31.A type-II supernovaA.occurs when a white dwarf's mass exceeds the : 1777247
31.A type-II supernova
A.occurs when a white dwarf's mass exceeds the Chandrasekhar limit.
B.is the result of helium flash.
C.is characterized by a spectrum that shows hydrogen lines.
D.occurs when the iron core of a massive star collapses.
E.c and d
32.Synchrotron radiation is produced
A.in planetary nebulae.
B.by red dwarfs.
C.massive stars as their iron core collapses.
D.in supernova remnants.
33.When material expanding away from a star in a binary system reaches the Roche surface
A.the material will start to fall back toward the star.
B.all of the material will accrete on to the companion.
C.the material is no longer gravitationally bound to the star.
D.the material will increase in temperature an eventually undergo thermonuclear fusion.
E.c and d
34.A white dwarf is composed of
A.hydrogen nuclei and degenerate electrons.
B.helium nuclei and normal electrons.
C.carbon and oxygen nuclei and degenerate electrons.
D.degenerate iron nuclei.
E.a helium burning core and a hydrogen burning shell.
35.A planetary nebula
A.produces an absorption spectrum.
B.produces an emission spectrum.
C.is contracting to form planets.
D.is contracting to form a star.
E.is the result of carbon detonation in a 1 star.
36.If the theory that novae occur in close binary systems is correct, then novae should
A.produce synchrotron radiation.
B.occur in regions of star formation.
C.not occur in old star clusters.
D.all be visual binaries.
E.repeat after some interval.
37.As a white dwarf cools its radius will not change because
A.pressure due to nuclear reactions in a shell just below the surface keeps it from collapsing.
B.pressure does not depend on temperature for a white dwarf because the electrons are degenerate.
C.pressure does not depend on temperature because the white dwarf is too hot.
D.pressure does not depend on temperature because the star has exhausted all its nuclear fuels.
E.material accreting onto it from a companion maintains a constant radius.
38.The diagram below shows a light curve from a supernova. How many days after maximum light did it take for the supernova to decrease in brightness by a factor of 100?
A.less than 50
E.more than 250
39.A planetary nebula has a radius of 0.5 pc and is expanding at 20 km/sec. What is the approximate age of this planetary nebula? (1 pc is equal to 3 ´ 1013 km and 1 year is equal to 3.15 ´ 107 seconds.)
40.About how long will a 0.5 star spend on the main sequence?
A.5 billion years
B.57 billion years
C.570 million years
D.5 million years
E.500 thousand years