Exam 19: Our Galaxy

A) young stars.
B) globular clusters.
C) X-ray binaries.
D) high-mass,red supergiant stars.

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A) They are farther away.
B) They have higher masses than other stars in the galaxy.
C) They have fewer planets.
D) They have a smaller proportion of heavy elements.
E) They move slower than other stars in the galaxy.

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A) 27 light-years
B) 270 light-years
C) 2,700 light-years
D) 27,000 light-years
E) 27 million light-years

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A) It is probably a halo star that is currently passing through the disk.
B) It is a very young star,recently formed.
C) It has been pushed to high speed by the shock wave from a nearby supernova.
D) It is a very high mass star.

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A) as a flattened disk with a central bulge and barred-spiral arms.
B) as a faintly glowing band of light stretching all the way around the sky.
C) to fill the sky with widely spaced stars.
D) like a single,dim star.

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A) young,red,and dim and have fewer heavy elements.
B) young,blue,and bright and have much more heavy element material.
C) old,red,and dim and have fewer heavy elements.
D) old,red,and dim and have much more heavy element material.
E) old,red,and bright and have fewer heavy elements.

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A) atomic hydrogen
B) ionized hydrogen
C) molecular hydrogen
D) carbon monoxide
E) helium

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A) a cloud of hydrogen and helium that contracts to become a galaxy
B) a term once used historically to refer to any galaxy
C) the cloud-like halo that surrounds the disks of spiral galaxies
D) a cloud of gas that was once a galaxy

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A) Gas that changes only in very slow and steady ways,so that the movie would in fact be quite boring.
B) The entire disk of the Milky Way would pulsate in and out as it contracts to form stars and then blows out in supernovae and then contracts to form stars again and so on.
C) The movie would alternate back and forth between being very bright when there is a lot of gas and very dark when there is very little gas.
D) Gas that is often moving at high speed,particularly after one or more supernovae,and constantly changing form between molecular clouds,atomic hydrogen,and hot,ionized bubbles and superbubbles.

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A) We have discovered a jet of ionized gas shooting out of the bulge of our galaxy.
B) We have discovered that the entire galactic disk is being uniformly "rained on" by cool gas coming from the halo.
C) We see hot gas high above the region of the disk near our solar system,along with cool gas that appears to be raining down from the halo.
D) We have observed a lot of water molecules in the interstellar medium.

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A) The average age of disk stars is less than that of halo stars.
B) Disk stars are all younger than 5 billion years.
C) Disk stars have a higher proportion of heavy elements,on average,than halo stars.
D) Disk stars orbit in the same direction around the Galactic center.
E) The length of the disk is about 100 times its thickness.

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A) We observe an extremely bright X-ray source at the center of our galaxy.
B) We can see gas falling into an accretion disk and central mass at the center of our galaxy.
C) The motions of the gas and stars at the center indicate that it contains a million solar masses within a region only about 1 parsec across.
D) We observe a large,dark object that absorbs all light at the center of our galaxy.
E) all of the above

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A) It is reasonable,because we already know that interstellar dust obscures our view through the disk of the galaxy.
B) The 10% figure is too low,because most of the mass of the galaxy is in the form of interstellar dust.
C) The 10% figure is too high because there are not enough heavy elements to make that much dust.
D) It seems reasonable as long as we assume that red giant stars-which produce dust grains in their stellar winds-are more common than we thought.

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A) Most stars in the halo have cooler surface temperatures than the Sun.
B) Most stars in the halo are less luminous than the Sun.
C) Most stars in the halo contain a much lower percentage of heavy elements than the Sun.
D) Most stars in the halo have either died or are in their final stages of life,while the Sun is only in about the middle of its lifetime.

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A) winds and jets from newly-formed protostars
B) a supernova occurring in the halo
C) multiple supernovae occurring together
D) the combined effect of spiral density waves
E) molecular clouds falling towards the galactic center

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A) the Sun and other solar mass stars
B) O stars
C) red giant stars in spiral arms
D) Cepheid variables
E) globular clusters

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A) open clusters
B) O and B stars
C) K and M stars
D) gas and dust
E) all of the above

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