Astronomers Observe Potential First Superkilonova Event

On August 18, 2025, an unusual gravitational wave signal was detected by the LIGO detectors in Louisiana and Washington, along with Virgo in Italy. This signal indicated a merger between two astronomical objects, one of which was identified as being less massive than a typical neutron star. The event, initially designated ZTF 25abjmnps, was later renamed AT2025ulz by the International Astronomical Union Transient Name Server. Observations from the Zwicky Transient Facility (ZTF) revealed a rapidly fading red object located 1.3 billion light-years away, which exhibited characteristics similar to the previously observed kilonova GW170817.

Possible "Superkilonova" Exploded Not Once But TwicePossibly, the “superkilonova” exploded more than once

The AT2025ulz event has sparked debate among astronomers regarding its classification. While some researchers initially believed it to be a standard supernova, others, including Mansi Kasliwal from Caltech, suggested that it might represent a new category of cosmic explosion termed a "superkilonova." This hypothesis posits that the event could have resulted from a supernova that led to the formation of two neutron stars, which subsequently merged to create a kilonova. The initial observations showed the object glowing red, indicative of heavy elements like gold, before transitioning to a blue hue and displaying hydrogen in its spectrum, suggesting a supernova rather than a kilonova.

Discover MagazineScientific AmericanPossibly, the “superkilonova” exploded more than once

The presence of a neutron star with a mass less than that of the Sun raises questions about its formation. Theoretical models propose two scenarios: one involves a rapidly spinning massive star undergoing fission during a supernova, resulting in two smaller neutron stars. The other scenario, known as fragmentation, suggests that a disk of material forms around a collapsing star, leading to the creation of a tiny neutron star. Brian Metzger of Columbia University has indicated that the detection of such sub-solar neutron stars could provide insights into the formation of superkilonovae.

Possibly, the “superkilonova” exploded more than oncePossible "Superkilonova" Exploded Not Once But TwiceDiscover Magazine

The implications of the AT2025ulz event are significant, as it may represent the first observation of a superkilonova, a phenomenon that combines characteristics of both supernovae and kilonovae. However, researchers caution that more evidence is needed to confirm this theory. Future observations from advanced telescopes, including NASA's Nancy Roman Space Telescope and the Vera Rubin Observatory, will be crucial in identifying additional kilonova events and testing the superkilonova hypothesis.

Possibly, the “superkilonova” exploded more than once

David Reitze, executive director of LIGO, remarked on the intriguing nature of the event, stating, "While not as highly confident as some of our alerts, this quickly got our attention as a potentially very intriguing event candidate." Kasliwal emphasized the need for further investigation, noting, "We do not know with certainty that we found a superkilonova, but the event nevertheless is eye-opening."

Possibly, the “superkilonova” exploded more than once

There remains some disagreement within the astronomical community regarding the classification of AT2025ulz, with some researchers asserting it is a typical supernova rather than a kilonova. The lack of definitive evidence for the superkilonova theory highlights the need for ongoing research and observation.

Possibly, the “superkilonova” exploded more than once

• “The only way theorists have come up with to birth sub-solar neutron stars is during the collapse of a very rapidly spinning star,” — Brian Metzger, Columbia University

Possible "Superkilonova" Exploded Not Once But Twice

• “and when we attempt to unlock its mysteries, we should do so with eyes wide open!” — Mansi Kasliwal, Caltech

Scientific American