Astronomers using China's Einstein Probe telescope have observed a powerful X-ray flash that matches the predicted signature of a 'dirty fireball,' a theorized explosion from a dying massive star. The event, labeled EP241113a, originated from a galaxy about 9 billion light years away. This detection could reveal new details about how massive stars end their lives.
Xiang-Yu Wang of Nanjing University in China and his team identified the X-ray flash EP241113a with the Einstein Probe. The burst carried energy comparable to a gamma-ray burst but emitted primarily in X-rays. It began with a bright flash that faded into a glow lasting several hours before gradually dimming, resembling aspects of typical gamma-ray bursts from collapsing stars that form black holes or neutron stars. The 'dirty fireball' model proposes that a jet of radiation from the collapsing star becomes contaminated with heavier particles like protons and neutrons from the star's material. These particles slow the jet, converting gamma rays into X-rays. Theorized since the 1990s, such events had not been confirmed until now. Rhaana Starling at the University of Leicester in the UK called it 'a very exciting prospect,' noting that dirty fireballs were hypothesized in the 90s without compelling evidence. Gavin Lamb at Liverpool John Moores University suggested this indicates a possible continuum of jet strengths, from powerful gamma-ray bursts to weaker or absent jets. Om Sharan Salafia at Brera Astronomical Observatory in Italy urged caution, emphasizing the need to verify the explosion's distance from the claimed galaxy. Confirmation would provide insights into black hole formation across the universe. The findings appear in a preprint on arXiv.