Question 1

What causes massive stars to lose mass at a high rate through stellar winds?

Accepted Answer

A)  radiation pressure 
B)  high magnetic fields 
C)  rapid rotation 
D)  carbon fusion 
E)  emission of neutrinos 
A)  radiation pressure 
B)  high magnetic fields 
C)  rapid rotation 
D)  carbon fusion 
E)  emission of neutrinos A

Question 2

The Crab Nebula is about 10 light-years across and its glow is energized by the pulsar at its center, about 10 km in size.The shell of this nebula is expanding at almost 1,500 km/s.Estimate the age of the Crab Nebula.How does it reconcile with the documented records of a "guest star" from Chinese astronomers dating to 1054 CE?

Accepted Answer

If the "radius" of about 5 ly (recall that 1 ly =9.46 * 10¹² km)has been covered at a rate of about 1,500 km/s in about (5 * 9.46 *10¹² km)/(1,500 km/s)= 3.15 * 10¹⁰ s,that would translate to about 1,000 years of expansion,in agreement with the time elapsed since 1054.(A caveat should be pointed out,however.Considering that at the moment of the stellar explosion the ejected layers could have started at 30,000 km/s and scientists presently measure about 1,500 km/s,the average speed could be quite uncertain-it may be significantly larger than 1,500 km/s-and hence our rough estimate is a nice coincidence.)

Question 3

Massive stars explode soon after fusion to iron begins because

Accepted Answer

A)  iron has the smallest binding energy of all elements. 
B)  neutrinos emitted during the fusion to iron are captured by the star's lighter elements. 
C)  fusion of elements heavier than iron requires energy, so the star runs out of fuel and cannot hold itself up against gravity. 
D)  stars do not contain elements heavier than iron; these are made in supernovae explosions. 
E)  iron nuclei are unstable and rapidly break apart into lighter elements. 
A)  iron has the smallest binding energy of all elements. 
B)  neutrinos emitted during the fusion to iron are captured by the star's lighter elements. 
C)  fusion of elements heavier than iron requires energy, so the star runs out of fuel and cannot hold itself up against gravity. 
D)  stars do not contain elements heavier than iron; these are made in supernovae explosions. 
E)  iron nuclei are unstable and rapidly break apart into lighter elements. C

Question 4

Recent research revealed that stars like our Sun slow their rotation as they age while on the main sequence.Assuming that you find a nearby Sun-like star with a measured rotational period of only 4-5 days, it is likely that, compared with our Sun, the star will have

Accepted Answer

A)  a higher abundance of massive elements. 
B)  a very blue color. 
C)  a much smaller size. 
D)  no planets around it. 
E)  very weak gravity. 
A)  a higher abundance of massive elements. 
B)  a very blue color. 
C)  a much smaller size. 
D)  no planets around it. 
E)  very weak gravity.

Question 5

What provides us the best clues as to the age of a galaxy like ours?

Accepted Answer

A)  the periods of the fastest-spinning pulsars and Cepheid variables 
B)  the number of planetary nebulae 
C)  the observed frequency of high-mass-star supernovae 
D)  the H-R diagrams of globular clusters of stars 
E)  the luminosity of the most massive stars 
A)  the periods of the fastest-spinning pulsars and Cepheid variables 
B)  the number of planetary nebulae 
C)  the observed frequency of high-mass-star supernovae 
D)  the H-R diagrams of globular clusters of stars 
E)  the luminosity of the most massive stars

Question 6

Each kilogram of hydrogen that fuses into helium releases about 6 * 1014 joules of energy.How many tons of hydrogen are fused each second to power a massive main-sequence star with a luminosity of 100 LSUN? (Note that 1 LSUN = 4 *1026 joule/second and 1 ton= 103 kg.)

