Mapping the Galactic Center with Gravitational Wave Measurements using Pulsar Timing

TL;DR

This paper explores how pulsar timing with the SKA can detect gravitational waves from stars and black holes near the Galactic Center, offering a new method to resolve individual objects and intermediate mass black holes.

Contribution

It introduces a novel approach using pulsar timing to map the Galactic Center's gravitational wave environment and detect intermediate mass black holes.

Findings

Pulsar timing can detect BHs of 1000 Msun within 0.1-1 pc of SgrA*.

Gravitational wave signals are stronger closer to SgrA*, aiding resolution.

Interstellar scattering is the main observational challenge.

Abstract

We examine the nHz gravitational wave (GW) foreground of stars and black holes (BHs) orbiting SgrA* in the Galactic Center. A cusp of stars and BHs generates a continuous GW spectrum below 40 nHz; individual BHs within 1 mpc to SgrA* stick out in the spectrum at higher GW frequencies. The GWs and gravitational near-field effects can be resolved by timing pulsars within a few pc of this region. Observations with the Square Kilometer Array (SKA) may be especially sensitive to intermediate mass black holes (IMBHs) in this region, if present. A 100ns-10mus timing accuracy is sufficient to detect BHs of mass 1000 Msun with pulsars at distance 0.1-1 pc in a 3 yr observation baseline. Unlike electromagnetic imaging techniques, the prospects for resolving individual objects through GW measurements improve closer to SgrA*, even if the number density of objects increases inwards steeply. Scattering by the interstellar medium will pose the biggest challenge for such observations.