Question 1

The star that exploded to form the supernova SN 1987A probably had, before it blew up, a mass of:

Accepted Answer

A) about 20 M ε 
B) less than 1 M ε 
C) about 1.4 M ε 
D) about 40 to 50 M ε 
A) about 20 M ε 
B) less than 1 M ε 
C) about 1.4 M ε 
D) about 40 to 50 M ε

Question 2

According to our theories of stellar evolution, the Sun will probably end its active life as a:

Accepted Answer

A) red giant. 
B) black hole. 
C) pulsar. 
D) white dwarf. 
A) red giant. 
B) black hole. 
C) pulsar. 
D) white dwarf.

Question 3

The energy to produce a thermal pulse comes from:

Accepted Answer

A) hydrogen core fusion. 
B) the helium flash. 
C) helium core fusion. 
D) the helium shell flash. 
A) hydrogen core fusion. 
B) the helium flash. 
C) helium core fusion. 
D) the helium shell flash.

Question 4

The main source of energy for a solar mass star while it is on the horizontal branch is:

Accepted Answer

A) core hydrogen fusion. 
B) core helium fusion. 
C) shell hydrogen fusion. 
D) shell helium fusion. 
A) core hydrogen fusion. 
B) core helium fusion. 
C) shell hydrogen fusion. 
D) shell helium fusion.

Question 5

A star of twice the mass of the Sun reaches the asymptotic giant branch (AGB) phase of its life and begins to eject large amounts of carbon and heavier elements into space. What process occurs to make this component easy to detect, particularly at radio wavelengths?

Accepted Answer

A) The carbon grains (soot!) are heated by radiation and reemit a cool thermal continuum spectrum whose peak is at radio wavelengths. 
B) The carbon nuclei acquire electrons and become neutral atoms in an excited state, which then emit an easily detected spectrum as they de-excite. 
C) Carbon and oxygen nuclei have such high velocities that they undergo nuclear fusion in a shell surrounding the star to produce heavier elements whose emissions are at radio wavelengths. 
D) Carbon and oxygen combine chemically to produce the easily detected CO molecule. 
A) The carbon grains (soot!) are heated by radiation and reemit a cool thermal continuum spectrum whose peak is at radio wavelengths. 
B) The carbon nuclei acquire electrons and become neutral atoms in an excited state, which then emit an easily detected spectrum as they de-excite. 
C) Carbon and oxygen nuclei have such high velocities that they undergo nuclear fusion in a shell surrounding the star to produce heavier elements whose emissions are at radio wavelengths. 
D) Carbon and oxygen combine chemically to produce the easily detected CO molecule.

Question 6

As a red giant evolves, its temperature decreases but its luminosity increases. As a white dwarf ages, its temperature decreases, and its luminosity also decreases. Why this difference?

Accepted Answer

A) A red giant experiences nuclear fusion on its surface while a white dwarf no longer experiences fusion. 
B) A white dwarf expels much soot, and this blocks its increasing luminosity from being seen. 
C) A red giant expands greatly as it cools, but a white dwarf shrinks as it cools. 
D) A red giant expands greatly as it cools. Because of degeneracy pressure, a white dwarf maintains the same size as it cools. 
A) A red giant experiences nuclear fusion on its surface while a white dwarf no longer experiences fusion. 
B) A white dwarf expels much soot, and this blocks its increasing luminosity from being seen. 
C) A red giant expands greatly as it cools, but a white dwarf shrinks as it cools. 
D) A red giant expands greatly as it cools. Because of degeneracy pressure, a white dwarf maintains the same size as it cools.

Question 7

What is Cherenkov radiation?

