CHAPTER 11—THE DEATHS OF STARS

MULTIPLE CHOICE

	1.	As a star exhausts hydrogen in its core, it 
a.	becomes hotter and more luminous	
b.	becomes hotter and less luminous	
c.	becomes cooler and less luminous	
d.	becomes larger in radius and hotter	

ANS:	B	PTS:	1

	2.	A star will experience a helium flash if
a.	it is less massive than about 3 solar masses	
b.	its has become a red giant star	
c.	its has formed a helium core 	
d.	the material in the core has gradually become degenerate	
e.	All of the above must be true.	

ANS:	E	PTS:	1

	3.	In degenerate matter
a.	pressure depends only on the temperature.	
b.	temperature depends only on density.	
c.	pressure does not depend on temperature.	
d.	pressure does not depend on density.	
e.	b and c	

ANS:	C	PTS:	1

	4.	Giant and supergiant stars are rare because
a.	they do not form as often as main sequence stars.	
b.	the star blows up before the giant or supergiant stage is reached	
c.	the giant or supergiant stage is very short.	
d.	the giant or supergaint stage is very long 	

ANS:	C	PTS:	1

	5.	A(n) ____ is a collection of 100 to 1000 stars in a region about 25 pc in diameter. The stars in the collection are typically quite young.
a.	Herbig Haro object	
b.	globular cluster	
c.	open cluster	
d.	giant cluster	
e.	supernova	

ANS:	C	PTS:	1

	6.	A(n) ____ is a collection of 105 to 106 stars in a region 10 to 30 pc in diameter. The stars in the collection tend to be more than 109 years old and mostly yellow and red stars.
a.	Herbig Haro object	
b.	globular cluster	
c.	open cluster	
d.	giant cluster	
e.	supernova	

ANS:	B	PTS:	1

	7.	Stars within a cluster that are at the turnoff point
a.	have life expectancies that are equal to the age of the cluster.	
b.	are stars that are just becoming white dwarfs.	
c.	are stars that are just entering the main sequence portion of their evolution.	
d.	are stars that are about to supernova.	
e.	are stars that are generally spectral type G stars.	

ANS:	A	PTS:	1

	8.	In star clusters, the ____ stars are giant stars fusing helium in their cores and then in their shells.
a.	turnoff point	
b.	main sequence	
c.	turnon point	
d.	hydrogen flash	
e.	horizontal branch	

ANS:	E	PTS:	1

	9.	The ____________ are places in the orbital plane of a binary star system where a bit of matter can reach stability.  The one located directly between the two stars is the point where the Roche lobes meet.
a.	turnoff points	
b.	horizontal branch	
c.	Lagrangian points	
d.	synchrotron points	
e.	radiation belts	

ANS:	C	PTS:	1

	10.	A mass is transferred through the inner Langragria point in a binary system toward a white dwarf, the material forms a rapidly growing whirlpool of material known as a(n)
a.	accretion disk.	
b.	Lagrangian point.	
c.	Algol paradox.	
d.	planetary nebula.	
e.	supernova remnant.	

ANS:	A	PTS:	1

	11.	____ is a form of electromagnetic radiation produced by rapidly moving electrons spiraling through magnetic fields.
a.	Lagrangian radiation	
b.	Accretion	
c.	Ultraviolet radiation	
d.	Synchrotron radiation	
e.	Infrared radiation	

ANS:	D	PTS:	1

	12.	The Crab nebula is
a.	a planetary nebula.	
b.	a Bok globule.	
c.	an open cluster.	
d.	an absorption nebula.	
e.	supernova remnant.	

ANS:	E	PTS:	1

	13.	Star clusters are important to our study of stars because
a.	all stars formed in star clusters.	
b.	the sun was once a member of a globular cluster.	
c.	they give us a method to test the our theories and models of stellar evolution.	
d.	they are the only objects that contain Cepheid variables.	
e.	all of the above	

ANS:	C	PTS:	1

	14.	What is the approximate age of the star cluster in the HR diagram below? (Hint:  Main Sequence Stars of spectral between types A and B core supply of hydrogen is sufficient to last about 250 million years.  Between A and F about 2 billion years.  Type G about 10 billion years.  Between K and M about 30 billion years..)

a.	200 million years	
b.	2 billion years	
c.	10 billion years	
d.	30 billion years	
e.	The age of the cluster can not be estimated from an HR diagram of the cluster.	

