On the rates of binary star collisions around hypermassive black holes
Abstract
Observations of the Milky Way show that galaxies have binary stars in their centres. Using Monte Carlo simulations, we model the population statistics of encounters of such binaries with galactic central black holes (BHs) of mass 10^5-10^{10} Msun (hypermassive BHs >= 10^8 Msun HMBHs). Whereas main-sequence single stars cannot undergo tidal disruption events around HMBHs, stellar collisions of main-sequence binary stars may produce observable transients. We use the post-Newtonian Einstein-Infeld-Hoffmann (EIH) equations as implemented in the three-body code Multistar. We simulate 100,000 models each for six BH masses and 10 different binary parameter distributions. We find that stellar collisions occur in all models, with collision fractions ranging from ~7% for circular, equal-mass binaries to ~0.2% for the observationally motivated Moe2017 binary distribution. Most collisions occur for prograde, tight binaries at low impact parameters beta = r_t/r_p, where the tidal force of the BH drives up the binary eccentricity during pericentre passage. Collision velocities are close to the binary escape velocity for lower-mass BHs (<= 10^8 Msun), but span a wider range for higher-mass BHs, implying an increasing fraction of stellar mergers. Using empirical loss-cone rates and the local BH mass function, we estimate detectable LSST collision rates of ~8,600 and ~3,000 events per year for our Kroupa mass function, Opik's law, inclined orbit model and our MS17 model, respectively, around 10^6 Msun BHs; ~330 and ~150 events per year around 10^8 Msun BHs; and ~3.5 and ~2.8 events per year around 10^9 Msun BHs. These results suggest that binary stellar collisions around HMBHs represent a potentially observable population of nuclear transients that may contribute to the growing sample of ambiguous nuclear transients detected by wide-field optical surveys.
Related
- Stellar Collisions from Self-consistent Stellar Dynamics around Growing Supermassive Black Holes
- Stellar Collisions from Self-consistent Stellar Dynamics Around Growing Supermassive black Holes
- Hierarchical Inference of the Supermassive Black Hole Binary Merger Rates from Joint Searches using Pulsar Timing Arrays
- One Merger, Three Bands: Multiband Detection Rates and Parameter Estimation of Stellar-mass Binary Black Hole Coalescences from Millihertz to Kilohertz
- Cosmic merger rates and population evolution of binary black hole mergers in AGN disks
BibTeX
@misc{sharma2026rates,
title = {{On the rates of binary star collisions around hypermassive black holes}},
author = {Megha Sharma and Alexander Heger and Evgeni Grishin and Daniel J. Price},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27492},
eprint = {2609.27492},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27492},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - On the rates of binary star collisions around hypermassive black holes
AU - Megha Sharma
AU - Alexander Heger
AU - Evgeni Grishin
AU - Daniel J. Price
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.27492
UR - https://arxiv.org/abs/2609.27492
AB - Observations of the Milky Way show that galaxies have binary stars in their centres. Using Monte Carlo simulations, we model the population statistics of encounters of such binaries with galactic central black holes (BHs) of mass 10^5-10^{10} Msun (hypermassive BHs >= 10^8 Msun HMBHs). Whereas main-sequence single stars cannot undergo tidal disruption events around HMBHs, stellar collisions of main-sequence binary stars may produce observable transients. We use the post-Newtonian Einstein-Infeld-Hoffmann (EIH) equations as implemented in the three-body code Multistar. We simulate 100,000 models each for six BH masses and 10 different binary parameter distributions. We find that stellar collisions occur in all models, with collision fractions ranging from ~7% for circular, equal-mass binaries to ~0.2% for the observationally motivated Moe2017 binary distribution. Most collisions occur for prograde, tight binaries at low impact parameters beta = r_t/r_p, where the tidal force of the BH drives up the binary eccentricity during pericentre passage. Collision velocities are close to the binary escape velocity for lower-mass BHs (<= 10^8 Msun), but span a wider range for higher-mass BHs, implying an increasing fraction of stellar mergers. Using empirical loss-cone rates and the local BH mass function, we estimate detectable LSST collision rates of ~8,600 and ~3,000 events per year for our Kroupa mass function, Opik's law, inclined orbit model and our MS17 model, respectively, around 10^6 Msun BHs; ~330 and ~150 events per year around 10^8 Msun BHs; and ~3.5 and ~2.8 events per year around 10^9 Msun BHs. These results suggest that binary stellar collisions around HMBHs represent a potentially observable population of nuclear transients that may contribute to the growing sample of ambiguous nuclear transients detected by wide-field optical surveys.
ER -