We may have seen the explosion of a “dirty fireball” star for the first time.

Astronomers believe they have seen for the first time a type of explosion created 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 several ways. If the collapse creates a black hole, an extremely powerful beam of radiation can shoot through the star, creating a burst of high-energy light called a gamma-ray burst.

These bursts are among the most powerful explosions in the universe and can emit energy equivalent to the total output of smaller stars like the Sun in a single beam. But astronomers still don’t know exactly how the process works or how variations between different massive stars affect the jet.

Physicists hypothesized that we might see something else if the jet somehow became contaminated with heavier matter from the star, such as protons and neutrons. These particles would act like a sponge, slowing down the current and causing it to emit X-rays rather than gamma rays. But until now, this “dirty fireball” scenario has not been observed.

Xiang Yu Wang at Nanjing University in China and his colleagues have now captured a burst of X-rays called EP241113a that matches the image 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, containing as much energy as a gamma-ray burst, but at X-ray frequencies instead. The initial explosion faded into a glow that lasted for several hours before gradually dying out, much like a typical gamma ray burst.

“It’s a very exciting prospect,” he says Rhaana Starling at the University of Leicester in the UK. “[Dirty fireballs] They have been theorized to exist since the 1990s, but in reality there has been no conclusive evidence for them.”

While we know of thousands of gamma-ray bursts, the event causing this burst is likely to be different from the others, Starling says. It could be, for example, a black hole or a neutron star that interacts with the jet in an interesting physical way. “If it is a black hole, then we are able to get a more complete picture of the formation of black holes in the universe,” he says.

It also shows us that the gamma-ray bursts we usually see may be an observational anomaly, and there may be many more of these or fainter ones, he says Gavin Lamb at Liverpool John Moores University, UK. “There could be a continuum that goes all the way down to no jets.

But we can’t be sure it’s a dirty fireball yet, he says Om Sharan Salafia at the Brera Astronomical Observatory in Italy. First, we need to find out if the explosion really came from a galaxy as far away as Wang and his team claim. “If all of this is true, then this transient phenomenon is a bit puzzling,” he says.

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