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arXiv · 2609.37234

The Irreversible Depletion of Dark Matter Spikes by Extreme-Mass-Ratio Inspirals

Charlie Sharpe·Yonadav Barry Ginat·Thomas F. M. Spieksma·Alexander Heger·Bence Kocsis
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Abstract

Dense dark matter spikes around massive black holes (MBHs) have been widely predicted to produce gravitational-wave dephasing in extreme-mass-ratio inspirals (EMRIs) that are potentially observable by LISA. We show that EMRIs, the very objects used to probe these spikes, also destroy them. Combining Fokker-Planck models of nuclear star clusters with post-Newtonian three-body simulations of EMRI-dark matter encounters, we demonstrate that repeated gravitational slingshots irreversibly eject dark matter particles from the cluster's loss cone over gigayear time-scales. For MBHs at $z = 3$ with masses $\lesssim 10^5 \,M_\odot$, even conservative EMRI rates of $\mathcal{O}(1-10) \, \mathrm{Gyr}^{-1}$ suffice to deplete the spike density by orders of magnitude; for more realistic rates of $\mathcal{O}(100-300) \, \mathrm{Gyr}^{-1}$, the mass range extends to $\lesssim 10^6 \,M_\odot$. As a result, the gravitational-wave dephasing expected from such systems is greatly reduced, narrowing the prospects of detecting DM through this channel. Only heavy, high-redshift systems with sufficiently low EMRI rates -- for example, a $\sim 10^6 \,M_\odot$ MBH at $z \gtrsim 5$ with $\lesssim 100$ EMRIs per Gyr -- can induce dephasing that exceeds one radian.

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Charlie Sharpe, Yonadav Barry Ginat, Thomas F. M. Spieksma, Alexander Heger, Bence Kocsis. 2026-09-29. The Irreversible Depletion of Dark Matter Spikes by Extreme-Mass-Ratio Inspirals. https://arxiv.org/abs/2609.37234

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