The unique potential of extreme mass-ratio inspirals for gravitational-wave astronomy

TL;DR

Extreme mass-ratio inspirals (EMRIs) are promising gravitational-wave sources for LISA, capable of delivering detailed insights into black hole properties, stellar dynamics, and cosmology through their intricate signals.

Contribution

This paper highlights the unique potential of EMRIs for gravitational-wave astronomy, emphasizing their high-precision measurement capabilities and scientific applications.

Findings

LISA can measure EMRI parameters with fractional errors of 10^{-4} to 10^{-6}

EMRIs can determine black hole spins and masses with high accuracy

They can provide insights into stellar dynamics and test strong-gravity theories

Abstract

The inspiral of a stellar-mass compact object into a massive ($\sim 10^{4}$-$10^{7} M_{\odot}$) black hole produces an intricate gravitational-wave signal. Due to the extreme-mass ratios involved, these systems complete $\sim 10^{4}$-$10^{5}$ orbits, most of them in the strong-field region of the massive black hole, emitting in the frequency range $\sim10^{-4}-1~$Hz. This makes them prime sources for the space-based observatory LISA (Laser Interferometer Space Antenna). LISA observations will enable high-precision measurements of the physical characteristics of these extreme-mass-ratio inspirals (EMRIs): redshifted masses, massive black hole spin and orbital eccentricity can be determined with fractional errors $\sim 10^{-4}$-$10^{-6}$, the luminosity distance with better than $\sim 10\%$ precision, and the sky localization to within a few square degrees. EMRIs will provide valuable information about stellar dynamics in galactic nuclei, as well as precise data about massive black hole populations, including the distribution of masses and spins. They will enable percent-level measurements of the multipolar structure of massive black holes, precisely testing the strong-gravity properties of their spacetimes. EMRIs may also provide cosmographical data regarding the expansion of the Universe if inferred source locations can be correlated with galaxy catalogs.