General Astronomy -
Spring 2013
Homework #7 - due March 11
1. (3 pt) List three
different types of galaxies and describe their stellar orbits and
gas content.
2. (3 pt) Assuming the Hubble constant is 60 km/s/Mpc,
estimate the age of the Universe. Explain your reasoning.
3. (3 pt) A galaxy has a measured recession velocity of 8,000
km/s. How far away is it? (Assume that the Hubble constant
is 71 km/s/Mpc.)
4. (4 pt) The Sun collapses to a white dwarf with a radius equal to
Earth’s. Assume that angular momentum is conserved and that
the Sun can be modeled as a sphere of uniform density rigidly
rotating once each 25 days. What will be the rotation rate of
the white dwarf?
5. (4 pt) Calculate the power output from a pulsar with a mass of
one solar mass and a radius of 14 km, with a spin down rate of -1×10-10
s-2 and an initial spin rate of 20 Hz. Convert your
answer to solar luminosities.