'It is observed that the velocity of stars in a galaxy about a point A is proportional to r; where r is the distance from A. This implies that the mass density of matter in the galaxy varies as r/2'
Added by Kristin I.
Step 1
Step 1: Assume stars move in circular orbits about A and the mass distribution is spherically symmetric, so the gravitational acceleration at radius r is due to the mass M(r) enclosed within r and equals G M(r)/r^2. Show more…
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