X-ray frequencies instead. The initial burst turned into a flare that lasted for several hours, before gradually fizzling out, similar to a typical gamma ray burst.
“It’s a very exciting prospect,” says Rana Starling At the University of Leicester, UK. “The existence of (dirty fireballs) has been believed since the ’90s, but there’s really no solid evidence for them.”
Starling says that while we know of thousands of gamma ray bursts, the event that produced this burst is likely different from the others. For example, it could be a black hole or neutron star that is interacting with the jet in interesting physical ways. “If it is a black hole, we are able to get a more complete picture of black hole formation throughout the universe,” she says.
It also tells us that the gamma ray bursts we typically see may be an observational bias, and there may be more such ones, more numerous or weaker, say. gavin lamb at Liverpool John Moores University, UK. “There may be a continuum that goes all the way down to the bottom without any jets.”
However, we can’t be sure yet that this is a dirty fireball Om Sharan Salafia At the Brera Astronomical Observatory in Italy. First, we need to establish whether the explosion actually came from a galaxy as Wang and his team claim. “If all this is true, then actually, this momentary one is a little disturbing,” he says.
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