Download PREVIEW-Reading Quiz 09 - Chapter 15

Reading Quiz 09 - Chapter 15
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Started: Sep 26 at 10:39am
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Reading Quiz 09 - Chapter 15 of Understanding Our Universe
Space is not empty. Here is a small section of our galaxy showing the central bulge. This image, taken at visible wavelengths, emphasizes characteristics common to
all spiral galaxies, including barred spirals. Use this image for answering the next two questions.
Question 1
What are the darkest "clouds" of material seen in this image made of?
All of these answers are correct.
interstellar dust, solid grains of carbon, silicon, and iron.
interstellar gas, primarily hydrogen and helium
Warm intercloud gas at a temperature of ~8000 K.
Cold intercloud gas at a temperature of ~100 K
1 pts
Question 2
1 pts
Why is the material that snakes in front of the background stars is so dark, with no light shining through?
There are so many atoms and molecules in the cool gas of the Galaxy that the absorption lines are dominating spectra.
This image was take at radio wavelengths and the dark curvy material is the dark matter of the Galaxy.
The dark lane that runs through the plane of the Galaxy is the region that splits the disk in half.
This image is taken at visible wavelengths, and dust efficiently blocks light from stars behind it.
Question 3
1 pts
The Trifid (left) and Lagoon (right) nebulae are located towards the center
of the Milky Way.
If we were to take a spectrum of the red parts of either of these nebulae, we might see something like the spectrum shown at right,
above. What information do we get from the image and the spectrum?
Via Kirchhoff's laws, this is a diffuse hot gas emitting photons.
Tantalizingly, all of these answers are most likely correct.
Ultraviolet radiation from hot, luminous O and B stars must be providing the energy.
There are probably some newly born stars and active star formation occurring.
These nebulae represent HII regions, with the H-alpha line dominating.
Question 4
1 pts
The interaction between the nucleus and the electron of a hydrogen atom is at a lower energy when the proton and electron have opposite spins (magnetic poles point
in opposite directions), than when they spin in the same direction.
Our observations of the Milky Way at the 21-cm line wavelength tell us a lot about our galaxy. All of the following are correct except one. Which one is certainly wrong?
The motion of the solar system complicates the pattern of rotation.
The Galaxy is expanding away from other galaxies.
Clues as to the overall structure of the Galaxy.
The Galaxy is spinning; we have plotted its rotation curve.
Question 5
1 pts
Each of the following types of particles can be classified as being a type of cosmic ray, except one. Which one should have been omitted?
protons
muons (a subatomic particle)
nuclei of helium
electrons
photons
Question 6
1 pts
What mechanism gives the cosmic rays such extremely high energies?
All of these mechanisms individually or together give the cosmic rays high energies.
The collapse of the giant molecular clouds due to gravity.
The high spinning velocity of the Galaxy close to its supermassive black hole.
Shock waves produced by supernovae explosions.
We need to correct the information given on page 392 of the textbook. Cepheid variables, as we have defined them, are not found in globular clusters since Cepheid
variables represent a stage that massive stars go through, and globular clusters have mostly low-mass stars present today, the massive stars having gone supernova
billions of years ago. The variable stars found in globular clusters are RR Lyrae variables, a stage in the evolution of stars having close to solar masses.
Question 7
Each of the following statements lists a characteristic common to the globular clusters of the Milky Way, except one. Which statement is incorrect?
The more than 150 globular clusters contain about 40% of the total stars of the Milky Way.
The stars in the globular cluster have typical ages of around 12 billion years.
Globular clusters orbit the gravitational center of the Galaxy and obey Kepler's laws.
About 75% of the globular clusters reside in the spherical volume called the halo.
1 pts
Question 8
1 pts
What is the theory behind the observations that the halo stars - such as those found in globular clusters - are all "metal-poor," meaning that they have a very low
percentage of elements heavier than helium, while stars located in the disk of the Galaxy have higher, and sometimes much higher, abundances of "heavy elements,"
such as carbon, nitrogen, oxygen, iron, magnesium, etc.
Halo stars formed shortly after the Big Bang when the composition of the Universe was mainly hydrogen and helium.
Disk stars have compositions enriched with heavy elements from supernovae explosions, planetary nebulae, and stellar winds.
All of these answers are part of the theory of the chemical enrichment of the Milky Way.
Star formation in the disk happened later than that in the halo and is still an ongoing process.
Halo stars formed first and there has been little or no star formation there in the past 10+ billion years.
Question 9
1 pts
Which one of the following choices gives the strongest evidence that there must have been a population of massive stars even before galaxies and their globular
clusters formed?
Huge numbers of cosmic rays have been detected from the edges of the visible universe.
Even the oldest, most "metal poor" stars show traces of elements heavier than helium.
Theoretical calculations indicate that current day supernovae couldn't provide those elements.
The remnant microwave radiation left from the Big Bang shows massive star emission lines.
Question 10
1 pts
What evidence supports the theory of a supermassive black hole at the center of our galaxy?
Required.
High-energy X-rays being emitted from the central region.
All of these observations provide evidence in support of the theory.
The high orbital velocities of stars near the center.
Strong magnetic fields having loops of plasma.
Question 11
4 pts
Choose among open clusters, globular clusters, neither, both.
Are part of a smaller galaxy inside the Milky Way.
Found in the disk of the Milky Way.
Found in the halo of the Milky Way.
[ Choose ]
[ Choose ]
[ Choose ]
Contain extremely small percentages overall of elements
heavier than helium.
Loosely bound and easily disrupted by tidal forces.
Some contain the youngest stars known.
All formed in the same region at about the same time.
Stars of these are among the oldest objects known.
[ Choose ]
[ Choose ]
[ Choose ]
[ Choose ]
[ Choose ]
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