Astronomy High-Mass Stars

A main-sequence star of 25 solar masses has about 25 times the luminosity of a 10-solar-mass star (recall the mass-luminosity relation presented in the previous chapter). This is because the more massive star a. has a hotter core, and therefore nuclear burning proceeds more rapidly. b. has more convection in its core, which heats up the material there. c. has more hydrogen to burn. d. has more carbon available, which speeds up the CNO cycle. e. is probably younger than the 10 solar mass star.

A

Each stage of nuclear burning in a 25 M star is __________ in duration than in a star of 15 M. a. much shorter b. a little shorter c. equally long d. a little longer e. much longer

A

Essentially all the elements heavier than iron in our Milky Way 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. e. during the initial stages of the Big Bang.

A

How do we understand the very fast rotation of neutron stars? a. It is a consequence of the conservation of angular momentum applied to collapsing objects. b. The convection in the cores of high-mass stars is responsible for this. c. The high temperature in the cores of high-mass stars imprints fast rotations. d. The degenerate iron core leads to fast spins. e. The fast rotation is due to their huge gravity on their surface.

A

How does the formation of elements by nuclear fusion depend on the mass of the star? a. With increasing mass, progressively heavier nuclei are forged deeper and deeper inside the star. b. With increasing mass, the heaviest elements can form only in the outermost layers of the star. c. With increasing mass, elements between helium and gold are formed in the cores. d. With increasing mass, only elements between helium and carbon can form in the cores. e. All stars more massive than 8 solar masses create elements from helium through uranium in their cores

A

In young clusters the light is dominated by a. luminous hot, blue, and some red supergiants. b. luminous red giants and red dwarfs. c. numerous Sun-like stars. d. large numbers of protostars. e. accreting white dwarfs.

A

Nucleosynthesis refers to the formation of a. massive atoms from less massive ones. b. less massive atoms by fragmentation of more massive ones. c. various isotopes of the same element. d. a star at the center of a collapsing nebula. e. first life forms on planets.

A

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

The collapse of the core of a high-mass star at the end of its life lasts approximately a. one second. b. one minute. c. one hour. d. one week. e. one year.

A

What causes massive stars to lose mass at a high rate through stellar winds? a. radiation pressure b. high magnetic fields c. rapid rotation d. carbon fusion e. emission of neutrinos

A

During the main-sequence evolution of a massive star, progressively more massive elements are fused in the core, giving the core support for a. longer and longer times. b. shorter and shorter times. c. an approximately equal amount of time. d. approximately 10,000 years. e. only a few days.

B

In the CNO cycle, carbon is used as a catalyst for the fusion of hydrogen into helium. This means that a. three helium nuclei fuse to form carbon. b. carbon facilitates the reaction but is not consumed in it. c. carbon boosts the energy from the reaction, which is why massive stars are luminous. d. carbon breaks apart into three helium nuclei. e. the reaction produces carbon nuclei in addition to helium

B

Iron has 26 protons in its nucleus, and gold has 79 protons. Where did all the gold on the Earth come from? a. nucleosynthesis on the surfaces of neutron stars b. nucleosynthesis that took place in supernova explosions c. nucleosynthesis in the cores of low-mass stars d. nucleosynthesis in the cores of massive stars e. nucleosynthesis in red giant and horizontal-branch stars

B

Once silicon burning initiates in the core of a high-mass star, the star has only a few __________ left to live. a. seconds b. days c. months d. years e. million years

B

The fundamental stellar property that determines the major evolutionary differences in the life history of stars is a. distance from Earth. b. mass. c. location within a galaxy. d. rotation. e. presence/absence of planets around stars.

B

The luminosity of a Cepheid star varies in time because a. the entire star pulsates from its core to its surface. b. the outer envelope of the star contracts and expands radially. c. the star rotates too quickly. d. the star is too massive to be stable. e. the star undergoes large surface temperature fluctuations.

B

We can identify only a fraction of all the radio 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. e. neutron stars have tiny radii and are hard to detect even with large telescopes.

B

What mechanism provides the internal pressure inside a neutron star? a. ordinary pressure from hydrogen and helium gas b. degeneracy pressure from neutrons c. degeneracy pressure from electrons d. rapid rotation e. strong magnetic fields

B

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 make neutrons. c. iron nuclei disintegrate into neutrons. d. neutrinos escaping from the core carry away most of the electric charge. e. the collapse releases a large number of protons, which soon decay into neutrons.

B

What is one way in which high-mass stars differ from low-mass stars? a. They are found at cooler temperatures on the main sequence. b. They fuse carbon through silicon without leaving the main sequence. c. Convection is important in their cores, which mixes up helium throughout the core. d. They turn into red giants explosively. e. Most of their energy is produced by fission rather than fusion.

