Deck 12: Predicting the Violent End of the Largest Stars

Question 1

Stars with masses between 8 and 14 times the mass of the Sun will end their lives as neutron stars.

Answer 1

False

Question 2

Because light cannot escape from a black hole,there is no evidence that they actually exist.

Answer 2

False

Question 3

In 1054,the imperial astronomer to the Chinese court recorded observing a "guest star" in the sky.We know now that this "guest star" was a supernova explosion within our Galaxy.

Answer 3

True

Question 4

In general,a Type Ia supernova is brighter than a Type II supernova.

Question 5

Type Ia supernovae are generally brighter than Type II supernovae.

Question 6

After the core collapse and bounce in a supernova explosion,neutrinos pour out of the developing neutron star to propel the shock wave outward.

Question 7

Every year,two or three supernovae are seen within our own Galaxy.

Question 8

A Type Ia supernova is thought to result from the thermonuclear explosion of a white dwarf star in a close binary system with a larger companion star.

Question 9

When a star becomes a black hole,its gravitational pull becomes stronger.

Question 10

Supermassive black holes are generally thought to develop in the relatively empty space between galaxies.

Question 11

In general,an isolated pulsar speeds up as it ages,so its pulse period decreases.

Question 12

A supergiant star can keep adding shells to its core "onion" structure until it produces uranium as a byproduct.

Question 13

The event horizon surrounding a black hole describes the "surface" in space where the escape velocity equals the speed of light.

Question 14

X-ray bursters,like novae,are thought to involve close binaries whose stars are engaged in mass transfer.

Question 15

Jocelyn Bell,a young graduate student at Cambridge University in 1967,and her colleagues detected the first pulsar using an array of radio antennas.

Question 16

The evolutionary stage of a very large star that lasts the longest is when it is going through hydrogen fusion.

Question 17

All supernova remnants that have been observed are spherical in shape.

Question 18

When a star with an initial mass greater than about 8 solar masses nears the end of its life,it becomes a red supergiant and its energy comes from a series of concentric fusing shells.

Question 19

The Schwarzschild radius describes the maximum radius that a white dwarf can have.

Question 20

All black holes have the same amount of gravitational force.

Question 21

How much energy is released in the supernova explosion of a massive star?

A) Almost as much energy as the Sun emits over its entire lifetime
B) Almost as much energy as the entire Galaxy emits over its lifetime
C) As much energy as the Sun emits over its entire lifetime
D) 100 times as much energy as the Sun emits over its entire lifetime

Question 22

Which of the following will a high-mass star NOT do at or near the end of its life?

A) Emit copious amounts of neutrinos
B) Eject its outer layers and become a neutron star
C) Eject its outer layers and become a white dwarf
D) Convert silicon into iron in its core

Question 23

A typical supernova,in the hours following its explosion,is as bright as

A) 1000 typical spiral galaxies.
B) an entire galaxy.
C) 1000 Sun-like stars.
D) a million Sun-like stars.

Question 24

Which of the following is NEVER a consequence of a supernova explosion?

A) Condensation of matter into a solid nuclear star composed entirely of neutrons
B) Triggering of star formation by shock waves moving through interstellar space
C) Formation of a planetary nebula
D) Manufacture of the nuclei of heavy elements

Question 25

When a supernova explosion results from core collapse in a massive star it appears to leave behind

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

Question 26

Which nuclear fusion cycle follows the helium fusion phase as a massive star evolves?

A) Silicon "burning"
B) Carbon "burning"
C) Iron "burning"
D) Oxygen "burning"

Question 27

For a massive star,core hydrogen burning lasts for several million years.In contrast,core silicon burning lasts for only about

A) 1 day.
B) 1 minute.
C) 600 years.
D) 1 year.

Question 28

The capture of free neutrons by heavy atomic nuclei is

A) easy because neutron capture always produces a stable product nucleus.
B) easy because the neutron has no electric charge.
C) difficult,unless the nucleus is already unstable.
D) difficult,unless the neutron is moving rapidly.

Question 29

The supergiant stars Betelgeuse and Rigel in the Orion region of the sky appear particularly bright because

A) they are in a region of low interstellar medium density and,therefore,are not heavily obscured compared to equivalent stars elsewhere.
B) they are close in our spiral arm.
C) they are very luminous.
D) their high surface temperatures make them easy to see,even though they are intrinsically faint and far away,because most of their light is concentrated in the visible range.

