Forecasted Detection Limits on the (Dark) Matter Density in Supermassive Black Hole Binaries for LISA

TL;DR

This paper investigates how dark matter spikes around supermassive black hole binaries influence gravitational wave signals detectable by LISA, enabling constraints on dark matter density profiles through future observations.

Contribution

It simulates the impact of dark matter spikes on GW signals and forecasts detection limits for dark matter density using LISA data.

Findings

Dark matter spikes significantly alter GW signals from SMBHBs.

LISA can set upper limits on dark matter density around SMBHs.

Comparison with SIDM models informs dark matter profile expectations.

Abstract

Supermassive black hole binaries (SMBHBs) are among the most powerful known sources of gravitational waves (GWs). Accordingly, these systems could dominate GW emission in the micro- and millihertz frequency range. Within this domain, SMBHs evolve rapidly and merge with each other. Dynamical friction from stars and gas at the centers of galaxies typically helps to bring together two SMBHs when they are at relatively far separations ($\approx$ kpc $-$ 100 pc), but becomes less efficient at smaller separations. However, dark matter (DM) spikes around SMBHs could enhance dynamical friction at close separations and, thus, shorten the evolution times. In this paper, we simulate the effects of DM spikes on GW signals in the micro- to millihertz frequency range and confirm that the GW signals from SMBHBs with DM spikes can be clearly distinguished from those without any additional matter. Making use of the projected sensitivity curve of the Laser Interferometer Space Antenna (LISA), we forecast upper limits for the (dark) matter density for given future SMBHB observations. We then compare these thresholds with the theoretical density profiles expected for self-interacting dark matter (SIDM) spikes.