Extensions to the Standard Model suggest the existence of new ultralight fundamental fields, potentially describing dark matter, that are up to 10^28 times lighter than the electron. In a Physical Review Letters, Francisco, Caio, Rodrigo and Vitor explore, for the first time, how such dark matter influences the trajectory and gravitational-wave signature of black hole binaries in galactic centres using Einstein's General Relativity. We quantify the impact of various field configurations and demonstrate that upcoming gravitational-wave observations can test the existence of these hypothetical particles.

These ultralight fields behave as waves on macroscopic scales, forming either boson stars or superradiant clouds around black holes. Galactic centers, home to supermassive black holes, often host extreme-mass-ratio binaries —- key targets for the upcoming Laser Interferometer Space Antenna (LISA), a space-based gravitational-wave detector launching in the 2030s.

As smaller black holes move through the dark matter, they create a dense trailing wake, akin to a swimmer's water wake. This wake exerts an additional gravitational attraction on the black hole, slowing it and altering its gravitational wave signals. Our study, the first of its kind using General Relativity, calculates the density required for an observable effect, allowing us to constrain the possible values of the field's mass and shed light on our understanding of dark matter.