Extreme mass ratio inspirals from the Hills mechanism, The eccentricity distribution of Hills EMRIs in LISA

@misc{sersante2026extreme,
  title = {{Extreme mass ratio inspirals from the Hills mechanism, The eccentricity distribution of Hills EMRIs in LISA}},
  author = {Biancamaria Sersante and Davide Mancieri and Kevin Leopoldo Muñoz Zavala and Luca Broggi and Zephyr Penoyre and Elena Maria Rossi and Alberto Sesana},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.13294},
  eprint = {2610.13294},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.13294},
}

TY  - UNPB
TI  - Extreme mass ratio inspirals from the Hills mechanism, The eccentricity distribution of Hills EMRIs in LISA
AU  - Biancamaria Sersante
AU  - Davide Mancieri
AU  - Kevin Leopoldo Muñoz Zavala
AU  - Luca Broggi
AU  - Zephyr Penoyre
AU  - Elena Maria Rossi
AU  - Alberto Sesana
PY  - 2026
DA  - 2026/10/09
PB  - arXiv
DO  - 10.48550/arxiv.2610.13294
UR  - https://arxiv.org/abs/2610.13294
AB  - Extreme mass ratio inspirals (EMRIs) are promising sources for future space-based gravitational-wave detectors. We investigate EMRIs produced through the Hills mechanism, in which a stellar-mass black-hole binary (BBH) is tidally separated by a massive black hole (MBH), leaving one component bound to it. We present the first self-consistent modelling of this channel, combining an orbit-averaged Fokker-Planck treatment of the nuclear star cluster (NSC), three-body modelling of the binary-MBH encounter, Monte Carlo evolution of captured black holes (BHs), and fully relativistic EMRI trajectories to follow the evolution from binary supply down to final plunge. We find that Hills EMRIs are substantially more circular than classical EMRIs formed through two-body relaxation. For an MBH of 4 × 10^6 M_⊙ and circular, equal-mass BBHs of 20 M_⊙ with initial separation of $0.1$ AU, EMRI mean eccentricities are approximately $0.097$ at our adopted LISA-band entry threshold and $0.034$ at plunge, compared with $0.478$ and $0.228$, respectively, for classical EMRIs. Of the initial BBHs, approximately $0.4$ per cent become EMRIs, whereas approximately $60$ per cent of captured BHs do. For comparable NSC initial compact-object mass, we find approximately 1.6 × 10^−8 Hills EMRIs per year per galaxy, approximately $12$ per cent of the classical EMRI yield. The Hills channel contribution to the overall eccentricity distribution depends strongly on the binary mass fraction in NSCs. We discuss implications for identifying EMRI formation channels with LISA and for quasi-periodic eruptions.
ER  -