Gravitational waves from extreme mass ratio inspirals: Challenges in mapping the spacetime of massive, compact objects

TL;DR

This paper discusses the challenges and recent progress in modeling gravitational waves from extreme mass ratio inspirals, which can be used to test the nature of massive compact objects and map their spacetime.

Contribution

It highlights the key theoretical challenges in waveform modeling for EMRIs and reviews recent advances in generating accurate waveforms for spacetime mapping.

Findings

Identification of major theoretical challenges in waveform modeling.

Recent progress in producing accurate EMRI waveforms.

Potential for gravitational waves to distinguish black holes from exotic objects.

Abstract

In its final year of inspiral, a stellar mass ($1 - 10 M_\odot$) body orbits a massive ($10^5 - 10^7 M_\odot$) compact object about $10^5$ times, spiralling from several Schwarzschild radii to the last stable orbit. These orbits are deep in the massive object's strong field, so the gravitational waves that they produce probe the strong field nature of the object's spacetime. Measuring these waves can, in principle, be used to ``map'' this spacetime, allowing observers to test whether the object is a black hole or something more exotic. Such measurements will require a good theoretical understanding of wave generation during inspiral. In this article, I discuss the major theoretical challenges standing in the way of building such maps from gravitational-wave observations, as well as recent progress in producing extreme mass ratio inspirals and waveforms.