21.The lowest-mass stars cannot become giants becauseA.they do not contain : 1777246
21.The lowest-mass stars cannot become giants because
A.they do not contain helium.
B.they rotate too slowly.
C.they cannot heat their centers hot enough.
D.they contain strong magnetic fields.
E.they never use up their hydrogen.
22.A planetary nebula is
A.the expelled outer envelope of a medium mass star.
B.produced by a supernova explosion.
C.produced by a nova explosion.
D.a nebula within which planets are forming.
E.a cloud of hot gas surrounding a planet.
23.The Chandrasekhar limit tells us that
A.accretion disks can grow hot through friction.
B.neutron stars of more than 3 solar masses are not stable.
C.white dwarfs more massive than 1.4 solar masses are not stable.
D.stars cannot travel through space too fast
E.stars with a mass less than 0.5 solar masses will not go through helium flash.
24.A Type I supernova is believed to occur when
A.the core of a massive star collapses.
B.hydrogen detonation occurs.
C.a white dwarf exceeds the Chandrasekhar limit.
D.the cores of massive stars collapse.
E.neutrinos in a massive star become degenerate and form a shock wave that explodes the star.
25.Massive stars cannot generate energy through iron fusion because
A.iron fusion requires very high density.
B.stars contain very little iron.
C.no star can get hot enough for iron fusion.
D.both fusion or fission of iron nuclei absorb energy
E.massive stars supernova before they create an iron core.
26.The theory that the collapse of a massive star's iron core produces neutrinos was supported by
A.the size and structure of the Crab nebula.
B.laboratory measurements of the mass of the neutrino.
C.the brightening of supernovae a few days after they are first visible
D.underground counts from solar neutrinos.
E.the detection of neutrinos from the supernova of 1987.
27.Synchrotron radiation is produced by
A.objects with temperature below 10,000 K.
B.high-velocity electrons moving through a magnetic field.
C.cold hydrogen atoms in space.
D.the collapsing cores of massive stars.
28.A nova is almost always associated with
A.a very massive star.
B.a very young star.
C.a star undergoing helium flash.
D.a white dwarf in a close binary system.
E.a solar like star that has exhausted its hydrogen and helium.
29.The Algol paradox is explained by considering
A.the degenerate nature of the hydrogen on the surface of the white dwarf.
C.the rate of expansion of the shock wave inside the supernova.
D.the rotation rate of a neutron star.
E.mass transfer between the two stars in a binary system.
30.Stars with masses between 0.4 and 4
A.undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
B.undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
C.produce type-I supernovae after they exhaust their nuclear fuels.
D.produce type-II supernovae after they exhaust their nuclear fuels.
E.undergo carbon detonation.