ANS:	C	PTS:	1

	15.	The triple alpha process
a.	controls the pulsations in Cepheid variable stars.	
b.	is the nuclear fusion of hydrogen to helium in massive stars.	
c.	is the process that produces the neutrinos we receive from the sun.	
d.	requires a temperature of about 5,000,000 K to operate	
e.	occurs during helium flash.	

ANS:	E	PTS:	1

	16.	Which of the following nuclear fuels does a one solar mass star use over the course of its entire evolution?
a.	hydrogen	
b.	hydrogen and helium	
c.	hydrogen, helium and carbon	
d.	hydrogen, helium, carbon, and neon	
e.	hydrogen, helium, carbon, neon, and oxygen.	

ANS:	B	PTS:	1

	17.	Helium flash occurs
a.	because helium is very explosive and cannot be controlled when the nuclear reactions occur.	
b.	because degenerate electrons in the core do not allow the core to expand as it heats up.	
c.	in Cepheid variables.	
d.	in stars with masses less than 0.4 M.	
e.	none of the above	

ANS:	B	PTS:	1

	18.	Stars in a star cluster
a.	all have the same age.	
b.	all have the same chemical composition.	
c.	all have the same luminosity.	
d.	all of the above	
e.	a and b above	

ANS:	E	PTS:	1

	19.	If the stars at the turnoff point of a cluster have a mass of 3 M¤, what is the age of the cluster?
a.	3.0 ´ 1010 years	
b.	3.3 ´ 109 years	
c.	6.4 ´ 108 years	
d.	1.6 ´ 1011 years	
e.	The age of a star cluster can not be determined from the mass of stars at the turnoff point.	

ANS:	C	PTS:	1

	20.	In the diagram below, which point indicates the location on the HR diagram of a one solar mass star when it undergoes helium flash?

a.	1	
b.	2	
c.	3	
d.	4	
e.	5	

ANS:	E	PTS:	1

	21.	The lowest-mass stars cannot become giants because
a.	they do not contain helium.	
b.	they rotate too slowly.	
c.	they cannot heat their centers hot enough.	
d.	they contain strong magnetic fields.	
e.	they never use up their hydrogen.	

ANS:	C	PTS:	1

	22.	A planetary nebula is
a.	the expelled outer envelope of a medium mass star.	
b.	produced by a supernova explosion.	
c.	produced by a nova explosion.	
d.	a nebula within which planets are forming.	
e.	a cloud of hot gas surrounding a planet.	

ANS:	A	PTS:	1

	23.	The Chandrasekhar limit tells us that
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 cannot travel through space too fast	
e.	stars with a mass less than 0.5 solar masses will not go through helium flash.	

ANS:	C	PTS:	1

	24.	A Type I supernova is believed to occur when
a.	the core of a massive star collapses.	
b.	hydrogen detonation occurs.	
c.	a white dwarf exceeds the Chandrasekhar limit.	
d.	the cores of massive stars collapse.	
e.	neutrinos in a massive star become degenerate and form a shock wave that explodes the star.	

ANS:	C	PTS:	1

	25.	Massive stars cannot generate energy through iron fusion because
a.	iron fusion requires very high density.	
b.	stars contain very little iron.	
c.	no star can get hot enough for iron fusion.	
d.	both fusion or fission of iron nuclei absorb energy	
e.	massive stars supernova before they create an iron core.	

ANS:	D	PTS:	1

	26.	The theory that the collapse of a massive star's iron core produces neutrinos was supported by
a.	the size and structure of the Crab nebula.	
b.	laboratory measurements of the mass of the neutrino.	
c.	the brightening of supernovae a few days after they are first visible	
d.	underground counts from solar neutrinos.	
e.	the detection of neutrinos from the supernova of 1987.	

ANS:	E	PTS:	1

	27.	Synchrotron radiation is produced by
a.	objects with temperature below 10,000 K.	
b.	high-velocity electrons moving through a magnetic field.	
c.	cold hydrogen atoms in space.	
d.	the collapsing cores of massive stars.	
e.	helium flash.	

ANS:	B	PTS:	1

	28.	A nova is almost always associated with
a.	a very massive star.	
b.	a very young star.	
c.	a star undergoing helium flash.	
d.	a white dwarf in a close binary system.	
e.	a solar like star that has exhausted its hydrogen and helium.	

