Leicester researchers shed new light on extragalactic event

Space scientists in Leicester have made exciting new discoveries about an event which began outside of our galaxy.

Experts from the University of Leicester and its £100 million science and innovation park, Space Park Leicester, have shed new light on our understanding of an extragalactic burst of X-rays known as an Fast X-ray Transient (FXT).

The scientists have examined an FXT called EP250108a and have discovered it is the result of a massive star exploding.

Their research has been made possible by discoveries made by the Liverpool Telescope and the Einstein Probe which is equipped with a new generation of X-ray instruments with high sensitivity and a very wide view. Before the Einstein Probe’s launch last year, the quality and capability of its Wide-Field X-ray Telescope were tested by a team of space scientists from the University of Leicester, and it is now surveying the sky for some of the universe’s most extreme and elusive explosions.

Dr Robert Eyles-Ferris and Professor Paul O’Brien, of Space Park Leicester and the University of Leicester’s School of Physics and Astronomy, have been involved in two new papers on the FXT.

Dr Eyles-Ferris, who was the lead author on one of the papers, said: “FXTs are bursts of X-rays, tens to thousands of seconds in length, that have traditionally been very hard to detect and have unclear origins.

“However, the new Einstein Probe mission, which has Leicester involvement, and its Wide-field X-ray Telescope allow the discovery and follow-up of these transients in real time.

“My follow-up program on the 2m Liverpool Telescope identified the optical counterpart to EP250108a and our multinational team have conducted an extensive study into the object.

“Our observations and modelling show EP250108a is the result of a massive star exploding. Often such stellar explosions produce relativistic jets, columns of matter travelling at close to the speed of light which produce gamma-ray bursts.

“However, in this case, the jet was trapped by the outer layers of the star or the dense matter surrounding it resulting in a ‘cocoon’, the FXT and a ‘blue’ optical transient.”

Professor O’Brien, who is a professor of Astrophysics and Space Science, added: “This is a great example of how combining the power of space and ground facilities reveals the complexity of a powerful object.

“Einstein Probe found the source using X-rays, enabling a search for the optical light using the Liverpool Telescope, which precisely located it on the sky, enabling a detailed exploration of these unique phenomena.”

Professor O’Brien and Dr Eyles-Ferris have also contributed to a companion paper, looking at the supernova that followed the FXT, which has been led by Jillian Rastinejad, of Northwestern University in the US.

She said: “Once we realised how nearby this FXT was in the nearby Universe, our large, international team jumped to observe its supernova with several large telescopes around the world and in space, including the James Webb Space Telescope.

“Thanks to this coordinated observational effort, we’re able to say what type of star created the FXT and what the star was doing in the final stages of its life, pushing our understanding of the spectacular ways that stars can explode.”

The papers can be read at EP 250108a/SN 2025kg: Observations of the most nearby Broad-Line Type Ic Supernova following an Einstein Probe Fast X-ray Transient and The kangaroo’s first hop: the early fast cooling phase of EP250108a/SN 2025kg

Main image: Discovery images of EP250108a.