Astronomers detected a gravitational-wave signal on August 18, 2025, that may indicate a second kilonova event, though its connection to a preceding supernova complicates interpretation.
Gravitational-wave alert triggered rapid multi-messenger follow-up
The Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Louisiana and Washington, along with the Virgo detector in Italy, recorded the signal within minutes and issued an alert to astronomers worldwide. The alert noted the likely origin was two merging objects, with at least one appearing less massive than a typical neutron star. David Reitze, executive director of LIGO and research professor at Caltech, said the alert quickly gained attention as a potentially intriguing candidate despite lower confidence than some prior alerts.
Optical observations revealed evolving characteristics over days
A few hours after the gravitational-wave detection, the Zwicky Transient Facility (ZTF) at Palomar Observatory identified a fading red source in the sky. Mansi Kasliwal, professor of astronomy at Caltech and director of the Palomar Observatory, noted that for about three days the emission resembled the 2017 kilonova GW170817 before shifting to appear more like a supernova. Her team’s analysis, published in The Astrophysical Journal Letters, suggests the event could represent a superkilonova — a kilonova triggered by a supernova — though no such event has been observed before.
Link to prior supernova raises questions about classification
AT2025ulz appears tied to a supernova that occurred just hours earlier, which may have obscured key details and made the event harder to interpret. While only one clear kilonova — GW170817 from 2017 — has been confirmed to date, this candidate could indicate a new class of cosmic explosions if the superkilonova hypothesis holds. Researchers continue to analyze the data to determine whether the signal originates from neutron star merger, supernova interaction, or another process entirely.
What is a kilonova and why is it significant?
A kilonova is an explosion resulting from the merger of two neutron stars, producing heavy elements like gold and uranium and emitting both gravitational waves and light.
How does AT2025ulz differ from the 2017 kilonova GW170817?
AT2025ulz initially resembled GW170817 but later showed supernova-like characteristics and may be linked to a preceding supernova, suggesting a possible new explosion type called a superkilonova.
