Astronomers witness a star’s failed death

In a cosmic twist worthy of a sci-fi thriller, astronomers have just caught a massive star in the act of dying, not with a bang, but with a stifled X-ray-powered whisper.

Using a global network of telescopes, including the International Gemini Observatory and the SOAR Telescope in Chile, astronomers have observed the closest-ever example of a mysterious cosmic event called a fast X-ray transient (FXT). This particular flash, named EP 250108a, was spotted in January 2025 by the newly launched Einstein Probe, and it’s helping astronomers rewrite the story of how stars die.

FXTs are brief, powerful bursts of X-rays from distant galaxies that last just seconds to hours. They’ve puzzled astronomers for years, until now. EP 250108a, located a mere 2.8 billion light-years away (close by cosmic standards), gave scientists their best look yet.

Once the Einstein Probe raised the alarm, telescopes around the world sprang into action. Gemini South’s FLAMINGOS-2 and Gemini North’s GMOS captured the event in infrared and optical light, revealing the glowing aftermath of a supernova.

Researchers detected the brightest gamma-ray burst

But this wasn’t your typical supernova. Instead of blasting jets of energy into space like a gamma-ray burst (GRB), this star’s jets got stuck inside, heating up the star’s outer layers and releasing X-rays in the process. Think of it as a cosmic pressure cooker.

“This FXT supernova is nearly a twin of past supernovae that followed GRBs,” said Rob Eyles-Ferris, lead author of one of two companion studies. “But here, the jets failed to escape.”

That failure turned out to be a scientific jackpot. By watching the event unfold over days and weeks, astronomers confirmed that the FXT was tied to a Type Ic broad-lined supernova, SN 2025kg, likely from a star 15–30 times the mass of our Sun.

“The X-ray data alone cannot tell us what phenomena created the FXT,” says Jillian Rastinejad, PhD student at Northwestern University and lead author of the second companion paper. “Our optical monitoring campaign of EP 250108a was key to identifying the aftermath of the FXT and assembling the clues to its origin.”

It takes two stars to make a gamma-ray burst

After the initial X-ray flash from EP 250108a, astronomers noticed the area getting brighter in optical light for a few weeks before fading. The light also showed special patterns, called broad absorption lines, that revealed the FXT was linked to a powerful kind of explosion known as a Type Ic broad-lined supernova.

To learn more, the team used the SOAR Telescope in Chile to observe the event in near-infrared light. These observations helped them estimate how bright the explosion got and what kind of star caused it.

Their best guess? A massive star weighing 15 to 30 times more than our Sun, a true cosmic heavyweight that ended its life with a dramatic if slightly muffled, bang

“Our analysis shows definitively that FXTs can originate from the explosive death of a massive star,” says Rastinejad. “It also supports a causal link between GRB-supernovae and FXT-supernovae, in which GRBs are produced by successful jets and FXTs are produced by trapped or weak jets.”

A super-bright stellar explosion gave birth to a compact object

FXTs are now being detected several times a month, while GRBs are rare, only about once a year. This suggests that “failed” jet explosions like EP 250108a may be far more common than their flashier cousins.

“This discovery opens a new window into how massive stars die,” said Jillian Rastinejad, co-author of the second study. “It shows that even when a star’s final act is muted, it still has a powerful story to tell.”

With the upcoming Vera C. Rubin Observatory set to launch its Legacy Survey of Space and Time, astronomers expect to uncover even more of these hidden stellar dramas. And thanks to the rapid-response power of observatories like Gemini, we’ll be ready to catch them in the act.

Journal References:

1. Rob A. J. Eyles-Ferris, Peter G. Jonker, Andrew J. Levan, Daniele Bjørn Malesani, Nikhil Sarin, Christopher L. Fryer, Jillian C. Rastinejad, Eric Burns, Nial R. Tanvir, Paul T. O’Brien, Wen-fai Fong, Ilya Mandel, Benjamin P. Gompertz, Charles D. Kilpatrick, Steven Bloemen, Joe S. Bright, Francesco Carotenuto, Gregory Corcoran, Laura Cotter, Paul J. Groot, Luca Izzo, Tanmoy Laskar, Antonio Martin-Carrillo, Jesse Palmerio, Maria E. Ravasio, Jan van Roestel, Andrea Saccardi, Rhaana L. C. Starling, Aishwarya Linesh Thakur, Susanna D. Vergani, Paul M. Vreeswijk, Franz E. Bauer, Sergio Campana, Jennifer A. Chacón, Ashley A. Chrimes, Stefano Covino, Joyce N. D. van Dalen, Valerio D’Elia, Massimiliano De Pasquale, Nusrin Habeeb, Dieter H. Hartmann, Agnes P. C. van Hoof, Páll Jakobsson, Yashaswi Julakanti, Giorgos Leloudas, Daniel Mata Sánchez, Christopher J. Nixon, Daniëlle L. A. Pieterse, Giavanna Pugliese, Jonathan Quirola-Vásquez, Ben C. Rayson, Ruben Salvaterra, Ben Schneider, Manuel A. P. Torres, Tayyaba Zafar. The kangaroo’s first hop: the early fast cooling phase of EP250108a/SN 2025kg. The Astrophysical Journal Letters. DOI: 10.48550/arXiv.2504.08886
2. J. C. Rastinejad (Northwestern), A. J. Levan, P. G. Jonker, C. D. Kilpatrick, C. L. Fryer, N. Sarin, B. P. Gompertz, C. Liu, R. A. J. Eyles-Ferris, W. Fong, E. Burns, J. H. Gillanders, I. Mandel, D. B. Malesani, P. T. O’Brien, N. R. Tanvir, K. Ackley, A. Aryan, F. E. Bauer, S. Bloemen, T. de Boer, C. R. Bom, J. A. Chacon, K. Chambers, T.-W. Chen, A. A. Chrimes, J. N. D. van Dalen, V. D’Elia, M. De Pasquale, M. D. Fulton, P. J. Groot, R. Gupta, D. H. Hartmann, A. P. C. van Hoof, M. E. Huber, L. Izzo, W. Jacobson-Galan, P. Jakobsson, A. Kong, T. Laskar, T. B. Lowe, E. A. Magnier, E. Maiorano, A. Martin-Carrillo, L. Mas-Ribas, D. Mata Sanchez, M. Nicholl, C. J. Nixon, S. R. Oates, G. Paek, J. Palmerio, D. Paris, D. L. A. Pieterse, G. Pugliese, J. A. Quirola Vasquez, J. van Roestel, A. Rossi, A. Rouco Escorial. R. Salvaterra, B. Schneider, S. J. Smartt, K. Smith, I. A. Smith, S. Srivastav, M. A. P. Torres, C. Ventura, P. Vreeswijk, R. Wainscoat, Y.-J. Yang, S. Yang. EP 250108a/SN 2025kg: Observations of the most nearby Broad-Line Type Ic Supernova following an Einstein Probe Fast X-ray Transient. Astrophysical Journal Letters. DOI: 10.48550/arXiv.2504.08889