ANS:	D	PTS:	1

	29.	The Algol paradox is explained by considering
a.	the degenerate nature of the hydrogen on the surface of the white dwarf.	
b.	synchrotron radiation	
c.	the rate of expansion of the shock wave inside the supernova.	
d.	the rotation rate of a neutron star.	
e.	mass transfer between the two stars in a binary system.	

ANS:	E	PTS:	1

	30.	Stars with masses between 0.4  and 4 
a.	undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon.	
b.	undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium.	
c.	produce type-I supernovae after they exhaust their nuclear fuels.	
d.	produce type-II supernovae after they exhaust their nuclear fuels.	
e.	undergo carbon detonation.	

ANS:	A	PTS:	1

	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	

ANS:	E	PTS:	1

	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.	
e.	neutrinos	

ANS:	D	PTS:	1

	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	

ANS:	C	PTS:	1

	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.	

ANS:	C	PTS:	1

	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.	

ANS:	B	PTS:	1

	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.	

ANS:	E	PTS:	1

	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.	

ANS:	B	PTS:	1

	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	
b.	50	
c.	150	
d.	250	
e.	more than 250	

ANS:	C	PTS:	1

	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.)
a.	240 years	
b.	790,000 years	
c.	96,000 years	
d.	960 years	
e.	24,000 years	

ANS:	E	PTS:	1

	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	

ANS:	B	PTS:	1

	41.	For a star of Sun-like mass, what is the last stage of the nuclear fusion?
a.	Hydrogen to helium.	
b.	Helium to carbon and oxygen.	
c.	Carbon to magnesium.	
d.	Fusion goes all the way up to iron.	

ANS:	B	PTS:	1

	42.	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.	

ANS:	D	PTS:	1

	43.	What nuclear fusion mechanism does an isolated white dwarf use to generate energy?
a.	Proton-proton chain	
b.	CNO cycle	
c.	Triple alpha process	
d.	White dwarfs don't generate their own energy.	

ANS:	D	PTS:	1

	44.	Stars that have ejected a planetary nebula eventually become
a.	protostars.	
b.	brown dwarfs.	
c.	white dwarfs.	
d.	red giants.	

ANS:	C	PTS:	1

	45.	After what evolutionary stage does a star become a white dwarf?
a.	Protostar	
b.	Pre-main sequence	
c.	Main sequence	
d.	Giant	

ANS:	D	PTS:	1

	46.	Where are elements heavier than iron primarily produced?
a.	Brown dwarfs	
b.	White dwarfs	
c.	Supergiants	
d.	Supernovae	

ANS:	D	PTS:	1

	47.	The explosion of a supernova typically leaves behind
a.	a planetary nebula.	
b.	a shell of hot, expanding gas with a white dwarf at the center.	
c.	a shell of hot, expanding gas with a pulsar at the center.	
d.	nothing is ever left behind.	

ANS:	C	PTS:	1

	48.	The density of a neutron star is
a.	about the same as that of a white dwarf.	
b.	about the same as that of the sun.	
c.	about the same as an atomic nucleus.	
d.	zero	

ANS:	C	PTS:	1

	49.	The ____________ of a black hole is the radius from a black hole at which the escape velocity is approximately equal to the speed of light.
a.	Roche limit	
b.	Lagrangian point	
c.	Chandraskhar limit	
d.	Hubble radius	
e.	event horizon	

ANS:	E	PTS:	1

	50.	Observations from the Compton Gamma Ray Observatory showed that gamma-ray bursters were located throughout the sky. This told us that
a.	the bursts were not produced among stars in the disk of our galaxy.	
b.	the bursts were not produced among stars in the nuclear bulge of our galaxy.	
c.	the bursts are not associated with planets in our solar system	
d.	the bursts were not produced in our Sun	
e.	All of the above	

ANS:	E	PTS:	1

	51.	Hypernovae are
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.	one theory to explain the production of gamma ray bursters.	
e.	both c and d above	

ANS:	E	PTS:	1

	52.	____ occurs 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 redshift	
d.	A X-ray burst	
e.	A pulsar wind	

ANS:	C	PTS:	1

	53.	A _____________ has a radius of about 10 km and is supported by the pressure associated with degenerate neutrons.
a.	black hole	
b.	neutron star	
c.	white dwarf	
d.	supernova remnant	
e.	red dwarf	

ANS:	B	PTS:	1

	54.	A neutron star is expected to spin rapidly because
a.	they conserved angular momentum when they collapsed.	
b.	they have high orbital velocities.	
c.	they have high densities.	
d.	they have high temperatures.	
e.	the energy from the supernova explosion that formed them made them spin faster.	

