General Astronomy - Spring
2011
Homework #9 - due April 11
1. (6 pt) Muons are unstable, sub-atomic particles with
a life time of
2.2 microseconds. Many muons are produced by interactions of
cosmic rays in Earth's upper atmosphere. Can a muon produced at
an altitude of 10 km reach the ground before decaying? Explain
and calculate the velocity required.
2. (6 pt) An AGN ejects two blobs of matter
moving in diametrically
opposite directions inclined by 20° to our line of sight to the
AGN. Each blob is moving at a speed of 0.9 c relative to the
AGN. The AGN is at rest relative to us. How fast do the
blobs appear to move on the sky as seen by us?
3. (2 pt) A
galaxy cluster contains: stars, dark matter, and X-ray emitting
gas. Put these three components in order of largest fraction of
cluster mass to smallest.
4. (6 pt) A galaxy cluster at a distance of
200 Mpc has a velocity dispersion of 600 km/s and a half-light radius
of 0.5 degrees. What is its mass?