Practice Questions for Final

True-False

The diameter of the stellar disk of the Milky Way is about one million light years.

Spiral galaxies wind up their spirals because the dark matter slows their rotation.

Elliptical galaxies eventually become spiral galaxies.

Hot B stars are more common in spiral galaxies than in elliptical galaxies.

Nearby spiral arms can be traced by looking at ionized nebulae associated with hot young stars.

One reason we think the Sun is not at the center of the Galaxy is that there are no globular clusters in the general direction of the Galactic bulge.

Nebulae seen in reflection will be bluish, while ionized emission nebulae
tend to look reddish.

Quasars are valuable to the study of cosmology because they are so bright they may be the source of the microwave background.

Some galaxies are observed by radio telescopes to be shooting two oppositely directed jets of material millions of light years into intergalactic space.

All of the helium in the Universe was produced by hydrogen fusion in stars.

COBE saw such large structures in the microwave background that the Universe has to much older than previously thought.

Multiple  Choice

Which of the following probably does NOT involve an accretion disk?
 
\a  the radio jet from active galactic nucleus
\b  the formation of the solar system
\c  the radio beam from a pulsar
\d  X-rays from galactic stellar black holes
\e  a classical nova

The ``critical density''  of the Universe refers to:
 
\a  the density of the Big Bang just before inflation
\b  the density of the microwave photons
\c  the density at which quark formation cannot occur
\d  the overall density above which recollapse will occur
\e  the local density at which primordial black holes form

Distant quasars appear to be receding most quickly (of any observed objects) because
 
\a  they are the objects ejected most quickly during the Big Bang
\b  they are the brightest and therefore the fastest objects known
\c  supermassive black holes eject matter at the greatest speeds
\d  they are furthest from most of the matter in the Universe
\e  there is the most expanding space between us and them

Which of the following statements is TRUE about stars in the disk of a spiral galaxy?
 
\a  High mass stars tend to be found between the spiral arms.
\b  A given spiral arm will always contain the same stars.
\c  A low mass star will pass through more than one spiral arm during its lifetime.
\d  No stars are found between the spiral arms.
\e  Stars in spiral arms have density waves on their surfaces.

Which of the following is evidence for the ``dark matter''?
 
\a we see small rocky bodies floating everywhere
\b stars are difficult to see on the other side of the Galaxy
\c there are great voids without galaxies in intergalactic space
\d galaxies move within clusters faster than we expect
\e primordial black--bodies must generate the gamma ray background

Which of the following is NOT true of the Big Bang sometime during the first day, according to theory?
 
\a  photons were so energetic they spontaneously turned into matter and antimatter
\b  the entire observable Universe was contained in a space much smaller than the solar system
\c  the sky was dark in all directions because the Universe was opaque
\d  there was no difference between the strong and weak nuclear forces
\e  a nuclear fusion throughout space produced most of the helium we see today

The recession velocity of a galaxy one billion ly away (using a Hubble constant of 25 km/s/$10^6$ly) is
 
\a  25,000 km/s
\b  the speed of light
\c  4000 km/s
\d 25$\times 10^6$ km/s
\e  40,000 km/s

Which of the following is more true of elliptical galaxies than spiral galaxies?
 
\a  they tend to have more Type II supernovae
\b  they tend to have younger stars
\c  they tend to have more interstellar gas
\d  they tend to be found by themselves (outside of clusters)
\e  they tend to be the result of galaxy collisions

In the inflationary theory, the observed Universe is flat. This means that
 
\a  the edge of space is just beyond the horizon
\b  it will last essentially forever
\c  it will always expand at the same rate
\d  all matter must stay on its surface
\e  parallel beams of light eventually come together