Deck 8: The Deaths of Stars

Question 1

When mass is transferred toward a white dwarf in a binary system,the material forms a rapidly growing whirlpool of material.What is that whirlpool called?

A)an accretion disk
B)an Algol paradox
C)a planetary nebula
D)a supernova remnant

Answer 1

an accretion disk

Question 2

Refer to the H-R diagram.What type of star do the two data points above spectral type "A" represent?

A)massive main-sequence stars
B)massive supergiant stars
C)white dwarfs with mass less than the sun's mass
D)white dwarfs with mass greater than twice the sun's mass

Answer 2

white dwarfs with mass less than the sun's mass

Question 3

As a star exhausts the hydrogen in its core,what happens?

A)It becomes hotter and more luminous.
B)It becomes hotter and less luminous.
C)It becomes cooler and less luminous.
D)It becomes cooler and more luminous.

Answer 3

It becomes cooler and more luminous.

Question 4

What is the approximate age of the star cluster in the H-R diagram?
(Hint: Main sequence stars of spectral types O and B have a core supply of hydrogen that is sufficient to last about 250 million years;types A and F,about 2 billion years;type G about 10 billion years;types K and M about 30 billion years.The apparent magnitude scale means that larger numbers are toward the bottom of the vertical axis.)

A)200 million years
B)2 billion years
C)10 billion years
D)30 billion years

Question 5

What is the defining characteristic of stars within a cluster that are at the turnoff point?

A)They are just leaving the main sequence.
B)They are just becoming white dwarfs.
C)They are just entering the main sequence.
D)They are about to explode in supernovae.

Question 6

What is the term for a collection of 100 to 1000 young stars in a region about 80 light-years in diameter?

A)Herbig-Haro object
B)globular cluster
C)open cluster
D)giant cluster

Question 7

Refer to the H-R diagram.How would the H-R diagram of a more distant star cluster look different?

A)The points would shift down, because all of the stars would have larger apparent magnitudes.
B)The points would shift to the right, because all of the stars would appear to be cooler.
C)The points would shift up, because all of the stars would have smaller apparent magnitudes.
D)The points would shift to the left, because all of the stars would appear to be hotter.

Question 8

What is the term for the form of electromagnetic radiation produced by rapidly moving electrons spiralling through magnetic fields?

A)Lagrangian radiation
B)ultraviolet radiation
C)synchrotron radiation
D)infrared radiation

Question 9

What property is the same for all stars in a star cluster?

A)age
B)mass
C)luminosity
D)radius

Question 10

When does a star experience helium fusion?

A)when it is on the horizontal branch
B)after it has become a red giant star
C)just before it enters the main sequence
D)before it leaves the main sequence

Question 11

Which of the following correctly describes a relationship between pressure,temperature,and density in degenerate matter?

A)Pressure depends only on the temperature.
B)Pressure does not depend on temperature.
C)Temperature depends only on density.
D)Pressure does not depend on density.

Question 12

What type of object is the Crab nebula?

A)a planetary nebula
B)an open cluster
C)an absorption nebula
D)a supernova remnant

Question 13

What do we call the region of the HR diagram that represents giant stars that are fusing helium in their cores and then in their shells?

A)turnoff point
B)horizontal branch
C)turn-on point
D)main sequence

Question 14

Which nuclear fuels does a one solar mass star use over the course of its entire lifespan?

A)hydrogen
B)hydrogen and helium
C)hydrogen, helium, and carbon
D)hydrogen, helium, carbon, and oxygen

Question 15

Refer to the H-R diagram.How would the H-R diagram of an older star cluster look different?

A)The points would shift to the right, because all of the stars would have lower temperatures.
B)The lower main sequence would look the same, but the turnoff would be at spectral type K or M.
C)The points would shift down, because all of the stars would have lower luminosities.
D)The lower main sequence would look the same, but the turnoff would be at spectral type F or A.

Question 16

What is the term for a collection of 10⁵ to 10⁶ old stars in a region 30 to 100 light-years in diameter?

A)Herbig-Haro object
B)globular cluster
C)open cluster
D)giant cluster

Question 17

Why are giant and supergiant stars rare?

A)The giant and supergiant stages are very short.
B)The star blows up before the giant or supergiant stage is reached.
C)They do not form as often as main sequence stars.
D)The giant or supergiant stage is very long.

Question 18

If the stars at the turnoff point of a cluster have a mass of 3 times the mass of the Sun,what is the age of the cluster?

A)6.4×10⁸ years
B)3.3×10⁹ years
C)3.0×10¹⁰ years
D)1.6×10¹¹ years

Question 19

Why are star clusters important to our study of stars?

A)because all stars formed in star clusters
B)because they allow us to test our theories and models of stellar evolution
C)because the Sun was once a member of a globular cluster
D)because they are the only objects that contain Cepheid variables

Question 20

What principle explains why matter flowing from one star in a binary system to its companion forms an accretion disk?

