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Ch 17 &18

Our Sun is considered to be a ______.

low-mass star

Which of the following types of data provide evidence that helps us understand the life tracks of low-mass stars?

H-R diagrams of globular clusters

Why is a 1 solar-mass red giant more luminous than a 1 solar-mass main sequence star?

Fusion reactions are producing energy at a greater rate in the red giant.

Which of the following describes a star with a hydrogen-burning shell and an inert helium core?

It is a subgiant that grows in luminosity until helium fusion begins in the central core.

Which of the following observations would not be likely to provide information about the final, explosive stages of a star's life?

decades of continuous monitoring of red giants in a globular cluster

Which is more common: a star blows up as a supernova, or a star forms a planetary nebula/white dwarf system?

Planetary nebula formation is more common.

Carbon fusion occurs in high-mass stars but not in low-mass stars because _________.

the cores of low-mass stars never get hot enough for carbon fusion

Which of the following statements about various stages of core nuclear burning (hydrogen, helium, carbon, etc.) in a high-mass star is not true?

Each successive stage lasts for approximately the same amount of time

Which event marks the beginning of a supernova?

The sudden collapse of an iron core into a compact ball of neutrons.

Suppose that the star Betelgeuse (the upper left shoulder of Orion) were to supernova tomorrow (as seen here on Earth). What would it look like to the naked eye?

Betelgeuse would remain a dot of light, but would suddenly become so bright that, for a few weeks, we'd be able to see this dot in the daytime.

Suppose that hydrogen, rather than iron, had the lowest mass per nuclear particle. Which of the following would be true?

Nuclear fusion could not power stars.

Observations show that elements with atomic mass numbers divisible by 4 (such as oxygen-16, neon-20, and magnesium-24) tend to be more abundant in the universe than elements with atomic mass numbers in between. Why do we think this is the case?

The apparent pattern is thought to be a random coincidence.

A spinning neutron star has been observed at the center of a ______.

supernova remnant

You discover a binary star system in which one star is a 15 MSun main-sequence star and the other is a 10 MSun giant. How do we think that a star system such as this might have come to exist?

The giant must once have been the more massive star, but is now less massive because it transferred some of its mass to its companion.

Tidal forces are very important to the Algol system today, but were not important when both stars were still on the main sequence. Why not?

Main sequence stars in a system like the Algol system are small compared to their physical separation.

Which of the following statements about degeneracy pressure is not true?

Degeneracy pressure can arise only from interactions among electrons.

The more massive a white dwarf, the _________.

smaller its radius

Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?

Electron degeneracy pressure depends on the speeds of electrons, which approach the speed of light as a white dwarf's mass approaches the 1.4-solar-mass limit.

The white dwarf that remains when our Sun dies will be mostly made of ______.

carbon

Which statement about accretion disks is not true?

The primary factor determining whether a white dwarf has an accretion disk is the white dwarf's mass.

According to present understanding, a nova is caused by _________.

hydrogen fusion on the surface of a white dwarf

Which of the following is not true about differences between novae and supernovae?

Supernovae eject gas into space but novae do not.

Will our Sun ever undergo a white dwarf supernova explosion? Why or why not?

No, because it is not orbited by another star.

Which of the following best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly (for unexplained reasons) to appear in your home town?

The entire Earth would end up as a thin layer, about 1 cm thick, over the surface of the neutron star.

Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star?

Pulsars are easy to identify by their almost perfectly steady periods of pulsation.

Which statement about pulsars is not thought to be true?

Pulsars can form only in close binary systems

How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?

The accretion disk around a neutron star is much hotter and emits higher-energy radiation

Which statement concerning black hole masses and Schwarzschild radii is not true?

In a binary system with a black hole, the Schwarzschild radius depends on the distance from the black hole to the companion star.

Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?

Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.

Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.

A spaceship passing near a 10 solar mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10 solar mass main-sequence star.

When we see X rays from an accretion disk in a binary system, we can't immediately tell whether the accretion disk surrounds a neutron star or a black hole. Suppose we then observe each of the following phenomena in this system. Which one would rule out the possibility of a black hole?

intense X-ray bursts

Which of the following observatories is most likely to discover a black hole in a binary system?

the Chandra X-Ray Observatory

Which of the following statements about gamma ray bursts is not true?

The events responsible for gamma ray bursts apparently produce only gamma rays, and no other light that we can hope to detect

Imagine an advanced civilization living on a planet orbiting at a distance of 10 AU (1.5 billion kilometers) from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole. The black hole is surrounded by an accretion disk. Sometime within the next million years or so, the civilization's planet is likely to be doomed because ________.

the red giant will probably supernova within the next million years

Consider again the civilization described in the previous question. (They live on a planet orbiting 10 AU from a close binary star system that consists of a 15 MSun red giant star and a 10 MSun black hole surrounded by an accretion disk.) One foolhardy day, a daring individual in their space force (let's call him Major Tom) decides to become the first of his species to cross the event horizon of the black hole. To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least to start the process of killing him first)?

X rays from the accretion disk

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