29:50 Modern Astronomy
Fifth Hour Exam
December 15, 1997
Form A
Although the lesson is ever the same, people ever fail to understand
Heraclitus

1. Billions of years in the future, the Sun will have become one of the following objects as its ``end point'', i.e. the end of its stellar evolution. Which is it?
   (a) red supergiant
   (b) white dwarf
   (c) neutron star
   (d) red dwarf
   (e) T Tauri star
   
2. Consider a very massive star on the Main Sequence, with perhaps 25 solar masses. In the future, this star will become one of the following objects as its ``end point'', i.e. the end of its stellar evolution. Which is it?
   (a) red supergiant
   (b) white dwarf
   (c) neutron star
   (d) red dwarf
   (e) T Tauri star
   
3. Which of the following characteristics of the Milky Way can you deduce from very simple, naked eye observations?
   (a) the existence of the spiral arms
   (b) the distance to the galactic center
   (c) the disk shape of the galaxy
   (d) the distance to the globular clusters
   (e) the number of star formation regions
   
4. What is the approximate distance from us to the center of the Milky Way galaxy?
   (a) 8000 parsecs
   (b) 70 parsecs
   (c) 2300 astronomical units
   (d) 700,000 parsecs
   (e) 250 Megaparsecs
   
5. In class I discussed how we determined the distance to the center of the Milky Way galaxy. This involved measurement of the distribution (i.e. distance and location) of what kind of astronomical objects?
   (a) planetary nebulae
   (b) neutron stars
   (c) open star clusters
   (d) globular star clusters
   (e) molecular clouds
   
6. In class I described our picture (i.e. size and shape) of the Milky Way. I pointed out that there is a major class of astronomical object which contains similar objects. This class contains
   (a) giant molecular clouds
   (b) quasars
   (c) irregular galaxies
   (d) elliptical galaxies
   (e) spiral galaxies
   
7. Stellar evolution theory says that low mass stars enter a phase in which they throw off a large fraction of their mass into interstellar space, revealing the core of the star. What class of observed phenomena are interpreted as stars in this phase of their evolution?
   (a) protostars
   (b) giant branch stars
   (c) white dwarfs
   (d) planetary nebulae
   (e) neutron stars
   
8. Approximately how far away are the nearest major galaxies?
   (a) a couple of parsecs
   (b) a couple of Megaparsecs
   (c) hundreds of parsecs
   (d) hundreds of Megaparsecs
   (e) thousands of astronomical units
   
9. Astronomers generate a certain sort of plot which allows them to deduce the total mass of a galaxy, as well as how the mass is distributed (spread out) through the galaxy. This is a plot of
   (a) absolute magnitude of the galaxy versus spectral type.
   (b) distance to the galaxy versus speed of recession.
   (c) orbital speed versus mass.
   (d) orbital velocity versus distance from the center of the galaxy.
   (e) distance from the center of the galaxy versus color of the starlight.
   
10. What are galaxies made of? In other words, in what form is most of the matter?
    (a) stars
    (b) hydrogen gas
    (c) white dwarfs
    (d) strong magnetic fields
    (e) 90 % is in an unknown form termed ``Dark Matter''
    
11. Which of the following observations is evidence that the universe began in a ``Big Bang''?
    (a) All matter in the universe is seen to be quite hot, indicating energy leftover from an explosion.
    (b) Galaxies in all directions are seen moving away from us.
    (c) The galaxies are interpreted as smaller pieces of a larger structure, termed the Universal Hegemon which disintegrated at the time of the Big Bang.
    (d) The number of galaxies tapers off with increasing distance from the Milky Way.
    (e) Distant galaxies are fixed in space, suggesting that they will shortly begin a contraction process.
    
12. Which of the following numbers is a good estimate for the age of the universe.
    (a) 500 - 1000 million years
    (b) 12 - 15 billion years
    (c) 50 - 100 billion years
    (d) 4 - 5 billion years
    (e) 200 - 300 billion years
    
13. In class and the problem sets we extensively discussed the ages of star clusters. How do we do this? In words, what concepts and observations do we use to put a number on the age of a group of stars?
    (a) Stars become steadily more luminous as they age. We look for the line which describes the most luminous stars in a star cluster, and from this value obtain the age.
    (b) The heavy element composition of the universe has been changing throughout its history. We carry out a chemical analysis of the stars in a cluster and thereby calculate the time when the cluster formed.
    (c) You look for the most massive star still on the Main Sequence. From a knowledge of the Main Sequence lifetimes of stars, we extract the age of the entire cluster.
    (d) When we look at star clusters, we are seeing them as they were, not as they are. We know the age of a star cluster by calculating the time when the light we are presently seeing left the cluster.
    (e) Certain types of stars only form billions of years after the first stars form. Red dwarf stars do not appear until 5-7 billion years after the type O stars. By seeing if there are red dwarfs, and how many, we can deduce the age of a cluster.
    
14. What kind of star is the Sun?
    (a) a spectral class G Main Sequence star.
    (b) a spectral class O star.
    (c) a red dwarf
    (d) an asymptotic giant branch star
    (e) a Cepheid variable.
    
15. Roughly, what is the Main Sequence lifetime of the Sun?
    (a) 1 billion years
    (b) 10 billion years.
    (c) 200 billion years.
    (d) 10 million years.
    (e) 4000 years.
    
16. According to our current understanding of astrophysics, the end fate of the Sun (i.e. what it will be in the far distant future; stellar eschatology) is
    (a) a white dwarf.
    (b) a neutron star.
    (c) a black hole.
    (d) a radio galaxy.
    (e) a giant molecular cloud.
    
17. White dwarfs are predominantly formed of two elements. What are they?
    (a) plutonium and uranium
    (b) hydrogen and helium
    (c) carbon and oxygen
    (d) silicon and iron
    (e) water vapor and ammonia
    
18. Stellar evolution theory says that low mass stars go from being supergiants to white dwarfs by throwing most of their mass out into space. What observed objects correspond to this intermediate state?
    (a) globular clusters
    (b) T Tauri stars
    (c) red dwarfs
    (d) green dwarfs
    (e) planetary nebulae
    
19. Stellar evolution predicts the formation of objects called neutron stars. What is the status of attempts to find the neutron stars? In other words, do we know of any astronomical objects which are confidently identified as neutron stars?
    (a) Pulsars are neutron stars.
    (b) Red supergiant stars are known to be neutron stars.
    (c) Despite several decades of searching, there are no known examples of neutron stars.
    (d) The companion to the bright star Sirius is a neutron star. A few other similar examples are known.
    (e) The first neutron star was recently found as a companion to the star Gliese 229.
    
20. The end result of evolution of a very massive star is quite different from that of a low mass star. Which of the following is a product of such evolution?
    (a) a white dwarf
    (b) a red dwarf
    (c) a supernova explosion
    (d) a Main Sequence star
    (e) a brown dwarf
    
21. In what way is a Black Hole formed?
    (a) By compressing all the material in a mass M inside a radius called the Schwarzschild Radius
    (b) By taking a roughly spherical object and spinning it up until it possesses units of angular momentum.
    (c) A Black Hole is formed when a star builds up Coulombs of electrical charge.
    (d) By the expanding winds in stars of the R Corona Borealis type.
    (e) Black Holes have so far only been formed in laboratories by intense plasma wave activity.
    
22. Which of the following objects is currently believed to be (or contain) a Black Hole?
    (a) There is no current astronomical evidence that Black Holes exist.
    (b) Cygnus X-1
    (c) The Ophiuchi molecular cloud.
    (d) The Sirius star system.
    (e) The Ring Nebula M57.
    
23. The Milky Way is an example of which class of astronomical objects?
    (a) Jovian planets
    (b) open star clusters
    (c) globular star clusters
    (d) spiral galaxies
    (e) elliptical galaxies.
    
24. Roughly how far is it to the center of the Milky Way?
    (a) 10 parsecs
    (b) 150 astronomical units
    (c) 500,000 kilometers
    (d) 950 parsecs
    (e) 8000 parsecs
    
25. When you look in the night sky in the directions of the constellations of Aquila and Cygnus (for example) you see a diffuse band of light which we call the Milky Way, in addition to individual stars. When we look in the direction of the constellation Virgo, about 90 degrees away, we see only a sprinkling of stars on a dark background. What is the significance of this simple observation?
    (a) When we look in the direction of Aquila, we are looking perpendicular to the galactic plane. When we look at Virgo we are looking parallel to the galactic plane.
    (b) When we are looking towards Aquila, we are looking into the plane of the galactic disk; in Virgo we are looking out of the plane.
    (c) We can see much greater distances in space in the direction of Aquila and Cygnus. In the direction of Virgo there is a massive dark cloud which obscures the more distant stars.
    (d) The direction of Virgo is expecially known for the presence of ``Dark Matter'', so there is very little light. The direction of Cygnus and Aquila contains luminous matter so we see many stars.
    (e) Cygnus and Aquila contain most of the known O stars, which photoionize the gas in their vicinity and thus produce a general glow which forms the Milky Way. All of the stars in Virgo are faint stars and are incapable of photoionization, so we see only dark space.
    
26. What is the current status of our knowledge concerning the composition of the Milky Way galaxy (i.e. what is it made of)?
    (a) Most of the mass of the Milky Way is in the form of an unknown ``Dark Matter''
    (b) Most of the mass of the Milky Way is in the form of stars.
    (c) Interstellar gas is the primary constituent of the Milky Way.
    (d) Most of the mass of the Milky Way is in the form of electromagnetic radiation.
    (e) There are more planets than stars in the Milky Way, and they furnish most of the mass.
    

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