Circularization vs. Eccentrification in Intermediate Mass Ratio Inspirals inside Dark Matter Spikes

TL;DR

This paper studies how dark matter spikes influence the orbital evolution of intermediate mass ratio inspirals, revealing that dynamical friction tends to circularize orbits, which can help probe dark matter properties via gravitational wave observations.

Contribution

It introduces a general condition for orbital circularization or eccentrification due to dissipative forces like dark matter dynamical friction in IMRI systems.

Findings

Dynamical friction in dark matter spikes tends to circularize IMRI orbits.

A general condition for orbital circularization or eccentrification is derived.

Circularization rate can serve as a probe for dark matter properties.

Abstract

Inspirals of an Intermediate Mass Black Hole (IMBH) and a solar mass type object will be observable by space based gravitational wave detectors such as The Laser Interferometer Space Antenna (LISA). A dark matter overdensity around an IMBH - a dark matter spike - can affect the orbital evolution of the system. We consider here such Intermediate Mass Ratio Inspirals on eccentric orbits, experiencing dynamical friction of the dark matter spike. We find that by including the phase space distribution of the dark matter, the dynamical friction tends to circularize the orbit, in contrast to previous inquiries. We derive a general condition for circularization or eccentrification for any given dissipative force. In addition to the dephasing, we suggest using the circularization rate as another probe of the dark matter spike. Observing these effects would be an indicator for the particle nature of dark matter.