Researchers have created a fully relativistic model showing that gravitational waves might carry hidden clues about dark matter near massive black holes.

New research from scientists at the University of Amsterdam outlines how gravitational waves produced by black holes could offer a way to detect dark matter and learn more about its behavior. Central to the study is a model based on Einstein’s general relativity that describes, with high precision, how a black hole interacts with nearby material.

Rodrigo Vicente, Theophanes K. Karydas, and Gianfranco Bertone of the UvA Institute of Physics (IoP) and the GRAPPA centre for Gravitation and Astroparticle Physics Amsterdam reported their findings in Physical Review Letters. Their research presents a refined method for predicting how dark matter near black holes can influence the gravitational waves that these systems generate.

Extreme mass-ratio inspirals

The study examines extreme mass-ratio inspirals, or EMRIs: systems in which a compact object that is relatively small (for example, a black hole created from the collapse of a single star) orbits and gradually moves inward toward a far more massive black hole often located at a galaxy’s center. During this inward journey, the smaller body produces a continuous gravitational-wave signal.

Future space missions such as the European Space Agency’s LISA space antenna, planned for launch in 2035, are expected to record these signals for months or even years, tracking hundreds of thousands to millions of orbital cycles. If modelled accurately, these “cosmic fingerprints” can reveal how matter – especially the mysterious dark matter that is thought to make up most of the matter in the Universe – is distributed in the immediate surroundings of massive black holes.

A relativistic point of view

Before missions like LISA begin taking data, it is crucial to predict in detail what kinds of signals we should expect and how to extract as much information as possible from them. Until now, most studies have relied on simplified descriptions of how the environment affects EMRIs. The new paper by the IoP/GRAPPA physicists closes this gap for a broad class of environments. It provides the first fully relativistic framework – meaning that it uses Einstein’s theory of gravity in full, instead of simpler approximations based on Newtonian gravity – to describe how the surroundings of a massive black hole modify an EMRI’s orbit and the resulting gravitational waves.

The study focuses in particular on dense concentrations of dark matter – often called “spikes” or “mounds” – that may form around massive black holes. By embedding their new relativistic description into state-of-the-art waveform models, the authors show how such structures would leave a measurable imprint on the signals recorded by future detectors. This work represents a fundamental step in a long-term program that aims to use gravitational waves to map the distribution of dark matter in the Universe and shed light on its fundamental nature.