Scientists may have spotted a remarkable cosmic event: a dying star that split and then merged again, leading to a unique explosion. This event, known as AT2025ulz, combines elements of two well-known cosmic blasts—supernovas and kilonovas.
In typical scenarios, massive stars die with a spectacular supernova explosion, scattering elements like carbon and iron throughout the universe. On the other hand, kilonovas occur when neutron stars, the remnants of collapsed stars, collide. These collisions can create even heavier elements, including gold.
AT2025ulz seems to be a rare occurrence that merges both types of explosions, a phenomenon scientists have speculated about but never witnessed before. If validated, it could be the first recorded instance of a “superkilonova,” where one object produces two powerful explosions.
Mansi Kasliwal from Caltech, who led the study, emphasizes that while it’s uncertain if they truly discovered a superkilonova, the findings are exciting. These observations were detailed in a study published in The Astrophysical Journal Letters.
The event caught the attention of astronomers on August 18, 2025. Gravitational wave detectors, operated by LIGO and its European counterpart, detected a faint signal suggesting the merger of two compact objects. Shortly after, the Zwicky Transient Facility observed a rapidly fading red light in the same area, indicating a fresh source of heavy elements like gold and platinum.
Unlike expected, AT2025ulz started to brighten again. Further observations showed light shifting to bluer wavelengths, revealing hydrogen—a sign of a supernova. This prompted researchers to conclude that the massive star had lost most of its hydrogen layers before the explosion.
To understand this unusual sequence, scientists proposed that a fast-spinning star collapsed and exploded as a supernova. Instead of forming one neutron star, its core split into two, which then merged, triggering a kilonova amidst the expanding debris of the supernova.
The gravitational wave data offers more clues. Researchers noted a 99% chance that at least one of the merging neutron stars was less massive than the sun. This challenges existing theories about neutron stars, which generally can’t weigh under 1.2 solar masses. This result suggests a link to very rapidly spinning stars undergoing collapse.
While these findings are fascinating, the complexity of the data makes it hard to conclude whether these signals come from one event or multiple nearby incidents. Future research and next-gen sky surveys, like those from the Vera C. Rubin Observatory, might uncover more similar events.
Experts believe if superkilonovae exist, we will discover more of them soon. Tracking patterns in such events could redefine our understanding of stellar evolution. As Antonella Palmese from Carnegie Mellon University puts it, “If we keep finding associations like this, then maybe this was the first.”
For more on cosmic explosions, you can check studies from NASA and the European Space Agency on their sites and ESA.
