ISP205, Section 3, Hufnagel & Stein

MIDTERM 3, THE COSMOS April 22, 1997

                                        Name: ________________________


                                        Student Number: ______________

  1. (3 Pts) What is the source of energy of a Quasar?a Black Hole

  2. (3 Pts) Of the 5 galaxies shown at the end of the test, which is likely to be the most distant?

  3. (3 Pts) Professor Stein measures the Hubble constant to be 35 km/s/MLY and Dr. Hufnagel measures the Hubble constant to be 20 km/s/MLY. Which value of the Hubble constant corresponds to a larger age for the universe?
    1. 35 km/s/MLY
    2. The age of the universe has nothing to do with the value of the Hubble constant.
    3. 20 km/s/MLY

  4. (3 Pts) One scenario for the Fate of the Universe is that it will continue to expand forever. Our current era is dominated by stars like our Sun. After all the stars now born have died, the next era will be the
    1. Dark Era, with only electrons and neutrinos.
    2. Degenerate Era, with stellar remnants: white dwarfs, neutron stars and black holes.
    3. Radiation Dominated Era, because everything but photons will have decayed.
    4. Bleak Era, with only black holes.
    5. Big Crunch, when the Universe collapses back on itself and then starts a new cycle.

  5. (3 Pts) Which of the following is evidence that the Universe is evolving, i.e., is evidence against the Steady State Model?
    1. The universe is uniformly filled with cold photons (3K).
    2. The types of galaxies seen now differ from the types of galaxies seen at the beginning of the universe.
    3. There is too much helium everywhere to have been made inside stars: it must have been made at a time when the universe itself was hot and dense.
    4. The quasars are not seen in the current universe, but only at high redshifts.
    5. All of these.

  6. (3 Pts) You randomly select a star from the Nuclear Bulge of the Milky Way. What is the most likely stage of evolution for this star?
    1. black hole
    2. neutron star
    3. main-sequence star
    4. white dwarf
    5. red giant

  7. (3 Pts) Choose the best description of the distribution of galaxies in the Universe.
    1. clumped in uniformly distributed clusters
    2. clumped like Swiss cheese
    3. clumped in clusters in thin shells around voids
    4. clumped in randomly distributed clusters
    5. uniformly spread through the universe

  8. (4 Pts) List TWO of the many things we can learn about the universe from observations of the 3 K Background Radiation.
    (i)The uniform distribution of current radiation tells us the early universe was very uniform.
    (ii)Since galaxy observations tell us that the universe is expanding, the (hot) temperature of the early universe can be calculated from the current (cool) 3K temperature.
    (iii)The early universe had to be very hot and hence radiation-dominated and opaque.
    (iv)The Milky Way's motion through the universe.

    It CANNOT tell us the age or size of the universe, nor how fast it is expanding, or even if it's currently expanding at all.

  9. (3 Pts) The Background Radiation we now observe has a temperature of 3 K. Why is this evidence that the universe was once hot?
    1. The radiation was once hotter because the universe is expanding.
    2. The radiation is seen at nearly the same temperature from all directions.
    3. The center of the universe is redshifted from us.
    4. The radiation is blueshifted in the direction towards which the Milky Way is moving.
    5. The radiation has cooled down because the universe is very old.

  10. (3 Pts) If a galaxy is observed to contain mostly red stars, this means that
    1. The stars are very massive.
    2. The stars are old.
    3. The stars are made mostly of iron.
    4. All of these.
    5. The galaxy is far away.

  11. (3 Pts) Of these three steps in the evolution of the early universe according to the Big Bang Model, which is the correct order of events?
    1. recombination, galaxy formation, primordial nucleosynthesis
    2. galaxy formation, primordial nucleosynthesis, recombination
    3. recombination, primordial nucleosynthesis, galaxy formation
    4. primordial nucleosynthesis, recombination, galaxy formation
    5. primordial nucleosynthesis, galaxy formation, recombination

  12. (3 Pts) In the Big Bang theory, the fusion of protons and neutrons to make helium stopped at about 30 minutes after the big bang because
    1. the density of matter in the universe became too small for fusion.
    2. ns None of the above.
    3. the density of matter in the universe became too large for fusion.
    4. the temperature of the universe became too cold for fusion.
    5. all the protons became fused into helium.

