astronomy ch 13 hw

How does a white dwarf generate its energy? A) It no longer generates energy but is slowly cooling as it radiates away its heat. B) Nuclear fusion of hydrogen into helium is producing energy in its core. C) Nuclear fission of heavy elements in the central core is releasing energy. D) Gravitational potential energy is released as the star slowly contracts.

A) It no longer generates energy but is slowly cooling as it radiates away its heat.

Type II supernovae show prominent lines of hydrogen in their spectra, whereas hydrogen lines are absent in spectra of Type Ia supernovae. Explain. (Hint: Think about the type of star that gives rise to each of the two types of supernova.) A) Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen. B) White dwarfs have a thick surface layer of hydrogen, whereas neutron stars contain no hydrogen at all. C) Massive stars have fused all their hydrogen into heavier elements, whereas low-mass stars still have large hydrogen-rich envelopes. D) Massive stars contain large amounts of hydrogen, whereas neutron stars contain no hydrogen at all.

A) Massive stars contain large amounts of hydrogen, whereas white dwarfs are mostly carbon and oxygen.

Which of the following statements does NOT describe a consequence of core collapse at the end of the life of a massive star? A) The silicon core is converted to iron by fusion reactions. B) Electrons combine with protons to form neutrons. C) Great numbers of neutrinos are produced. D) The core density approaches the density of an atomic nucleus.

A) The silicon core is converted to iron by fusion reactions.

The explosion of a supernova appears to leave behind A) a rapidly expanding shell of gas and a central neutron star. B) a rapidly rotating shell of gas, dust, and radiation, but no central object. C) a rapidly expanding shell of gas and a compact white dwarf star at its center. D) nothing; the explosion changes all the matter completely into energy, which then radiates into space at the speed of light.

A) a rapidly expanding shell of gas and a central neutron star.

The "star" that is seen at the center of a planetary nebula is A) a small, hot, and very dense white dwarf star. B) composed almost entirely of neutrons and spinning rapidly. C) the accretion disk around a black hole. D) a planet in the process of formation.

A) a small, hot, and very dense white dwarf star.

The Crab Nebula is A) a supernova remnant. B) a planetary nebula surrounding a hot star. C) a cool, gaseous nebula in which stars are forming. D) the active nucleus of a nearby spiral galaxy.

A) a supernova remnant.

The structure of the deep interior of a low-mass star near the end of its life is a(n) A) carbon-oxygen core, a shell around the core where helium nuclei are undergoing fusion, and a surrounding shell of hydrogen. B) inactive hydrogen core and a helium shell undergoing nuclear fusion surrounded by a carbon-oxygen shell. C) turbulent mixture of hydrogen, helium, carbon, and oxygen in which only helium continues to undergo nuclear fusion. D) helium core surrounded by a thin hydrogen shell undergoing nuclear fusion with very small concentrations of heavier nuclei.

A) carbon-oxygen core, a shell around the core where helium nuclei are undergoing fusion, and a surrounding shell of hydrogen.

Which force induces the core to contract inward and get hotter in massive stars at the conclusion of each episode of nuclear fusion, such as the carbon-, oxygen-, and silicon- fusion cycles? A) gravity B) gas pressure produced by the very high gas temperatures C) electron degeneracy pressure D) nuclear attractive force between nuclei and between neutrons and protons

A) gravity

A star ascending the red-giant branch for the second time in the asymptotic giant branch phase will have A) no nuclear reactions in the core, but a helium-fusion shell outside the core, which itself is surrounded by a shell of hydrogen. B) no fusion reactions; the star has used up all its nuclear fuel. C) hydrogen-fusion reactions occurring in the core. D) no nuclear reactions occurring in the core but hydrogen fusion in a shell outside the core.

A) no nuclear reactions in the core, but a helium-fusion shell outside the core, which itself is surrounded by a shell of hydrogen.

