Everdust
Get the app
‹ All scenes
‹›Get the app

Cosmos

Galaxy simulator

A galaxy simulator moves stars by gravity so you can watch a galaxy turn, and what happens when two of them meet. Galaxy Sculptor is a free one in your browser with no download: spawn the Milky Way, Andromeda, the Whirlpool or eight other real galaxy types, built from published measurements, pick one up and throw it into another. A second here is about 19 million years, so a merger that takes a billion years or more plays out in a minute or two.

Whole galaxies float in front of you: pick one up by its glowing core, throw it at another and watch them merge, or replay the classic encounters, the Cartwheel first.

Press a glowing core and drag to carry a galaxy; let go while moving to throw it. Spawn (top right) adds galaxies and classic encounters. Drag the sky to look around.

The idea
Every galaxy is built from published parameters (dark-matter halo, bulge, disk, bar) and its stars feel every galaxy's full gravity, so mergers take their real time: a second here is about 19 million years. The Cartwheel, the Antennae and the Mice start on their real orbits.
With music
Kicks send a starburst wave through every galaxy, bass lights the gas knots, vocals brighten the cores and hi-hats make the stars twinkle. Tap Demo beat for our own beat, or Your music to let it hear the room.
How it runs
It’s the same live simulation as in the Everdust apps, running in your browser on WebGL 2. If your device struggles, it lowers the detail a step at a time to keep the motion smooth.

What you can do

How do you simulate a galaxy?

A galaxy is a few hundred billion stars, gas and a much larger, invisible halo of dark matter, all held together by their own gravity. No computer can follow every star, so simulations use stand-ins. The biggest research runs follow billions of particles, each standing for thousands of suns, on supercomputers for months.

Galaxy Sculptor takes a lighter path, the one Alar and Juri Toomre used in 1972 to explain tidal tails. Each galaxy's gravity comes from smooth, published models of its parts: a dark matter halo, a central bulge, a flat disk and, for barred spirals, a rotating bar, with masses and sizes from measurements of the real galaxy. Its stars are test particles that orbit in the combined pull of every galaxy on screen, started with the speeds and random motions a real disk has.

The galaxies' centers pull on each other, and when one plows through another's halo it loses speed to dynamical friction, the drag of the dark matter its gravity gathers behind it. That drag is why real galaxies merge instead of passing through each other, and why a merger here takes about as long as a real one, a billion years or more.

The shortcuts: stars don't pull on each other, halos don't lose mass when they are stripped, a soft spring keeps runaways in view, and the bright starbursts are a stand-in for star formation where the tides are strongest.

Questions

Is this galaxy simulator free?
Yes. It runs free in your web browser on WebGL 2, with no download, no account and no ads. On a slower device it renders at a lower resolution to keep the motion smooth.
Are the galaxies real?
They are models of real galaxies, not photographs. Each type is built from published measurements: the Milky Way from Bland-Hawthorn and Gerhard (2016) and McMillan (2017), Andromeda from Geehan and colleagues (2006), the Large Magellanic Cloud from van der Marel and Kallivayalil (2014), and so on; the Whirlpool's two arms are laid out at its measured pitch angle.
Can I collide the Milky Way and Andromeda?
Yes: pick Milky Way + Andromeda under the classic encounters. It starts at their first close pass, which in reality is a few billion years away. Measurements with the Hubble and Gaia space telescopes in 2025 put the chance of a merger within the next ten billion years at about one in two.
How does a ring galaxy form?
When a small galaxy drops straight through the middle of a big disk, its pull yanks the disk's stars inward, and they rebound outward as an expanding ring, like a stone dropped in a pond. The Cartwheel Galaxy, 500 million light-years away, formed this way. Throw a small core face-on through a big one to try it.
How is this different from the galaxy collision simulator?
The galaxy collision simulator plays one encounter of two disk galaxies with about 200,000 stars that you watch and turn. Galaxy Sculptor is hands-on: you choose the galaxies, carry them and throw them, and the encounter depends on how you do it.
Is there an app version?
Yes. The Everdust app is free on the App Store for iPhone, iPad and Apple Vision Pro, where galaxy collisions run with up to about a million stars, on Google Play for Android, and on the Meta Horizon Store for Meta Quest 3 and 3S.

This is one world, in your browser

The full version is in the Everdust app.

The app has many more live worlds at full detail, games built on the same physics and narrated stories you step inside. It’s free to download, with no ads, on the App Store for iPhone, iPad, Apple Vision Pro and Apple TV, on Google Play for Android phones and tablets, on the Meta Horizon Store for Meta Quest and from everdust.ai for Mac.