Accepted Answer

A)  2*106 tons 
B)  7 * 107 tons 
C)  2 *109 tons 
D)  7 *1010 tons 
E)  2 *1011 tons 
A)  2*106 tons 
B)  7 * 107 tons 
C)  2 *109 tons 
D)  7 *1010 tons 
E)  2 *1011 tons

Question 7

The Crab Nebula is an important test of our ideas about supernova explosions because

Accepted Answer

A)  people saw the supernova and later astronomers found a pulsar inside the nebula. 
B)  the system contains an X-ray binary. 
C)  the nebula is expanding slowly, as expected from mass-loss rates in massive stars. 
D)  the original star must have been like the Sun before it exploded. 
E)  astronomers observed the merger of the two stars. 
A)  people saw the supernova and later astronomers found a pulsar inside the nebula. 
B)  the system contains an X-ray binary. 
C)  the nebula is expanding slowly, as expected from mass-loss rates in massive stars. 
D)  the original star must have been like the Sun before it exploded. 
E)  astronomers observed the merger of the two stars.

Question 8

The energy released during the process of nuclear fusion comes from

Accepted Answer

A)  the change in nuclear binding energy. 
B)  the electric (Coulomb) force. 
C)  the gravitational attraction between protons and neutrons. 
D)  the absorption of neutrinos. 
E)  the formation of gravity waves. 
A)  the change in nuclear binding energy. 
B)  the electric (Coulomb) force. 
C)  the gravitational attraction between protons and neutrons. 
D)  the absorption of neutrinos. 
E)  the formation of gravity waves.

Question 9

Suppose you observe a distant galaxy (effectively a "cluster" of several hundred billion stars) that used up the last of its star-forming gas 10 billion years ago.What types of stars do you expect to find in this galaxy?

Accepted Answer

As 10 Gyr is the main-sequence lifetime

Question 10

Explain why the pulsars we see might be only a fraction of the neutron stars in the Milky Way.

Accepted Answer

Pulsars are rapidly spinning neutron sta

Question 11

You observe three different star clusters and find that the main-sequence turnoff stars in Cluster 1 have spectral type F, the main-sequence turnoff stars in Cluster 2 have spectral type A, and the main-sequence turnoff stars in Cluster 3 have spectral type G.Which star cluster is the youngest and which one is the oldest?

Accepted Answer

A)  Cluster 1 is the youngest and Cluster 2 is the oldest. 
B)  Cluster 2 is the youngest and Cluster 1 is the oldest. 
C)  Cluster 2 is the youngest and Cluster 3 is the oldest. 
D)  Cluster 3 is the youngest and Cluster 1 is the oldest. 
E)  Cluster 3 is the youngest and Cluster 2 is the oldest. 
A)  Cluster 1 is the youngest and Cluster 2 is the oldest. 
B)  Cluster 2 is the youngest and Cluster 1 is the oldest. 
C)  Cluster 2 is the youngest and Cluster 3 is the oldest. 
D)  Cluster 3 is the youngest and Cluster 1 is the oldest. 
E)  Cluster 3 is the youngest and Cluster 2 is the oldest.

Question 12

Which of the clusters in the figure shown below are open clusters?

Accepted Answer

A)  NGC 290 and M53 
B)  NGC 290 and M55 
C)  NGC 290 and NGC 6530 
D)  M53 and M55 
E)  M53 and NGC 290 
A)  NGC 290 and M53 
B)  NGC 290 and M55 
C)  NGC 290 and NGC 6530 
D)  M53 and M55 
E)  M53 and NGC 290

Question 13

The fundamental stellar property that determines the major evolutionary differences in the life history of stars is

Accepted Answer

A)  distance from Earth. 
B)  mass. 
C)  location within a galaxy. 
D)  rotation. 
E)  presence/absence of planets around stars. 
A)  distance from Earth. 
B)  mass. 
C)  location within a galaxy. 
D)  rotation. 
E)  presence/absence of planets around stars.

Question 14

Which of the following is a common characteristic of a neutron star?