Question 30

The sequence of thermonuclear fusion processes inside massive stars can transform elements such as carbon,oxygen,and so forth,into heavier elements AND generate excess energy,until iron has been produced.Why is it not possible for fusion reactions to release energy from iron nuclei?

A) It has been found that iron nuclei never undergo fusion reactions.
B) The magnetic properties of iron produce extra repulsion that,along with the electrostatic repulsion,prevents fusion of iron nuclei with protons.
C) Iron is the heaviest possible element in nature,and fusion of heavier elements is not possible.
D) The electrostatic repulsion between the iron nucleus and the proton is so great that fusion requires extra energy,rather than releasing it.

Question 31

The majority of massive stars,at the point in time when they explode as supernovae,have become

A) red supergiants.
B) neutron stars.
C) blue supergiants.
D) white dwarfs.

Question 32

At the end of the life of a massive star,during the process of core collapse,the time taken from the start of collapse to the attainment of nuclear density is about

A) 1/4 second.
B) 1/2000 second.
C) 8 minutes.
D) a few hours.

Question 33

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) nuclear fusion has produced a significant amount of iron in its core.
C) the core becomes as dense as an atomic nucleus.
D) the density reaches a threshold at which electron degeneracy pressure begins to play a role.

Question 34

Which force induces the core to condense and collapse in massive stars at the conclusion of each episode of nuclear fusion,such as the carbon,oxygen,and silicon fusion cycles?

A) Gravity
B) The nuclear attractive force between nuclei and between neutrons and protons
C) Gas pressure produced by the very high gas temperatures
D) Electron degeneracy pressure

Question 35

During the late stages of evolution (e.g. ,oxygen burning)in massive stars,nuclear reactions produce many free neutrons.What very important effect do these neutrons have on the composition of the star?

A) The neutrons,being uncharged,escape from the star,thus carrying away energy from the core of the star and lowering its temperature.
B) The neutrons are captured by atomic nuclei and can produce heavy elements that would not form from nuclear fusion alone.
C) The neutrons are captured by atomic nuclei,causing the nuclei to split by fission reactions into lighter elements that would otherwise be very rare in the universe.
D) The neutrons decay into protons and electrons,thus increasing the amount of hydrogen in the core and extending the life of the star.

Question 36

What is the source of energy that allowed supernova 1987A to continue to brighten slowly for a few months after its initial explosion?

A) Radioactive decay of specific nuclei produced in the explosion
B) Thermonuclear reactions between iron nuclei and protons,neutrons,and helium nuclei
C) Thermonuclear reactions between hydrogen nuclei in the shell of gas surrounding the supernova,triggered by the shock wave from the explosion
D) Slow gravitational compression of the remnant core of the supernova and the consequent release of gravitational potential energy

Question 37

Where are core-collapse supernovae detected?

A) Only in spiral galaxies,never in ellipticals
B) In our Galaxy and many others
C) Only in our Galaxy
D) Only in elliptical galaxies,never in spirals

Question 38

Ancient Chinese astronomers recorded the appearance of what phenomenon in 1054 A.D.?

A) A nearby nova explosion in a nearby galaxy
B) A brilliant auroral display covering the whole Earth
C) A supernova,visible in daylight,within our Galaxy
D) A bright binary star undergoing eclipse

Question 39

A sequence of thermonuclear fusion processes inside massive stars can continue to transform the nuclei of elements such as carbon,oxygen,and so forth,into heavier nuclei AND also generate excess energy,up to a limit beyond which no further energy-producing reactions can occur.The element that is produced when this limit is reached is

A) lead.
B) oxygen.
C) uranium.
D) iron.

Question 40

An old high-mass star can have a number of shells (hydrogen,helium,carbon,neon,oxygen,silicon)plus an iron core.Fusion generally takes place everywhere EXCEPT in the

A) hydrogen shell.
B) helium shell.
C) silicon shell.
D) iron core.

Question 41

Among the following locations in the universe,where would you expect to find a pulsar?

A) At the center of the Galaxy
B) At the center of the Sun
C) In the Orion Nebula
D) In the Crab Nebula

Question 42

In what year was the first pulsar discovered?

A) 1978
B) 1967
C) 1960
D) 1930

Question 43

Black holes are so named because

A) they emit a perfect blackbody spectrum.
B) no light or any other electromagnetic radiation can escape from inside them.
C) all their electromagnetic radiation is gravitationally redshifted to the infrared,which leaves no light in the optical region.
D) they emit no visible light,their only spectral lines are in the radio and infrared.

Question 44

Pulsars are

A) pulsating white dwarfs.
B) pulsating neutron stars.
C) pulsating black holes.
D) rotating neutron stars.

