Astronomical observations of our milky way galaxy indicate that it has a mass of about 8x1011 solar masses. A star orbiting near the galaxy's periphery is 5.6x104 light years from its center. a.) What should be the orbital period (in years) of that star be? b.) If its period is 6.4x107 years instead, what is the mass (in solar masses) 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 center of some galaxies.

Astronomical observations of our milky way galaxy indicate that it has a mass of about 8x1011 solar masses. A star orbiting near the galaxy's periphery is 5.6x104 light years from its center. a.) What should be the orbital period (in years) of that star be? b.) If its period is 6.4x107 years instead, what is the mass (in solar masses) 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 center of some galaxies.