  13. (3 Pts) When we observe a galaxy that is 6 billion lightyears away from us, we are seeing it as it
    1. is today.
    2. will be 6 billion years from now.
    3. was before the Earth formed.
    4. there is not enough information to tell.
    5. none of these.

  14. (3 Pts) The expansion of the universe is being speeded up by the
    1. supernova explosions
    2. force of gravity
    3. pressure of the microwave background photons
    4. fusion of hydrogen into helium
    5. ns the expansion of the universe is actually slowing down

  15. (3 Pts) At what temperature does primordial nucleosynthesis occur? You may want to use the graph at the back of the exam.
    1. 102 K
    2. 106 K
    3. 104 K
    4. 108 K
    5. 1010 K

  16. (3 Pts) Although we are inside our Milky Way galaxy, we can determine the position of the Solar System relative to the center of the Milky Way by
    1. Counting the number of stars visible in different directions around us.
    2. Looking for a star similar to the Sun in another galaxy and measuring its distance from the center of its galaxy.
    3. Sending a probe to find the center of the Milky Way.
    4. Using Kepler's Third Law to determine the distance of the Solar System from the center of the Milky Way.
    5. Measuring the positions of the globular clusters and determining their center.

  17. (3 Pts) At the end of the exam are pictures of 5 galaxies. Which one is an elliptical galaxy?

  18. (3 Pts) The Coma cluster of galaxies is moving away from us with a speed of 6700 km/sec. The Pegasus cluster of galaxies is twice as far away from us as the Coma cluster. How fast are the galaxies in the Pegasus cluster moving away from us?

    13,400 km/s. Double the speed of Coma.
    or
    about 13,000-15,000 km/s. Use the Hubble Diagram at the end of the exam.

  19. (4 Pts) We compared the galaxies in the Hubble Deep Field with those nearby. Most distant galaxies in the Hubble Deep Field are primarily irregulars and spirals. Most of the galaxies nearby are ellipticals. In a few sentences, present a possible theory to explain this observation.

    To be "possible," your proposed theory must include the concept that the distant galaxies are also younger galaxies, due to the "look-back" time effect of light having a finite speed and thus taking time to get to us.
    One possible theory is that since younger galaxies are primarily irregulars and spirals, and older galaxies are ellipticals, the irregulars and spirals evolve into ellipticals. (Particularly good answers were self-critical, pointing out the problem that the Milky Way is a spiral in the current universe.) If you assume the Steady State model, then you might postulate that young ellipticals were very small and faint and thus harder to see when they were young.

  20. (3 Pts) You are taking a cruise around the world, which includes rounding the southern tip of South America. (This is the same route that the explorer Magellan took.) You look up in the sky and notice that there is a large but shapeless concentration of mostly bluish stars. What type of galaxy are you looking at?
    1. elliptical
    2. globular cluster
    3. irregular
    4. spiral
    5. merging

  21. (3 Pts) You observe several galaxies receding at different speeds. Which galaxy is farthest away? (You may wish to use the Hubble Diagram at the back of the exam.)
    1. Galaxy receding at 10,000 km/s
    2. You don't have enough information to tell.
    3. Galaxy receding at 20,500 km/s
    4. Galaxy receding at 50,000 km/s
    5. They are all the same distance from us.

  22. (3 Pts) Andromeda is more massive than the Milky Way. You observe a star with the same mass as the Sun but in the red-giant phase of its life. It is the same distance away from the center of Andromeda as the Sun is from the center of the Milky Way. How would its orbital velocity compare with that of the Sun?
    1. The Andromeda star would move more slowly, because it formed 10-billion years ago.
    2. The Andromeda star would move more slowly, because of the ``look-back'' time delay.
    3. The Andromeda star would move faster, because Andromeda has stronger gravity.
    4. The Andromeda star would move faster, because the entire galaxy is blue-shifted with respect to the Milky Way.
    5. It's impossible to get spectra for stars in Andromeda; it's too far away.