ANS:	A	PTS:	1

	55.	___________ are neutron stars that have magnetic fields 100 times stronger than the average neutron star.
a.	Hypernovae	
b.	Collapsars	
c.	Pulsars	
d.	Kerr singularities	
e.	Magnetars	

ANS:	E	PTS:	1

	56.	The slowing of clocks in strongly curved space time is known as
a.	gravitational radiation.	
b.	time dilation.	
c.	gravitational curvature.	
d.	gravitational red shift.	
e.	hyperspace drag.	

ANS:	B	PTS:	1

	57.	Although neutron stars are very hot, they are faint and not easy to see at visual wavelengths because
a.	light does not escape from their event horizon.	
b.	most lie beyond dense dust clouds.	
c.	they have only a small surface area from which to emit.	
d.	the peak of their thermal emission is at much shorter wavelengths than visual	
e.	both c and d	

ANS:	E	PTS:	1

	58.	In A.D. 1054, Chinese astronomers observed the appearance of a new star, whose location is now occupied by
a.	a pulsar.	
b.	a neutron star.	
c.	a supernova remnant.	
d.	all of the above	

ANS:	D	PTS:	1

	59.	Pulsars cannot be spinning white dwarfs because
a.	white dwarfs are not that common.	
b.	white dwarfs are not dense enough.	
c.	white dwarfs do not have magnetic fields.	
d.	a white dwarf spinning that fast would fly apart.	
e.	all of the above	

ANS:	D	PTS:	1

	60.	Pulsars’ rotations are believed to slow down because
a.	they are losing angular momentum into space via outward streaming particles	
b.	they are dragging companions stars around in their magnetic field.	
c.	they are getting tired	
d.	of conservation of angular momentum.	
e.	their mass is increasing.	

ANS:	A	PTS:	1

	61.	The event horizon
a.	is believed to be a singularity.	
b.	is a crystalline layer.	
c.	has a radius equal to the Schwarzschild radius.	
d.	marks the inner boundary of a planetary nebula.	
e.	is located at the point where synchrotron radiation is created around a pulsar.	

ANS:	C	PTS:	1

	62.	An isolated black hole in empty intergalactic  space would be difficult to detect because
a.	there would be no stars behind it whose light it could bend or lens gravitationally	
b.	it could not emit light from inside its event horizon	
c.	no companion stars would be affected by its gravitational field	
d.	no  matter would be falling into it to create an x-ray emitting accretion disk	
e.	All of the above	

ANS:	E	PTS:	1

	63.	Cygnus X-1 and LMC X-3 are black holes if the masses of the unseen companions are
a.	less than 5 solar masses.	
b.	more than 5 solar masses.	
c.	between 0.4 and 1.4 solar masses.	
d.	less than 0.4 solar masses	
e.	not larger than the masses of the stars that we can see.	

ANS:	B	PTS:	1

	64.	The peculiar system SS 433

I.	is emitting beams of energy and matter.	
II.	is producing a spectrum with both a red and a blue shift.	
III.	probably contains an accretion disk.	
IV.	is the result of a planetary nebula.	

a.	I	
b.	III	
c.	II & III	
d.	I, II, & III	
e.	I, II, III, & IV	

ANS:	D	PTS:	1

	65.	Which of the following objects is considered to possibly contain a black hole?
a.	The central star of the Crab nebula	
b.	The Orion nebula.	
c.	LMC X-3	
d.	Algol	
e.	PSR 1257+12	

ANS:	C	PTS:	1

	66.	The orbit of the binary pulsar, PSR 1936+16, studied by Taylor and Hulse
a.	is so small that the orbital period is smaller than the pulsar period.	
b.	is growing smaller, presumably by emitting gravitational waves.	
c.	provides evidence that it is being orbited by at least 6 planets the size of Jupiter.	
d.	shows large changes each time an X-ray burst is emitted from the system.	
e.	contains a white dwarf and a black hole.	

