UCD astronomers co-lead discovery of mysterious never-before-seen cosmic explosion
11 September 2025
The orange dot at the centre of this image, taken with the ESO’s Very Large Telescope, is a powerful gamma-ray burst nested within another galaxy Credit: ESO/A. Levan, A. Martin-Carrillo et al.
A gamma-ray explosion unlike any discovered before has been observed by an international team of researchers, including astronomers from the UCD School of Physics.
Telescopes on Earth and in space detected an unusual series of repeated gamma-ray bursts from outside the Milky Way galaxy over the course of a day.
Gamma-ray bursts (GRB) are among the most powerful explosions in the universe, and are normally caused by the catastrophic destruction of stars but no known scenario can completely explain the long and recurrent explosion observed in July.
“This event is unlike any other seen in 50-years of GRB observationsm” said UCD’s (opens in a new window)Dr Antonio Martin-Carrillo, who co-led a study on the signal published in (opens in a new window)The Astrophysical Journal Letters.
“GRBs are catastrophic events so they are expected to go off just once because the source that produced them does not survive the dramatic explosion. This event baffled us not only because it showed repeated powerful activity but also because it seemed to be periodic, which has never seen before.
“If a massive star – about 40 times the mass of the Sun – had died, like in typical GRBs, then it had to be a special type of death where some material kept powering the central engine.
“Alternatively, the periodicity of the flashes of gamma-ray radiation could be caused by a star being ripped apart by a black hole, a phenomenon known as a tidally disruption event (TDE).
“However, unlike more typical TDEs, to explain the properties of this explosion would require an unusual star being destroyed by an even more unusual black hole, likely the long-sought ‘intermediate mass black hole’. Either option would be a first, making this event extremely unique.”
The unusual signal, GRB 250702B, was first detected on 2 July by NASA’s Fermi Gamma-ray Space Telescope, which picked up three separate bursts from the same source within hours.
Data from the Einstein Probe, an X-ray mission led by the Chinese Academy of Sciences with European partners, later revealed the source had been active nearly a day earlier.
This behaviour is highly unusual since these kinds of bursts normally last just minutes or even milliseconds.
"This is 100-1000 times longer than most GRBs,” said Andrew Levan, astronomer at Radboud University, The Netherlands, and co-lead author of the study.
With only an approximate location at first, the team used the European Southern Observatory’s Very Large Telescope (VLT) in Chile to track the source.
Observations with the VLT’s HAWK-I camera showed the explosion originated not in the Milky Way galaxy but in a more distant one.
To learn more about the unusual GRB, Dr Martin-Carrillo and his colleagues continue to monitor the aftermath of the explosion with different telescopes and instruments, including the VLT’s X-shooter spectrograph and the James Webb Space Telescope, a joint project of NASA, ESA and the Canadian Space Agency.
“We are still not sure what produced this, but with this research we have made a huge step forward towards understanding this extremely unusual and exciting object,” he added.
By: David Kearns, Digital Journalist / Media Officer, UCD University Relations (with materials from Caroline Byrne, UCD Research and Innovation)
To contact the UCD News & Content Team, email: newsdesk@ucd.ie
