ASTR 121 HW 9
Which of the following is NOT a characteristic of a spiral galaxy?
when we take spectra of its stars, they have far less of the heavier elements than the Sun
Roughly how many galaxies make up our Local Group?
about 60 or so
By examining rich clusters of galaxies, such as the Coma Clusters, astronomers have discovered that spiral galaxies
are found mostly in the outer regions of such clusters, not in the middle
When astronomers have examined rich clusters of galaxies with their instruments, they have found that these clusters
are more likely to contain giant elliptical galaxies than poor clusters
Astronomers believe that the large elliptical galaxies formed
from the collision and merger of many smaller fragments
What do the surveys of the three-dimensional distribution of groups of galaxies reveal about how groups and clusters of galaxies are organized?
galaxy groups are organized into huge filaments with great voids between them -- something like the structure one would see taking a cross-section of some soap bubbles
To map out how clusters of galaxies are distributed in the universe, astronomers needed to know where each cluster was in the sky AND
how far away from us each cluster was
In a distant galaxy, whose light is just arriving from 10 billion light years away, our spectroscope should reveal that the most common element is
hydrogen
Which of the following statements about the implications of Hubble's Law is FALSE?
if you were observing the universe from a distant galaxy, you would NOT see all the galaxies (except those in your own group) moving away from YOU
Which of the following statements about the different types (shapes) of galaxies is correct?
collisions and mergers between galaxies can sometimes change a galaxy's type (shape)
If we want to see what galaxies looked like at a time close to the beginning of the universe, where should we look?
in a direction away from the plane of the Milky Way, where we can see very faint galaxies that are more than 10 billion light years away
Which of the following is not true about the Local Group of galaxies (of which the Milky Way is a member)?
it has about a thousand member galaxies
Which of the following does NOT happen when two galaxies collide?
many of the stars in one galaxy collide with the stars in the other
According to Hubble's Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will
move away from us three times faster than A
Which of the following is not a way that astronomers can find how much dark matter there is in cluster of galaxies?
observe the radio waves coming from all dark matter; from the strength of the radio waves from each cluster, estimate the amount of dark matter needed to produce them
Our Milky Way Galaxy is what type of galaxy?
spiral
The type of galaxy that sometimes has a distinct bar of stars running across the central region is
spiral
Why do galaxies collide, while stars almost never do?
stars are much further apart (compared to how big they are) than galaxies are
How do astronomers currently think the amount of detectable (observable) matter in the universe compares to the amount of dark matter and dark energy?
the amount of detectable matter is far less than the amount of dark matter & energy (<5%)
Which of the following statements about our modern ideas of how spiral galaxies form and develop is TRUE?
the central bulges of spiral galaxies formed first and their disks formed later
If you wanted to write a complete "cosmic address" for yourself, including every location or structure you live in, which of the following would NOT be part of that address?
the coma cluster
An astronomer is observing a distant galaxy which looks blue. Which of the following can she conclude from this observation?
the galaxy must have a lot of star formation going on at the time we are seeing it
If a very distant galaxy looks blue overall to astronomers, from this they can conclude that:
the galaxy must have a lot of young stars and thus active star formation must still be going in it
An astronomer discovers a massive galaxy which has four nuclei. What is a likely explanation for a galaxy having more than one nucleus?
the galaxy must have swallowed several smaller galaxies that were its neighbors
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?
they are (for galaxies) very close to us, so they are easy to study
Astronomers can now report that active star formation was going on at a time when the universe was only 20% as old as it is today. When astronomers make such a statement, how can they know what was happening inside galaxies way back then?
they examine the spectra of galaxies (or the overall colors of galaxies) with the highest redshifts they can find
The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that:
this particular nearby galaxy is moving toward us
One important way astronomers can learn in some detail about what happens when galaxies collide is
to simulate galaxy collisions on a large computer and watch what the simulation predicts
The "great voids" that astronomers studying galaxies are finding are:
very large regions of intergalactic space, where relatively few galaxies or galaxy clusters can be found
Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
you must take a spectrum of the galaxy and measure the red shift
Why is the use of Hubble's Law to measure distances to galaxies so important to astronomers?
Most galaxies are so far away, the only way to get distances to them is to use Hubble's Law
Galaxies that we see as they were 11 billion years ago or more, as compared to galaxies today, are generally:
blue and smaller
According to our current understanding, giant elliptical galaxies form:
by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies
Which type of galaxy is very difficult to see, but (astronomers recently realized) may be very common?
dwarf eliptical
The type of galaxy that consists almost entirely of old stars and is thus less blue (more yellow and reddish) than the other types is:
eliptical
Which type of galaxy is observed to contain mostly older stars?
eliptical
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
faster it is moving away from us
