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accretion disk
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The whirling disk of gas that forms around a compact object such as a white dwarf, neutron star, or black hole as matter is drawn in. (p. 216)
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angular momentum
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A measure of the tendency of a rotating body to continue rotating. Mathematically, the product of mass, velocity, and radius. (p. 215)
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black dwarf
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The end state of a white dwarf that has cooled to low temperature. (p. 211)
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Chandrasekhar limit
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The maximum mass of a white dwarf, about 1.4 solar masses. A white dwarf of greater mass cannot support itself and will collapse. (p. 211)
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degenerate matter
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Extremely high-density matter in which pressure no longer depends on temperature due to quantum mechanical effects. (p. 204)
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globular cluster
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A star cluster containing 100,000 to 1 million stars in a sphere about 75 ly in diameter. Generally old, metal-poor, and found in the spherical component of the galaxy. (p. 208)
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helium flash
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The explosive ignition of helium burning that takes place in some giant stars. (p. 205)
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horizontal branch
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In the H-R diagram, stars fusing helium in a shell and evolving back toward the red giant region. (p. 209)
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inner Lagrangian point
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The point of gravitational equilibrium between two orbiting stars through which matter can flow from one star to the other. (p. 214)
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Lagrangian points
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Points of gravitational stability in the orbital plane of a binary star system, planet, or moon. (p. 214)
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nova
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From the Latin, meaning "new," a sudden brightening of a star making it appear as a new star in the sky. Believed to be associated with eruptions on white dwarfs in binary systems. (p. 200)
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open cluster
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A cluster of 100 to 1000 stars with an open, transparent appearance. The stars are not tightly grouped. Usually relatively young and located in the disk of the galaxy. (p. 208)
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planetary nebula
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An expanding shell of gas ejected from a star during the latter stages of its evolution. (p. 207)
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Roche lobe
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The volume of space a star controls gravitationally within a binary system. (p. 214)
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Roche surface
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The dumbbell-shaped surface that encloses the Roche lobes around a close binary star. (p. 214)
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supernova
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The explosion of a star in which it increases its brightness by a factor of about a million. (p. 200)
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supernova remnant
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The expanding shell of gas marking the site of a supernova explosion. (p. 222)
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synchrotron radiation
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Radiation emitted when high-speed electrons move through a magnetic field. (p. 220)
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turnoff point
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The point in an H-R diagram at which a cluster's stars turn off of the main sequence and move toward the red-giant region, revealing the approximate age of the cluster. (p. 208)
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type I supernova
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A supernova explosion caused by the collapse of a white dwarf. (p. 220)
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type II supernova
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A supernova explosion caused by the collapse of a massive star. (p. 219)
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