66) A star (no matter what its mass) spends most : 1828918
66) A star (no matter what its mass) spends most of its life
A) as a protostar.
B) as a main-sequence star.
C) as a planetary nebula.
D) as a red giant or supergiant.
E) as a T-Tauri variable star.
67) When a star's inward gravity and outward pressure are balanced, the star is said to be
A) in gravitational collapse.
B) in thermal expansion.
C) in rotational equilibrium.
D) in hydrostatic equilibrium.
E) a stage 2 protostar.
68) What temperature is needed to fuse helium into carbon?
A) 5,800 K
B) 100,000 K
C) 15 million K
D) 100 million K
E) one billion K
69) When a low mass star first runs short of hydrogen in its core, it becomes brighter because
A) it explodes as a nova.
B) helium fusion gives off more energy than does hydrogen.
C) its outer, cooler layers are shed, and we see the brighter central core.
D) the core contracts, raising the temperature and extending the hydrogen burning shell outward.
E) the helium flash increases the size of the star immensely.
70) A star is on the horizontal branch of the H-R diagram. Which statement is true?
A) It is burning both hydrogen and helium.
B) It is about to experience the helium flash.
C) It is burning only helium.
D) The star is contracting.
E) The star is about to return to the main sequence.
71) The helium flash converts helium nuclei into
72) During the hydrogen shell burning phase
A) the star grows more luminous.
B) the star becomes less luminous.
C) helium is burning in the core.
D) the core is expanding.
E) hydrogen is burning in the central core.
73) Can a star become a red giant more than once?
A) yes, before and after the helium flash
B) yes, before and after the Type II supernova event
C) no, the planetary nebula blows off all the outer shells completely
D) no, it will lose so much mass as to cross the Chandrasekhar Limit
E) no, or we would see them as the majority of naked-eye stars
74) A solar-mass star will evolve off the main sequence when
A) it completely runs out of hydrogen.
B) it expels a planetary nebula to cool off and release radiation.
C) it explodes as a violent nova.
D) it builds up a core of inert helium.
E) it loses all its neutrinos, so fusion must cease.
75) A white dwarf has the mass of the Sun and the volume of
D) the Moon.