Galaxy Rotation Curves — Station Card

Name: ________________________________ Section: __________ Date: __________

Station: __________ Group members: ________________________________________________

Goal: explain why flat galaxy rotation curves imply missing mass (or modified gravity) beyond visible stars and gas.

Station card: Galaxy Rotation (12-15 minutes) Artifact: one radial profile table + one interpretation claim.

Start with No dark matter and note the outer slope from $30$ to $50\,{\rm kpc}$ .

Switch to Milky Way-like and compare $V_{\rm total}$ and $V_{\rm Kep}$ at the same radius.

Increase halo mass and describe how the outer curve changes.

Switch to mass mode and identify where $M_{\rm dark}$ first exceeds $M_{\rm vis}$ .

Record the baryon fraction at $R=50\,{\rm kpc}$ and compare to $f_{b,\rm cosmic}=0.157$ .

Toggle MOND and compare curve shape agreement at galaxy scale.

Run one mystery challenge (predict -> check -> explain), then use Copy challenge evidence.

Case	$R$ (kpc)	$V_{\rm total}$ (km/s)	$V_{\rm Kep}$ (km/s)	$V_{\rm MOND}$ (km/s)	$M_{\rm total}(<R)$ ( $10^{10}M_\odot$ )	$M_{\rm vis}(<R)$ ( $10^{10}M_\odot$ )	$M_{\rm dark}(<R)$ ( $10^{10}M_\odot$ )	$M_{\rm dark}/M_{\rm vis}$	$f_b$
Snapshot
$R=2$
$R=5$
$R=10$
$R=15$
$R=20$
$R=30$
$R=40$
$R=50$

Claim prompt

At what radius does dark matter become dominant in your run?

What does your $f_b(50\,{\rm kpc})$ value suggest about where most mass resides?

One sentence: why is “galaxy behaves like solar system” not a good default model here?