A star near the visible edge of a galaxy travels in a uniformcircular orbit. It is 48,400 ly (light-years) from the galacticcenter and has a speed of 275 km/s.
a)  Estimate the total mass of the galaxy (billionsolar mass) based on the motion of the star. Gravitational constantis 6.674×10−11 m3/(kg·s2) and massof the Sun Ms=1.99 × 1030 kg.
b)Â Â The total visible mass (i.e., matter wecan detect via electromagnetic radiation) of the galaxy is1011 solar masses. What fraction of the total mass ofthe galaxy is visible, according to this estimate?
