Probing New Particles through Gravitational Wave Signals from Merging Black Holes

In a recent study published in the journal Physical Review Letters, scientists from Copenhagen and Amsterdam said merging black hole pairs could provide details on possible new particles. The study incorporates several recent findings that University of Amsterdam researchers have made throughout the last six years.

When two black holes merge, their gravitational waves are released, and these waves include intricate information on the composition and trajectory of the component orbits.

According to a recent study by University of Amsterdam Physicists Giovanni Maria Tomaselli and Gianfranco Bertone, as well as former UvA master's student Thomas Spieksma, who is currently at the Niels Bohr Institute in Copenhagen, a thorough examination of this data may point to the existence of new particles in nature.

Superradiance

Black hole superradiance is the mechanism that enables the discovery of new particles in the universe. A black hole that rotates quickly enough can release some of its mass into the surrounding “cloud” of particles; because the black hole-cloud system resembles the electron cloud surrounding a proton, it is called a “gravitational atom.”

Superradiance is only effective when particles are significantly lighter than those currently measured in experiments, so this process offers a rare chance to investigate the possibility of new particles called ultralight bosons, whose existence could provide answers to several mysteries in particle physics, cosmology, and astrophysics.

Over the past six years, UvA physicists have conducted several significant studies on the orbital development of binary black holes in the presence of lightweight boson clouds. Resonant transitions, in which the cloud “jumps” from one state to another, akin to an electron in an ordinary atom switching between orbits, are a significant new phenomenon that was found.

Ionization, a novel event in which a portion of the cloud is expelled, is once again comparable to the behavior of regular atoms. The specifics of these imprints are dependent upon the particle cloud's current state, which is still unknown, but both of these processes leave distinctive marks on the gravitational waves that are emitted.

The new study incorporates all the other findings and traces the history of the system from the genesis of the binary black hole to the black hole merger in an attempt to fill in the remaining details.

Two Possibilities

The major conclusions provide new insights into the gravitational atoms in binary systems. The evolution of such a system might have two equally intriguing results, the researchers discovered. The cloud can be detected through its ionization, which leaves a distinct signature on the gravitational waves if the black holes and the cloud-first rotate in opposing directions.

In this scenario, the cloud remains in the state created by superradiance. In all other scenarios, the cloud is destroyed by resonant transitions, and the gravitational wave signal can be used to determine the precise eccentricity and inclination values that the binary's orbit has acquired.

The new result thus offers a new and robust search strategy for new particles, either by observing an anomalous excess of systems with the predicted values of eccentricity and inclination in one case or by detecting ionization effects in gravitational waveforms in the other. In both scenarios, forthcoming comprehensive gravitational wave observations will provide intriguing insights into the topic of the existence of new ultralight particles.

Journal Reference:

Tomaselli, M. G., et al. (2024) Legacy of Boson Clouds on Black Hole Binaries. Physical Review Letters. doi.org/10.1103/PhysRevLett.133.121402.