A)conservation of tidal forces
B)conservation of temperature
C)conservation of angular momentum
D)conservation of energy

Question 21

As a white dwarf cools,why does its radius NOT change?

A)because pressure due to nuclear reactions in a shell just below the surface keeps it from collapsing
B)because pressure does not depend on temperature for a white dwarf, since the electrons are degenerate
C)because pressure does not depend on temperature, since the star has exhausted all its nuclear fuels
D)because material accreting onto it from a companion maintains a constant radius

Question 22

When material expanding away from a star in a binary system reaches the edge of its Roche lobe,what happens?

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 will no longer be gravitationally bound to the star.
D)The material will increase in temperature and eventually undergo thermonuclear fusion.

Question 23

Where is synchrotron radiation produced?

A)in planetary nebulae
B)in the outer layers of red dwarfs
C)in the collapsing iron cores of massive stars
D)in supernova remnants

Question 24

Why can't massive stars generate energy through iron fusion?

A)because iron fusion requires very high density
B)because no star can get hot enough for iron fusion
C)because both fusion and fission of iron nuclei absorb energy
D)because massive stars go supernova before they create an iron core

Question 25

What is a white dwarf 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

Question 26

What does the Chandrasekhar-Landau limit tell us?

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 with a mass less than 0.5 solar masses will not go through helium flash.

Question 27

Why can't the lowest mass stars become giants?

A)Their centres never get hot enough.
B)Their rotation is too slow.
C)They do not contain helium.
D)They never use up their hydrogen.

Question 28

After they leave the main sequence,what happens to stars with masses between 0.4 and 4 solar masses?

A)They undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.
B)They undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.
C)They produce type-I supernovae after they exhaust their nuclear fuels.
D)They produce type-II supernovae after they exhaust their nuclear fuels.

Question 29

When does a type-II supernova occur?

A)when a white dwarf's mass exceeds the Chandrasekhar-Landau limit
B)when the iron core of a massive star collapses
C)directly following a helium flash
D)when two neutron stars collide

Question 30

Which of the following is almost always associated with a nova?

A)a very massive star
B)a star undergoing helium burning
C)a white dwarf in a close binary system
D)a solar-like star that has exhausted its hydrogen and helium

Question 31

What is a planetary nebula?

A)the expelled outer envelope of a medium mass star
B)a cloud of hot gas produced by a supernova explosion
C)a nebula within which planets are forming
D)a cloud of hot gas surrounding a planet

Question 32

What produces synchrotron radiation?

A)objects with temperatures below 10,000 K
B)high-velocity electrons moving through a magnetic field
C)cold hydrogen atoms in space
D)helium burning in a massive star

Question 33

The diagram shows a light curve from a supernova.How many days after maximum light did it take for the supernova to decrease in brightness by 5 magnitudes?

A)less than 50
B)50
C)150
D)250

Question 34

What does a planetary nebula do?

A)produces an absorption spectrum
B)produces an emission spectrum
C)contracts to form planets
D)contracts to form a star

Question 35

The diagram shows a light curve from a supernova.About how long did it take for the supernova to reach its maximum luminosity?

A)25 days
B)50 days
C)100 days
D)200 days

Question 36

Suppose you discover a binary star system with a 0.7 solar mass giant star and a 2 solar mass main sequence star.Why is this surprising?

A)0.7 solar mass stars are not expected to become giants.
B)All 2 solar mass stars should have left the main sequence.
C)Giant stars are expected to destroy their companions, so the 2 solar mass star shouldn't exist.
D)The 2 solar mass star should have become a giant before the 0.7 solar mass star.

Question 37

If the hypothesis that novae occur in close binary systems is correct,then which of the following should novae do?

A)They should produce synchrotron radiation.
B)They should occur in regions of star formation.
C)They should all be visual binaries.
D)They should repeat after some interval.

Question 38

Which point indicates the location on the H-R diagram of a one-solar-mass star when it stars to fuse helium?

A)1
B)2
C)3
D)4

Question 39

Which of the following offered support for the theory that the collapse of a massive star's iron core produces neutrinos?

A)the detection of neutrinos from the supernova of 1987
B)the brightening of supernovae a few days after they are first visible
C)underground counts of solar neutrinos
D)laboratory measurements of the mass of the neutrino

Question 40

Under what conditions are Type Ia supernovae believed to occur?

A)when the core of a massive star collapses
B)when a white dwarf exceeds the Chandrasekhar-Landau limit
C)when hydrogen detonation occurs
D)when neutrinos in a massive star form a shock wave that explodes the star

Question 41

After what evolutionary stage does a star become a white dwarf?

