Deck 11: Neutron Stars and Black Holes

Question 1

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.

Answer 1

a white dwarf spinning that fast would fly apart.

Question 2

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

Answer 2

event horizon

Question 3

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.

Answer 3

more than 5 solar masses.

Question 4

____ 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

Question 5

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.

Question 6

The mass of a neutron star is

A) several time that of the sun.
B) about the same as that of the sun.
C) about the same as Earth.
D) smaller than any of these.

Question 7

The size of a neutron star is

A) about the same as that of our Solar System.
B) about the same as that of the sun.
C) about the same as Earth.
D) smaller than any of these.

Question 8

____ 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

Question 9

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.

Question 10

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.

Question 11

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

Question 12

Neutron stars are 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.

Question 13

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

Question 14

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

Question 15

The peculiar system SS 433

A) I
B) III
C) II & III
D) I, II, & III
E) I, II, III, & IV

Question 16

An isolated black hole in empty intergalactic space would be difficult to detect because

A) there would be no stars behind it whose light would be affected by gravitational lensing.
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.

Question 17

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.

Question 18

Similar to our sun, 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.

Question 19

The slowing of clocks in strongly curved space time is known as

A) gravitational radiation.
B) time dilation.
C) gravitational curvature.
D) gravitational redshift.
E) hyperspace drag.

Question 20

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.

Question 21

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.

Question 22

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

Question 23

A black hole can be thought of as

A) a very massive object of finite size.
B) a shell of material expanding from a white dwarf.
C) a massive body of infinitely small size.
D) a burnt out white dwarf.

Question 24

The escape velocity of an object depends on

A) I, II, III, & IV
B) I & II
C) I & III
D) I, II, & IV
E) I, III, & IV

Question 25

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

Question 26

For a point mass equal to that of the sun, how far does the Schwarzschild radius extend from its center?

A) A few kilometers away
B) A few solar radii away
C) A few astronomical units (AU) away
D) A few parsecs away

Question 27

Millisecond pulsars that are very old are

A) believed to be the result of mass transfer from a companion that increased the spin of the pulsar.
B) all single objects.
C) not spinning as rapidly as they seem because they have four hot spots that produce the flashes.
D) X-ray binaries.
E) gamma-ray bursters.

Question 28

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*¹³ km or 1 pc.

Question 29

A pulsar requires that a neutron star

A) I & III
B) I & IV
C) II, III, & IV
D) I, III, & IV
E) I, II, III, & IV

Question 30

The object left behind after the 1054 AD supernova explosion has been observed at the center of the Crab nebula. The object is a

A) white dwarf.
B) neutron star.
C) red giant.
D) protostar.

Question 31

The Schwarzschild radius of a 2- black hole is approximately

A) 6 km.
B) 4 km.
C) 2 km.
D) 12 km.
E) 36 km.

Question 32

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.

Question 33

None of the pulsars emit pulses of visible light because

A) pulsars are too 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 redshifted.
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.

Question 34

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

Question 35

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 quit 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.

Question 36

At extremely high densities and temperatures, electrons can be forced to fuse with protons. This reaction produces

A) hydrogen.
B) helium and energy.
C) degenerate electrons.
D) neutrons and neutrinos.
E) large amounts of radio radiation.

Question 37

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.

Question 38

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 at X-ray wavelengths.
D) as the material slows down it converts thermal energy to gravitational potential energy.
E) none of the above.

Question 39

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.

Question 40

An isolated black hole in space would be difficult to detect because

A) there would be no light source nearby.
B) it would not be rotating rapidly.
C) it would be stationary.
D) very little matter would be falling into it.
E) there would be very few stars behind it whose light the black hole could block out.

Question 41

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

Question 42

Which of the kinds of stars below would you expect to find in a 11-billion-year-old globular cluster of stars?

A) cool, low luminosity main sequence stars
B) white dwarfs
C) neutron stars
D) red giants
E) all of the above

Question 43

The figure shows an image of an isolated black hole. A black hole emits

A) light with wavelengths in the black color region.
B) no light from inside the event horizon.
C) light which is blueshifted to shorter wavelengths as it escapes.
D) light which is redshifted to shorter wavelengths as it escapes.

Question 44

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

Question 45

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

Question 46

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

Question 47

When a star of mass comparable to the sun dies it become a black hole.

Question 48

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

Question 49

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

Question 50

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

Question 51

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

Question 52

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

Question 53

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.

Question 54

Neutron stars were first discovered in the 1930's.

Question 55

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

Question 56

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

Question 57

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

Question 58

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.

Question 59

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

Question 60

Unseen objects in our galaxy have been found by the bending effect they have on more distant stars' light passing near them. These small objects that don't emit light are calculated to have masses of about 10* the mass of the sun. Which is the best choice for these objects?

A) black hole
B) neutron star
C) white dwarf
D) main-sequence stars

Question 61

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

Question 62

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

Question 63

What evidence do we have that pulsars are neutron stars?

Question 64

What observational evidence do we have that black holes exist?

Question 65

How are neutron stars and white dwarfs similar?

Question 66

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

Question 67

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

Question 68

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

Question 69

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

Question 70

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