Kavli Affiliate: Scott A. Hughes
| First 5 Authors: Devin R. Becker, Scott A. Hughes, , ,
| Summary:
Black hole binaries with small mass ratios will be critical targets for the
forthcoming Laser Interferometer Space Antenna (LISA) mission. They also serve
as useful tools for understanding the properties of binaries at general mass
ratios. In its early stages, such a binary’s gravitational-wave-driven inspiral
can be modeled as the smaller body flowing through a sequence of geodesic
orbits of the larger black hole’s spacetime. Its motion through this sequence
is determined by the rate at which backreaction changes an orbit’s integrals of
motion $E$, $L_z$, and $Q$. Key to the motion being close to a geodesic at any
moment is the idea that the effect of backreaction is small compared to a
“restoring force” arising from the potential which governs geodesic motion.
This restoring force holds the small body on a geodesic trajectory as the
backreaction causes that geodesic to slowly evolve. As the inspiraling body
approaches the last stable orbit (LSO), the restoring force becomes weaker and
the backreaction becomes stronger. Once the small body evolves past the LSO,
its trajectory converges to a plunging geodesic. This work aims to smoothly
connect these two disparate regimes: the slowly evolving adiabatic inspiral and
the final plunge. Past work has focused on this transition to plunge for
circular systems. Here, we study the transition for binaries with eccentricity.
A well-defined eccentric transition will make it possible to develop
small-mass-ratio binary waveform models that terminate in a physically
reasonable way, rather than abruptly terminating as an inspiral-only model
ends. A model that can explore the parameter space of eccentricity may also be
useful for understanding the final cycles of eccentric binaries at less extreme
mass ratios, such as those likely to be observed by ground-based detectors.
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