Ejected and Rejected: Strong Scatterings in Dense Star Clusters
Abstract
Understanding the evolution of collisional stellar systems is key to predicting both the bulk evolution of dense star clusters and also the rates of tidal disruption events, extreme mass ratio inspirals (EMRIs), stellar ejections, and other loss cone phenomena. Although a majority of the evolution is dictated by weak, small-angle scatterings, rare close encounters resulting in strong scatterings can sometimes produce qualitatively different outcomes. To systematically determine the astrophysical importance of strong scatterings, we derive the exact differential rate distribution of velocity kicks in isotropic and spherically symmetric distribution functions representing globular and nuclear star clusters, while also deriving the distribution boundaries and approximate rate scalings. We then extend this formalism to derive approximate rates of energy and angular momentum kicks for objects in the nuclear star cluster, and then apply this framework to study (i) ejections and (ii) ``cancellation'' of extreme mass ratio inspirals. We find that ejection rates are complicated in some regimes due to the saturation of the strong kick distribution and the breakdown of the weak limit, likely enhancing the effect of loss cone shielding. We also determine that a sizable fraction of proto-EMRIs will likely be canceled by strong scatterings, highlighting the need for future work to determine to what degree strong scatterings impact the true EMRI rate.
Related
- FROST-CLUSTERS – III. Metallicity-dependent intermediate-mass black hole formation by runaway collisions in dense star clusters
- Black hole spin-mass correlation and accretion disks at birth stage of dense star clusters
- Survival Analysis of Intermediate-mass Black Holes in Dense Star Clusters
- The Contribution of Disrupted Dense Star Clusters to Gaia’s Compact Object Binaries
- Gravitational-wave signatures of primordial black hole clusters and the imprint of an early dense-core collapse
BibTeX
@misc{distler2026ejected,
title = {{Ejected and Rejected: Strong Scatterings in Dense Star Clusters}},
author = {Adam Distler and Nicholas C. Stone},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.37775},
eprint = {2610.37775},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.37775},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Ejected and Rejected: Strong Scatterings in Dense Star Clusters
AU - Adam Distler
AU - Nicholas C. Stone
PY - 2026
DA - 2026/10/27
PB - arXiv
DO - 10.48550/arxiv.2610.37775
UR - https://arxiv.org/abs/2610.37775
AB - Understanding the evolution of collisional stellar systems is key to predicting both the bulk evolution of dense star clusters and also the rates of tidal disruption events, extreme mass ratio inspirals (EMRIs), stellar ejections, and other loss cone phenomena. Although a majority of the evolution is dictated by weak, small-angle scatterings, rare close encounters resulting in strong scatterings can sometimes produce qualitatively different outcomes. To systematically determine the astrophysical importance of strong scatterings, we derive the exact differential rate distribution of velocity kicks in isotropic and spherically symmetric distribution functions representing globular and nuclear star clusters, while also deriving the distribution boundaries and approximate rate scalings. We then extend this formalism to derive approximate rates of energy and angular momentum kicks for objects in the nuclear star cluster, and then apply this framework to study (i) ejections and (ii) ``cancellation'' of extreme mass ratio inspirals. We find that ejection rates are complicated in some regimes due to the saturation of the strong kick distribution and the breakdown of the weak limit, likely enhancing the effect of loss cone shielding. We also determine that a sizable fraction of proto-EMRIs will likely be canceled by strong scatterings, highlighting the need for future work to determine to what degree strong scatterings impact the true EMRI rate.
ER -