Accepted Answer

A)  high luminosity 
B)  enormous magnetic field 
C)  low density 
D)  large radius 
E)  low temperature 
A)  high luminosity 
B)  enormous magnetic field 
C)  low density 
D)  large radius 
E)  low temperature

Question 15

Massive stars explode when they

Accepted Answer

A)  accrete mass from their binary star companion. 
B)  generate uranium in their cores. 
C)  merge with another massive star. 
D)  run out of useful nuclear fuel in their core, and the cores collapse. 
E)  lose a lot of mass in a stellar wind. 
A)  accrete mass from their binary star companion. 
B)  generate uranium in their cores. 
C)  merge with another massive star. 
D)  run out of useful nuclear fuel in their core, and the cores collapse. 
E)  lose a lot of mass in a stellar wind.

Question 16

What characteristic of a star cluster is used to determine its age?

Accepted Answer

A)  the chemical composition of stars in the cluster 
B)  the luminosity of the faintest stars in the cluster 
C)  the color of the main-sequence turnoff in the cluster 
D)  the total number of stars in the cluster 
E)  the apparent diameter of the cluster 
A)  the chemical composition of stars in the cluster 
B)  the luminosity of the faintest stars in the cluster 
C)  the color of the main-sequence turnoff in the cluster 
D)  the total number of stars in the cluster 
E)  the apparent diameter of the cluster

Question 17

Describe how free neutrons released in supernovae create new heavy elements.

Accepted Answer

Neutrons have no electric charge,so ther

Question 18

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

Accepted Answer

They have very strong winds because thei

Question 19

What is the meaning of nuclear binding energy?

Accepted Answer

The binding energy of a nucleus is the e

Question 20

How does convection in the core of a high-mass star affect the star's main-sequence lifespan?

Accepted Answer

Convection in the core mixes hydrogen an

Exam 17: Evolution of High-Mass Stars

What causes massive stars to lose mass at a high rate through stellar winds?

Massive stars explode soon after fusion to iron begins because

Recent research revealed that stars like our Sun slow their rotation as they age while on the main sequence.Assuming that you find a nearby Sun-like star with a measured rotational period of only 4-5 days, it is likely that, compared with our Sun, the star will have

What provides us the best clues as to the age of a galaxy like ours?

Each kilogram of hydrogen that fuses into helium releases about 6 * 1014 joules of energy.How many tons of hydrogen are fused each second to power a massive main-sequence star with a luminosity of 100 LSUN? (Note that 1 LSUN = 4 *1026 joule/second and 1 ton= 103 kg.)

The Crab Nebula is an important test of our ideas about supernova explosions because

The energy released during the process of nuclear fusion comes from

Suppose you observe a distant galaxy (effectively a "cluster" of several hundred billion stars) that used up the last of its star-forming gas 10 billion years ago.What types of stars do you expect to find in this galaxy?

Explain why the pulsars we see might be only a fraction of the neutron stars in the Milky Way.

Which of the clusters in the figure shown below are open clusters?

The fundamental stellar property that determines the major evolutionary differences in the life history of stars is

Which of the following is a common characteristic of a neutron star?

Massive stars explode when they

What characteristic of a star cluster is used to determine its age?

Describe how free neutrons released in supernovae create new heavy elements.

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

What is the meaning of nuclear binding energy?

How does convection in the core of a high-mass star affect the star's main-sequence lifespan?

Thinking Like an Astronomer

Patterns in the Skymotions of Earth and the Moon

Motion of Astronomical Bodies

Gravity and Orbits

Light

The Tools of the Astronomer

The Formation of Planetary Systems

The Terrestrial Planets and Earths Moon

Atmospheres of the Terrestrial Planets

Worlds of Gas and Liquidthe Giant Planets

Planetary Moons and Rings

Dwarf Planets and Small Solar System Bodies

Taking the Measure of Stars

Our Starthe Sun

The Interstellar Medium and Star Formation

Evolution of Low-Mass Stars

Relativity and Black Holes

Galaxies

The Milky Waya Normal Spiral Galaxy

The Expanding Universe

Cosmology

Large-Scale Structure in the Universe

Life

Filters

Each kilogram of hydrogen that fuses into helium releases about 6 * 10¹⁴ joules of energy.How many tons of hydrogen are fused each second to power a massive main-sequence star with a luminosity of 100 L_SUN? (Note that 1 L_SUN = 4 *10²⁶ joule/second and 1 ton= 10³ kg.)