Labs / Astronomy
Galaxy Rotation Curve
Stars far from a galaxy's center should orbit slowly, the way distant planets crawl around the Sun — yet real galaxies keep their outer stars racing at nearly constant speed. Drag across the plot to read the orbital speed at any radius, then dial up a dark-matter halo until the model curve rises to meet the flat curve we observe.
r 12.0 kpcv 0 km/sv(visible) 0 km/sdark/visible 0×
What to try
- With no dark matter, why does the model speed peak and then fall off toward the edge of the galaxy?
- How much dark-matter mass do you need before the outer stars keep pace with the observed flat curve — more or less than the visible stars you can see?
- Does making the halo larger (bigger core) or heavier do more to flatten the curve at large radius?
- Turn the visible mass all the way up. Can ordinary stars alone ever reproduce a flat curve, or does it always droop?
- Watch the motion streaks on the outer stars. What happens to how fast they sweep around as you add the halo?