The Largest Gravitational Wave Catalog Ever Just Added 161 Black Hole Collisions

On 1 July, astronomers released the biggest gravitational wave catalogue to date. It adds 161 newly confirmed black hole collisions in one go and brings the running total to 390 confirmed detections since LIGO first caught the shiver of two merging black holes back in 2015. Ten years, from one detection to almost four hundred.

Gravitational waves are ripples in spacetime itself, thrown off when massive objects like black holes spiral into each other. The detectors that catch them, LIGO in the United States, Virgo in Italy, and KAGRA in Japan, measure a wobble thousands of times smaller than a proton. Every confirmed collision sharpens the map of how black holes form, how heavy they get, and how often they find each other across cosmic history.

The signal that has cosmologists arguing again

Buried in the same data is one unusual signal that has revived a decades old idea. Most black holes we know about formed when a giant star ran out of fuel and collapsed. But some theorists have long suspected another kind exists: primordial black holes, formed in the first second after the Big Bang, before any star had a chance to shine. If confirmed, they would be older than the stars themselves.

Nobody is claiming a confirmed primordial black hole yet. The signal is a hint, not a headline, and it will take more detections and careful modelling to know what it really is. But it points at a question cosmologists have argued over since the 1970s, and for the first time the data might actually settle it.

A busy month for the sky

The catalogue is not the only thing happening overhead this month. Japan's Hayabusa2 spacecraft is set to pass the near Earth asteroid Torifune, and China's Tianwen-2 mission is collecting its first samples from the small asteroid Kamo'oalewa, both firsts for their respective missions. For a slow news week on the ground, space is having a genuinely eventful one.