Astronomers Detect Unusual Cosmic Event Possibly Linking Supernova and Kilonova
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Astronomers have observed a candidate cosmic event, AT2025ulz, that displayed characteristics of both a kilonova and a supernova. The event was detected in the same region as a gravitational-wave signal from a merger involving an unusually small object. This unusual combination could provide new insights into the formation of rare, low-mass neutron stars and the origins of heavy elements.
Facts First
- A candidate event named AT2025ulz was identified by the Zwicky Transient Facility (ZTF) at Palomar Observatory.
- The event was located in the same region as a gravitational-wave signal recorded on August 18, 2025, by the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo.
- Observations showed a rapidly fading red source similar to a kilonova, then later brightened and shifted to blue light with hydrogen signatures typical of a supernova.
- The gravitational-wave signal indicated at least one merging object was unusually small, potentially a sub-solar mass neutron star.
- The study was published in The Astrophysical Journal Letters and involved a dozen telescopes worldwide.
What Happened
On August 18, 2025, LIGO detectors, along with Virgo in Italy, recorded a gravitational-wave signal from a merger that indicated at least one of the merging objects was unusually small. Around the same time, the Zwicky Transient Facility (ZTF) identified a candidate event named AT2025ulz, located approximately 1.3 billion light years away. Observations showed the event initially displayed a rapidly fading red source, similar to the only confirmed kilonova, GW170817, from 2017. A few days later, AT2025ulz brightened and showed characteristics typical of a 'stripped-envelope core-collapse' supernova.
Why this Matters to You
This discovery may refine our understanding of where the elements that make up our world come from. Kilonovas are known to produce heavy elements like gold and uranium, while supernovae scatter elements like carbon and iron. A single event that shows traits of both could challenge existing models of cosmic chemical factories. Furthermore, the detection of an unusually small merging object could lead to new theories about the formation of neutron stars.
What's Next
The findings from AT2025ulz will likely be studied further as astronomers seek to confirm its nature. Upcoming astronomical projects, such as the Vera Rubin Observatory, NASA's Nancy Roman Space Telescope, and Caltech's Cryoscope in the Antarctic, could provide more sensitive tools to detect and analyze similar rare events in the future. These observations may help test theories for forming sub-solar mass neutron stars.