A pulsar is a(n) A) rapidly spinning neutron star. B) type of variable star, pulsating rapidly in size and brightness. C) very precise interstellar beacon perhaps operated by intelligent life forms. D) accretion disk around a black hole, emitting light as matter is accumulated on the disk.

A) rapidly spinning neutron star.

What is a cosmic ray shower? A) shower of particles produced when a cosmic ray strikes atoms in Earth's atmosphere B) burst of high-energy atomic nuclei arriving at Earth from interstellar space C) Another name for a meteor shower D) pulse of gamma rays arriving at Earth from a rotating, magnetized neutron star

A) shower of particles produced when a cosmic ray strikes atoms in Earth's atmosphere

The very strong magnetic field on a neutron star is created by A) the collapse of the star, which significantly intensifies the original weak magnetic field of the star. B) differential rotation of the star, with the equator rotating faster than the poles, similar to sunspot formation. C) a burst of neutrinos produced by the supernova explosion, the equivalent of a very large electrical current flowing for a short time. D) turbulence in the electrical plasmas during the collapse of the star; the original star would have had no magnetic field.

A) the collapse of the star, which significantly intensifies the original weak magnetic field of the star.

Planetary nebulae are so named because A) they were extended objects, often green-colored, that looked like planets when first seen by nineteenth-century observers through their telescopes. B) the ejected material is rich in carbon and oxygen, necessary elements for the manufacture of planets in the nebulae surrounding stars. C) they rotate slowly and condense into planetary objects around a central star. D) their spectra appear to be similar to the spectra of the giant gas planets in the solar system.

A) they were extended objects, often green-colored, that looked like planets when first seen by nineteenth-century observers through their telescopes.

White dwarfs radiate most strongly in the ultraviolet, with a peak wavelength of perhaps 300 nm. What would be the surface temperature of a white dwarf? A) 12,600 K B) 9700 K C) 7800 K D) 3500 K

B) 9700 K

Low-mass stars can undergo two evolutionary phases called red-giant phases. What is the difference between them? A) In the first, the primary production of energy is from hydrogen burning in the core. In the second, the primary production of energy is from helium burning in the core. B) In the first, the primary production of energy is from helium burning in the core. In the second, the primary production of energy is from helium burning in a shell around the core. C) In the first, the star's track on the Hertzsprung-Russell diagram lies along the red- giant branch. In the second, the track lies along the horizontal branch. D) During the first red-giant phase, the star moves up and to the right along the red-giant branch. During the second red-giant phase the star's track is down and to the left along the same red-giant branch.

B) In the first, the primary production of energy is from helium burning in the core. In the second, the primary production of energy is from helium burning in a shell around the core.

From observations of supernova explosions in distant galaxies, it is predicted that there should be about five supernovae per century in our Galaxy, whereas we have seen only about one every 300 years from Earth. Explain. A) The majority of supernovae produce no visible light, only radio and X-ray radiation, which we have been able to observe from Earth for only the past three decades. B) Most supernovae occur in the galactic plane, where interstellar dust has hidden them from our view from Earth. C) Most supernovae occur in the Milky Way and can be seen only from the southern hemisphere, where there have been very few observers until recently. D) The majority of stars in the Galaxy are old, well beyond the supernova stage of evolution.

B) Most supernovae occur in the galactic plane, where interstellar dust has hidden them from our view from Earth.

Can a white dwarf explode? A) Yes, but only if another star collides with it; stars are so far apart in space that this is unlikely ever to have happened in our Galaxy. B) Yes, but only if it is in a binary star system. C) Yes, but only if nuclear reactions in the white dwarf core reach the stage of silicon fusion, producing iron. D) No. White dwarfs are held up by electron degeneracy pressure, and this configuration is stable against collapse or explosion.

B) Yes, but only if it is in a binary star system.

