Overview
- LIGO and Virgo registered a low-confidence signal on August 18, 2025 that hinted at a merger involving an unusually low-mass object.
- Within hours, the Zwicky Transient Facility spotted AT2025ulz about 1.3 billion light-years away, which first faded like a red kilonova before brightening and showing blue, hydrogen-rich features typical of a supernova.
- A Caltech-led team proposes a scenario in which a rapidly rotating star’s collapse produced two low-mass neutron stars that quickly merged, creating a kilonova partly veiled by supernova ejecta.
- Some researchers regard AT2025ulz as an ordinary supernova unrelated to the gravitational-wave signal, leaving both the association and the superkilonova interpretation unconfirmed.
- The analysis, published in The Astrophysical Journal Letters, outlines how future multimessenger observations could test for similar disguised events and refine search strategies for heavy-element production.