A)protostar
B)pre-main sequence
C)main sequence
D)giant

Question 42

For a star with a mass similar to that of the Sun,what is the last stage of the nuclear fusion?

A)hydrogen to helium
B)helium to carbon and oxygen
C)carbon to magnesium
D)silicon to iron

Question 43

What happens when light travels out of a gravitational field,loses energy,and its wavelength grows longer?

A)a gravitational blue shift
B)the solar wind
C)a gravitational red shift
D)a pulsar wind

Question 44

What is the density of a neutron star?

A)about the same as that of a white dwarf
B)about the same as that of the Sun
C)about the same as that of an atomic nucleus
D)zero

Question 45

Why can't pulsars be spinning white dwarfs?

A)White dwarfs are not very common.
B)White dwarfs are not dense enough to produce bright pulses.
C)White dwarfs do not have magnetic fields.
D)White dwarfs are too large to produce such short pulses.

Question 46

What are the two longest stages in the life of a one solar mass star?

A)protostar, pre-main sequence
B)protostar, white dwarf
C)protostar, main sequence
D)main sequence, white dwarf

Question 47

What is the source of the energy radiated by a white dwarf?

A)the proton-proton chain
B)the CNO cycle
C)gravitational contraction after becoming a white dwarf
D)gravitational contraction during the white dwarf formation phase

Question 48

About how long will a 0.5 solar mass star spend on the main sequence?

A)5 million years
B)570 million years
C)5 billion years
D)57 billion years

Question 49

If you had an extremely sensitive radio telescope,could you detect every pulsar in the Milky Way galaxy?

A)Yes, because all pulsars emit radio waves.
B)Yes, because all pulsars are nearby.
C)No, some pulsars don't flash all of the time.
D)No, some pulsar beams don't point in the direction of Earth.

Question 50

Which of the following has a radius of about 10 kilometres and is supported by the pressure associated with degenerate neutrons?

A)black hole
B)neutron star
C)white dwarf
D)supernova remnant

Question 51

What happens to stars that have ejected a planetary nebula?

A)They become protostars.
B)They become brown dwarfs.
C)They become white dwarfs.
D)They become red giants.

Question 52

In the year 10⁵4 CE,Chinese astronomers observed the appearance of a new star.What occupies that location now?

A)a molecular cloud
B)a planetary nebula with a white dwarf in the centre
C)a supernova remnant with a pulsar in the centre
D)nothing

Question 53

What does the explosion of a type II supernova typically leave behind?

A)a planetary nebula
B)a shell of hot, expanding gas with a white dwarf at the centre
C)a shell of hot, expanding gas with a pulsar at the centre
D)nothing is ever left behind

Question 54

What are hypernovae?

A)supernovae that occur when two red dwarfs collide
B)supernovae that occur when 10 solar mass stars explode
C)supernovae that occur when stars more massive than 25 solar masses explode
D)supernovae that occur when two black holes collide

Question 55

Why are neutron stars expected to spin rapidly?

A)They conserve angular momentum when they collapse.
B)They have high orbital velocities.
C)They have high densities.
D)The energy from the supernova explosion that formed them makes them spin faster.

Question 56

Why do astronomers sometimes say "black holes don't suck"?

A)Black holes can have accretion disks around them.
B)The distance between a black hole event horizon and singularity is not very large.
C)Material that falls into a black hole can come out later.
D)A black hole's gravity is the same as that of any other object of the same mass.

Question 57

What is the term that describes the slowing of clocks in strongly curved space-time?

A)gravitational radiation
B)time dilation
C)gravitational red shift
D)hyperspace drag

Question 58

Although neutron stars are very hot,they are faint and not easy to see at visual wavelengths.Why is this?

A)Light does not escape from their event horizon.
B)Most neutron stars lie beyond dense dust clouds.
C)They have only a small surface area from which to emit light.
D)The peak of their thermal emission is at infrared wavelengths.

Question 59

What is the term for the distance from a black hole at which the escape velocity is approximately equal to the speed of light?

A)Lagrangian point
B)Chandrasekhar-Landau limit
C)Hubble radius
D)Schwarzschild radius

Question 60

Observations from the Compton Gamma Ray Observatory showed that gamma ray bursts were located all over the sky.What did astronomers conclude from this?

A)The bursts were produced by stars in the disk of our galaxy.
B)The bursts were associated with planets in our solar system.
C)The bursts were produced by sources in distant galaxies.
D)The bursts were produced in our Sun.

Question 61

What has greater density than a white dwarf?

A)a neutron star
B)a red dwarf
C)a brown dwarf
D)a red giant

Question 62

The rotation speed of pulsars slows down over time.What is believed to be the reason for this?

A)They are losing angular momentum into space via outward streaming particles.
B)They are dragging companion stars around in their magnetic fields.
C)They are conserving angular momentum.
D)Their mass is increasing.

