Some theories that go beyond the Standard Model of particle physics predict the existence of new ultralight particles, with masses much below the lightest known particles in nature. When these particles have very weak interactions with ordinary matter, they are hard to detect by particle colliders and dark matter detectors. However, as a new paper by physicists Daniel Baumann and Horng Sheng Chia from the University of Amsterdam (UvA) together with Rafael Porto from DESY (Hamburg) shows, such particles could be detectable in gravitational wave signals originating from merging black holes. The research was published in Physical Review D this week.