Question 45

The first pulsar was detected using

A) the infrared satellite IRAS.
B) a British radio telescope.
C) the unaided eye,by Chinese astronomers.
D) the 200-inch telescope at Mount Palomar.

Question 46

What is a pulsar?

A) A pulsating white-dwarf star,fluctuating rapidly in brightness
B) A rapidly rotating neutron star,producing beams of radio energy and in some cases,light and X-rays
C) A rotating black hole,producing two jets of gas in opposite directions and pulses of gravitational energy
D) A Cepheid variable star with a period of a few days

Question 47

Which of the following astronomical objects are most closely associated with pulsars?

A) Neutron stars
B) Black holes
C) Red-giant stars
D) White-dwarf stars

Question 48

What range in the electromagnetic spectrum was being observed when the first pulsars were discovered?

A) X-ray
B) Visible
C) Radio
D) Gamma rays

Question 49

What is the relationship between neutron stars and the Chandrasekhar limit?

A) The Chandrasekhar limit is an upper-mass limit for the stability of any massive system;it applies to any system,no matter how it was formed,including neutron stars.
B) The Chandrasekhar limit applies only to systems stabilized by degenerate electrons;neutron stars are stabilized by the pressure of the neutron degeneracy.
C) The Chandrasekhar limit applies specifically to the neutron degeneracy and thus to neutron stars.
D) The Chandrasekhar limit applies to radius,not mass.Thus,as long as a neutron star is big enough,it will not be affected by the Chandrasekhar limit.

Question 50

A pulsar is most probably formed

A) in the core of a star as it evolves through its main-sequence phase.
B) in the center of a supernova explosion.
C) within a huge gas cloud,by collisions between stars.
D) just after the formation of a protostar by gravitational condensation.

Question 51

A pulsar is a(n)

A) interstellar beacon manufactured by little green persons (LGPs).
B) type of variable star,pulsating rapidly in size and brightness.
C) rapidly spinning neutron star.
D) accretion disk around a black hole,emitting light as matter is accumulated on the disk.

Question 52

The very strong magnetic field of a neutron star is created by

A) a burst of neutrinos produced by the supernova explosion because this would be the equivalent of a very large electrical current flowing for a short time.
B) the collapse of a star,which significantly intensifies the original weak magnetic field of the star.
C) differential rotation of the neutron star,its equator rotating faster than the poles,similar to sunspot formation.
D) turbulence generated in electrical plasmas during the collapse of a star,even though this star had no magnetic field originally.

Question 53

Neutron stars are believed to be created primarily by

A) explosions in main-sequence stars.
B) Type Ia supernovae (explosions in white dwarfs).
C) Type II supernovae (explosions in high-mass stars).
D) supernovae of either Type Ia or Type II.

Question 54

A neutron star will be detected from Earth as a pulsar by its regular radio pulses ONLY if Earth lies

A) in the plane of the neutron star's magnetic equator,halfway between its magnetic poles.
B) almost directly in line with the magnetic axis of the neutron star at some time during the star's rotation.
C) directly above the rotation axis of the rotating neutron star.
D) in the neutron star's "equator," the plane perpendicular to its spin axis.

Question 55

Which of the following descriptions does NOT represent a property of neutron stars?

A) Emitters of relatively narrow beams of radio energy and other electromagnetic radiation
B) Rotation rates from 1 to 30 times per second
C) Strong gravitational fields but weak magnetic fields
D) Composed almost entirely of neutrons

Question 56

The pulsed nature of the radiation at all wavelengths that is seen to come from a pulsar is produced by the

A) mutual orbiting and eclipsing of two very hot stars in a close binary system.
B) rapid pulsation in size and hence brightness of a small white-dwarf star.
C) rapid rotation of a neutron star that is producing two oppositely directed beams of radiation.
D) extremely hot matter that is rapidly orbiting a black hole just prior to descending into it.

Question 57

The pulsation periods of most pulsars range from

A) 1/1000 second to a few seconds.
B) 10^-6 to 10^-3 second.
C) minutes to hours.
D) many hours to a few days.

Question 58

The diameter of a typical neutron star of 1 solar mass is predicted to be approximately

A) 1 km.
B) that of the Sun.
C) that of an average city,about 30 km.
D) that of Earth,12,800 km.

Question 59

As time progresses,the pulse rate for most solitary pulsars is

A) slowing down because rotational energy is being used to generate the pulses.
B) absolutely constant: Pulsars provide ideal frequency standards or clocks.
C) varying periodically as the neutron star undergoes periodic expansions and contractions.
D) speeding up,as the neutron star slowly contracts under gravity.