Question 63

Why is the material that accretes onto a neutron star or black hole expected to emit X-rays?

A)The material contains magnetic fields that will produce synchrotron radiation.
B)Hydrogen nuclei begin to fuse and emit high energy photons.
C)The material will become hot enough that it will radiate most strongly at X-ray wavelengths.
D)As the material slows down it converts thermal energy to gravitational potential energy.

Question 64

How are millisecond pulsars unusual compared to other pulsars?

A)Their spin rates are fast for their age.
B)They only emit millimetre-wave radiation.
C)They have strong magnetic fields.
D)They are all X-ray binaries.

Question 65

What is interesting about the orbit of the binary pulsar,PSR 1936+16,studied by Taylor and Hulse?

A)It is so small that the orbital period is smaller than the pulsar period.
B)It is growing smaller, presumably by emitting gravitational waves.
C)It provides evidence that it is being orbited by at least 6 planets the size of Jupiter.
D)It shows large changes each time an X-ray burst is emitted from the system.

Question 66

What is the approximate size of the Schwarzschild radius of a one solar mass black hole?

A)3 kilometres
B)1,500,000 kilometres, the size of the Sun
C)150,000,000 kilometres, or 1 AU
D)1013 kilometres, or 1 light-year

Question 67

Cygnus X-1 and LMC X-3 are binary systems with one component not visible.What must the unseen component masses be for astronomers to be certain that these systems contain a black hole?

A)less than 0.4 solar masses
B)between 0.4 and 1.4 solar masses
C)less than 5 solar masses
D)more than 5 solar masses

Question 68

Which of the following would be most likely to indicate the presence of an isolated black hole?

A)bending of light from background stars
B)emission of light from within an event horizon
C)gravitational effects on a binary companion
D)X-ray emission from an accretion disk

Question 69

Which of the following is NOT a property of pulsars?

A)strong magnetic field
B)rapid rotation
C)radius of at least 100 km
D)association with supernova remnants

Question 70

Do all supernova remnants contain pulsars?

A)Yes, pulsars are visible in all supernova remnants.
B)No, some supernova explosions form white dwarfs instead of the neutron stars necessary for pulsars.
C)No: all supernova remnants start out having pulsars but the pulsars can disappear before the supernova remnant dissipates.
D)Yes, but some pulsars' pulses are not visible from Earth because of the direction of their rotational axis.

Question 71

Which of the following mechanisms would be involved in extracting energy from compact objects?

A)time dilation
B)white holes
C)gravitational redshifts
D)jets and accretion disks

Question 72

Which of the following objects is believed to possibly contain a black hole?

A)the central star of the Crab nebula
B)the Orion nebula
C)LMC X-3
D)PSR 1257+12

Question 73

Why is the name pulsar a poor description of the object?

A)Pulsars are neutron stars.
B)Pulsars' radio emissions are irregular.
C)Pulsars vibrate rather than pulsate.
D)Pulsars flash rather than pulsate.

Question 74

Who discovered the first pulsar,in November of 1967?

A)Jocelyn Bell
B)Russel Hulse and Joseph Taylor
C)Walter Baade
D)Edwin Hubble

Question 75

What is odd about the existence of planets around PSR J1257+12?

A)The gravitational pull of the pulsar should have pulled the planets down onto it.
B)Planets would not be expected to survive the supernova explosion that created the pulsar.
C)The planets should have been destroyed by the radiation from the pulsar.
D)The pulsar is rotating so fast that the planets should have been flung into space.

Question 76

What is the Schwarzschild radius?

A)the distance between a neutron star's centre and its surface
B)the distance between a black hole and its event horizon
C)the inner boundary of a planetary nebula
D)the point where synchrotron radiation is created around a pulsar

Question 77

Which of the following factors does the escape velocity from the surface of an object depend on?

A)the object's mass and radius
B)the object's mass only
C)the object's radius and the mass of the object trying to escape
D)the object's radius and the speed of light

Question 78

When searching for black holes,what associated phenomena do astronomers search for?

A)single stars that emit large quantities of X-rays
B)X-ray binaries where the compact companion has a mass in excess of 3 solar masses
C)large spherical regions from which no light is detected
D)pulsars with periods of less than one millisecond

Question 79

Where is the singularity of a black hole found?

A)It is found outside the event horizon.
B)It is located within the event horizon.
C)It is located at the Lagrangian point if the black hole is in a binary system.
D)It doesn't exist, since all black holes have a finite size.

Question 80

Which of the following is an example of time dilation?

A)As material approaches a black hole event horizon, it appears redder and redder.
B)The time that a star spends as a giant is much shorter than its main-sequence lifetime.
C)Pulsars' pulsation periods slow down as they age.
D)As a star approaches a black hole's event horizon, it appears to move more and more slowly.