29:50 Stars, Galaxies, and the Universe
Third Hour Exam
November 14, 2007
Form A

There are 22 questions worth 30 points. Note that different questions have different numbers of points. Read through each question and all the answers before choosing. Budget your time. No whining.

Walk with Ursus!

1. (1pt) The Milky Way is an example of what type of astronomical object?
   (a) a galaxy $\ast$
   (b) a main sequence star
   (c) a planet
   (d) a molecular cloud
   (e) a pulsar
2. (2pts) In class I showed a picture of the star Betelgeuse, taken through the Hubble Space Telescope. The picture had a scale next to it, showing how large the star is. How do we know the size of Betelgeuse?
   (a) The scale is completely hypothetical. We don't know the diameter of this star.
   (b) We use the Airy equation relationship between the spectral type of a star and its diameter.
   (c) Betelgeuse is a pulsar, and we know the sizes of pulsars.
   (d) Betelgeuse is an example of a Cepheid variable star, whose sizes can be determined from the amount of change in their apparent magnitudes.
   (e) We measure the angular size of Betelgeuse and determine its distance. These two numbers give the diameter or radius of the object. $\ast$
3. (1pt) Which of the following is an odd (but true) property of white dwarf stars?
   (a) More massive white dwarfs are larger in size than less massive ones.
   (b) White dwarf stars emit radiation only at x-ray wavelengths.
   (c) White dwarf stars emit radiation only at radio wavelengths.
   (d) All known white dwarf stars are located in the outer solar system, in what is called the ``Kuiper Belt''.
   (e) More massive white dwarfs are smaller in size than less massive ones. $\ast$
4. (2pts) A binary star consists of a main sequence A star (slightly more massive than the Sun), and a white dwarf star. In what follows, I will refer to the A main sequence star as ``the primary''. Which of the following statements about the white dwarf companion must be true?
   (a) The white dwarf must have been captured from interstellar space.
   (b) When it was a main sequence star, the companion must have been more massive than the primary. $\ast$
   (c) When it was a main sequence star, the companion must have been less massive than the primary.
   (d) The white dwarf was produced in a supernova explosion.
   (e) The primary was produced in a supernova explosion.
5. (2pts) In ``Friday Questions'', we discussed how one could prove or disprove the contention that a supernova occurs in the Milky Way every 50 - 100 years.An effective method for doing this would be to
   (a) observe the night sky every night for a period of 5 to 10 years.
   (b) use a neutrino telescope to search for a sudden burst of neutrinos. $\ast$
   (c) make observations with radio telescopes at times of opposition of the planet Neptune, and look for new radio sources in the ecliptic.
   (d) look for a diffuse glow in x-rays in the direction opposite to the Sun.
   (e) use an infrared telescope to search for a bright object in the direction of the galactic center.
6. (1pt) Which of the following astronomical objects corresponds to a region where massive stars are forming at the present time?
   (a) the Ring Nebula in Lyra
   (b) the Crab Nebula in Taurus
   (c) the globular star cluster M13 in Hercules
   (d) the Orion Nebula in Orion $\ast$
   (e) the Pleiades star cluster in Taurus
7. (2pts) Which of the following statements most accurately describes our understanding of where stars come from?
   (a) Matter forms spontaneously from empty space in a process called the two photon mechanism. Electromagnetic forces cause the matter to clump up into massive objects which correspond to stars.
   (b) Stars form directly from atomic gas in the space between the stars. Gravity does not play an important role in the formation of stars.
   (c) Dilute gas in the space between the stars is compressed, contracts under its own gravity to form molecular clouds, and clumps form within the molecular clouds to form stars. $\ast$
   (d) The stars which are presently in the Milky Way did not form here, but formed in elliptical galaxies outside the Milky Way, and were subsequently captured.
   (e) Stars are formed from the material which makes the interstellar grains. Electrostatic forces cause the grains to stick together into larger and larger clumps.
8. (1pt) For many years, astronomers were unable to identify objects which contained the ``raw material'' from which stars form. These objects were identifed as
   (a) clouds of atomic gas (atomic clouds)
   (b) clouds of molecular gas (molecular clouds) $\ast$
   (c) open clusters of stars (open clusters)
   (d) dense concentrations of nuclear matter (neutron stars)
   (e) leftovers from supernova explosions (supernova remnants)
9. (1pt) Some scientists believe that life on Earth might have had its origins in outer space. A major basis of such a belief is
   (a) the fact that we have detected numerous Earthlike planets around spectral class G stars like the Sun.
   (b) amino acids, which are the basis for life on Earth, are very abundant in the Sun's photosphere.
   (c) ultraviolet radiation is essential for the existence of life, and it is abundant in outer space, being produced by spectral class O stars.
   (d) the presence in space of cosmic rays, which help foster mutations and speed up the development of life.
   (e) the fact that many complex, organic molecules are found in the dark clouds where stars form. $\ast$
10. (1pt) In discussing star formation, astronomers and physicists have derived an equation for a critical size at which gravity balances gas pressure. The name for this size scale is
    (a) Jean's length $\ast$
    (b) de Broglie wavelength
    (c) Planck-Wheeler scale
    (d) ion-inertial length
    (e) Matthaeus critical length scale
11. (1pt) Which of the three sets of astronomical objects listed below constitutes a group of ``dead stars'', which are the end points of stellar evolution?
    (a) white dwarf stars, main sequence G stars, Cepheid variable stars
    (b) molecular clouds, globular star clusters, planetary nebulae
    (c) white dwarf stars, neutron stars, black holes $\ast$
    (d) Wolf-Rayet stars, UV Ceti stars, neutron stars
    (e) open star clusters, globular star clusters, the Orion Nebula
12. (2pts) A white dwarf star can exist as a stable object for an infinite period, whereas the Sun has a finite main sequence lifetime. A major reason for this, which was discussed in class, is the fact that
    (a) the force of gravity is much weaker for a white dwarf than it is for the Sun.
    (b) white dwarf stars do not emit electromagnetic radiation, and so are not losing energy to space.
    (c) the gas in the interior of a white dwarf is ``degenerate'', meaning that the pressure does not depend on the temperature. $\ast$
    (d) time runs more slowly in the vicinity of a white dwarf than a solar type star.
    (e) white dwarfs are made of antimatter rather than normal matter.
13. (2pts) Which of the following statements is correct regarding the existence of white dwarfs?
    (a) They are extremely unusual objects, but three have been discovered, all in other galaxies.
    (b) At the present, white dwarfs remain a prediction of theoretical physics. None have actually been observed.
    (c) We know of hundreds of stars which will become white dwarfs billions of years in the future (including the Sun), but the universe is not old enough to have produced any yet.
    (d) Several thousand white dwarfs have been discovered and cataloged. $\ast$
    (e) White dwarfs are the most common type main sequence star, so very many are known.
14. (2pts) The astronomical search for black holes consists of finding an object with one of the following sets of characteristics. Which is it?
    (a) a binary star with a main sequence star and a red giant star possessing an apparent magnitude brighter than 5.0
    (b) a binary star containing a nonluminous, nonstellar companion with a mass in excess of 3 solar masses $\ast$
    (c) a dark, roughly circular region of no light seen against a bright nebula such as the Orion Nebula
    (d) a binary star containing a nonluminous, nonstellar companion with a mass less than 1.4 solar masses
    (e) two solar-type stars surrounded by a cloud of intense radio emission
15. (1pt) A bright comet has appeared in the sky in the last few weeks. In which constellation is this comet?
    (a) Scorpius
    (b) Perseus $\ast$
    (c) Sagittarius
    (d) Leo
    (e) Virgo
16. (1pt) The post main sequence evolution of a star varies drastically depending on one of the stellar parameters listed below. Which one is it?
    (a) age
    (b) chemical composition
    (c) mass $\ast$
    (d) location in the Milky Way
    (e) apparent magnitude
17. (1pt) Neutron stars exist as one of the following types of astronomical object. Which is it?
    (a) pulsars $\ast$
    (b) quasars
    (c) radio galaxies
    (d) asymptotic giant branch stars
    (e) spectral class B main sequence stars
18. (1pt) Physically, supernovas correspond to
    (a) the collapse of a core of a massive star. $\ast$
    (b) a flaring of an accretion disk around a white dwarf.
    (c) gigantic versions of solar flares that occur on RS Canum Venaticorum stars.
    (d) release of energy by the gravitational collapse of a star cluster.
    (e) annihilation of matter and antimatter in the center of the Milky Way.
19. (2pts) Which of the following is a physically correct description of a black hole?
    (a) an object that has a temperature of absolute zero, so it emits no light
    (b) a large concentration of mass in a small volume of space, such that there is infinite curvature of spacetime $\ast$
    (c) an object where the magnetic force is so strong that no light is emitted from it, or its nearby surroundings
    (d) any star with a mass greater than 3.25 solar masses
    (e) the region between the Milky Way and M33
20. (1pt) A basic statement of the physical content of the theory of General Relativity is
    (a) the presence of electrical charge triggers ripples in the cosmic electromagnetic field
    (b) to every action there is an opposite and equal reaction
    (c) gravitational forces correspond to mass being converted to the strong nuclear force
    (d) all measurements in the physical sciences are relative, and without objective basis
    (e) the presence of mass warps or bends spacetime $\ast$
21. (1pt) Which of the following characteristics of the Milky Way galaxy can you deduce on the basis of naked eye observations?
    (a) the fact that the Sun lies very near the center of the Milky Way
    (b) the fact that it is an approximately spherical system of stars
    (c) the distance to the center of the Milky Way
    (d) the fact that magnetic fields are involved in the establishment of the overall helical shape
    (e) the fact that the galactic center lies in the direction of the constellation Sagittarius $\ast$
22. (1pt) What bright, well-known star has a white dwarf as a companion?
    (a) Sirius $\ast$
    (b) Vega
    (c) Fomalhaut
    (d) Capella
    (e) No star visible to the naked eye has a white dwarf companion