Accepted Answer

A) x-ray radiation emitted directly from supernova eruptions 
B) gamma radiation emitted directly from neutrinos 
C) the shock wave emitted when neutrinos move faster than the speed of light in water 
D) the shock wave emitted when recoil positrons move faster than the speed of light in water 
A) x-ray radiation emitted directly from supernova eruptions 
B) gamma radiation emitted directly from neutrinos 
C) the shock wave emitted when neutrinos move faster than the speed of light in water 
D) the shock wave emitted when recoil positrons move faster than the speed of light in water

Question 8

Neutrino detectors for astronomical purposes are built and operated deep underground to:

Accepted Answer

A) shield them against other high-energy radiation from space or from natural radioactivity. 
B) reduce the effect of rotational speed produced by Earth's rotation, because the sensitive neutrino detection techniques are adversely affected by Doppler shifts. 
C) utilize the gravitational focusing of neutrinos that occurs in Earth's core. 
D) ensure that they are absolutely light-tight, because they depend on the detection of very faint flashes of light. 
A) shield them against other high-energy radiation from space or from natural radioactivity. 
B) reduce the effect of rotational speed produced by Earth's rotation, because the sensitive neutrino detection techniques are adversely affected by Doppler shifts. 
C) utilize the gravitational focusing of neutrinos that occurs in Earth's core. 
D) ensure that they are absolutely light-tight, because they depend on the detection of very faint flashes of light.

Question 9

What fraction of the material returned to the interstellar medium of a galaxy by stars is contributed by planetary nebulae as they eject their shells?

Accepted Answer

A) about 15% 
B) only about 1 part in a million 
C) less than about 1% 
D) about 80%, or most of the returned material 
A) about 15% 
B) only about 1 part in a million 
C) less than about 1% 
D) about 80%, or most of the returned material

Question 10

Because it has ceased nuclear burning in its interior and therefore no longer generates energy, why is it that a white dwarf does not shrink rapidly under the force of gravity as it cools?

Accepted Answer

A) The rapid reduction of radius before the white-dwarf phase produces a very rapid rotation, thereby generating a large centrifugal force that prevents the star from shrinking. 
B) The very low luminosity of a white dwarf means that it cools slowly and maintains a high temperature and therefore a high internal pressure that opposes gravity. 
C) The star has lost so much mass in earlier phases that the remaining mass generates insufficient gravitational force to produce further shrinkage. 
D) The electrons within it are in a degenerate state and will not allow further shrinkage. 
A) The rapid reduction of radius before the white-dwarf phase produces a very rapid rotation, thereby generating a large centrifugal force that prevents the star from shrinking. 
B) The very low luminosity of a white dwarf means that it cools slowly and maintains a high temperature and therefore a high internal pressure that opposes gravity. 
C) The star has lost so much mass in earlier phases that the remaining mass generates insufficient gravitational force to produce further shrinkage. 
D) The electrons within it are in a degenerate state and will not allow further shrinkage.

Question 11

Just before the outer layers of a high-mass star are thrown into space in a supernova explosion, the density in its core is about that:

Accepted Answer

A) of iron metal, 7.5 × 103 kg/m3. 
B) of degenerate gases in white dwarf stars, about 103 kg/m3. 
C) at the center of the Sun, about 1.5 × 105 kg/m3. 
D) of nuclear matter in a normal nucleus, about 4 × 1017 kg/m3. 
A) of iron metal, 7.5 × 103 kg/m3. 
B) of degenerate gases in white dwarf stars, about 103 kg/m3. 
C) at the center of the Sun, about 1.5 × 105 kg/m3. 
D) of nuclear matter in a normal nucleus, about 4 × 1017 kg/m3.

Question 12

If two white dwarf stars have the same composition, then the more massive one always has:

Accepted Answer

A) a smaller radius than the less massive one. 
B) a larger radius than the less massive one. 
C) the same radius as the less massive one, since electron degeneracy causes all white dwarfs to be the same size. 
D) a size that depends critically on composition (metallicity) rather than mass. 
A) a smaller radius than the less massive one. 
B) a larger radius than the less massive one. 
C) the same radius as the less massive one, since electron degeneracy causes all white dwarfs to be the same size. 
D) a size that depends critically on composition (metallicity) rather than mass.

