Download ASTR 001 Introduction to the Cosmos

ASTR 001 Introduction to the Cosmos
Practice Midterm Exam #2
Name: HASSEN M. YESUF
• Select the answer (letter choices AE) that BEST fits the question.
• Write and bubble in your name and student ID on the Scantron sheet.
• Write your name on this exam script.
• Turn in BOTH your Scantron and this exam script to one of the proctors at the end of the exam.
• Dont worry about the Test Form bubble on the Scantron; we will fill that in for you.
Other notes:
• There are 40 questions in this practice exam. The actual exam is a bit longer. I recommend you plan to
spend 60 minutes on this practice exam.Answers are provided on the page 8.
• This practice exam is almost the actual exam in disguise study it very carefully. By this I mean know what
different terms and concepts mean even though they may not be related directly to the question asked.
• NO talking please!!!! If the exam proctors see a student talking or exchanging information with any of the
other students during the exam, they will make a note on the exam script of the student(s) in question, and
the student(s) will fail the exam.
• NO calculators, laptops, cell phones, iPods, or any other electronic devices please! The required math should
be doable on pencil/paper without the need for a calculator.
• This is an OPEN BOOK / OPEN NOTES exam, so textbooks and notes ARE allowed during the exam.
Good luck ,
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1. At a certain point in the Universes history, the density of matter in the Universe was 64 times larger
than it is today while the energy density of radiation in the Universe at that time was 256 times than what it
is today. This means the the average distance between galaxies at that time was
A) 8 times larger than it is today
B) 4 times smaller than it is today
C) 3 times smaller than it is today
D) 4 times larger than it is today
E) The same as it is today.
2. Compared to spiral galaxies, elliptical galaxies are
A) Redder and rounder
B) Redder and flattened
C) Blue and flattened
D) Gas rich and dusty
E) Always much smaller
3. What is Hubble’s law?
A) The square of the recession velocity of a galaxy is proportional to a cube of its distance.
B) The recession velocity of a galaxy is directly proportional to its distance from us.
C) The recession velocity of a galaxy is inversely proportional to its distance from us.
D) The faster a spiral galaxy’s rotation speed, the more luminous it is.
E) The faster a spiral galaxy’s rotation speed, the less luminous it is.
4. Which is of the following is not true about the Schwarzschild radius of a black hole ?
A) Nothing can escape from inside this radius
B) It depends on the mass of a black hole
C) The gravitation influence of a black hole can be experienced outside this radius
D) The accretion disk of hot gas around a black hole is inside this radius
E) None of the above
5. Hubble’s “constant” is constant in
A) time.
B) space.
C) space and time.
D) our Galaxy but different in others.
6. Based on current estimates of the value of Hubble’s constant, how old is the Universe?
A) between 4 and 6 billion years old
B) between 8 and 12 billion years old
C) between 12 and 16 billion years old
D) between 16 and 20 billion years old
E) between 20 and 40 billion years old
7. Why can’t we see past the cosmological horizon?
A) The universe extends only to this horizon.
B) Beyond the cosmological horizon, we are looking back to a time before the universe had formed.
C) We do not have telescopes big enough.
D) Every galaxy in the entire universe (not just the observable universe) exists within the cosmological horizon, so
there’s nothing to see beyond it.
E) The cosmological horizon is infinitely far away, and we can’t see to infinity.
8. Which of the following statements about types of galaxies is not true?
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A) Spiral galaxies have younger stars than elliptical galaxies.
B) Spiral galaxies have ordered rotation.
C) Spiral galaxies did not evolve from Elliptical galaxies.
D) Elliptical galaxies are bluer and contain more dust than spiral galaxies.
9. The most basic difference between elliptical galaxies and spiral galaxies is that
A) elliptical galaxies lack anything resembling the halo of a spiral galaxy
B) elliptical galaxies have a spheroidal component (of stars distributed spherically about the galactic center), and
spiral galaxies do not
C) elliptical galaxies lack anything resembling the disk of a spiral galaxy
D) elliptical galaxies have inactive black holes at the center while spiral do not.
.
