Download Sample Exam 3

Part III Sample Test.
1) The amount by which time appears to slow down for an object moving relative to you is called the:
A) Doppler Effect.
C) Aberration of starlight.
B) Lorentz factor.
D) Chromatic Aberration.
2) If you see Jackie going to your left at exactly 0.99c and Bob going to your right at exactly 0.99c,
Jackie will say that Bob is going away from her
A) at 1.98c.
D) at about 0.98c.
B) at exactly 0.99c.
E) faster than 0.99c, but slower than c.
C) at exactly c.
3) What would be the most accurate description of the planetary systems so far discovered?
A) Quite similar to the structure of the Solar System.
B) Most of the planets orbit much farther from their stars than in the Solar System.
C) Massive planets orbiting much closer to their stars than in the Solar System.
D) Mostly low-mass objects that would probably be too small to be called planets in the Solar System
4) SETI experiments are currently trying to identify signals from intelligent beings in what wavelength
range?
A) X-rays
D) radio waves
B) ultraviolet radiation
E) gamma rays
C) visible light
5) Up through the start of the 20th century, astronomers like Herschel and Kapteyn used counts of stars in
the Milky Way to estimate the structure of the star system in which we live. From this evidence they
concluded that
A) the Sun was near the middle of a disk-like system of millions of stars.
B) stars existed out to such large distances that the Universe must be infinite.
C) the Sun was on the outer edge of a giant spiral nebula.
D) other stars orbit the Sun but look faint because they are in the outer part of the Solar System.
6) Recent observations indicate that the Milky Way is orbited by many _____, which will eventually
merge with it.
A) dwarf galaxies
C) supermassive black holes
B) galaxy clusters
D) quasars
7) Images of star clusters sometimes show a blue haze surrounding the stars. What causes this “haze”
A) ultraviolet emission by ionized hydrogen
B) scattering of light by dust particles
C) bending of light by dark, massive objects in the cluster
D) intense magnetic fields which make electrons move relativistic spiral patterns
E) it is a problem caused by poor optics in the telescopes
8) Roughly how long does it take the Solar System to orbit the Galactic Center?
A) hundreds of years
C) hundreds of millions of years
B) tens of thousands of years
D) tens of billions of years
9) In Hubble’s classification scheme the Milky Way might be classified as an SBc. This implies that the
Milky Way has all of the following EXCEPT
C) almost no interstellar gas
A) spiral structure
B) a bar-shaped structure in its central
D) loosely-wrapped arms
region.
10) Why would the unknown presence of dust in interstellar space have caused astronomers to
overestimate the distances to distant stars?
A) Without including the gravitational effect of this dust, they estimated the orbits were much larger.
B) The dust makes the star look dimmer, so the brightness formula indicates they are farther than we
thought.
C) The dust reflects light from the stars making them more luminous than we expect.
D) The presence of dust indicates that the stars must be Population I class, which are generally nearer
than Population II class stars.
11) Few galaxies are seen in the “Zone of Avoidance” because
A) the supermassive black hole near the center of the Milky Way deflects their light away from this
direction.
B) most nearby galaxies lie instead within the Local Supercluster.
C) the galaxies in this direction are close to the direction of the Big Bang and therefore highly
redshifted.
D) dust in the galactic plane blocks the light from galaxies in those directions.
12) If you are falling toward a black hole feet first (several Schwarzchild radii out), and throw a baseball
horizontally away from you, you will see the baseball
A) travel away from you in a straight line.
B) fly away and downwards in a curved path, falling faster than you into the black hole.
C) appear to move more slowly than you expect.
D) fly away and upwards in a curved path relative to you, as you fall faster.
13) Most elliptical galaxies in the universe are found
A) in rich clusters of galaxies
B) in poor groups of galaxies
C) equally in clusters and groups
D) on their own.
14) The gas in the center of a rich cluster of galaxies shows about 1/3 to 1/2 the abundance of heavy
elements (metals) as found in the Sun. This is good evidence that
A) The stars in the cluster use different fusion reactions than stars in our galaxy.
B) Gas has been stripped out of galaxies as they fall towards the gravitational center of the cluster.
C) The gas in the cluster center is leftover material produced during Big Bang nucleosynthesis.
D) The gas in the cluster center is mostly made up of dark matter WIMPs.
15) Massive Compact Halo Objects would probably mostly be
C) Tiny, non-interacting, subatomic
A) Supermassive black holes
particles
B) Cooled white dwarfs and dead brown
D) Dense hydrogen clouds
dwarfs
16) The idea that light waves can be stretched out if the space they travel through is expanding is an
example of ___________ predicted by ___________.
A) Gravitational redshift, General
D) Cosmological redshift, General
Relativity
Relativity
B) Doppler redshift, Special Relativity
E) Time dilation, Special Relativity
C) Cosmological redshift, Special
Relativity
17) Consider light from a distant quasar traveling through a gravitational lens. According to Einstein’s
General Theory of Relativity,
A) The light’s path is bent by the gravitational attraction of matter in the lens.
B) The light takes the straightest path through space warped by matter in the lens.
C) Some of the energy of the light is converted into mass, deflecting its path.
D) The path of the light is deflected because the universe has expanded since the light was emitted.
18) The Big Bang theory predicts that over about five minutes of time,
A) 24% of the mass of the universe would be converted from H to He
B) The universe would expand a factor of 1020 in total size.
C) Quarks would combine into stable nuclear particles and all the antimatter in the universe would be
annihilated.
D) Recombination happens.
19) Tiny quantum fluctuations in the energy density of the universe at 10-33 s after the Big Bang are
actually responsible for the later
A) expansion of the universe.
B) widespread existence of matter, instead of anti-matter or no matter, in the universe.
C) formation of large scale structure of the universe.
D) formation of solar systems in the universe.
20) Cosmologies permitted by General Relativity explain all of the following except
A) Hubble’s observations of redshifts of distant galaxies.
B) The spectra of quasars.
C) Gravitational lensing.
D) The rotation curves of galaxies.
E) Why and how light does not escape from the Schwarzchild radius of a black hole.
21) Why can’t we use Hubble’s Law to find the distances to nearby stars?
A) The law has never been tested on stars.
B) Stars don’t rotate as fast as galaxies, for which the law was developed.
C) The redshifts of nearby objects are not caused by the expansion of the universe.
D) Stars don’t move, so we can’t measure a velocity for them.
E) It can be used to find the distances of nearby stars.
22) Observations today suggest that spacetime in our universe is closest to being
A) curved with positive curvature.
C) curved with neutral curvature.
B) curved with negative curvature.
D) flat with zero curvature
E) The presence
23) We use supernovae Ia instead of Cepheid variable stars to measure the distance to very distant
galaxies, from only a billion years or so after the Big Bang, because
A) there were no Cepheids in early galaxies.
B) Cepheids are not bright enough to pick out.
C) supernovae Ia events last longer than Cepheids.
D) the periods of Cepheid stars are too long to observe in distant galaxies.
24) The Hubble Space Telescope has been used to observe supernova type Ia in distant galaxies, to
measure the distance using the brightness law—independent of the velocity redshift distance. The last
supernova Ia in the Milky Way happened about 400 years ago, but many type Ia’s have been observed
by Hubble in just a few years. This is possible because
A) stars lived much shorter lives in the early universe.
B) the Milky Way has an abnormally small number of binary systems that produce Ia supernovae.
C) the cosmological redshift makes it easier to identify type Ia supernovae in distant galaxies than
nearby ones.
D) there were more stars, therefore more supernovae, in the early galaxies observed by Hubble.
E) the Hubble observations can monitor many galaxies, increasing the odds of seeing an event in one
of them.
25) What kind of galaxy has almost no Population I stars?
A) an elliptical galaxy
B) a starburst galaxy
C) a quasar
D) a spiral galaxy
26) If the Milky Way collided with another galaxy which of the following is HIGHLY UNLIKELY to
happen?
A) rapid star formation in the Milky Way
B) collisions between interstellar gas clouds
C) a direct collision of the Sun with stars in the other galaxy
D) gravitational disturbance of the outer Solar System
E) the Solar System flung out of the Milky Way
27) There are probably about ______________ galaxies we could observe with current telescopes.
A) 106
D) 1015
8
B) 10
E) 10100
11
C) 10
28) If a spectral line normally found at 100 nm is observed in a galaxy shifted to 110 nm, the redshift of
the galaxy is
A) 0.1
D) 100
B) 1
E) 110
C) 10
Short Answers
1. On the following graph, draw and label lines which indicate the past and future size of the universe for
the following cosmological models:
(1) Collapsing universe
(2) Critical universe (expands, but constantly slowing)
(3) Constant-expansion universe
(4) Accelerating universe
Size of
Universe
now
2. Which values of Ωmatter correspond to each of the scenarios in 1?
Time
3. What is Olbers’ paradox and how is it resolved?
4. Briefly recount the major stages in the history of the universe from the Big Bang to the present. Include
the approximate length of time and/or the time since the Big Bang to
the best of your ability.
5. Use the Drake equation to estimate the number of civilizations in the Milky Way. Justify your choices
for each variable.