Question 13

Why can we not have a white dwarf of 2 M ? ?

Accepted Answer

A) Even the largest main-sequence stars always lose enough mass so that they reduce to 1.4 M ? after they form a planetary nebula. 
B) A white dwarf of more than 1.4 M ? could not be supported by electron degeneracy. 
C) When a star reaches the white dwarf stage with more than 1.4 M ? , the intensity of nuclear radiation in its core makes it explode. 
D) A white dwarf is like a giant nucleus; if it has a mass of more than 1.4 M ? , it fissions into two parts like an unstable nucleus. 
A) Even the largest main-sequence stars always lose enough mass so that they reduce to 1.4 M ? after they form a planetary nebula. 
B) A white dwarf of more than 1.4 M ? could not be supported by electron degeneracy. 
C) When a star reaches the white dwarf stage with more than 1.4 M ? , the intensity of nuclear radiation in its core makes it explode. 
D) A white dwarf is like a giant nucleus; if it has a mass of more than 1.4 M ? , it fissions into two parts like an unstable nucleus.

Question 14

What process is necessary for a star with twice the Sun's mass to become a carbon star?

Accepted Answer

A) dredge-up by convection of carbon that has been produced in the stellar core by nuclear fusion 
B) nuclear fusion reactions on the surface of the star, producing carbon nuclei by combination of three helium nuclei during the helium flash 
C) ejection of the outer hydrogen and helium layers by the helium flash in the star's interior, revealing the stellar carbon core 
D) nuclear fission reactions splitting magnesium nuclei (24Mg, charge = 12) into carbon nuclei (12C, charge = 6) on the star's surface 
A) dredge-up by convection of carbon that has been produced in the stellar core by nuclear fusion 
B) nuclear fusion reactions on the surface of the star, producing carbon nuclei by combination of three helium nuclei during the helium flash 
C) ejection of the outer hydrogen and helium layers by the helium flash in the star's interior, revealing the stellar carbon core 
D) nuclear fission reactions splitting magnesium nuclei (24Mg, charge = 12) into carbon nuclei (12C, charge = 6) on the star's surface

Question 15

A Type Ib supernova is believed to result from the:

Accepted Answer

A) collapse of a blue supergiant star to form a black hole. 
B) explosion of a massive star that has lost its hydrogen-rich outer layers through a stellar wind or by mass transfer in a binary star system. 
C) explosion of a white dwarf in a binary star system after matter transferred to it from its companion has increased its mass above the Chandrasekhar limit. 
D) explosion of a massive, hydrogen-rich star after silicon burning has produced a core of iron nuclei. 
A) collapse of a blue supergiant star to form a black hole. 
B) explosion of a massive star that has lost its hydrogen-rich outer layers through a stellar wind or by mass transfer in a binary star system. 
C) explosion of a white dwarf in a binary star system after matter transferred to it from its companion has increased its mass above the Chandrasekhar limit. 
D) explosion of a massive, hydrogen-rich star after silicon burning has produced a core of iron nuclei.

Question 16

Is it possible for an alpha particle (helium nucleus) to fuse with an iron nucleus to form a heavier nucleus?

Accepted Answer

A) No, iron is the heaviest stable nucleus. 
B) No, iron is not the heaviest stable nucleus, but the iron nucleus already has a complete set of protons and refuses to accept the constituents of an additional alpha particle. 
C) Yes, adding an alpha particle to iron is the next energy-generating reaction after silicon fusion. 
D) Yes, but this reaction does not take place spontaneously in stars, because it requires energy rather than producing energy. 
A) No, iron is the heaviest stable nucleus. 
B) No, iron is not the heaviest stable nucleus, but the iron nucleus already has a complete set of protons and refuses to accept the constituents of an additional alpha particle. 
C) Yes, adding an alpha particle to iron is the next energy-generating reaction after silicon fusion. 
D) Yes, but this reaction does not take place spontaneously in stars, because it requires energy rather than producing energy.

