Deck 13: Evolution of High-Mass Stars

Question 1

Why does the luminosity of a high-mass star remain nearly constant as the star burns heavy elements in its core,even though it is producing millions of times more energy per second than it did on the main sequence?

A) Most of the energy is trapped in the core, increasing the core's temperature.
B) All of the extra energy goes into heating the shells of fusion surrounding the core.
C) Most of the energy is absorbed by the outer layers of the star, increasing the star's radius but leaving its luminosity unchanged.
D) Most of the energy is carried out of the star by escaping neutrinos.

Answer 1

Most of the energy is carried out of the star by escaping neutrinos.

Question 2

If you measure the average brightness and pulsation period of a Cepheid variable star,you can also determine its:

A) age.
B) rotation period.
C) distance.
D) mass.

Answer 2

distance.

Question 3

An iron core cannot support a massive main-sequence star because iron:

A) has poor nuclear binding energy.
B) cannot fuse with other nuclei to produce energy.
C) supplies too much pressure.
D) fusion only occurs in a degenerate core.

Answer 3

cannot fuse with other nuclei to produce energy.

Question 4

In the figure below,when elements from section A undergo fusion,energy is ________.Because of this fact,it would be ________ to find a high-mass main-sequence star with a high concentration of elements from section B.

A) released; likely
B) absorbed; likely
C) released; unlikely
D) absorbed; unlikely

Question 5

The collapse of the core of a high-mass star at the end of its life lasts approximately:

A) 1 second.
B) 1 hour.
C) 1 week.
D) 1 year.

Question 6

What is the minimum-mass main-sequence star that becomes a Type II supernova?

A) 4 M¤
B) 8 M¤
C) 12 M¤
D) 25 M¤

Question 7

Once carbon begins burning in the core of a high-mass star,the outer layers begin to fall inward,driving up the fusion rates and speeding up the star's evolution primarily because:

A) the number of particles in the core is decreasing, which now take up less space.
B) most of the energy is now carried away from the core by escaping neutrinos, which have few if any obstacles to leaving the star.
C) carbon is a more stable element that appears to settle the star.
D) the light given off by the fusion of carbon is a different wavelength than that given off by previous reactions, so the radiation pressure is much smaller.

Question 8

Which of the following is NOT a common characteristic of a neutron star?

A) extremely high density
B) enormous magnetic field
C) very short rotation period
D) All of these are common characteristics of a neutron star.

Question 9

Essentially all the elements heavier than iron in our galaxy were formed:

A) by supernovae.
B) during the formation of black holes.
C) by fusion in the cores of the most massive main-sequence stars.
D) during the formation of planetary nebulae.

Question 10

When the core of a massive star collapses,a neutron star forms because:

A) all the charged particles are ejected in the resulting explosion.
B) protons and electrons combine to form neutrons.
C) iron nuclei disintegrate into neutrons.
D) neutrinos escaping from the core carry away most of the electromagnetic charge.

Question 11

As a high-mass main-sequence star evolves off the main sequence,it follows a ________ on the H-R diagram.

A) nearly vertical path
B) path of constant radius
C) roughly horizontal path
D) None of the above answers is correct.

Question 12

If a 60-M¤ main-sequence star loses mass at a rate of 10⁻⁴ M¤/year,then how much mass will it lose in its 300,000-year lifetime?

A) 3 M¤
B) 8 M¤
C) 10 M¤
D) 30 M¤

Question 13

During the main-sequence evolution of a massive star,increasingly heavier elements are fused in the core,giving the core support for:

A) decreasingly shorter times.
B) increasingly longer times.
C) an approximately equal amount of time.
D) approximately 10,000 years.

Question 14

Which of the following is true about the instability strip on the H-R diagram?

A) evolved stars pulsate
B) location of RR Lyrae and Cepheids
C) stars show variability in their brightness
D) all of the above

Question 15

A Cepheid star varies in luminosity because the:

A) entire star pulsates from its core to its surface.
B) outer envelope of the star pulsates.
C) star rotates too quickly.
D) star is too massive to be stable.

Question 16

Neutron stars have masses that range from:

A) 3.5 M¤ to 25 M¤.
B) 1.2 M¤ to 30 M¤.
C) 2.5 M¤ to 10 M¤.
D) 1.4 M¤ to 3 M¤.

Question 17

What is the radius of the event horizon of a 10 solar mass black hole?