Which of the following phenomena is never a consequence of a supernova explosion? A) triggering of star formation by shock waves moving through interstellar space B) formation of a planetary nebula C) condensation of matter into a solid nuclear star composed entirely of neutrons D) generation of a pulse of neutrino emission

B) formation of a planetary nebula

What physical process provides the energy for the ejection of a planetary nebula from a low-mass star? A) transfer of hydrogen-rich material onto the surface of a white dwarf from its companion in a binary star system B) helium shell flashes in the helium fusion shell C) core collapse and the ensuing shock wave D) collision with another star

B) helium shell flashes in the helium fusion shell

In which order do the stages of core nuclear fusion occur in the evolution of a massive star? A) carbon, helium, oxygen, neon B) helium, carbon, neon, oxygen C) helium, oxygen, carbon, neon D) helium, carbon, oxygen, neon

B) helium, carbon, neon, oxygen

Thermonuclear reactions release energy because the product (ash) nucleus A) contains fewer protons than the original (fuel) nucleus since these protons have been converted into energy. B) is more tightly bound than the original (fuel) nucleus. C) is less tightly bound than the original (fuel) nucleus. D) is moving faster than the original (fuel) nucleus, and the excess kinetic energy shows up as heat.

B) is more tightly bound than the original (fuel) nucleus.

Where would you expect to find a core-collapse supernova? A) in a globular cluster B) near a star-forming region C) in a binary star system D) near a black hole

B) near a star-forming region

A planetary nebula is created A) over several hundred years, during mass transfer in a close binary star system. B) over a few thousand years or more, in a slow expansion away from a low-mass star, driven by a series of thermal pulses from helium fusion. C) in hours or less, during the explosion of a massive star. D) in seconds, during the helium flash in a low-mass star.

B) over a few thousand years or more, in a slow expansion away from a low-mass star, driven by a series of thermal pulses from helium fusion.

Which type of dwarf is largest? A) white dwarf B) red dwarf C) brown dwarf D) All are about the same size.

B) red dwarf

The pulsed nature of the radiation at all wavelengths that is seen to come from a pulsar is produced by A) the rapid pulsation in size and brightness of a small white dwarf star. B) the rapid rotation of a neutron star that is producing two oppositely directed beams of radiation. C) the mutual eclipses of two very hot stars orbiting in a close binary system. D) extremely hot matter that is rapidly orbiting a black hole just prior to descending into it.

B) the rapid rotation of a neutron star that is producing two oppositely directed beams of radiation.

What prevents a neutron star from collapsing and becoming a black hole? A) Gravity in the neutron star is balanced by an outward force due to neutron degeneracy. B) Gravity is balanced in neutron stars by the outward centrifugal force produced by their rapid rotation. C) Gravity in the neutron star is balanced by an outward force due to gas pressure, as in the Sun. D) Neutron stars are solid, and, like any solid sphere, they are held up by the repulsive forces between atoms in the solid matter.

C) Gravity in the neutron star is balanced by an outward force due to gas pressure, as in the Sun.

Which of the following sentences does NOT state a property of neutron stars? A) Neutron stars rotate from 1 to 30 times per second. B) Neutron stars emit relatively narrow beams of light and other radiation. C) Neutron stars contain strong gravitational fields but weak magnetic fields. D) Neutron stars are composed almost entirely of neutrons.

C) Neutron stars contain strong gravitational fields but weak magnetic fields.

What happens to the surface of a low-mass star after the helium core and shell fusion stages are completed? A) The star stabilizes at the size of a red giant star, radiation pressure from below balancing gravity from the core, and slowly cools for the rest of its life. B) The star is spun off into space to make a spiral structure known as a spiral galaxy. C) The star is propelled slowly away from the core to form a planetary nebula. D) The star contracts back onto the core and becomes hot enough to undergo further hydrogen fusion, leading to a very hot and active white dwarf star.

C) The star is propelled slowly away from the core to form a planetary nebula.

