We can study how galaxies evolve because ______.
the farther away we look, the further back in time we see.
The light from distant galaxies take a long time to get to us, so we see them as they were millions of years ago.
Which of the following statements is not an assumption used in models of galaxy formation?
Gas contracted to form the disks of galaxies before any stars were born.
One possible explanation for a galaxy’s type invokes the angular momentum of the protogalactic cloud from which it formed. Suppose a galaxy forms from a protogalactic cloud with a lot of angular momentum. Assuming its type has not changed as a result of other interactions, we’d expect this galaxy to be ______.
a spiral galaxy
Two ways in which the starting conditions in a protogalactic cloud might cause it to become an elliptical (rather than spiral) galaxy are if the cloud begins with either _________________.
relatively little angular momentum or relatively high density
Which of the following phenomena are not thought to be results of collisions or other interactions between galaxies?
The fact that spiral galaxies have both disk and halo components
If the Andromeda Galaxy collided with the Milky Way, what would most likely happen to Earth?
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Interactions among galaxies also are thought to influence a galaxy’s type in at least some cases. Which of the following does not support the idea that interactions can shape galaxies?
The fact that more distant galaxies have larger redshifts.
Observations indicated that over billions of years, galaxies in general tend to change from _________.
smaller and bluer to larger and redder
Which characteristic is not generally true of a starburst galaxy?
The observed features of the starburst are thought to be caused by the presence of a supermassive black hole in the galaxy’s center.
Why should galaxy collisions have been more common in the past than they are today?
Galaxies were closer together in the past because the universe was smaller.
A quasar’s spectrum is hugely redshifted. What does this large redshift tells us about the quasar?
the distance to the quasar
Most active galactic nuclei are found at large distances from us, with relatively few nearby. What does this imply?
Active galactic nuclei exist tend to become less active as they age.
Suppose we observe a source of X rays that varies substantially in brightness over a period of a few days. What can we conclude?
The X-ray source is no more than a few light-days in diameter.
All of the following observations are real. Which one does not support the model in which active galactic nuclei are powered by accretion disks around massive black holes?
The most luminous active galactic nuclei have huge redshifts.
Central black holes can be efficient for converting the mass-energy of in-falling matter to thermal energy in the accretion disk. Roughly what percentage of the mass-energy can be converted to other forms of energy as matter falls into a black hole?
The observed relationship between the masses of central black holes and the bulge masses of galaxies implies that:
Galaxy formation and supermassive black hole formation must be related somehow.
Quasar spectra often show many absorption lines that all appear to be as a result of the same electron transition (such as level 1 to level 2 in hydrogen) but that fall at different wavelengths in the spectrum. Why do we think this is the case?
We are seeing absorption lines from clouds of gas that lie between us and the quasar, and therefore each cloud has a different redshift.