Questions and Answers
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.
A typical white dwarf is as massive as the ____________ but only about as large in size as ________.
Sun; Earth
What is the basic definition of a black hole?
An object with gravity so strong that not even light can escape.
Which of these objects has the largest radius?
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Which of the following best describes why a white dwarf cannot have a mass greater than the 1.4-solar-mass limit?
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Order the following objects in increasing size (radius): Jupiter, neutron star, the Sun, white dwarf
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What happens to a white dwarf that is accreting hydrogen gas from a nearby star?
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Rank the following 4 items in order of increasing density (low to high): main-sequence star, black hole singularity, neutron star, white dwarf
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A white dwarf supernova leaves behind
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What property suggests that the companion to an evolved star is definitely a black hole?
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Imagine that our Sun were magically and suddenly replaced by a black hole of the same mass (1 solar mass). What would happen to Earth in its orbit?
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According to present understanding, a nova is caused by ________.
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End states of a neutron star:
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End states of a white dwarf:
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End states of a black hole:
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The maximum mass of a white dwarf is ________.
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According to our modern understanding, what is a nova?
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The white dwarf that remains when our Sun dies will be mostly made of ________.
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A white dwarf is what ________.
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Which statement about pulsars is NOT thought to be true?
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Study Notes
Black Holes and Event Horizons
- The event horizon is the boundary around a black hole where nothing can escape, not even light.
- A black hole is defined as an object with gravity so strong that light cannot escape.
White Dwarfs
- Typical white dwarfs have a mass comparable to the Sun but are roughly the same size as Earth.
- Cannot exceed a mass of approximately 1.4 solar masses due to electron degeneracy pressure limits.
- A white dwarf that accretes hydrogen gas can experience fusion bursts on its surface.
- The end state of a white dwarf is supported by electron degeneracy pressure and can explode as a supernova in a binary system.
Density and Size Comparisons
- A white dwarf has a larger radius than a 1.5Msun neutron star and a 3.0Msun black hole's event horizon.
- Order of increasing size: neutron star, white dwarf, Jupiter, Sun.
- Rank in order of increasing density: main-sequence star, white dwarf, neutron star, black hole singularity.
Stellar Evolution and End States
- A white dwarf will leave behind nothing after a supernova.
- The remains of a dying star that becomes a white dwarf will primarily consist of carbon.
- Pulsars, a type of neutron star end state, are characterized by strong magnetic fields and may appear as pulsars.
Mass Transfer and Companions
- A mystery companion object with a mass over 3 solar masses likely indicates it is a black hole.
- If the Sun were replaced by a black hole of equal mass, Earth's orbit would remain unchanged.
Nova and White Dwarf Dynamics
- A nova is caused by hydrogen fusion on the surface of a white dwarf in a close binary system.
- White dwarfs typically have diameters similar to Earth's size and support themselves against collapse through electron degeneracy pressure.
Misconceptions about Pulsars
- It is a misconception that pulsars can only form in close binary systems.
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Description
Test your knowledge on black holes with this quiz. Explore key concepts like event horizons and the characteristics of white dwarfs. Perfect for students eager to deepen their understanding of astrophysics topics.