Question 17

Supernovae are of particular importance in theories of stellar evolution because:

Accepted Answer

A) they are one of the few known mechanisms for producing the heaviest elements. 
B) the Sun will probably go through a supernova phase. 
C) there are several supernovae in the immediate vicinity of the Sun. 
D) they always result in black holes. 
A) they are one of the few known mechanisms for producing the heaviest elements. 
B) the Sun will probably go through a supernova phase. 
C) there are several supernovae in the immediate vicinity of the Sun. 
D) they always result in black holes.

Question 18

All of the 12C in the universe, including that in our bodies, is believed to come from:

Accepted Answer

A) the proton-proton chain of nuclear reactions in main-sequence stars. 
B) the triple alpha process in helium burning in giants. 
C) supernova explosions. 
D) many important sources, not just one. 
A) the proton-proton chain of nuclear reactions in main-sequence stars. 
B) the triple alpha process in helium burning in giants. 
C) supernova explosions. 
D) many important sources, not just one.

Question 19

The fraction of the mass of a red giant that is ejected as a shell in a planetary nebula is:

Accepted Answer

A) almost the whole star, greater than 90%. 
B) substantial, up to 40%. 
C) extremely small, less than 1 part in 104. 
D) small, close to 0.01, or 1%. 
A) almost the whole star, greater than 90%. 
B) substantial, up to 40%. 
C) extremely small, less than 1 part in 104. 
D) small, close to 0.01, or 1%.

Question 20

A shock wave is produced during a supernova explosion, caused by the outward movement of hot inflating bubbles. Where do these bubbles get their energy?

Accepted Answer

A) Kelvin-Helmholtz contraction 
B) energy from the final fusion reaction: iron + hydrogen = nickel 
C) gamma radiation from the core 
D) neutrinos 
A) Kelvin-Helmholtz contraction 
B) energy from the final fusion reaction: iron + hydrogen = nickel 
C) gamma radiation from the core 
D) neutrinos

Exam 20: Stellar Evolution: The Death of Stars

The star that exploded to form the supernova SN 1987A probably had, before it blew up, a mass of:

According to our theories of stellar evolution, the Sun will probably end its active life as a:

The energy to produce a thermal pulse comes from:

The main source of energy for a solar mass star while it is on the horizontal branch is:

A star of twice the mass of the Sun reaches the asymptotic giant branch (AGB) phase of its life and begins to eject large amounts of carbon and heavier elements into space. What process occurs to make this component easy to detect, particularly at radio wavelengths?

As a red giant evolves, its temperature decreases but its luminosity increases. As a white dwarf ages, its temperature decreases, and its luminosity also decreases. Why this difference?

What is Cherenkov radiation?

Neutrino detectors for astronomical purposes are built and operated deep underground to:

What fraction of the material returned to the interstellar medium of a galaxy by stars is contributed by planetary nebulae as they eject their shells?

Because it has ceased nuclear burning in its interior and therefore no longer generates energy, why is it that a white dwarf does not shrink rapidly under the force of gravity as it cools?

Just before the outer layers of a high-mass star are thrown into space in a supernova explosion, the density in its core is about that:

If two white dwarf stars have the same composition, then the more massive one always has:

Why can we not have a white dwarf of 2 M ? ?

What process is necessary for a star with twice the Sun's mass to become a carbon star?

A Type Ib supernova is believed to result from the:

Is it possible for an alpha particle (helium nucleus) to fuse with an iron nucleus to form a heavier nucleus?

Supernovae are of particular importance in theories of stellar evolution because:

All of the 12C in the universe, including that in our bodies, is believed to come from:

The fraction of the mass of a red giant that is ejected as a shell in a planetary nebula is:

A shock wave is produced during a supernova explosion, caused by the outward movement of hot inflating bubbles. Where do these bubbles get their energy?

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Optics and Telescopes

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

Filters

All of the ¹²C in the universe, including that in our bodies, is believed to come from: