Astronomers might have just spotted a groundbreaking cosmic event: a “superkilonova.” On August 18, 2025, they detected gravitational waves suggesting this unique explosion occurred. A kilonova happens when two neutron stars collide, creating heavy elements like gold. Superkilonovas kick off with a supernova explosion that forms two neutron stars, which then merge, resulting in a massive release of energy and gravitational waves.
Previously, the only confirmed kilonova event was in 2017 when LIGO and Virgo detected the gravitational wave signal GW170817. Astronomers observed this event using various telescopes, marking a significant moment in astronomy. Following this, astronomers celebrated when LIGO and Virgo detected a new signal, labeled AT2025ulz, hinting at another neutron star merger about 1.3 billion light-years away. Initial observations made it look like a typical kilonova, but things quickly turned more complicated.
Mansi Kasliwal, an astronomy professor at Caltech, led a team that noticed the event’s light pattern changed. Instead of sticking to the kilonova signature, it began to look like a supernova. “We thought we were simply observing another kilonova,” she shared. “Then it changed, and we realized it could be something much more unique.” They suggested that the event emerged from a supernova, hinting at the existence of superkilonovas, a phenomenon theorized but never observed before.
Analysis from other observatories, including the W. M. Keck Observatory in Hawai’i, supported these findings: AT2025ulz emitted a burst of red light, akin to the earlier GW170817 event. This red glow indicates heavy elements blocked shorter wavelengths like blue light. However, as time passed, the light began to brighten, shifting the color spectrum to blue. This change suggests hydrogen emissions typical of supernovae, creating confusion over its classification.
Experts noting the detection acknowledged that a supernova 1.3 billion light-years away should not produce detectable gravitational waves. Kasliwal’s team focused on a vital clue: one of the neutron stars appeared less massive than expected. This suggests a merger of smaller neutron stars, leading to a possible kilonova event obscured by the supernova’s debris.
In normal star life, massive stars explode into supernovas, collapsing their cores into neutron stars. However, there are hypotheses about creating lighter neutron stars. One theory suggests a star could split into two lighter neutron stars during a rapid explosion — a process called fission. Another theory proposes that material around a newly formed neutron star could gather to create another neutron star, similar to how planets are born.
The challenge lies in accurately identifying these cosmic events. The data is still limited, and Kasliwal emphasized, “Future events might not match previous kilonova patterns. We need more observations.” New tools like the Vera Rubin Observatory and NASA’s projects might help unravel these mysteries.
Ultimately, if confirmed, AT2025ulz could reshape our understanding of stellar explosions and the universe’s ability to create heavy elements. The team’s findings were detailed in a recent publication in The Astrophysical Journal Letters, adding a fascinating chapter to our cosmic knowledge.