10. Hubble’s galaxy classification diagram (the “tuning fork”)
A) explains active galactic nuclei
B) shows how galaxies evolve from one form to another
C) suggests the existence of black holes
D) relates galaxies according to their shapes, but not according to any evolutionary status
11. Today the Universe is
A) Larger
B) Colder
C) Denser
D) All of the above
E) A & B
12. In particle era,
A) Gamma-ray photons
B) Quarks
C) Microwave photons
D) Protons
E) WIMPS
than it was a billion years ago.
were constantly converted to electrons and positrons (anti-electrons)
13. Hubble’s constant is about 22 km/s/million light-years, implying an age of about 14 billion years for
the universe. If Hubble’s constant were 11 km/s/million light-years, the age of the universe would be about:
A) 7 billion years.
B) 14 billion years.
C) 28 billion years.
D) Impossible to say, because Hubble’s constant has no relationship to the age of the universe.
14. Why do we believe 90 percent of the mass of the Milky Way is in the form of dark matter?
A) The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are
feeling gravitational effects from unseen matter in the halo.
B) Although dark matter emits no visible light, it can be seen with radio wavelengths, and such observations confirm that the halo is full of this material.
C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as
much matter as we see in the Milky Way disk, suggesting that the halo is full of dark matter.
D) Our view of distant galaxies is sometimes obscured by dark blotches in the sky, and we believe these blotches
are dark matter located in the halo.
15. Measuring the mass of a clusters using the amount of distortion caused by a gravitational lens uses
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A) Kepler’s law
B) Hubble’s law
C) Newton’s universal gravitational law
D) Einstein’s general relativity
E) Doppler’s law
16. What is currently happening to the expansion of the Universe?
A) It is uniform
B) It is slowing down
C) It is speeding up
D) It cannot be known
17. What fraction of the mass needed to halt expansion is known to exist in the form of visible mass in
the universe?
A) 4 percent
B) 10 percent
C) 25 percent
D) 50 percent
18. Based on inventoried matter in the universe, including dark matter known to exist in galaxies and
clusters, the actual matter density of the universe is what fraction of the critical density?
A) 1 percent
B) 10 percent
C) 30 percent
D) 70 percent
E) 100 percent
19. Which of the following lists the types of matter in the correct chronological order in which they came
into existence in Universe’s history?
A) Neutron, quark, Helium, Carbon
B) Neutron, quark, Hydrogen, Helium
C) quarks, Neutron, Helium, Carbon
D) Hydrogen, quark,Helium, Carbon
E) A & B
20. Which model of the universe gives the youngest age for its present size?
A) “A recollapsing universe” which will end up in a Big Crunch in the future
B) “A coasting universe ” which will expand forever at a uniform rate
C) “An accelerating universe” which will expand increasingly with time forever
D) All models give the same age
21. What do we mean by inflation?
A) a rise in the price of precious metals produced in supernovae.
B) a sudden expansion of the universe after the strong force froze out from the GUT force
C) the expansion of the universe that we still observe today
D) the sudden release of photons when a particle and antiparticle annihilate each other
E) the separation that occurs after two photons collide and create a particle and an antiparticle
22. What happened to the quarks that existed freely during the particle era?
A) They combined in groups to make protons, neutrons, and their antiparticles.
B) They froze out of the soup of particles at the end of the era.
C) They evaporated.
D) They combined in groups to make electrons and neutrinos.
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23. Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from
predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with
observations. Four of the five statements below are real. Which one is fictitious?
A) The cosmic background radiation is expected to have a temperature just a few degrees above absolute zero, and
its actual temperature turns out to be about 3 K (actually 2.7 K).
B) The cosmic background radiation is expected to have a blackbody(continuous) spectrum, and observations from
the COBE spacecraft verify this prediction.
C) The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.
D) The cosmic background radiation is expected to look essentially the same in all directions, and it does.
E) The cosmic background radiation is expected to have tiny temperature fluctuations at the level of about 1 part
in 100,000. Such fluctuations were found in the COBE data.
24. The photons in the cosmic background radiation started to travel freely at
A) the moment of the Big Bang
B) the end of the Planck era
C) the end of nucleosynthesis
D) the beginning of the era of atoms
E) during the era of galaxy formation
25. Which of the following observations is not a piece of evidence supporting the Big Bang theory?
A) Darkness of the night sky
B) Recession speeds of far away galaxies relative to close ones
C) Observed helium abundance in the universe
D) Relative motions of galaxies in the Local Group
26. Which of the following is false ?
A) E7 galaxies have more elongated bulge than E0 galaxies
B) Sa galaxies have more tightly wound arms than Sc galaxies
C) Sa galaxies have more bulge component than Sc galaxies
D) Spiral galaxies have disks but no bulges
E) Spiral galaxies exhibit differential rotation.
