Under the hood

Every frame, the force on each body is the sum of Newton's inverse-square pull from all the others (F = G·m₁·m₂ / r²). The catch is turning those forces into motion accurately. A naive step (move by velocity, nudge velocity by force, repeat) slowly leaks energy, and orbits spiral apart within seconds.

• This uses velocity Verlet integration, which is symplectic: it conserves energy over long runs, so a circular orbit stays a circle instead of drifting.
• A small softening term added to the distance keeps the force finite during near-collisions, so bodies slingshot past each other rather than launching to infinity.
• Pin a heavy body as fixed to make a clean central star, or leave everything free and watch the whole system drift as momentum sloshes around.

Try the triple preset and reset it a few times: same setup, wildly different fates. That sensitivity is the n-body problem in a nutshell.