A) 3 km
B) 10 km
C) 30 km
D) 100 km

Question 18

Once silicon burning begins to fuse iron in the core of a high-mass main-sequence star,it only has a few ________ left to live.

A) seconds
B) days
C) months
D) years

Question 19

The main difference between Cepheid variable stars and RR Lyrae stars is:

A) their pulsation mechanisms.
B) their masses.
C) that Cepheids form at much greater distances from Earth.
D) that RR Lyrae were discovered much earlier than Cepheids.

Question 20

The CNO cycle in high-mass main-sequence stars burns ________ to ________in their cores.

A) hydrogen; helium
B) carbon; oxygen
C) carbon; nitrogen
D) This is a trick question as the CNO cycle does not operate in high-mass main-sequence stars.

Question 21

We can identify only a small fraction of all the pulsars that exist in our galaxy because:

A) gas and dust efficiently block radio photons.
B) few swing their beam of synchrotron emission in our direction.
C) most have evolved to become black holes, which emit no light.
D) massive stars are very rare.

Question 22

The event horizon of a black hole is defined as:

A) the point of maximum gravity.
B) the radius of the original neutron star before it became a black hole.
C) the point at which shock waves emanate from the strong gravitational distortion the black hole creates in the fabric of spacetime.
D) the radius at which the escape speed equals the speed of light.

Question 23

If the Sun were to be instantly replaced by a 1-M¤ black hole,the gravitational pull of the black hole on Earth would be:

A) much greater than it is now.
B) the same as it is now.
C) much smaller than it is now.
D) irrelevant because Earth would be quickly obliterated by the strong tidal force of the black hole.

Question 24

An astronaut would feel ________ as he or she crossed the event horizon of a stellar black hole.

A) incredibly strong tidal forces
B) intense heating
C) lighter
D) nothing

Question 25

Assume that a group of explorers traveled to the Orion Nebula,the nearest star-forming cloud at a distance of 1,300 light-years,using revolutionary technology that allowed them to travel at a speed very close to the speed of light.Observers back on Earth would say it took them ________ to get there,but the travelers would say it took them ________ to get there.

A) slightly more than 1,300 years; much less than 1,300 years
B) slightly more than 1,300 years; slightly less than 1,300 years
C) slightly less than 1,300 years; slightly more than 1,300 years
D) exactly 1,300 years; much less than 1,300 years

Question 26

________ is the result of mass distorting the fabric of spacetime.

A) Energy
B) Radiation
C) Fusion
D) Gravity

Question 27

Normally,muons created by cosmic rays at high altitudes decay in a very short time,a time so short that they should not reach the ground.From the figure below,which muon is most likely to be detected on the ground?

A) muon A
B) muon B
C) muon C
D) muon D

Question 28

Which of the following is a consequence of Einstein's special theory of relativity?

A) Moving clocks run quicker.
B) The velocity of light depends on the speed of the observer.
C) Distances appear shorter when traveling near the speed of light.
D) Gravity arises because mass distorts spacetime.

Question 29

The equivalence principle says that:

A) being stationary in a gravitational field is the same as being in an accelerated reference frame.
B) the universe is homogeneous and isotropic.
C) at any radius inside a star, the outward gas pressure must balance the weight of the material on top.
D) mass and energy are interchangeable, and neither can be destroyed.

Question 30

Hawking radiation is emitted by a black hole when:

A) the black hole rotates quickly.
B) the black hole accretes material.
C) a virtual pair of particles is created from the vacuum of space.
D) synchrotron radiation is emitted by infalling charged particles.

Question 31

The Type II supernova that created the Crab Nebula (image below)was seen by Chinese and Arab astronomers in the year A.D.1054.Because the star is 6,500 light-years away from us,we know the star exploded in the year:

A) A.D. 7554.
B) A.D. 1054.
C) 5446 B.C.
D) 7554 B.C.

Question 32

Photons have no mass,and Einstein's theory of general relativity says:

A) their paths through spacetime are curved in the presence of a massive body.
B) their apparent speeds depend on the observer's frame of reference.
C) they should not be attracted to a massive object.
D) their wavelengths must remain the same as they travel through spacetime.

Question 33

Black holes that are stellar remnants can be found by searching for:

A) dark regions at the centers of galaxies.
B) variable X-ray sources.
C) extremely luminous infrared objects.
D) objects that emit very faint radio emission.