27. Which of the following happened last in the Universe’s timeline?
A) Quark confinement into proton and neutron
B) production of Deuterium in the early universe
C) Inflation of the universe after strong force freeze out
D) recombination and the universe become transparent to CMBR photons
E) Formation of first black holes
28. Which of the following happened second to last in the Universe’s timeline.
A) Quark confinement into proton and neutron
B) production of Deuterium in the early universe
C) Inflation of the universe after strong force freeze out
D) recombination and the universe become transparent to CMBR photons
E) Formation of first black holes
29. Which of the following is not true about black holes?
A) Quasars (black holes) have broad emission lines.
B) The very luminous accretion disks around black holes are about couple of AUs in diameter.
C) The escape velocity at the event horizon is infinity.
D) Gravitational influence of a black hole is felt outside Schwarzschild radius.
E) Black holes have finite age and will not live forever.
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30. Which of the following is false ?
A) The Universe was matter dominated before it was cosmological constant dominated.
B) The Universe was radiation dominated before it was matter dominated.
C) The radiation density of the Universe drops faster than matter density as the Universe expands.
D) The energy density of the dark energy (the cosmological constant) was smaller in radiation dominated Universe
than its current value.
E) Inflation happened in radiation dominated universe and galaxies formed in matter dominated universe.
31. What kinds of objects lie in the halo of the Milky Way galaxy?
A) open clusters
B) O and B stars
C) Dark matter and stars
D) gas and dust
E) all of the above
32. Imagine a hypothetical universe where the temperature of a CMBR photons varies by 0.5 K for any
two places separated by 1.5 degrees. From the above fact only, which statement is valid about the hypothetical universe?
A) It violates the cosmological principle
B) It is currently dominated by dark energy
C) It is unlikely that it has undergone Inflation
D) It is flat
E) A & C
33. A spaceship is headed toward Alpha Centauri (the closest star) at 0.9c. According to us, the distance
to Alpha Centauri is about 4 light-years. How far away is Alpha Centauri according to the travelers in the
ship?
A) also about 4 light-years
B) more than 4 light-years
C) less than 4 light-years
34. Which of the following is correctly describes a Universe with “flat” spacetime geometry?
A) Ωm + ΩΛ = 1
B) Ωm + ΩΛ = 0
C) Ωm + ΩΛ < 2
D) Ωm + ΩΛ < 0
E) Ωm + ΩΛ = −1
35. Which of the following is a best explanation why the night sky is dark?
A) Because the average distance between stars is more than 10 light years.
B) Because the Universe is not infinite is space.
C) Because the Universe is mostly opaque to starlight.
D) Because the Universe is dominated by dark matter.
E) Because the matter distribution in the universe is not uniform on very large scale.
36. The spectra of most galaxies show redshifts. This means that
A) They have an old stellar population.
B) They have a young Stellar population.
C) They are moving away from us.
D) They have a higher intensity in the red part of the spectrum.
E) They are dusty.
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37. From laboratory measurements, we know that a particular spectral line formed by hydrogen appears
at a wavelength of 486.1 nanometers (nm). The spectrum of a particular star shows the same hydrogen line
appearing at a wavelength of 486.2 nm. What can we conclude?
A) The star is moving toward us.
B) The star is moving away from us.
C) The star is getting hotter.
D) The star is getting colder.
E) The star is a binary system.
38. Which of the following does Inflation help to explain?
A) The origin of Hydrogen.
B) The origin of Helium.
C) The origin antimatter.
D) The origin of Black holes.
E) The origin of Galaxies.
39. Which of the following is not true about Milky Way?
A) It has about 100 billion stars
B) It has an asymmetric distribution of globular clusters around the sun.
C) It has a disk of radius 50,000 light years
D) The vertical extent (height) of its disk is less than 50,000 light years.
E) None of the above
40. Primary source of a Quasar (Black hole) energy is
A) Gravitational potential energy
B) Nuclear energy
C) Chemical energy
D) Magnetic energy
E) Psychic energy
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Answers
1.B
2.A
3.B
4.D
5.B
6.C
7.B
8.D
9.C
10.D
11.E
12.A
13.C
14.A
15.D
16.C
17.A
18.C
19.C
20.A
21.B
22.A
23.C
24.D
25.D
26.D
27.E
28.D
29.C
30.D
31.C
32.E
33.C
34.E
35.B
36.C
37.B
38.E
39.E
40.A
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