ANS:	B	PTS:	1

	67.	The density of a ___________ is greater than the density of a ___________.
a.	white dwarf, neutron star	
b.	neutron star, black hole	
c.	pulsar, neutron star	
d.	pulsar, white dwarf	
e.	white dwarf, black hole	

ANS:	D	PTS:	1

	68.	The search for black holes involves searching for
a.	single stars that emit large amounts of X-rays.	
b.	X-ray binaries where the compact companion has a mass in excess of 3 .	
c.	large spherical regions from which no light is detected.	
d.	pulsars with periods less than one millisecond.	
e.	pulsars that are orbited by planets.	

ANS:	B	PTS:	1

	69.	The material that accretes onto a neutron star or black hole is expected to emit X-rays because
a.	the material 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 a X-ray wavelengths.	
d.	as the material slows down it converts thermal energy to gravitational potential energy.	
e.	none of the above	

ANS:	C	PTS:	1

	70.	Why don't all supernova remnants contain pulsars?
a.	All supernova remnants do contain pulsars.	
b.	Some supernova explosions form white dwarfs instead of the neutron stars necessary for pulsars.	
c.	Pulsars slow down and quite producing the pulses before the supernova remnant dissipates.	
d.	The pulsar may be tipped so that the beams do not sweep past Earth.	
e.	b and c above.	

ANS:	D	PTS:	1

	71.	Fraud in science is rare because it is difficult to commit. Why is it difficult to commit fraud in science?
a.	Science requires that experimental and theoretical findings be reproducible.	
b.	All scientists are bound by a code of ethics preventing them from publishing fraudulent work.	
c.	Scientific results are reviewed by other scientists before they are published.	
d.	Scientific journals only allow certain highly trusted individuals to publish their work.	
e.	a and c above	

ANS:	E	PTS:	1

	72.	As material flows into a black hole
a.	the material will experience time dilation.	
b.	the material will become hotter.	
c.	the material will produce an absorption spectrum.	
d.	the material will appear to us to fall into the black hole very rapidly.	
e.	a and b	

ANS:	E	PTS:	1

	73.	The first pulsar was discovered by __________ in November of 1967.
a.	Jocelyn Bell	
b.	Isaac Newton	
c.	Albert Einstein	
d.	Walter Baade	
e.	Edwin Hubble	

ANS:	A	PTS:	1

	74.	A pulsar requires that a neutron star

I.	rotate rapidly.	
II.	have a radius of at least 10 km.	
III.	have a strong magnetic field.	
IV.	rotate on an axis that is different from the axis of the magnetic field.	

a.	I & III	
b.	I & IV	
c.	II, III, & IV	
d.	I, III, & IV	
e.	I, II, III, & IV	

ANS:	D	PTS:	1

	75.	None of the pulsars emit pulses of visible light because
a.	pulsars are to hot to emit visible light.	
b.	pulsars contain black holes that won't let visible light escape.	
c.	the gravitational field of a pulsar is so great that the visible light emitted is red shifted.	
d.	pulsars are too far away for the visible light to be bright enough to be detected at Earth.	
e.	A few pulsars do emit visible light pulses.	

ANS:	E	PTS:	1

	76.	Millisecond pulsars that are very old are
a.	believed to be the result of mass transfer from a companion that increases the spin of the pulsar.	
b.	all single objects.	
c.	not spinning as rapidly they seem because they have four hot spots that produce the flashes.	
d.	X-ray binaries.	
e.	gamma-ray bursters.	

ANS:	A	PTS:	1

	77.	The Schwarzschild radius of a 1  black hole is approximately
a.	3 km.	
b.	1,500,000 km, the size of the Sun	
c.	150,000,000  km or 1 AU.	
d.	3 ´ 1013  km or 1 pc.	

ANS:	A	PTS:	1

	78.	The escape velocity of an object depends on

I.	the mass of that object.	
II.	the mass of the object trying to escape.	
III.	the distance from the center of the object and the escaping object.	
IV.	the speed of light.	

a.	I, II, III, & IV	
b.	I & II	
c.	I & III	
d.	I, II, & IV	
e.	I, III, & IV	

ANS:	C	PTS:	1

	79.	If the inner accretion disk around a black hole has a temperature of 106 K, at what wavelength will it radiate the most energy? Hint: wavelength in nm  =3,000,000/T in K
a.	106 nm	
b.	3 nm	
c.	3 ´ 106 nm	
d.	1 nm	
e.	3 ´ 1011 nm	

ANS:	B	PTS:	1

	80.	The singularity of a black hole
a.	is found outside the event horizon.	
b.	is located within the event horizon.	
c.	can only be located if the black hole is in a binary system.	
d.	doesn't exist since all black holes have a finite size.	

