K. Maeda

In a courtroom, there isn't always a video recording of the crime. Sometimes the verdict is based on witness testimony: what happened before, what happened after. That's exactly how physicists treated the signal GW250114, detected on January 14, 2025.

A star similar to our Sun but several times heavier sheds its outer layers before dying. The gas expands outward, forming something like onion rings around the star. When the star finally explodes as a supernova, the light of the explosion passes through these rings and illuminates them, like a flashlight shining through layers of fog.

After a supernova explosion, a neutron star neutron star remains: a city-sized ball of unimaginably dense matter, spinning hundreds of times per second. Any tiny bump on its surface would make it wobble like an off-balance spinning top, humming faintly through the fabric of space.