A nova is an explosion involving a white dwarf. Can a white dwarf become a nova more than once? Why or why not? A) No. The white dwarf's magnetic field is eliminated in the explosion. B) Yes. A white dwarf can become a nova more than once if its temperature is high enough for recurrent helium flashes in the core. C) Yes, A white dwarf can become a nova more than once if it continues to receive matter from a companion star. D) No. The white dwarf is destroyed in the explosion.

C) Yes, A white dwarf can become a nova more than once if it continues to receive matter from a companion star.

A white dwarf star, the surviving core of a low-mass star toward the end of its life, can be found on the Hertzsprung-Russell diagram A) at the upper left end of the main sequence since its surface temperature is extremely high. B) at the bottom end of the main sequence, along which it has evolved throughout its life. C) below and to the left of the main sequence. D) above and to the right of the main sequence since it evolved there after its hydrogen-fusion phase.

C) below and to the left of the main sequence.

A white dwarf star is supported from collapse under gravity by A) pressure of the gas heated by nuclear fusion reactions in its core. B) centrifugal force due to rapid rotation. C) degenerate-electron pressure in the compact interior. D) pressure of the gas heated by nuclear fusion reactions in a shell around its core.

C) degenerate-electron pressure in the compact interior.

A Type Ia supernova is the A) collapse of a blue supergiant star to form a black hole. B) explosion of a red giant star as a result of a helium flash in its core. C) explosion of a white dwarf in a binary star system after mass has been transferred onto it from its companion. D) explosion of a massive star after silicon fusion has produced a core of iron nuclei.

C) explosion of a white dwarf in a binary star system after mass has been transferred onto it from its companion.

The core collapse phase at the end of the life of a massive star is triggered when A) the helium flash and thermal pulses have expelled the star's envelope. B) the density reaches the threshold for electron degeneracy pressure to become important. C) nuclear fusion has produced a significant amount of iron in its core. D) the core becomes as dense as an atomic nucleus.

C) nuclear fusion has produced a significant amount of iron in its core.

At which phase of its evolutionary life is a white dwarf star? A) post-supernova phase, the central remnant of the explosion B) just at main-sequence, or hydrogen-fusion, phase C) very late for small-mass stars, in the dying phase D) in its early phases, soon after formation

C) very late for small-mass stars, in the dying phase

The Sun will end its life by becoming a A) molecular cloud. B) black hole. C) white dwarf. D) pulsar.

C) white dwarf.

Just before it exploded, the star that became supernova SN 1987A was a(n) A) pulsar. B) white dwarf. C) M2 I supergiant. D) B3 I supergiant.

D) B3 I supergiant.

A white dwarf star, as it evolves, undergoes which of the following changes? A) Its temperature remains constant, but its radius and therefore its luminosity decrease. B) Luminosity and size decrease while its temperature remains constant. C) It shrinks in size, the resulting release of gravitational energy keeping both luminosity and temperature constant. D) Luminosity and temperature decrease while its size remains constant.

D) Luminosity and temperature decrease while its size remains constant.

Usually, ideal gases increase their pressure and volume when heated and decrease their pressure and volume when cooled. Do these rules apply to stars? A) No. Stars never follow the rules for ideal gases even approximately. B) Yes. Stars in all stages follow these rules quite closely. C) No Protostars have cores of degenerate matter in which the pressure is independent of the temperature. D) No. White dwarfs are essentially degenerate matter in which the pressure is independent of the temperature.

D) No. White dwarfs are essentially degenerate matter in which the pressure is independent of the temperature.

During its life, a massive star creates heavier and heavier elements in its core through thermonuclear fusion, leading up to silicon and iron. What is the fate of the iron that is created? A) The nuclei are split apart by neutron bombardment, creating lighter elements such as carbon, oxygen, and neon. B) The iron is locked up inside the star forever. C) The iron is destroyed by later thermonuclear fusion reactions in the core that create even heavier elements such as lead, gold, and uranium. D) The iron is torn apart by high-energy photons at the end of the star's life.

