Dying stars can emit a powerful jet of radiation, as seen in an artist’s impression
Stocktrek Images, Inc./Alamy
Astronomers believe they have witnessed a previously unseen type of explosion from a dying star, known as a dirty fireball, which could provide insights into the death of massive stars.
As massive stars exhaust their fuel, they can collapse and explode in various ways. If the collapse results in a black hole, a powerful jet of radiation may pierce the star, producing a burst of high-energy light called a gamma ray burst.
These gamma ray bursts rank among the universe’s most powerful explosions, capable of emitting as much energy in a single blast as smaller stars, like the sun, release throughout their entire lifetimes. However, the exact mechanics of these events and how they differ among massive stars remain unclear to astronomers.
Physicists have suggested that if a jet is contaminated with heavy matter from the star, such as protons and neutrons, it might slow down and emit X-rays instead of gamma rays. This “dirty fireball” hypothesis had not been observed until now.
Xiang-Yu Wang from Nanjing University in China and his team have detected an X-ray flash named EP241113a that aligns with the dirty fireball model, using the new Einstein Probe space telescope.
Wang’s team observed a light flash from a galaxy approximately 9 billion light years away, which carried energy comparable to a gamma ray burst, but in X-ray form. The initial burst faded to a glow that persisted for several hours before gradually dissipating, similar to a typical gamma ray burst.
“It’s a very exciting prospect,” remarked Rhaana Starling from the University of Leicester, UK. “[Dirty fireballs] have been theorised to exist since the 90s, but there hasn’t really been any compelling evidence for them.”
Starling noted that while many gamma ray bursts have been recorded, this particular event seems distinct. It may involve a black hole or neutron star interacting with the jet in a unique way. “If it’s a black hole, then we are able to then get a more complete picture of black hole formation across the universe,” she explained.
According to Gavin Lamb at Liverpool John Moores University, UK, this discovery suggests that the gamma ray bursts we commonly observe might represent an observational bias. There could be many more similar or weaker events. “There could well be a continuum that goes right the way down to no jets,” he stated.
However, Om Sharan Salafia at Brera Astronomical Observatory in Italy expressed caution. He emphasized the need to confirm whether the explosion truly originated from a galaxy as distant as Wang’s team suggests. “If all of this holds, then indeed, this transient is a bit puzzling,” he commented.
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