Astronomers first recorded a mysterious supernova explosion that required the development of a new theory.

New type of cosmic explosion: “superkilonova”

ItemWhat happenedAfter detectionIn August 2025 gravitational‑wave detectors LIGO and Virgo recorded event AT2025ulz at a distance of 1.3 billion light‑years. First signalA gravitational pulse appeared, characteristic of the merger of low‑mass objects – like neutron stars. This reminded of GW170817 (2017) and became the second registered case of a kilonova birth. Coordinate determinationThe positional accuracy obtained by gravitational methods leaves much to be desired, complicating the search for an optical counterpart.

How the event unfolded
1. Classic start of a kilonova

- Telescopes around the world (including Palomar Observatory) observed a rapidly fading red glow typical of heavy‑element synthesis (gold, uranium).

2. Unexpected change

- A few days later the flare intensified, took on a blue tint and hydrogen appeared in the spectrum – signs of an ordinary supernova. This confused observers.

3. Localization problems

- Because the probability of two powerful catastrophes occurring simultaneously in one patch of sky is extremely low, scientists assumed it was a single, but unusual event.

Theoretical model
- Supernova collapse:

During the collapse of a rapidly rotating massive star fragmentation could have occurred, producing two super‑light “forbidden” neutron stars (mass < 1 M☉ – contradicting existing theories).

- Merger and kilonova:

These newly formed objects, spiraling around each other, collided almost instantaneously, triggering a kilonova and a gravitational signal.

- Persistent shock wave:

The shock wave from the initial supernova explosion continued to expand outward, creating a second optical trace – a typical supernova.

Thus a “cosmic matryoshka” was observed: two markedly different signals (kilonova and supernova) sequentially appeared in one event.

What next?
- New data needed

To confirm or refute the existence of such “superkilonovas,” further observations are required.

- Rubin and Roman observatories:

- *Rubin* already monitors fast‑evolving events.
- *Roman* is planned to launch into space in September 2026.

Good luck to both teams!