Question 34

Gravitational lensing occurs when ________ distorts the fabric of spacetime.

A) a star
B) dark matter
C) a black hole
D) any massive object

Question 35

If Earth were to be condensed down in size until it became a black hole,its Schwarzschild radius would be:

A) 1 cm.
B) 1 meter.
C) 1 km.
D) 10 km.

Question 36

A neutron star contains a mass of up to 3 M¤ in a sphere with a diameter approximately the size of:

A) an atomic nucleus.
B) a school bus.
C) a city.
D) Earth.

Question 37

Light is increasingly redshifted near a black hole because:

A) the photons are moving away from us very quickly as they are sucked into the black hole.
B) the photons are moving increasingly faster in order to escape the pull of the black hole.
C) time is moving increasingly slower in the observer's frame of reference.
D) the curvature of spacetime is increasingly stretched near the black hole, which in turn stretches the wavelengths of the photons.

Question 38

What would happen if mass were continually added to a 2-M¤ neutron star?

A) The star's radius would increase.
B) The star would eventually become a black hole.
C) The star would erupt as a nova.
D) All of the above would occur.

Question 39

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate the 10⁶-M¤ black hole at the center of our galaxy.Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole,maintaining a distance of 1 AU,while you remain much farther away in the spacecraft but from which you can easily monitor your colleague.After doing some experiments to measure the strength of gravity,your colleague signals the results back to you using a green laser.What would you see?

A) the signals, because he or she is orbiting well outside the event horizon
B) the signals, but shifted to a much redder wavelength because he or she is very close to the event horizon
C) nothing, because your colleague has crossed the event horizon
D) nothing, because no light can escape the gravitational pull of a black hole no matter how close the signal is to it

Question 40

Which of the following is NOT true about Cygnus X-1?

A) It is a binary star.
B) It contains a black hole.
C) It is a source of X-rays.
D) It is a neutron star.

Question 41

Explain how a pulsar comes to rotate more quickly than its original high-mass star that rotated much more slowly.

Question 42

Why are Cepheids important to study?

Question 43

Why are Type II supernova not good distance indicators like those of Type Ia?

Question 44

The figure below shows the relative abundances of different elements on Earth.Explain why elements less massive than iron are,in general,most common,why there is a small peak at iron,and why elements more massive than iron are less common.

Question 45

What supports a neutron star from collapsing to form a black hole?

Question 46

Normally,muons created by cosmic rays at high altitudes decay in a very short time,a time so short that they should not reach the ground.From the figure below,why does increasing speed of muons created by cosmic rays at high altitudes mean that additional muons will reach the ground before decaying?

Question 47

Galileo supposedly experimented with gravity by dropping two objects of different masses from the Leaning Tower of Pisa at the same instant and observing that they hit the ground at the same time.If Albert Einstein had done the experiment,how would his conclusion have differed from Galileo's?

Question 48

Why do large,high-mass main-sequence stars never become red giants?

Question 49

Explain why Einstein's theory of general relativity predicts the existence of gravitational lensing.

Question 50

Name at least two processes that speed the collapse of the core of a dying high-mass star.

Question 51

Where would be the best place to search for black holes?

Question 52

Examine the figure of a pulsar below.What are pulsars,and what circumstance must Earth be in for astronomers to observe one?

Question 53

How do Cepheid variable stars differ from RR Lyrae variable stars in their masses,luminosities,and periods?

Question 54

Why do main-sequence high-mass stars lose so much mass compared to low-mass stars?

Question 55

Although a Type II supernova shines with a luminosity of 100 billion L¤,most of the energy in the explosion is emitted in another way.What is it,and how much more energy does it carry compared to the light?

Question 56

Examine the figure below.Explain what the equivalence principle is in general relativity.

Question 57

What is the difference between the singularity and the event horizon of a black hole?

Question 58

Show where stars are variable in brightness in the figure below.What is this region called?

Question 59

While traveling the galaxy in a spacecraft,you and a colleague set out to investigate a 1-M¤ black hole.Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole maintaining a distance of 10 km from it,while you remain much farther away inside the spacecraft.After doing some experiments to measure the strength of gravity,your colleague signals the results back to you using a green laser.What would you see,and why?

Question 60

If an 8-M¤ star loses mass at an average rate of 10⁻⁶ M¤/year in a stellar wind,how many years would it take for its mass to be reduced to 6 M¤? Would this amount of mass loss be possible in the star's lifetime?