How do observations of distant galaxies help us learn about galaxy evolution?
answer
Observations at different distances show galaxies of different ages and therefore different stages of evolution.
question
Which of the following gives the two main assumptions of theoretical models of galaxy evolution?
answer
Hydrogen and helium filled all of space, and certain regions of the universe were slightly denser than others.
question
Which of the following types of protogalactic clouds is most likely to form an elliptical galaxy?
answer
a dense cloud with very little angular momentum
question
Why is a dense cloud more likely to produce an elliptical galaxy than a spiral galaxy?
answer
The higher gas density forms stars more efficiently, so all the gas is converted into stars before a disk can form.
question
What evidence supports the theory that elliptical galaxies come from denser clouds?
answer
Elliptical galaxies at high redshifts lack young, blue stars.
question
Why should galaxy collisions have been more common in the past than they are today?
answer
Galaxies were closer together in the past because the universe was smaller.
question
What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy?
answer
observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies
the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies
observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy
observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies
****all of the above
question
How many more stars does a starburst galaxy form, in one year, than the Milky Way?
answer
about a hundred
question
Why do we believe that starburst galaxies represent a temporary stage in galaxy evolution?
answer
Such galaxies produce so much light that they would have consumed all their gas long ago if they had always been forming stars at this high rate.
question
What first indicated that the quasars were very distant objects?
answer
determining their redshifts.
question
What is a quasar?
answer
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
question
Which of the following is evidence for supermassive black holes in active galaxies?
answer
the discovery of powerful jets coming from a compact core
rapid changes in the luminosity of the galaxy nucleus
quasars emit approximately equal power at all wavelengths from infrared to gamma rays
very high speed orbital motions around galactic nuclei
****all of the above
question
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
answer
Active galactic nuclei tend to become less active as they age.
question
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
answer
by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
question
Where are the X rays produced that are emitted by quasars and other active galactic nuclei?
answer
in hot gas in an accretion disk around a central black hole
question
All of the following are true. Which of these gives evidence that quasars were more common in the early stages of the universe?
answer
They are more common at very great distances.
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