gravax — Jaxstro — Anna Rosen, Ph.D.

A three-tier MSM ⊕ Hermite ⊕ SDAR engine that resolves close encounters exactly while accelerating cluster-wide gravity — mapping how dynamics preserves, transforms, or erases birth structure.

Readiness

In developmentIn active development

What's working

Three panels. (a) A 512-star cluster in the x-y plane, points sized and coloured by stellar mass, with projected half-mass radii circled at t=0 and after three crossing times, and a central massive binary. (b) Binary and cluster scales against time in units of the half-mass crossing time: the half-mass and 90-percent radii expand while the binary semimajor axis drops in three discrete steps at marked encounters. (c) A four-by-four matrix of logarithmic sensitivities of endpoint observables to birth parameters, showing strong diagonal structure: cluster radii respond to the initial half-mass radius, while binary semimajor axis and eccentricity respond to their own initial values. — PreliminaryWhat the Endpoint Remembers. **Birth conditions leave a readable fingerprint.** A 512-star EFF cluster carrying a primordial $30.8 + 28.3\,M_\odot$ binary, evolved to $3t_\mathrm{cr,h} = 2.447\,\mathrm{Myr}$ under exact, unsoftened Newtonian forces. **(a)** Open symbols are the initial distribution and filled symbols the endpoint; the projected half-mass radius grows from 0.71 to 0.88 pc. **(b)** Three binary-single encounters harden the binary by 10.4%, from $a_0 = 1000$ to $896\,\mathrm{AU}$ , while the cluster expands and the binary ends at $e = 0.538$ . **(c)** The point: each cell is the median logarithmic response $\partial\ln y(T)/\partial\ln\theta_0$ of an endpoint observable to a birth parameter, across five clusters. The structure is physically legible — cluster size remembers $r_{h,0}$ , while binary hardening and eccentricity remember $a_0$ and $e_0$ . Derivatives taken straight through the reversible adaptive timestep agree with complete finite-difference reruns to $3.24\times10^{-5}$ , so the differentiability claim is measured rather than asserted.

What's coming

In active development. The methods paper will cover the three-tier scheme and show where each tier is required rather than merely faster.