Probing Dark Matter Spikes via Gravitational Waves of Extreme Mass Ratio Inspirals

Abstract

The exact properties of dark matter remain largely unknown despite of the accumulating evidence. If dark matter is composed of weakly-interacting massive particles, it would be accreted by the black hole in galactic center and forms a dense cuspy spike. Dynamical friction from such a spike may have observable effects in a binary system. We consider extreme-mass-ratio inspiral (EMRI) binaries consisting of massive black holes harbored in dark matter spikes and stellar mass objects in elliptic orbits. We find the gravitational-wave waveforms in frequency domain can be significantly modified.In particular, we show dark matter can suppress the characteristic strain of gravitational wave at low frequency but enhance it at higher domain. These effects are more dramatic as the dark matter density increases. The results indicate that the signal-to-noise ratio of EMRIs could be strongly reduced around 10 −3 ∼ 0.3 Hz but enhanced around 1.0 Hz with a higher sensitivity, which could be probed via future space-borne GW detectors, LISA and TAIJI. The findings would have important impacts on the detection and parameter inference of EMRIs.