Cosmological Physics with Black Holes (and Possibly White Dwarfs)

TL;DR

This paper explores how gravitational wave observations of black hole and white dwarf mergers by LISA can provide new insights into cosmology, dark energy, and modified gravity theories over large scales.

Contribution

It proposes using LISA's detections of black hole and white dwarf inspirals to perform cosmological measurements and test gravity theories at cosmological distances.

Findings

Potential for high-precision cosmological measurements.

Possibility to detect deviations from general relativity.

Use of electromagnetic counterparts for source localization.

Abstract

The notion that microparsec-scale black holes can be used to probe gigaparsec-scale physics may seem counterintuitive, at first. Yet, the gravitational observatory LISA will detect cosmologically-distant coalescing pairs of massive black holes, accurately measure their luminosity distance and help identify an electromagnetic counterpart or a host galaxy. A wide variety of new black hole studies and a gravitational version of Hubble's diagram become possible if host galaxies are successfully identified. Furthermore, if dark energy is a manifestation of large-scale modified gravity, deviations from general relativistic expectations could become apparent in a gravitational signal propagated over cosmological scales, especially when compared to the electromagnetic signal from a same source. Finally, since inspirals of white dwarfs into massive black holes at cosmological distances may permit pre-merger localizations, we suggest that careful monitoring of these events and any associated electromagnetic counterpart could lead to high-precision cosmological measurements with LISA.