Question 60

Why are black holes called black holes?

A) Nothing,not even electromagnetic radiation,can escape from inside them.
B) Only nonvisible radiation longer than about 1000 nm wavelength (infrared and radio radiation)can escape from them.
C) They are always surrounded by an accretion disk,which absorbs all light escaping from the inside of the black hole.
D) They emit an electromagnetic spectrum,which matches that of a perfect blackbody.

Question 61

In a binary star system,an unseen component is found to have a mass of about 8 solar masses.If this were a normal star,then it would be visible,so it must be a collapsed object.Theoretical considerations tell us that it must be a

A) white dwarf.
B) black hole.
C) neutron star.
D) brown dwarf.

Question 62

A nova is a sudden brightening of a star that occurs when

A) material from a companion star is transferred onto the surface of a white dwarf in a binary system and is subsequently blasted into space by a runaway thermonuclear explosion,leaving the white dwarf intact to repeat the process.
B) the electron-degenerate iron core of a massive star collapses after its mass becomes larger than the Chandrasekhar mass limit.
C) material from a companion star is transferred onto a neutron star in a binary system,causing the neutron star to collapse into a black hole.
D) material from a companion star is transferred onto the surface of a white-dwarf star in a binary system,after which runaway carbon fusion reactions cause the entire white dwarf to be destroyed in an explosion.

Question 63

What is the difference between a nova and an X-ray burster? All of the following answers are correct EXCEPT one.Which one is the exception?

A) A nova involves stars in a close binary system,whereas an X-ray burster involves an individual star not in a binary system.
B) A nova is produced by a white dwarf,whereas an X-ray burster is produced by a neutron star.
C) A nova involves the nuclear explosion of hydrogen,whereas an X-ray burster involves the nuclear explosion of helium.
D) The system that emits X-ray bursts emits a constant stream of X-rays between bursts,whereas a system that produces nova does not.

Question 64

The diameter of the black hole candidate Cygnus X-1 has been estimated by

A) combining the amount of energy received at Earth per second with the distance to the source to estimate the total energy emitted per second.
B) measuring how quickly it flickers in intensity.
C) measuring how long it takes to block off the light from its companion star during an eclipse (i.e. ,as it passes in front of its companion star as seen from Earth).
D) combining its distance with its angular diameter to find its physical size.

Question 65

At first,it was thought that nothing could ever escape from a black hole,yet astronomers are now locating black hole candidates by the X-rays they emit.Do they really see X-rays coming from a black hole?

A) The X-rays come from highly compressed matter in the accretion disk outside the event horizon of the black hole.
B) The black hole modifies spacetime around it so much that particles and X-rays are created in the vacuum itself,just outside the event horizon.
C) The X-rays are produced by vibrations of the black hole itself,and therefore they come from the event horizon,and not from inside the black hole.
D) X-rays are neither light nor matter and therefore can escape from inside the black hole.

Question 66

A black hole can be thought of as

A) strongly curved space.
B) a star with a temperature of 0 K,emitting no light.
C) the point at the center of every star,providing the star's energy.
D) densely packed matter inside a small but finite volume.

Question 67

One object that is believed to be a black hole in our Galaxy is

A) the central star in the Ring Nebula in Lyra.
B) the central star in the Crab Nebula.
C) the undetected tenth planet in our solar system,whose presence has been inferred from its gravitational influence on the outer planets.
D) Cygnus X-1,a powerful X-ray source.

Question 68

Which of the following is NOT one of the reasons we believe gamma-ray bursters are supernova explosions in distant galaxies rather than eruptions in the nuclei of active galaxies?

A) Afterglow spectra are very similar to known supernova spectra.
B) The expanding shell of gas that follows the explosion is similar to that following a supernova.
C) Gamma-ray bursters do not appear at the centers of their host galaxies.
D) The amount of energy released in a burster is similar to that released in a normal supernova.

Question 69

What is believed to be the mass of the black hole candidate Cygnus X-1?

A) 30 solar masses
B) 1 billion solar masses
C) 7 solar masses
D) 1 solar mass

Question 70

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) Neutron stars are held up by centrifugal force due to their rapid rotation.
C) Neutron stars are solid,and like other solid spheres,are held up by the repulsive force between atoms in the solid.
D) Gravity in the neutron star is balanced by an outward force due to gas pressure,as in the Sun.

