Supermassive Black Hole Binary Environments: Effects on the Scaling Laws and Time to Detection for the Stochastic Background

Abstract

One of the primary gravitational wave (GW) sources for pulsar timing arrays (PTAs) is the stochastic background formed by supermassive black holes binaries (SMBHBs). In this paper, we investigate how the environments of SMBHBs will effect the sensitivity of PTAs by deriving scaling laws for the signal-to-noise ratio (SNR) of the optimal cross-correlation statistic. The presence of gas and stars around SMBHBs will accelerate the merger at large distances, depleting the GW stochastic background at low frequencies. We show that environmental interactions may delay detection by a few years or more, depending on the PTA configuration and the frequency at which the dynamical evolution transitions from being dominated by environmental effects to GW-dominated.