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A white dwarf is _____.
What most stars become when the die.
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A typical white dwarf is _____.
As massive as the Sun but only as large in size as Earth.
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If you had something the size of a sugar cube that was made of white dwarf matter, it would weigh _____.
As much as a truck.
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The maximum mass of a white dwarf is _____.
About 1.4 times the mass of our Sun.
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What is an accretion disk?
A disk of hot gas swirling rapidly around a white dwarf, neutron star, or black hole.
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According to our modern understanding, what is a nova?
An explosion on the surface of a white dwarf in a close binary system.
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Suppose that a white dwarf is gaining mass through accretion in a binary system. What happens if the mass someday reaches the 1.4 solar mass limit?
The white dwarf will explode completely as a white dwarf supernova.
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A neutron star is _____.
The remains of a star that died in a massive star supernova.
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a typical neutron star is more massive than our Sun and about the size of _____.
A small asteriod (10 km diameter).
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If you had something the size of a sugar cube, that was made of neutron star matter, it would weigh _____.
About as much as a large mountain.
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Pulsars are thought to be ______.
Rapidly rotating netron stars.
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how is an X-ray burst similar to a nova?
Both involve explosions on the surface of stellar corpse.
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what is the basic definition of a black hole?
An object with gravity so strong that not even light can escape.
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Based on current understanding, the minimum mass of a black hole that forms during a massive star supernova is roughly _____.
3 solar masses.
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What do we mean by the event horizon of a black hole?
It is the point beyond which neither light nor anything else can escape.
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Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass. What would happen to Earth in its orbit?
Nothing- Earth's orbit would remain the same.
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What do we mean by the singularity of a black hole?
It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
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what makes us think that the star system Cygnus X-1 contains a black hole?
It emits X rays characteristic of an accretion disk, but the unseen star in the system is too massive to be a neutron star.
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The Schwarzschild radius of ablack hole depends on _____.
Only the mass of the black hole.
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Based on current evidence, what statement about gamma ray bursts is true?
All those that we have detected occured in distant galaxies.
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What statement about electron degeneracy pressure and neutron degeneracy pressure is true?
Electron degeneracy pressure is the main source of pressure in white dwarfs, while neutron degeneracy is the main source of pressure in neutron stars.
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What statement about degeneracy pressure is not true?
Degeneracy pressure can arise only from interactions among electrons.
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The more massive a white dwarf, the _____.
Smaller its radius.
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What 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.
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The white dwarf that remains when our Sun dies will be mostly made of ______.
Carbon.
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What 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.
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According to present understanding, a nova is caused by _____.
Hydrogen fusion on the surface of a white dwarf.
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What is not true about differences between novae and supernovae?
Supernovae eject gas into space but novae do not.
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Will our Sun ever undergo a white dwarf supernova explosion?
No, because it is not orbited by another star.
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What best describes what would happen if a 1.5-solar-mass neutron star, with a diameter of a few kilometers, were suddenly 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.
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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 scientists choose pulsars rather than some other type of star?
Pulsars are easy to identify by their almost perfectly steady periods of pulsation.
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What statement about pulsars is not thought to be true?
Pulsars can form only in close binary systems.
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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.
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What statement concerning black hole masses and Schwarzschild radii is not true?
In a binary system, with a black hole, the Schwarzschild radii are typically a few to a few tens of kilometers.
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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.
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What statement about black holes is not true?
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.
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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.
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What observatory is most likely to discover a black hole in a binary system?
The Chandra X-ray Observatory.
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What statement about gamma rays 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.
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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.
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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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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.) Through a bizarre (and scientifically unexplainable) fluctuation in the space-time continuum, a copy of a book from that civilization arrives on your desk; it is entitled Iguoonos: How We Evolved. In the first chapter, you learn that these beings evolved from organisms that lived 5 billion years ago. Which of the following statements should you expect to find as you continue to read this book?
They evolved from primitive wormlike creatures that had 13 legs, 4 eyes, and bald heads, thus explaining why such critters are now considered a spectacular delicacy.
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