ANS:	B	PTS:	1

	81.	The escape velocity at the event horizon around a black hole is
a.	smaller than the speed of light.	
b.	equal to the speed of light.	
c.	much larger than the speed of light.	
d.	irrelevant since nothing (including light) can escape from a black hole.	

ANS:	B	PTS:	1

	82.	Which of the following can you never know about a black hole?
a.	Mass	
b.	Rotation	
c.	Electrical charge	
d.	The elements of the material that has fallen in.	

ANS:	D	PTS:	1

COMPLETION

	1.	A gas in which the pressure no longer depends on the temperature of the gas is said to be ____________________.

ANS:	degenerate

PTS:	1

	2.	The age of a star cluster can be determined from the ____________________ of the cluster.

ANS:	turnoff point

PTS:	1

	3.	The maximum mass of a white dwarf is ____________________ solar masses.

ANS:	1.4

PTS:	1

	4.	A(n) ____________________ is the expulsion of the outer layers of a moderate mass star that has a degenerate carbon and oxygen core.

ANS:	planetary nebula

PTS:	1

	5.	Electrons moving in a strong magnetic field emit ____________________ radiation.

ANS:	synchrotron

PTS:	1

	6.	Mass can flow from one star in a binary system to its companion through the first ____________________ point.

ANS:	Lagrangian

PTS:	1

	7.	A(n) ____________________ is a rapidly spinning neutron star that accelerates charged particles near the poles of its magnetic field.

ANS:	pulsar

PTS:	1

	8.	The ____________________ theory describes pulsars as rotating neutron stars with strong magnetic fields that confine high speed charged particles in two beams emanating from the magnetic poles of the neutron star.

ANS:	lighthouse

PTS:	1

	9.	The ____________________ of a black hole is the radius from the black hole at which the escape velocity is equal to the speed of light.

ANS:	
event horizon
Schwarzschild radius

PTS:	1

	10.	A(n) ____________________ periodically emits large amounts of X-ray radiation as material accretes around a neutron star or black hole.

ANS:	X-ray burster

PTS:	1

	11.	The ____________________ of a black hole in a binary system can emit X-rays and allow us to detect the presence of the black hole.