Question 71

What method is used by astronomers to infer the existence in space of a dark object with a mass of about 5 solar masses such as a black hole?

A) The measurement of the effect of its gravitational force on a companion object in a binary system
B) The measurement of the gravitational redshift of spectral lines in the spectrum of the object
C) The estimation of the luminosity of the object and the application of the mass-luminosity relationship
D) The photography or imaging of a region from which no light or radiation at all appears to come

Question 72

X-rays that come from the vicinity of a black hole actually originate from

A) well inside the event horizon.
B) its exact center,or singularity.
C) relatively far away from the black hole,where matter is still relatively cool.
D) just outside the event horizon,on the accretion disk.

Question 73

Type II supernovae show prominent lines of hydrogen in their spectra,whereas hydrogen lines are absent in spectra of Type Ia supernovae.Why is this? (Hint: Think about the type of star that gives rise to each of the two types of supernova. )

A) Massive stars have burned all of their hydrogen into heavier elements,whereas low-mass stars still have large hydrogen-rich envelopes.
B) Massive stars contain large amounts of hydrogen,whereas white dwarfs are mostly carbon and oxygen.
C) White dwarfs have a thick surface layer of hydrogen,whereas neutron stars contain no hydrogen at all.
D) Massive stars contain large amounts of hydrogen,whereas neutron stars contain no hydrogen at all.

Question 74

Can a white dwarf explode?

A) 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 nuclear reactions in the white dwarf core reach the stage of silicon burning,producing iron.
C) No,white dwarfs are held up by electron degeneracy pressure,and this configuration is stable against collapse or explosion.
D) Yes,but only if it is in a binary star system.

Question 75

If a black hole is truly black and has an escape velocity greater than the speed of light such that no light can escape it,where do the X-rays come from in the black hole candidates so far identified?

A) From stars behind the black hole,whose light is focused and concentrated by gravitational focusing to the point where it becomes X-ray radiation
B) The black hole is only black to visible radiation traveling at the speed of light,but because X-rays travel faster than the speed of light,they can escape.
C) From the normal star accompanying the black hole,its ordinary light being blueshifted into the X-ray spectral region by the intense gravity of the black hole
D) From the matter surrounding the black hole,which is highly condensed and hence very hot

Question 76

What is the main observational difference between a Type I and a Type II supernova?

A) Hydrogen lines are prominent in the spectrum of a Type II supernova but absent in that of Type I.
B) The spectrum of a Type II supernova shows strong lines of both hydrogen and helium,whereas that of Type I shows only hydrogen.
C) The spectrum of a Type I supernova shows strong lines of both hydrogen and helium,whereas that of Type II shows only hydrogen.
D) Hydrogen lines are prominent in the spectrum of a Type I supernova but absent in that of Type II.

Question 77

X-ray bursters are objects in the sky that emit sudden bursts of X-rays in addition to a steady,low-level,X-ray emission.These bursts of X-rays are believed to be caused by

A) material transferred onto the surface of a neutron star in a binary system,then subsequently ignited in a thermonuclear explosion that leaves the neutron star intact to repeat the process.
B) material from a companion star pulled into an accretion disk around a black hole,with periodic clumps of material falling from the disk into the black hole to produce the X-rays.
C) material transferred onto the surface of a neutron star,causing the neutron star to collapse suddenly into a black hole.
D) material transferred onto the surface of a white dwarf in a binary star system,producing a thermonuclear explosion at the surface while leaving the white dwarf intact to repeat the process.

Question 78

What is the likely final fate of a star that has a mass of greater than 15 solar masses after completing its nuclear fusion-burning phases?

A) It undergoes fission and immediately splits in two to become a binary star system.
B) The degeneracy of the electrons within the star prevents collapse beyond the diameter of a white dwarf.
C) It condenses to the point where it is composed completely of neutrons,the degeneracy of which prevents further shrinkage.
D) It collapses and becomes a black hole.

Question 79

If the Sun were replaced by a 1-solar-mass black hole,then Earth would

A) continue to orbit the black hole in precisely its present orbit.
B) move into an elliptical orbit passing close to the black hole,with its farthest distance from the black hole equal to 1 AU.
C) spiral quickly into the black hole.
D) head off into interstellar space along a straight line at a tangent to its original orbit around the Sun.

Question 80

Pairs of jets carrying material and radiation outward in opposite directions have been detected (or inferred)for all of the following types of objects EXCEPT

A) stellar-mass black hole candidates.
B) supermassive black hole candidates.
C) protostars.
D) white dwarfs.