Exam Practice Ch. 13b-14a Astronomy 100 Prof. Menningen 12/03/18 Name: _______________________________ 1. The helium fusion process works by fusing two helium nuclei into one beryllium nucleus. TRUE FALSE 2. Our Sun will end its life in a planetary nebula and become a white dwarf. TRUE FALSE 3. Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure. TRUE FALSE 4. A pulsar is a white dwarf that has an oscillating luminosity. TRUE FALSE The following 3 questions refer to the sketch below of an H-R diagram for a star cluster. 5. Based on its main-sequence turnoff point, the age of this cluster is a. about 1 billion years. b. about 4.5 billion years. c. about 10 billion years. d. more than 15 billion years. 6. Which statement about this cluster is NOT true? a. It is likely to be located in the halo of the galaxy. b. It contains some stars that are burning helium in their cores. c. It is the type of cluster known as an open cluster of stars. d. It probably contains no young stars at all. 7. Consider the star to which the arrow points. How is it currently generating energy? a. by gravitational contraction b. by hydrogen shell burning around an inert helium core c. by core helium fusion combined with hydrogen shell burning d. by both hydrogen and helium shell burning around an inert carbon core 8. Why does stellar main-sequence lifetime decrease with increasing stellar mass? a. It doesn't; higher mass stars have more hydrogen available for fusion, and thus have longer lifetimes. b. Strong stellar winds cause higher mass stars to lose mass quickly. c. Higher core temperatures cause fusion to proceed much more rapidly. d. Higher outward pressure prevents the core hydrogen from being replenished by the star's outer layers 9. Which of the following hypothetical observations would contradict our theories about the formation and evolution of white dwarfs? a. discovery of a white dwarf with a mass 1.8 times that of the Sun (1.8M) b. discovery of a white dwarf with a surface temperature of 6000 K c. discovery of a white dwarf at the center of a planetary nebula d. discovery of a white dwarf with a main-sequence companion star that has mass 1.8M 10. Which of the following is closest in size (radius) to a neutron star? a. Jupiter b. the Earth c. a city d. a football stadium e. a basketball .