B (check)

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. nearly horizontal path d. path of declining luminosity e. path of increasing temperature

C

If you measure the average brightness and pulsation period of a classical Cepheid variable star, you can also determine its a. age. b. rotation period. c. distance. d. mass. e. composition

C

List the H-R diagrams in the figure shown from oldest to youngest. a. 2, 1, 3, 4 b. 1, 4, 3, 2 c. 4, 3, 1, 2 d. 1, 2, 4, 3 e. 3, 1, 4, 2

C

Massive stars explode soon after fusion to iron initiates because 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

Massive stars synthesize chemical elements going from helium up to iron a. throughout the interior. b. primarily at the surface. c. only in the core of the star. d. along the equator of the star. e. in a deep convection zone in the interior of the star.

C

The collapse of the core in high-mass stars naturally explains all but which one of the following neutron stars properties? a. high density b. small size c. high magnetic field d. fast rotation e. large distance from Earth

C

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

C

What might be true about the oldest stars in the Milky Way? a. They would have lots of heavy elements, since they have been around for a long time and have undergone a lot of nucleosynthesis in their cores. b. They would be seen as supergiants. c. They would have few heavy elements, since there was not much chance for earlier generations of stars to explode as supernovae before these stars were formed. d. They would be massive, since they were among the first stars formed. e. They would likely be seen as pulsars.

C

Which of the following is not true about neutron stars? a. Their existence had been predicted 30 years before they were discovered. b. All neutron stars are observed as pulsars from Earth. c. Neutron stars often show fast expanding debris around them. d. Neutron stars can be members of X-ray binaries. e. Their densities are comparable to that of atomic nuclei

C (check)

A few hours before a high-mass star is blasting its outer layers in a colossal explosion, specialized detectors on Earth would be able to reveal a spike in the number of a. iron nuclei. b. carbon nuclei. c. protons. d. neutrinos. e. aurorae.

D

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. an apple. c. a school bus. d. a small city. e. the Earth

D

Massive stars explode when they a. accrete mass from their binary star companion. b. generate uranium in their cores. c. merge with another massive star. d. run out of nuclear fuel in their core, and the cores collapse. e. lose a lot of mass in a stellar wind.

D

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. e. 0.1M to 1.4 M.

D

The dominant mechanism by which high-mass stars generate energy on the main sequence is called a. the proton-proton chain. b. the carbon-carbon reaction. c. the triple-alpha process. d. the CNO cycle. e. neutrino cooling.

D

When the first pulsar was discovered, scientists thought it might be a signal from a distant extraterrestrial civilization. However, this idea was quickly discarded because a. they realized the signals were interference from cars and trucks passing by the radio observatory. b. the government made the scientists hide their original finding. c. they realized that Cepheid variables could produce the detected radio signals. d. more pulsars were discovered, which meant that these were natural phenomena. e. the technology required to create pulsed signals is beyond the power of any civilization.

D

Where did the iron in your blood come from? a. Nuclear reactions on the surfaces of neutron stars b. Nuclear reactions that took place in supernova explosions c. Nuclear reactions in the cores of low-mass stars d. Nuclear reactions in the cores of massive stars e. Nuclear reactions in red giant and horizontal-branch stars

D

Which of the following is not a common characteristic of a neutron star? a. extremely high density b. enormous magnetic field c. short rotation period d. large radius e. source of pulsars

D

An iron core cannot support a massive main-sequence star because iron a. has low nuclear binding energy. b. is not present in stellar interiors. c. supplies too much pressure. d. fusion occurs only in a degenerate core. e. cannot fuse to make heavier nuclei and produce energy.

E

One reason why we think neutron stars were formed in supernova explosions is that a. all supernova remnants contain pulsars. b. pulsars are made of heavy elements, such as those produced in supernova explosions. c. pulsars are often found near Cepheids and Wolf-Rayet stars, which are also signs of massive star formation. d. pulsars spin very rapidly, as did the massive star just before it exploded. e. pulsars sometimes have material around them that looks like the ejecta from supernovae.

E

Type Ia and Type II supernovae are respectively caused by what types of stars? a. white dwarfs; Cepheid variables b. white dwarfs; pulsars c. massive stars; white dwarfs d. massive stars; neutron stars e. white dwarfs; massive stars

E

Which of these fusion reactions begins first in the core of a massive star? a. silicon fusion to iron b. neon fusion to magnesium c. carbon fusion to neon d. helium fusion to carbon e. hydrogen fusion to helium

E