ANS:	accretion disk

PTS:	1

TRUE/FALSE

	1.	Stars swell into giants when hydrogen is exhausted in their centers.

ANS:	T	PTS:	1

	2.	The helium flash is the cause of some supernovae.

ANS:	F	PTS:	1

	3.	Helium fusion does not begin until the star has entered the giant region of the H-R diagram.

ANS:	T	PTS:	1

	4.	Even in degenerate matter, pressure depends on temperature.

ANS:	F	PTS:	1

	5.	Giant and supergiant stars are rare because that stage of stellar evolution is short.

ANS:	T	PTS:	1

	6.	Young star clusters have bluer turn-off points than old clusters.

ANS:	T	PTS:	1

	7.	Planetary nebulae are sites of planet formation.

ANS:	F	PTS:	1

	8.	Stars less massive than 0.4 solar mass never become giant stars.

ANS:	T	PTS:	1

	9.	Once a star ejects a planetary nebula, it becomes a white dwarf.

ANS:	T	PTS:	1

	10.	No known white dwarf has a mass greater than the Chandrasekhar limit.

ANS:	T	PTS:	1

	11.	Because more massive stars have more gravitational energy, they can fuse heavier nuclear fuels.

ANS:	T	PTS:	1

	12.	The sun will eventually become a supernova.

ANS:	F	PTS:	1

	13.	Type II supernovae are believed to occur when the cores of massive stars collapse.

ANS:	T	PTS:	1

	14.	Synchrotron radiation occurs when high speed electrons move through a magnetic field.

ANS:	T	PTS:	1

	15.	A Type II supernova produces a planetary nebula.

ANS:	F	PTS:	1

	16.	A nova destroys the star and leaves behind a white dwarf.

ANS:	F	PTS:	1

	17.	A star begins fusing hydrogen to helium the moment it leaves the main sequence.

ANS:	F	PTS:	1

	18.	The average size of a white dwarf is about the same size as the Earth.

ANS:	T	PTS:	1

	19.	Neutron stars have densities roughly the same as that of the atomic nucleus.

ANS:	T	PTS:	1

	20.	Neutron stars were first discovered in the 1930's.

ANS:	F	PTS:	1

	21.	Pulsars could not be pulsating stars because the pulses are too short.

ANS:	T	PTS:	1

	22.	We expect neutron stars to spin rapidly because they conserve angular momentum.

ANS:	T	PTS:	1

	23.	Many pulsars have periods that are gradually increasing as the spinning neutron stars lose energy.

ANS:	T	PTS:	1

	24.	The event horizon marks the boundary within which the density is roughly the same as that of the atomic nucleus.

ANS:	F	PTS:	1

	25.	Theory predicts that neutron stars may not exceed 3 solar masses.

ANS:	T	PTS:	1

	26.	If the accretion disk around a black hole emits X-rays outside the event horizon, the X-rays can escape.

ANS:	T	PTS:	1

	27.	To tell the difference between a neutron star and a black hole in an X-ray binary, we must find the temperature of the object.

ANS:	F	PTS:	1

	28.	LMC X-3 is a binary system that is believed to contain a black hole.

ANS:	T	PTS:	1

	29.	A scientific theory can be proven true if the correct experiments are performed.

ANS:	F	PTS:	1

	30.	When a star of mass comparable to the Sun dies, it becomes a black hole.

ANS:	F	PTS:	1

ESSAY

	1.	What properties of degenerate matter are important to the structure of stars? Why?

ANS:	
Answer not provided.

PTS:	1

	2.	Why does a helium flash occur under some circumstances and not under other circumstances when helium fusion begins?

ANS:	
Answer not provided.

PTS:	1

	3.	From what part of the H-R diagram have the giants in a star cluster evolved?

ANS:	
Answer not provided.

PTS:	1

	4.	Explain how we can find the age of a star cluster.

ANS:	
Answer not provided.

PTS:	1

	5.	On the diagram below, draw the evolutionary track of the sun from the time it reaches the main sequence until it becomes a white dwarf. Label the major stages on this track.

ANS:	
Answer not provided.

PTS:	1

	6.	Why can't lower main sequence stars become giant stars?

ANS:	
Answer not provided.

PTS:	1

	7.	If the sun and stars are supported by gas pressure, what supports a white dwarf?

ANS:	
Answer not provided.

PTS:	1

	8.	If white dwarfs have exhausted their fuel, why are they hot?

ANS:	
Answer not provided.

PTS:	1

	9.	Why can't a lower-mass star generate energy through carbon flash?

ANS:	
Answer not provided.

PTS:	1

	10.	Why can't a massive star generate energy through iron fusion?

ANS:	
Answer not provided.

PTS:	1

	11.	What is the difference between a supernova and a nova?

ANS:	
Answer not provided.

PTS:	1

	12.	What is the difference between a planetary nebula and a supernova remnant?

ANS:	
Answer not provided.

PTS:	1

	13.	What evidence do we have that some stars lose mass?

ANS:	
Answer not provided.

PTS:	1

	14.	If the sun and stars are supported by gas pressure, what supports a neutron star?

ANS:	
Answer not provided.

PTS:	1

	15.	Why do we not expect to find a 5 solar mass neutron star?

ANS:	
Answer not provided.

PTS:	1

	16.	If neutron stars contain no nuclear fuel, why are they hot?

ANS:	
Answer not provided.

PTS:	1

	17.	Why does our theory predict that neutron stars will spin rapidly?

ANS:	
Answer not provided.

PTS:	1

	18.	Why does our theory predict that neutron stars will have strong magnetic fields?

ANS:	
Answer not provided.

PTS:	1

	19.	What evidence do we have that pulsars are neutron stars?

ANS:	
Answer not provided.

PTS:	1

	20.	What observational evidence do we have that black holes exist?

ANS:	
Answer not provided.

PTS:	1

	21.	Why might we suspect that a black hole in a binary system could emit X-rays?

ANS:	
Answer not provided.

PTS:	1

	22.	How can an old pulsar have a very short pulsar period, say less than 0.03 seconds?

ANS:	
Answer not provided.

PTS:	1

	23.	How are neutron stars and white dwarfs similar?

ANS:	
Answer not provided.

PTS:	1