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NAME: __________________________
Spring 2014 – ASTR-1020: Stellar Astronomy
Exam 5 – Chapters 19, 20, & 21
Circle your answer clearly AND print the CAPITAL LETTER to the left of the question.
There are 30 multiple choice (3 pts. each) and 1 discussion (10 pts. each) question. Good luck.
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1. What did Edwin Hubble study in the Andromeda Galaxy that proved it was an individual galaxy and not part
of our own Milky Way?
a. Cepheid stars
b. Type I supernovae
c. globular clusters
d. red giant stars
e. RR Lyrae variables
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2. The spectra of most galaxies tell us that:
a. most galaxies appear to be moving away from us
b. their light comes predominantly from objects other than stars
c. most galaxies contain clouds of gas that are absorbing their favorite wavelengths
d. galaxies in the past rotated at a faster rate than they do today
e. galaxies are rushing through space at high speeds
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3. Galaxies move away from us in all directions because:
a. the force of gravity increases with distance
b. the force of gravity weakens with distance
c. space is expanding
d. our galaxy has expelled all other galaxies
e. we are at the center of the expansion of the universe
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4. Hubble’s constant, H0, represents:
a. the rate of expansion of the universe
b. the speed at which galaxies are moving away from us
c. the time it takes a galaxy to move twice as far away from us
d. the size of the universe
e. the amount of time since the Solar System formed
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5. Which of the following lists distance indicators that are used to measure distances ranging from the very
nearest to the very farthest?
a. Cepheids, parallax, main-sequence fitting, Type I supernovae
b. parallax, main-sequence fitting, Cepheids, Type I supernovae
c. parallax, main-sequence fitting, Type I supernovae, Cepheids
d. main-sequence fitting, parallax, Cepheids, Type I supernovae
e. Cepheids, Type I supernovae, main-sequence fitting, parallax
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6. If the Hubble constant had a value that was half of its current measured value of 70 km/s/Mpc, the age of the
Universe would be about
a. 7 billion years
b. 14 billion years
c. 22 billion years
d. 27 billion years
e. 33 billion years
____
7. The Hubble classification scheme for galaxies sorts them by:
a. their evolutionary state
b. their mass
c. the amount of dust
d. the amount of dark matter
e. their visual appearance
____
8. What type of galaxy is this?
a.
b.
c.
d.
e.
____
a giant elliptical
an ordinary spiral galaxy
an irregular galaxy
a barred spiral
a dwarf elliptical
9. In spiral galaxies, the size of the central bulge is correlated with the:
a. tightness of the spiral arms
b. luminosity of the galaxy
c. age of the galaxy
d. thickness of the disk
e. presence of an active nucleus
____ 10. Stars in elliptical galaxies have velocities that:
a. change constantly
b. are very large in size
c. are equal in all directions
d. are constant in time
e. are orientated in random in directions
____ 11. Elliptical galaxies appear red because:
a. they are moving away from us
b. they contain mostly ionized hydrogen gas
c. they contain mostly old stars
d. they contain lots of dust
e. they contain a mix of old and young stars
____ 12. The disks of spiral galaxies appear blue because:
a. they are moving toward us
b. they contain a relatively high concentration of low-mass stars
c. they contain active regions of star formation
d. they contain more metals that, when ionized, emit blue light
e. stars collide with each other frequently in these dense regions and explode as Type I
supernovae
____ 13. Why is 21-cm radiation a good tracer of spiral arm structure?
a. Emitted by neutral hydrogen, it traces the location of high concentrations of gas.
b. Emitted by O and B stars, it traces the location of newly formed stars.
c. Emitted by ionized hydrogen, it traces the location of H II regions.
d. Emitted by molecular hydrogen, it traces the location of clouds in the process of collapsing
into stars.
e. Emitted by red supergiants, it traces the presence of massive stars that are experiencing
high rates of mass loss.
____ 14. Why do rotation curves of galaxies imply that dark matter exists?
a. The velocity of stars rises dramatically at large distances from the centers of galaxies,
implying large amounts of dark matter cause these stars to move much faster than stars at
smaller distances.
b. The velocity of stars stays approximately constant at distances well beyond the visible
edges of galaxies, implying that galaxies contain much more matter than what we observe
in stars and gas.
c. The velocity of stars is low in the inner regions of galaxies, suggesting that dark matter is
impeding their motion.
d. The velocity of stars rises quickly in the inner regions of galaxies, suggesting that unseen
matter is gravitationally moving this material at faster rates than expected.
e. The velocity of stars falls slowly in the outer regions of galaxies, showing that while there
is a lot of dark matter it is distributed the same way as is the visible light.
