Astronomical observations of our Milky Way galaxy indicate that it has a mass of about 8 multiplied by 1011 solar masses. A star orbiting near the galaxy's periphery is 5.9 multiplied by 104 light years from its center.
(a) What should the orbital period of that star be?
y
(b) If its period is 6.0 multiplied by 107 y instead, what is the mass of the galaxy? Such calculations are used to imply the existence of "dark matter" in the universe and have indicated, for example, the existence of very massive black holes at the centers of some galaxies.
solar masses