  23. (3 Pts) If a galaxy is approaching us,
    1. its spectral lines will be blueshifted
    2. it will have a red color
    3. it must be an elliptical galaxy.
    4. none of these
    5. its spectral lines will be redshifted

  24. (3 Pts) From the perspective of the Local Group of Galaxies, it appears as if all of the galaxies in the entire universe are receding away from us. If you were living in a distant cluster of galaxies, what would you observe about galaxies outside your own cluster?
    1. It would not be possible to observe galaxies outside the cluster, because they would be blocked by other galaxies inside the cluster.
    2. None of them would be receding due to the immense mass and gravity of a cluster of galaxies.
    3. Most of the galaxies in the galaxy cluster would be elliptical.
    4. Since galaxy clusters only occurred in the early universe, the redshifts would be much smaller.
    5. All of them would be receding in a pattern similar to what we see.

  25. (3 Pts) You observe a galaxy receding from us at a speed of 45,000 km/s. How far away is it from us? You can use the Hubble Diagram at the back of the exam.

    1200 Mega-lightyears
    1400 Mega-lightyears

  26. (4 Pts) When Andromeda and the Milky Way collide and merge with each other in about 3 billion years, it is unlikely that a star like our Sun will collide and merge with another star. Explain, using one or two complete sentences, why this is so.

    The merger of two disk stars in a collision between two spiral galaxies is unlikely because the stars in the disk are so far apart.

  27. (3 Pts) At the end of the exam are pictures of 5 galaxies. Which one is likely to have the most young stars?

  28. (10 Pts) On the sky map for June below draw small circles around as many of the stars from your list of 16 brightest northern hemisphere stars as you can find and write their names next to each such star. [One point for each correct star, but minus 1/2 point for each incorrect star, so don't guess.]

    The ten stars were: Altair, Deneb, Vega, Arcturus, Antares, Spica, Capella, Castor, Pollux and Regulus.

  29. (5 Pts) Calculate the mass of the Milky Way. Procyon, a binary system of a F5 main sequence star and a white dwarf, moves in a nearly circular orbit around the center of the Milky way with a speed of 250 km/s, at a distance of 2 x 109 AU from the center of the galaxy, with a period of 2 x 108 years. Use one of the formulae from the list at the end of the exam. SHOW YOUR WORK!

    m1 + m2 = a3/P2
    m1 = the mass of the Milky Way and m2 = the mass of Procyon
    Since the mass of ANY one star or binary is so much less than the mass of an entire galaxy, you can ignore it.
    m1 = 2 x 109[AU]3 / 2 x 108[yrs]2
    m1 = 8 x 1027 / 4 x 1016
    m1 = 2 x 1011 MSun

  30. (3 Pts) The location of the Sun in the Milky Way galaxy is
    1. in an open cluster
    2. near the center
    3. in the Halo
    4. in a globular cluster
    5. in the Disk

Useful Formulae

F = m a

lambdapeak=3x107 / T
P2=a3
m1 + m2 = a3/P2
E = m c2

D=1/p

1 AU = 1.5 x 108 km

V = H D

D = V t

Galaxy pictures will be here shortly.

Galaxy A was a small OR distant elliptical: you have no way of telling which from an image.

Galaxy B was an irregular or a distant spiral.

Galaxy C was either a large or a closeby elliptical: you have no way of telling which from an image.

Galaxy D was a pair of interacting galaxies, the Antennae, which was pictured in your textbook.

Galaxy E was an edge-on spiral, the Sombrero, which was shown frequently in class.

The inherent ambiguity in looking at these images is why there were multiple correct answers to the questions about these pictures.

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Beth Hufnagel's home page, email: hufnage4@pilot.msu.edu
Bob Stein's home page , email: steinr@pilot.msu.edu