The promise of multi-band gravitational wave astronomy

TL;DR

Multi-band gravitational wave astronomy with eLISA can detect and localize black hole binaries years before they merge, enabling coordinated electromagnetic observations and advancing our understanding of these cosmic events.

Contribution

This paper demonstrates the potential of eLISA to detect and localize black hole binaries prior to their merger, facilitating multi-messenger astronomy.

Findings

eLISA can resolve thousands of BHBs individually.

Millions of BHBs will create a detectable confusion noise.

eLISA can predict BHB mergers in aLIGO band weeks in advance.

Abstract

We show that the black hole binary (BHB) coalescence rates inferred from the advanced LIGO (aLIGO) detection of GW150914 imply an unexpectedly loud GW sky at milli-Hz frequencies accessible to the evolving Laser Interferometer Space Antenna (eLISA), with several outstanding consequences. First, up to thousands of BHB will be individually resolvable by eLISA; second, millions of non resolvable BHBs will build a confusion noise detectable with signal-to-noise ratio of few to hundreds; third -- and perhaps most importantly -- up to hundreds of BHBs individually resolvable by eLISA will coalesce in the aLIGO band within ten years. eLISA observations will tell aLIGO and all electromagnetic probes weeks in advance when and where these BHB coalescences are going to occur, with uncertainties of <10s and <1deg^2. This will allow the pre-pointing of telescopes to realize coincident GW and multi-wavelength electromagnetic observations of BHB mergers. Time coincidence is critical because prompt emission associated to a BHB merger will likely have a duration comparable to the dynamical time-scale of the systems, and is only possible with low frequency GW alerts.