What did you change in the model?
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.
Labs / Astronomy / Galaxy Rotation Curve
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.
Why it matters
Why explore this?
Astronomy uses patterns in light and motion to explain objects we cannot touch directly. This model lets you change one part of a space system and see what the evidence would look like.
Explore
Try the model
r 12.0 kpcv 0 km/sv(visible) 0 km/sdark/visible 0×
Investigate
Questions to test
Predict first, try it in the model, then use what you observe to answer.
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?
Explain
Make sense of what happened
Look for a cause-and-effect rule: what did you change, what responded, and what stayed the same? Astronomers use those patterns to infer how distant systems work.
Check
Before you leave
What visible evidence changed?
What rule could explain that change?
If you can answer all three using evidence from the model, you understand the main idea. If not, return to Explore and change one setting at a time.