Guide

Galaxy CollisionsRestricted three-body, WebGPU

Encounter

New here? Start here — 60 seconds · What every control does

Orbit

Mass ratio

Pericentre

Eccentricity

Dynamical friction (lnΛ)

Disc orientation

Primary tilt

Secondary tilt

Primary disc retrograde Secondary disc retrograde

Spin direction matters more than closeness. Set one retrograde and one prograde to get a long tail on one galaxy and almost nothing on the other — that asymmetry, not the closeness of the passage, is the dominant effect in a tidal encounter. Measured here: prograde throws 15.1% of a disc beyond 20 kpc against 2.5% retrograde, a ratio of 6.0x on identical orbits.

Match a simulation to a real telescope image. How to use Detect

Observed system

Target

Image blend

Image scale

Viewing geometry

The orientation you are looking from is part of the fit, not a camera convenience. Drag in the view for the two angles; roll sets the position angle on the sky, which nothing else can supply.

Roll (position angle)

Published fit

Seven steps through the physics. What each step shows

Guided

Drag to feel the shape of parameter space. How to read the pad

Parameter space

Drag anywhere in the field. Horizontal is disc tilt, vertical is pericentre. The encounter rebuilds continuously, so the shape of the space is something you feel rather than read.

tilt −90° +90° close far

Tilt—

Pericentre—

Retrograde

Playback

Speed

Appearance

Splat size

Intensity

Exposure

Bloom

Dust extinction

Camera follows

Colour by

Science view (linear, no bloom, no dust)

Understanding what you are seeing
Full guide — modes, controls, how to read it
How to not fool yourself
What is established, and what is not
Build log — including what went wrong
Source on GitHub

This is a restricted three-body model: massless test particles in rigid analytic potentials. It reproduces tidal bridges and tails, and it does not model gas, star formation or disc self-gravity. Galaxy Zoo: Mergers data — Holincheck et al. 2016, MNRAS 459, 720.

Drag to orbit, shift-drag to pan, scroll to zoom. space play/pause, ← → step, r reset, f frame, s science view, 1–4 modes. Time runs backwards as genuine reversed integration, not replayed frames.

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— test particles

separation —

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pericentre

beforeafter