Astronomy Chapter 20 – Flashcards
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Why is the depletion of hydrogen in the core of a star such an important event?
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The star will begin to change its structure drastically.
It will start to become a red giant.
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Hydrogen-shell burning proceeds increasingly faster due to which of the following?
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heat released from the core's contraction
Higher temperatures cause the protons to move faster, so that they interact more often and fuse at a faster rate.
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As a low-mass main-sequence star runs out of hydrogen fuel in its core, it actually becomes brighter. How is this possible?
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The outer layers expand due to the higher rate of fusion in a shell around the dead core.
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In a white dwarf, what is the source of pressure that ultimately halts its contraction?
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electrons packed so closely that they become incompressible
This force, which occurs in high-density stars such as white dwarfs, is called the electron degeneracy pressure
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What is the primary composition of a white dwarf?
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carbon
Fusion in low-mass stars ends at carbon.
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In its last stage of evolution, what will the Sun become?
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The Sun will end its evolution as a white dwarf, which will slowly cool to become a black dwarf.
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What property of a star cluster helps determine its age?
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main-sequence turnoff
Finding the point where main sequence stars have just run out of hydrogen fuel tells us how long the cluster has been around.
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What is a contact binary?
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two nuclear-burning stellar cores surrounded by a single continuous common envelope
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A star (no matter what its mass) spends most of its life:
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as a main sequence star.
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Why are star clusters almost ideal "laboratories" for stellar studies?
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Stars in clusters have the same age, similar composition, and are at the same distance away.
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The most important fact about a cluster of stars that makes them useful for studying star formation is that
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all the stars formed at about the same time.
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When a star depletes its core supply of hydrogen, ________ dominates in the core and ________ dominates in the envelope.
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The core contracts due to gravity, whereas the envelope swells due to radiation pressure.
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What is the region of the Hertzsprung-Russell diagram known as the horizontal branch?
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It is a region of the H-R diagram where stars remain for a time as they undergo helium core fusion.
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What is a planetary nebula?
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an expanding shell of gas around a white dwarf star
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What is the size of the core of a typical white dwarf star?
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about the size of Earth
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As a 4-10 solar mass star leaves the main sequence on its way to becoming a red supergiant, its luminosity:
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remains roughly constant.
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What is the age range among the globular clusters associated with our Galaxy?
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The globular clusters range from 10 to 12 billion years old.
