Can I play Galaxy 3D right now?

Yes. It is in development, so it opens in the studio and runs with sound on our default settings. Export is off until release, and voting for it moves it up the queue.

Is every star pulling on every other star?

No. That would be over four billion force terms per step at this particle count. It uses a dominant-mass potential instead, which is what real galaxies are dominated by and what produces the disc and the arms.

Where do the spiral arms come from?

Differential rotation. Inner orbits are faster than outer ones, so any density variation in the disc is progressively wound into a spiral.

What does mass injection do?

It adds stars on a musical cue, which disturbs a settled disc and starts a fresh round of arm formation, so the run keeps developing.

How should I frame it?

Face on, from above the plane. Edge on, a spiral galaxy is a bright line and the structure is invisible.

Galaxy 3D: Galaxy Formation Particle Videos

Galaxy 3D is being built right now

The engine, the physics and the look are done enough to watch. What is not finished is everything around them: the settings, the presets and the export path. So we shipped it as a preview instead of sitting on it.

The order is decided by these votes rather than by us, and the most-voted modes go first. If this is the one you want, say so.

What you can do now: Open it in the studio and watch a full run, with sound, exactly as it stands today.
What is held back: Settings, randomize and export. The preview runs on our defaults so every viewer judges the same version.
When it ships: The most-voted unfinished mode is the one we take next.

What Galaxy 3D does

A cloud of stars collapsing under gravity into a flattened spinning disc with spiral arms, with new mass injected on the drop.

Galaxy 3D is galaxy formation as a loop. A cloud of GPU particles starts loose and collapses under gravity, flattening as it spins until it is a disc with spiral arms shearing through it. Then the beat injects new mass and it does it again.

It is not an all-pairs n-body solve, and it should not be. A true all-pairs step over sixty-five thousand particles is more than four billion force terms, which is not something a fragment shader is going to do at sixty frames a second without compute shaders.

It uses the dominant-mass approximation instead, which is closer to the truth than it sounds. Real galaxies are dominated by a central mass plus a few heavy clumps, and the visual signature people recognise, the flattened disc, the arms, the shear, comes from that potential rather than from every star pulling on every other one.

How a run plays out

The exact sequence the engine runs in this mode, from the first frame to the moment the run resolves.

1.
A loose cloud starts spinning
Stars begin distributed through a volume with an initial rotation. Gravity and spin are the two numbers that decide everything that follows.
2.
Collapse flattens it
The cloud contracts under the dominant potential and flattens into a disc, because rotation resists collapse in the plane but not along the axis.
3.
Shear draws the arms
Inner orbits are faster than outer ones, so any density variation is wound into a spiral. The arms are a consequence of differential rotation rather than a drawn feature.
4.
The drop injects mass
A musical cue adds new stars, which disturbs the disc and restarts the formation process, so the run keeps building instead of settling.

Every control in Galaxy 3D

These are the settings this mode adds on top of the shared physics, visual, audio, and export controls. Names match the studio sidebar exactly.

Gravity and spin

Gravity & Spin

These two together decide whether the cloud collapses to a tight core, settles into a broad disc, or never flattens at all.

Stars

Stars
Star Count

Count is the density of the disc. High counts are what make the arms read as continuous structure rather than as scattered points.

Look

Look
Colour By
Ramp Start
Ramp End

Colouring by radius or velocity separates the fast bright core from the slow outer disc, which is what gives the image depth.

Beat response

Beat Response
Inject Mass On Beat
Own Sounds
Injection Sound

Mass injection is the mode’s event. Without it, a formed disc is stable and the second half of the run has nothing happening.

Why Galaxy 3D videos hold attention

What keeps people watching this mechanic.

Formation is a visible process

A cloud becoming a disc is a transformation with a clear before and after, which gives an abstract visual a narrative shape.

Spiral arms are recognisable

Everyone knows what a galaxy looks like, so the moment the arms appear the viewer knows what they have been watching form.

Injection restarts the interest

Adding mass on the drop disturbs a settled disc, so the run has repeated formation events rather than one.

Scale reads instantly

Tens of thousands of points moving coherently communicates size without any reference object.

Videos you can make in this mode

Each of these is a different configuration of the same mode, so one setup session produces a batch of related uploads.

Single formation

One collapse from loose cloud to formed disc. The clearest demonstration of the process.

Drop injection

Mass injected on the track’s drop so the disc is disturbed exactly when the music peaks.

Radius-coloured

Colour by radius so the core and the outer disc are clearly different, which makes the structure readable.

Tight core

High gravity with low spin for a dense concentrated centre rather than a broad disc.

Broad spiral

Lower gravity with higher spin, which produces a wide disc where the arms are the dominant feature.

Face-on framing

The camera above the plane so the spiral structure is fully visible rather than seen edge on.

Make your first Galaxy 3D video

The order that works. Following it out of sequence usually means retuning settings you already set.

1.
Balance gravity and spin
These two decide whether you get a tight core, a broad disc, or a cloud that never flattens. Adjust them together.
2.
Raise the star count
The arms only read as structure at high density. This is the setting that makes the difference.
3.
Colour by radius
Separate the core from the outer disc so the image has depth rather than being uniform brightness.
4.
Set the injection
Put mass injection on the drop, so the biggest visual disturbance lands with the biggest musical moment.
5.
Frame face on
Shoot from above the plane. Edge on, a galaxy is a line and the arms are invisible.

Settings that make the difference

Star count is what makes arms look like arms. Below a certain density they are just scattered points.
Face-on framing is almost always right, because the spiral structure is the reason to use this mode.
Injection on the drop is the single most effective audio link available here.
Colour by radius rather than by a flat value, so the core reads as brighter and hotter than the rim.
The dominant-mass approximation is what makes this run at all, so do not expect star-to-star interactions.

What breaks a run

Edge-on framing, which reduces a spiral galaxy to a bright line.
A low star count, where the disc reads as sparse noise rather than as structure.
No mass injection, which leaves a settled disc doing nothing for the second half of the run.
Gravity and spin set so the cloud never flattens, which removes the entire formation arc.

Why this is not an all-pairs n-body

The textbook n-body simulation computes the force between every pair of particles. For sixty-five thousand stars that is more than four billion force terms per step, and it has to happen sixty times a second. Without compute shaders and shared memory, it is simply not available.

The dominant-mass approximation replaces that with a potential from a central mass plus a few heavy clumps. Every star is pulled by that potential rather than by every other star, which reduces the cost from quadratic to linear in the star count.

Crucially, it keeps the part that matters visually. Real galaxies are dominated by exactly that kind of potential, and the flattened disc, the spiral arms and the shear all come from it rather than from star-to-star interaction. What is lost is local clumping between neighbouring stars, which is invisible at this scale anyway.

Where the arms come from

Spiral arms are not drawn and they are not a texture. They are what differential rotation does to any density variation in a disc: inner orbits complete faster than outer ones, so a radial feature is progressively wound into a spiral.

That is why the arms appear only after the cloud has flattened. A spherical cloud has no differential rotation to speak of in the plane of view, and until the collapse produces a disc with a real radial velocity gradient, there is nothing for the shear to act on.

It is also why mass injection is so effective. Adding stars creates fresh density variations in an already-shearing disc, so a new set of arms winds up within a second or two of the drop, which is exactly the kind of visible consequence a musical cue wants.

Galaxy 3D questions

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