Negative Dynamical Friction in Dark Matter Spikes around Rotating Black Holes
Abstract
Dark matter may affect extreme-mass-ratio inspirals (EMRIs) through orbital-energy exchange and a conservative metric response. Here we show that dark matter spikes around rotating massive black holes can drive negative dynamical friction, supplying orbital energy to secondary black holes on stable prograde circular orbits. The energy-gain region extends beyond the innermost stable circular orbit once the black-hole spin exceeds a model-dependent threshold. For an illustrative four-year inspiral with Milky Way--like halo parameters and mass ratio q=10−5, the total dynamical-friction contribution produces a phase difference of order 102 radians relative to vacuum. For the same system, the fixed-frequency environmental redshift correction is comparable in magnitude and opposite in sign to the first-order conservative self-force correction. Both environmental energy exchange and the conservative metric response are therefore essential to precision EMRI modeling.
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BibTeX
@misc{xiong2026negative,
title = {{Negative Dynamical Friction in Dark Matter Spikes around Rotating Black Holes}},
author = {Wei Xiong and Peng-Cheng Li and Bin Chen},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.11380},
eprint = {2611.11380},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.11380},
}
RIS
TY - UNPB
TI - Negative Dynamical Friction in Dark Matter Spikes around Rotating Black Holes
AU - Wei Xiong
AU - Peng-Cheng Li
AU - Bin Chen
PY - 2026
DA - 2026/11/08
PB - arXiv
DO - 10.48550/arxiv.2611.11380
UR - https://arxiv.org/abs/2611.11380
AB - Dark matter may affect extreme-mass-ratio inspirals (EMRIs) through orbital-energy exchange and a conservative metric response. Here we show that dark matter spikes around rotating massive black holes can drive negative dynamical friction, supplying orbital energy to secondary black holes on stable prograde circular orbits. The energy-gain region extends beyond the innermost stable circular orbit once the black-hole spin exceeds a model-dependent threshold. For an illustrative four-year inspiral with Milky Way--like halo parameters and mass ratio q=10^−5, the total dynamical-friction contribution produces a phase difference of order 10^2 radians relative to vacuum. For the same system, the fixed-frequency environmental redshift correction is comparable in magnitude and opposite in sign to the first-order conservative self-force correction. Both environmental energy exchange and the conservative metric response are therefore essential to precision EMRI modeling.
ER -