____ 15. What makes up the majority of the mass of an individual spiral galaxy?
a. a central supermassive black hole
b. dark matter
c. massive O- and B-type stars
d. cold molecular gas clouds
e. low-mass G-, K-, and M-type stars
____ 16. AGNs appear to be powered by:
a. extremely dense star clusters
b. supermassive black holes
c. ultradense molecular clouds
d. decaying dark matter
e. supernova explosion
____ 17. How do we know that AGNs have sizes on the order of our Solar System?
a. Quasars and Seyfert galaxies are stellar-like sources.
b. Their brightness varies by factors of a few.
c. The emission lines in their spectra show gas rotating at speeds of thousands of km/s.
d. Their brightness varies on timescales ranging from hours to a day.
e. We can measure their angular size, which gives us the physical size when we know the
distance.
____ 18. The unified model of AGN suggests that quasars, Seyfert galaxies, and radio galaxies:
a. are unrelated, although they are all very luminous galaxies at radio wavelengths
b. are powered by similar mass accretion rates onto supermassive black holes
c. are driven by violent mergers of two gas-rich spiral galaxies
d. are similar phenomena but viewed from different orientation angles
e. are all powered by high rates of star formation and supernova explosions
____ 19. The Milky Way Galaxy is a(n) __________ galaxy.
a. irregular
b. elliptical
c. nonbarred spiral
d. barred spiral
e. lenticular
____ 20. What type of standard candle is used to determine distances to globular clusters?
a. O-type main-sequence stars
b. Cepheid variable stars
c. T Tauri stars
d. Type I supernovae
e. RR Lyrae stars
____ 21. By comparing globular clusters, you find that Cluster A’s RR Lyrae stars are 100 times fainter than Cluster
B’s RR Lyrae stars. You know that both clusters have approximately the same chemical composition and age,
and thus their RR Lyrae stars should have the same luminosities. Which is true about the clusters’ distances?
a. Cluster A is 10 times farther away than Cluster B.
b. Cluster A is 10 times closer to us than Cluster B.
c. Clusters A and B are approximately the same distances from us.
d. Cluster A is 100 times farther away than Cluster B.
e. Cluster A is 100 times closer to us than Cluster B.
____ 22. The Sun is located approximately:
a. halfway out in the disk
b. one-third of the way out in the halo
c. one-quarter of the way out in the bulge
d. three-quarters of the way out in the disk
e. near the galactic center
____ 23. What observed property of the Milky Way suggests that it contains a large amount of matter not in the form
of stars?
a. the rotation curve
b. the velocities of the open star clusters
c. the number and shape of the spiral arms
d. the thickness of the disk
e. the presence of a black hole at the galactic center
____ 24. The chemical composition of a star’s atmosphere tells us:
a. how much nuclear burning has gone on in the star
b. the star’s evolutionary stage
c. how many planets have fallen onto the star in its lifetime
d. the chemical composition of the cloud from which the star formed
e. the amount of heavy elements the entire galaxy had when the star was formed
____ 25. The stars in the disk of the Milky Way near the Sun have:
a. chemical abundances similar to the Sun
b. much higher velocities than the Sun
c. chemical abundances that are on average 10 times higher than the Sun
d. much lower velocities than the Sun
e. chemical abundances that are on average 10 times lower than the Sun
____ 26. Open star clusters primarily inhabit which part of spiral galaxies?
a. disk
b. halo
c. bulge
d. nucleus
e. satellite galaxies
____ 27. Sagittarius A*, the radio source located at the center of our galaxy, is believed to be:
a. a massive star cluster
b. a supernova remnant
c. a quasar
d. a Seyfert nucleus
e. a supermassive black hole
____ 28. How have astronomers measured the mass of the black hole at the center of our galaxy?
a. using the rotation curve derived from 21-cm emission
b. by observing the motions of stars near the center of the galaxy
c. by measuring the brightness of the quasar
d. by measuring the Doppler shift of Sagittarius A*
e. by counting the number of supernova explosions near the black hole during the last
century
____ 29. The presence of dwarf galaxies around the Milky Way supports what picture of our galaxy’s formation?
a. The galaxy formed by the merger of two large galaxies, which scattered their dwarf
companions to large distances.
b. The galaxy originally formed with no dark matter but gained its dark matter by the
absorption of smaller dwarf systems.
c. The galaxy formed in a giant explosion caused by the violent collisions of clouds of dark
matter.
d. The galaxy formed a long time ago and has been passively evolving since.
e. The galaxy formed by the merger of smaller systems.
____ 30. What is ripping apart the Sagittarius dwarf spheroidal galaxy?
a. a supermassive black hole at the center of the dwarf galaxy
b. pressure from its passage through the dark matter in the Milky Way
c. a violent episode of star formation
d. the gravitational tidal force of the Milky Way
e. supernova explosions occurring in the dwarf galaxy
Short Answer Discussion (10 pts.)
What is a standard candle, and why is it useful for measuring distances? Name three “rungs” in the distance
ladder that let us estimate the value of the Hubble constant. Which of these are “standard candles”?