Chapter 18 Questions And Answers – Flashcards
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Degeneracy pressure is the source of the pressure that stops the crush of gravity in all the following EXCEPT a. a neutron star. b. a white dwarf. c. a very massive main-sequence star. d. a brown dwarf. e. the central core of the Sun after hydrogen fusion ceases but before helium fusion begins.
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A very massive main-sequence star
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White dwarfs are so called because
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They are both very hot and very small
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Which of the following is closest in mass to a white dwarf?
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the Sun
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Why is there an upper limit to the mass of a white dwarf?
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The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, so more mass cannot be added without breaking the degeneracy pressure.
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What is the ultimate fate of an isolated white dwarf?
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It will cool down and become a cold black dwarf.
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What kind of pressure supports a white dwarf?
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electron degeneracy pressure
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Suppose a white dwarf is gaining mass because of accretion in a binary system. What happens if the mass someday reaches the 1.4-solar-mass limit?
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The white dwarf undergoes a catastrophic collapse, leading to a type of supernova that is somewhat different from that which occurs in a massive star but is comparable in energy.
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What is the upper limit to the mass of a white dwarf?
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1.4 solar masses
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Which of the following is closest in size (radius) to a white dwarf?
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Earth
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What kind of star is most likely to become a white-dwarf supernova?
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a white dwarf star with a red giant binary companion
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Observationally, how can we tell the difference between a white-dwarf supernova and a massive-star supernova?
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The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
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After a massive-star supernova, what is left behind?
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either a neutron star or a black hole
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What is the upper limit to the mass of a neutron star?
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There is an upper limit less than 3 solar masses, but we do not yet know precisely what it is.
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Which of the following is closest in size (radius) to a neutron star? a. 1 solar mass b. 1.4 solar masses c. There is no upper limit. d. There is an upper limit less than 3 solar masses, but we do not yet know precisely what it is. e. precisely 2 solar masses
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d. There is an upper limit less than 3 solar masses, but we do not yet know precisely what it is.
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Which of the following is closest in size (radius) to a neutron star? a. a football stadium b. a city c. Earth d. a basketball e. the Sun
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b. A city
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From an observational standpoint, what is a pulsar?
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An object that emits flashes of light several times per second or more, with near perfect regularity
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What causes the radio pulses of a pulsar?
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As the star spins, beams of radio radiation sweep through space. If one of the beams crosses Earth, we observe a pulse.
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From a theoretical standpoint, what is a pulsar?
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A rapidly rotating neutron star
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What is the basic definition of a black hole?
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Any object from which the escape velocity exceeds the speed of light
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How does the gravity of an object affect light?
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Light coming from a compact massive object, such as a neutron star, will be redshifted.
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How does a black hole form from a massive star?
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During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy of the core, the core will be compressed until it becomes a black hole.
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What do we mean by the singularity of a black hole?
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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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If you were to come back to our Solar System in 6 billion years, what might you expect to find?
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d. a white dwarf
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Brown dwarfs, white dwarfs, and neutrons stars are all kept from collapsing by degeneracy pressure.
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True
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The upper limit to the mass of a white dwarf is 1.4 solar masses.
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True
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More massive white dwarfs are smaller than less massive white dwarfs
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True
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Our Sun will likely undergo a nova event in about 5 billion years.
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True
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All pulsars are neutron stars, but not all neutron stars are pulsars.
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True
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All massive-star supernovae leave behind black holes as remnants.
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False
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Which of these objects has the smallest radius? a. a 1.2MSunwhite dwarf b. a 0.6MSun white dwarf c. Jupiter
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a. a 1.2MSun white dwarf
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Which of these objects has the largest radius? a. a 1.2MSun white dwarf b. a 1.5MSun neutron star c. a 3.0MSun black hole
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a. a 1.2MSun white dwarf
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What would happen to a neutron star with an accretion disk orbiting in a direction opposite to the neutron star's spin?
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Its spin would slow down.
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Where do gamma-ray bursts tend to come from?
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Extremely distant galaxies
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If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.
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At a constant, normal rate as you approach the event horizon
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If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.
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Accelerate as you fall and cross the event horizon completely unhindered
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What is the Schwarzschild radius of a 267 million-solar-mass black hole? The mass of the Sun is about 2×10^30kg, and the formula for the Schwarzschild radius of a black hole of mass M is: Rs=(2GM/c^2) (G= (6.67×10^−11) m^3/(kg×s2); c=3×10^8m/s)
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800 million km
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Calculate the Schwarzschild radius (in kilometers) for each of the following: A 2×10^8 MSun black hole in the center of a quasar.
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RSchwarzschild = 6.0×108km
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Calculate the Schwarzschild radius (in kilometers) for each of the following: A 6 MSun black hole that formed in the supernova of a massive star.
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RSchwarzschild = 18 km
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Calculate the Schwarzschild radius (in kilometers) for each of the following: A mini-black hole with the mass of the Moon.
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RSchwarzschild = 1.1×10−7 km
