Drag the radius slider to see why spiral-galaxy rotation speeds do not slow down at the edge the way visible mass alone predicts.
Published teaching figures: the Milky Way's rotation speed stays close to 220-240 km/s from roughly the Sun's distance (~8 kpc) out to about 25 kpc, instead of falling off the way visible-mass-only physics predicts.
Drag to orbit and scroll or pinch to zoom. Move the radius slider to see the observed and predicted speeds at that distance, and toggle the faint dark-matter halo on or off.
Dark Matter Rotation Curves 3D Explorer
freetoolonline.com editorial team
This browser explorer compares two rotation speeds for a spiral galaxy at any distance from the center: the speed Newtonian physics predicts from the visible stars and gas alone, and the speed that is actually observed. Drag the radius slider to see the two curves split apart past the edge of the visible disk - the classic evidence for a dark-matter halo.
For the Milky Way, the visible stars and gas thin out at roughly 10 kpc from the center. If that visible matter were all there is, orbital speed should decline past that point the way Kepler's laws describe for a planet far from a star - the farther out, the slower. Instead, measurements show the rotation speed holds close to 220-240 km/s from around the Sun's own distance (about 8.1 kpc, per the GRAVITY Collaboration's precise measurement, often rounded to 8 kpc or 26,000 light-years) out to about 25 kpc using individual stars as tracers, and stays flat even farther out, to 50 kpc or beyond, based on the orbital motion of the Milky Way's satellite galaxies.
This mismatch between the predicted decline and the observed flat curve is one of the primary lines of evidence for dark matter, first shown clearly in spiral-galaxy surveys by Vera Rubin, Kent Ford, and Norbert Thonnard in the 1970s and 1980s. The gap implies a large, mostly invisible mass distribution extending well past the visible disk - a dark-matter halo - inferred from its gravity, never directly imaged.
- Radius slider drags a test-star marker around the disk and updates the observed-vs-predicted speeds live
- Two rising 3D curve traces show the observed (cyan) and visible-mass-only-predicted (orange) speeds side by side across the whole radius range
- Toggle button shows or hides the faint, much larger dark-matter halo standing in for the inferred mass
- Drag to orbit the camera, scroll or pinch to zoom
- Runs fully in the browser with the vendored three.js engine - no account, no upload
Students see exactly where the two curves diverge and why that gap - not a single number - is the evidence; teachers use the toggle to separate "what is measured" (the observed curve) from "what is inferred, not directly seen" (the halo); curious readers get a feel for why astronomers are confident dark matter exists even though no telescope has ever photographed it.
| Quantity | Value |
|---|---|
| Sun's distance from galactic center | ~8.1-8.2 kpc (~26,000-27,000 light-years) |
| Sun's / flat-curve orbital speed | ~220-240 km/s (commonly rounded to ~220 km/s) |
| Visible-disk edge (Milky Way) | ~10 kpc |
| Flat curve confirmed by stellar tracers out to | ~25 kpc |
| Flat curve inferred via satellite galaxies out to | ~50 kpc or beyond |
This page is about the scientific EVIDENCE for dark matter from how fast galaxies spin, not about what a galaxy looks like. For a freely spinnable, generic spiral-galaxy shape, the collection's Galaxy 3D Explorer covers that; for a labeled top-down map of the Milky Way's own spiral arms and the Sun's position within them, see the Milky Way Map 3D Explorer - both are different reader tasks from the rotation-curve comparison here.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached; no scene data is sent to a server.
This is an educational approximation, not a gravitational simulation - the "predicted" curve uses an illustrative Keplerian-decline shape rather than a per-galaxy measured figure, while the "observed" curve reflects the cited Milky Way measurements; the halo shown is inferred from the rotation curve, not a direct image of dark matter.
Frequently Asked Questions
What does the Dark Matter Rotation Curves 3D Explorer show?
A spinning disk of stars plus two rising curves: the observed rotation speed of the Milky Way at each distance from the center, and the speed that would be expected if only the visible stars and gas provided the gravity. The radius slider lets you compare the two at any distance.
Why does a flat rotation curve prove dark matter exists?
If only the visible mass were pulling on stars, orbital speed should decline the farther out you go, the way planets slow down farther from the Sun. Instead, the Milky Way's rotation speed stays close to 220-240 km/s well past the edge of the visible disk. The extra gravity needed to keep stars moving that fast implies unseen mass - dark matter.
How fast does the Sun orbit the galactic center?
About 220-240 km/s, at a distance of roughly 8.1-8.2 kpc (about 26,000-27,000 light-years) from the galactic center, per the GRAVITY Collaboration's precise measurement.
How far out has the flat rotation curve actually been measured?
Individual stars used as tracers confirm the flat curve out to about 25 kpc. The orbital motion of the Milky Way's satellite galaxies suggests it stays flat even farther out, to 50 kpc or beyond.
Who first showed this evidence for dark matter?
Vera Rubin, Kent Ford, and Norbert Thonnard's rotation-curve surveys of spiral galaxies in the 1970s and 1980s are the classic studies that made the flat-rotation-curve evidence widely recognized.
Is the dark-matter halo in this scene a real image of dark matter?
No. Dark matter has never been directly photographed. The faint halo shown is a visual stand-in for the mass distribution that is inferred from the rotation curve's shape, not a detected substance. The scene's "predicted" curve is also an illustrative Keplerian-decline shape, not a per-galaxy measured figure - only the observed-curve numbers are direct Milky Way measurements.