Flyby Survival Simulator

Full radius-sweep reimplementation of Paper E, Figure 1: per-bin Monte Carlo of gravitationally focused stellar flybys across the whole feasibility envelope, median & 16–84% survival band. For a single-point (one mass, one radius) version, see flyby-survival.html.

Speculative register · MTH engineering
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Method (Paper E Appendix A, browser-reduced sample counts). For each log-spaced radius bin a ∈ [6 rg, stripping radius] AU (the grid starts at the Schwarzschild ISCO, inside which no circular orbits exist): draw encounters with impact parameter from the gravitationally focused distribution truncated at bmax = 30a, speed from a Rayleigh of scale σ shifted up by 0.3σ, and mass from the perturber mass function; compute the impulsive eccentricity-kick variance ⟨δ²⟩; convert to a survival time via the random-walk first-passage estimate n = ecross²/⟨δ²⟩ divided by the encounter rate, with CLT scatter giving the 16–84% band; cap at 12 Gyr.

Perturber mass function, perturber mass, and the fBH control (Paper E v0.6). The background is two-component stellar (0.35 M☉ weight 0.70, 0.60 M☉ white-dwarf tail weight 0.30). A mass-segregated heavy-remnant extension adds neutron stars (1.4 M☉, fixed number fraction fNS = 2%) and stellar-mass black holes at the perturber mass set by the control, segregated fraction f_BH (fiducial 1%, grid 0.1/1/3%). The heavy tail is the controlling perturber, because kick variance scales as ⟨m²⟩, so both the fraction and the mass matter and the mass matters more. The default perturber mass is now 31 M☉, the mean mass of black holes inspiraling into the IMBH in the González Prieto et al. (2025) ω Cen models, which name 10 M☉ as the assumption they are correcting; the metal-poor progenitors of a cluster at [Fe/H] ~ −1.5 leave heavier remnants than the solar-metallicity default. Moving from 10 to 31 M☉ at fixed fBH = 1% raises ⟨m²⟩ by a factor 8.0 and shortens the impulsive floor from ~5×10⁸ to ~6×10⁷ yr, a larger displacement than the whole 0.1–3% fraction bracket produces at fixed mass. Set the control back to 10 M☉ to reproduce the pre-2026-07-30 curves; set fBH = 0 to recover the stars-only baseline (~1.8×10⁹ yr).

The adiabatic correction, and why the impulsive floor was only a floor. The impulsive kernel above is valid only when the encounter is short compared with the orbit, x = ωorbτenc = (b/a)(vorb/v) ≪ 1. For this system x is 2.2 at the cluster stripping radius and ~4×10³ at the ISCO, so unbound cluster stars are adiabatically decoupled from every orbit an installation could occupy: the impulsive numbers above are the conservative floor for a channel that does not operate, not a physical estimate. Ticking the adiabatic-correction control applies the Gnedin & Ostriker (1999) kernel A(x) = (1+x²)−5/2 to δ² per encounter, the less-suppressing of the standard choices and calibrated against N-body results. With it, the fiducial median reaches the 12 Gyr cluster-age cap inside ~3 AU and stays above ~3×10⁸ yr at the envelope edge. The flat, scale-free profile is a property of the impulsive kernel; the corrected curve rises inward.

The bound-cusp channel (Paper E D1-MODEL, 2026-07-30). What actually binds at the envelope edge is the bound cusp population: members move at the local Keplerian speed, so x ~ 1 for them (not ≪ 1), the impulsive kernel with the same adiabatic correction applies, and they are granular rather than diffuse. Each species follows Ns(<r) ∝ r3−γs = 1.3, γNS = 1.5, γBH = 2.0, González Prieto et al. 2025); at γBH = 2 the expected black-hole count is ≲ 1 everywhere in the envelope, so each history draws a Poisson perturber count from the local shell rather than using a smooth rate, and the resulting lifetime distribution is bimodal: a bound black hole is present in 53% of histories at the envelope edge, giving a diffusion floor of ~4×10⁷ yr (16th percentile ~2×10⁷ yr); when none is drawn the channel reaches the cluster-age cap. The perturber population is now anchored jointly rather than assembled from separate figures: fBH,central = 10 × (Mdark/mBH)/(7×10⁶ stars), fiducial 1.15% at Mdark = 2.5×10⁵ M☉ and mBH = 31 M☉ (Bañares-Hernández et al. 2025 pulsar timing), narrowing the old 0.1–3% fraction bracket (factor 30 in variance) to a factor 3.1 in the Mdark/mBH bracket. The same bound remnant also forces the orbit secularly (Kozai–Lidov): tsec(a) = (M/mpert)(rp/a)³Porb(a) with the outermost bound black hole fixed at rp = 4×10³ AU, but relativistic apsidal precession quenches the resonance (tsec/tGR ∝ a−4) inward of a ≈ 4×10² AU, where tsec ≈ tGR ≈ 3.7×10⁷ yr. That forcing is coherent and oscillatory, not diffusive, so it is a station-keeping cadence over its 4×10²–4×10³ AU operating window, not a third survival curve. Tick overlay bound-cusp channel above (with paper reference mode) to plot both against the unbound impulsive/adiabatic curves; this channel is not yet live-sampled in the browser, only the published fiducial run is shown.

Paper reference mode. Ticking paper reference plots the exact fiducial arrays from fig1_results.json verbatim (2×10⁵ encounter draws × 2×10⁴ histories × 40 bins, fixed seed 20260717, σ = 21 km/s, fig1_envelope.py, full bundle at /papers/source/): no live sampling, so it reproduces the published numbers rather than approximating them. The live MC trades sample count for interactivity; expect its median to sit inside the reference band, not land on it. The paper MC floor summary card always shows the published floor for the grid fBH nearest your setting, for side-by-side comparison. σ default from measurements.js clusterParams (18.2 km/s, cluster-averaged); Paper E adopts σ = 21 km/s, the midpoint of the 20–23 km/s central-region range of Baumgardt & Vasiliev (2021) and Nitschai et al. (2023). The difference lengthens survival times by tens of per cent and is inside the paper’s stated parameter variations.
→ single-point calculator → fuel budget → Paper E, Section 2 (the envelope)