Black Hole Retention Estimator

Physics Model

This tool estimates the natal retention fraction of black holes in a star cluster. It assumes black holes receive a natal kick drawn from a Maxwellian distribution, scaled down from the neutron star distribution ($\sigma_{NS} = 265$ km/s).

$$ P(v) = \sqrt{\frac{2}{\pi}} \frac{v^2}{\sigma_{bh}^3} \exp\left(-\frac{v^2}{2\sigma_{bh}^2}\right) $$

132.5

Current σ_BH (km/s)

187.4

Peak Velocity (km/s)

1.2%
Retention %

12
Est. BHs Retained

Parameters

Scaling Physics

Scaling Fraction 0.50 Ratio σ_BH / σ_NS (Ref σ_NS = 265 km/s)

Environment

Escape Velocity 50 km/s Cluster escape threshold (v_esc)

Total BHs Formed Initial number of BH progenitors

Note: This estimates natal retention only. It does not account for long-term dynamical ejection.