Answer the remaining problems on
separate sheets of paper. Remember to use only significant figures in
the answers and show all work! Remember to include units for all
numerical answers.
We can only see a neutron star as a pulsar when the beamed emission of the neutron star is pointed in the direction of the Earth.
Time dilation is an effect of special relativity that causes clocks in frames that are moving at speeds near the speed of light to run more slowly than clocks in frames at rest.
The distance to a nearby galaxy can only be determined by Variable Stars, Tully-Fisher, Type Ia Supernovae. Spectroscopic parallax can only be used in our own Milky Way as the individual stars in a cluster need to be resolved so that we can place each star on the HR diagram. We can only do this within our own glalaxy. A nearby galaxy has local motions that make Hubble's Law inapplicable.
Variable Stars: Measure the period of the luminosity change. Then use the relationship between period and absolute luminosity to get the absolute magnitude. We observe the apparent magnitude. Use .
Tully Fisher: Measure the rotational velocity of a galaxy. Tully Fisher found a correlation between the rotational velocity of a galaxy and its absolute luminosity, thus absolute magnitude. We observe the apparent magnitude. Use .
Type Ia SNe: White dwarfs that siphon mass from a binary companion. When the mass of the white dwarf reaches 1.4 M, the star explodes in a supernova. These explosions all involve the same type of star at the same mass, so every Type Ia SN has the same explosion, and the same absolute luminosity. Use the absolute luminosity to get the absolute magnitude. We observe the apparent magnitude. Use .
Disk, Bulge, Halo
For 1 billion :
Rotational curves of galaxies point to missing mass in the outer halos of galaxies (including our own). Also examining the motions of galaxies in galaxy clusters lead to the conclusion that unseen mass must be present to explain the motions of the galaxies due to gravity.
Hubble Law: