Astronomy 1002, Section 425

Homework #6



1. Magnetic fields inside sunspots are __________ those in surrounding regions.

A. much stronger than

B. slightly stronger than

C. the same as

D. much weaker than



2. How long is the sunspot cycle, on average?

A. 100 days

B. 11 years

C. 2 years

D. 70 years



3. By what mechanism does radiation reach the Sun's surface from its interior?

A. Ionization.

B. Neutrinos.

C. Convection.

D. The solar wind.



4. What is it about the Sun's corona that astronomers don't understand?

A. No one knows why that part of the Sun's atmosphere does not drift away into space.

B. During total solar eclipses, the corona sometimes disappears from view.

C. The Sun's corona extends to the outer reaches of the solar system.

D. The corona is much hotter than layers of the Sun that are closer to the solar interior.



5. The light we see from the Sun comes from which layer?

A. chromosphere

B. photosphere

C. corona

D. convective zone



6. What is the net result of the proton-proton chain?

A. 2 heliums are fused into 1 carbon, 1 neutrinos + energy

B. 4 hydrogens are fused into 1 helium, 2 neutrinos + energy

C. 2 hydrogens and 1 helium are fused into 1 carbon + energy

D. 2 protons and 2 neutrons are fused into 1 carbon + energy



7. Interstellar gas is composed mainly of:

A. Hydrogen and helium.

B. Carbon.

C. Ammonia, methane, and water vapor.

D. Hydrogen and carbon.



8. Some regions of the Milky Way appear dark because:

A. There are no stars there.

B. Stars in that direction are obscured by interstellar gas.

C. Stars in that direction are obscured by interstellar dust.

D. There are numerous black holes that capture all the star light behind them.



9. Which two ingredients are needed to make an emission nebula?

A. Interstellar gas and dust.

B. Cool stars and interstellar dust.

C. Hot stars and interstellar gas.

D. Cool stars and interstellar gas.



10. Most stars probably formed:

A. Alone.

B. In clusters.

C. From constellations.

D. In the nucleus of the Galaxy.



11. For gravity to contract a spinning interstellar cloud, there needs to be sufficient:

A. Heat.

B. Mass.

C. Magnetism.

D. Rotation.



12. What is characteristic of a main sequence star?

A. Rapid rotation and a strong stellar wind.

B. Nuclear fusion in the core varies according to the amount of gravitational contraction that occurs.

C. The rate of nuclear energy generated in the core equals the rate of energy radiated from the surface.

D. all of the above

E. none of the above



13. What is the key factor that determines the temperature, density, radius, luminosity, and pace of evolution of a prestellar object?

A. Rotation.

B. Magnetism.

C. Mass.

D. Heat.



14. Which event marks the birth and emergence of a star?

A. Fusion of hydrogen atoms into helium atoms.

B. Collapse of an interstellar cloud.

C. Formation of a photosphere.

D. Instability in an interstellar cloud.



15. A typical protostar may be several thousand times more luminous than the Sun. What is the source of this energy?

A. Nuclear fusion in its core.

B. The ionization of the gas as it heats up.

C. Nearby hot stars or supernovae that have initiated the star formation process.

D. The release of gravitational energy as the protostar continues to shrink.



16. What is the critical temperature at which hydrogen can begin to fuse into helium in the core of a star?

A. 10,000 K.

B. 1 million K.

C. 5 million K.

D. 10 million K.



17. The final core element for a massive star is

A. carbon

B. oxygen

C. silicon

D. iron



18. A high-mass star dies more violently than a low-mass star because:

A. It generates more heat and its core eventually collapses.

B. It cannot fuse elements heavier than carbon.

C. Gravity is weakened by its high luminosity.

D. It is most often found as part of a binary system.



19. Which of the following represents the last observed stage in the evolution of a low-mass star?

A. Red giant.

B. Planetary nebula.

C. Brown dwarf.

D. White dwarf.



20. A star spends most of its life:

A. As a protostar.

B. In explosions lasting millions of years.

C. As a red giant or supergiant.

D. As a main sequence star.



21. Which statement is true, in terms of stellar evolution?

A. Sooner or later, gravity loses.

B. Sooner or later, gravity wins.

C. Sometimes gravity wins and sometimes gravity loses.

D. Gravity lets up under certain circumstances.



22. What event leads to the formation of a red giant?

A. A contracting core of helium.

B. Hydrogen shell burning.

C. Expanding outer layers.

D. all of the above

E. none of the above



23. What characteristic of a star cluster is used to determine its age?

A. The number of red giants.

B. The faintest stars seen in the cluster.

C. The main sequence turnoff.

D. The total number of stars in the cluster.



24. What inevitably forces a star like the Sun to evolve away from being a main sequence star?

A. It completely runs out of hydrogen.

B. It explodes violently.

C. It builds up a core of helium.

D. The core becomes too cool to fuse hydrogen.

E. The core loses all of its neutrinos, so fusion ceases.



25. What is the source of pressure in the core of a red giant that resists the force of gravity?

A. electrons which have become incompressible

B. normal thermal pressure of the hot gas

C. neutrons which resist being pressed together beyond a certain density

D. helium nuclei which repulse each other strongly because they each contain two protons



26. Which of the following is true regarding planetary nebulae?

A. They are the result of the mass loss during the red giant stage.

B. They are the rings of material surrounding newly formed stars that will eventually form the planetary systems.

C. They are the ejected envelopes of highly evolved low-mass stars.

D. They are the coronas surrounding most red giants.



27. Which of the following best describes the evolutionary track followed in the HR diagram for the most massive stars?

A. Diagonally to lower right, then vertical, then horizontally left

B. Horizontally right, diagonally to lower left, then horizontally right

C. Horizontally right, then forms a clockwise loop

D. Vertically up, then diagonally to lower right

E. Horizontally right



28. What is not the same for each star in a cluster?

A. age

B. mass

C. composition

D. distance from Earth



29. Nearly all the elements found in our environment were formed inside stars. The major exceptions are:

A. Iron and nickel.

B. Oxygen and carbon.

C. Silver and technetium.

D. Hydrogen and helium.



30. A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?

A. Nova.

B. Type-I supernova.

C. Type-II supernova.

D. Contact binary.



31. What evidence is there that supernovae really have occurred?

A. Crab Nebula.

B. Supernova remnants.

C. The explosions themselves.

D. all of the above

E. none of the above



32. An iron core cannot support a star because:

A. Iron has poor nuclear binding energy.

B. Iron cannot fuse with other nuclei to produce energy.

C. Iron supplies too much pressure.

D. Iron is in the form of a gas, not a solid, in the center of a star.



33. The heaviest nuclei of all are formed:

A. During a supernova explosion

B. During a nova explosion

C. During carbon burning

D. During all stages of stellar evolution of massive stars



34. A star can be a supernova:

A. Many times.

B. At various times, depending on the mass of the star.

C. Once.

D. Early in its evolution.



35. What is the only way that a white dwarf can suddenly explode?

A. it never can explode

B. if it passes through a large dust cloud

C. if it is a member of a mass-transfer binary

D. if it finally cools off to under 2000 K



36. What compelling evidence links pulsars to neutron stars?

A. Both pulsars and neutron stars can be found in globular star clusters.

B. Only a small rotating source of radiation is thought to be able to emit precisely timed pulses such as those from pulsars.

C. Pulsars are known to evolve into neutron stars.

D. Both pulsars and neutron stars have been discovered near the Sun.



37. Which of the following is not an argument for Cygnus X-1's being a true black hole?

A. Spectroscopic evidence suggests that hot gas is flowing from the companion B star onto Cygnus X-1.

B. Cygnus X-1's mass is estimated to be between 5 and 10 solar masses.

C. The mass of the companion B star is even greater than that of Cygnus X-1, at around 30 solar masses.

D. X-rays from Cygnus X-1 vary on time scales as short as a millisecond.



38. Which of the following can actually escape a black hole?

A. electrons

B. very high energy gamma-rays

C. very low energy radio waves

D. all of the above

E. none of the above



39. What is Cygnus X-1?

A. an experimental spacecraft designed to travel close to the speed of light

B. a leading candidate for being a black hole

C. a binary neutron star system

D. a millisecond pulsar with two planets

E. the first discovered X-ray burster



40. The key to identifying a black hole candidate in a binary system is the following.

A. one of the two stars can not be seen

B. the unseen companion in the system must have a sufficiently high mass

C. the system must be a very strong source of radio emissions

D. the seen companion must be an evolving main sequence or giant star

E. matter must be seen disappearing into the black hole