D) The iron is torn apart by high-energy photons at the end of the star's life.

What will be the mass of the Sun at the end of its asymptotic giant branch (AGB) phase, due to mass loss to space by its stellar wind? A) still almost 1 solar mass since mass loss is negligible for a low-mass star like the Sun B) between 0.1 and 0.2 solar mass C) about 0.8 solar mass D) about 0.5 solar mass

D) about 0.5 solar mass

Nuclear fusion reactions of helium produce primarily A) nitrogen and neon nuclei. B) iron nuclei. C) beryllium and lithium nuclei. D) carbon and oxygen nuclei.

D) carbon and oxygen nuclei.

In the process of helium shell fusion in a low-mass star near the end of its life, the star moves upward and to the right on the asymptotic giant branch of the Hertzsprung-Russell diagram. In this process, the star is A) contracting, cooling, and hence becoming less luminous. B) expanding, heating up, and becoming more luminous. C) contracting, becoming hotter, and becoming much less luminous. D) expanding, cooling, and becoming more luminous.

D) expanding, cooling, and becoming more luminous.

In a star's evolutionary life, the asymptotic giant branch (AGB) is the A) helium core fusion phase. B) pre-main-sequence core hydrogen fusion phase. C) hydrogen shell fusion phase prior to helium ignition in the core. D) helium shell fusion phase.

D) helium shell fusion phase.

What is the Chandrasekhar limit? A) time limit of the existence of a planetary nebula, beyond which the nebula dissipates and becomes too rarified to see B) time limit for the transfer of mass to a white dwarf in a close binary system, beyond which the white dwarf erupts in a nova C) mass limit to the total mass of a white dwarf, beyond which it will erupt in a nova D) mass limit to the total mass of a white dwarf, beyond which the electron degeneracy pressure will be overcome and the core will collapse

D) mass limit to the total mass of a white dwarf, beyond which the electron degeneracy pressure will be overcome and the core will collapse

The mechanism that gives rise to the phenomenon of the nova is A) the impact and subsequent explosion of a large comet nucleus on a star's surface. B) material falling into a black hole and being condensed to the point where a thermonuclear explosion is produced. C) the complete disintegration of a massive star due to a runaway thermonuclear explosion in the star's interior. D) matter from a companion star falling onto a white dwarf in a close binary system, eventually causing a nuclear explosion on the dwarf's surface.

D) matter from a companion star falling onto a white dwarf in a close binary system, eventually causing a nuclear explosion on the dwarf's surface.

The interior of a neutron star is believed to consist of A) neutrons compressed into a crystalline lattice structure by very high pressure. B) a dense gas consisting mostly of neutrons. C) a metallic fluid of almost pure iron. D) neutrons in a superfluid state.

D) neutrons in a superfluid state.

At the center of the remnant of a Type Ia supernova you would expect to find A) a black hole or neutron star. B) a white dwarf. C) the binary companion of the supernova. D) nothing special.

D) nothing special.

Which of the following important components does a planetary nebula contribute to the interstellar medium? A) molecules such as NH3 and CH4, which contribute to giant molecular clouds B) UV light that photoionizes hydrogen. The hydrogen, on recombination, produces the red Balmer- light by which we see interstellar emission nebulae. C) rotational motion from the original star, which serves to concentrate interstellar matter into new stars and planetary systems D) nuclei of moderately heavy elements, major components of planets such as our own

D) nuclei of moderately heavy elements, major components of planets such as our own

Neutron stars are believed to be created by A) all types of supernovae. B) type Ia supernovae, i.e., exploding white dwarfs. C) explosions of main-sequence stars. D) type II supernovae, i.e., explosions of high-mass stars.

D) type II supernovae, i.e., explosions of high-mass stars.

Stars that have ejected a planetary nebula go on to become A) red giants. B) supernovae. C) protostars. D) white dwarfs.

D) white dwarfs.