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20 Cards in this Set
- Front
- Back
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A stars’ mass determines
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its luminosity
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what happens to star formation once it reaches the main sequence?
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On the Main Sequence, the contraction stops because gravity and internal pressure exactly balance each other.
Nuclear reactions occur at exactly the right rate to balance gravity. |
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Most of a star's gaseous content is hydrogen. What happens to it?
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Nuclear reactions slowly convert H to He in the core. This process takes about 10 billion years (the length of which a star is a "main sequence" star)
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What happens when the core Hydrogen is used up?
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Nuclear reactions stop.
Core pressure decreases. Core contracts and gets hotter - heating overlaying layers. |
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what happens during Post-main sequence?
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4H to 1He reactions occur faster than before.
The star gets brighter (more luminous)! The hot shell causes the outer layers to expand and cool! The star moves off the Main Sequence, …up the “Red Giant” branch. (LARGE BUT NOT AS HOT) |
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What happens in the core as it continues to contract and get hotter?
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TRIPLE ALPHA-
Helium begins to fuse into Carbon at >108 K 3 He forms 1 C atom |
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What happens as a result of the carbon burning?
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HELIUM FLASH- Temperature rises rapidly and the star becomes a little smaller.
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Eventually an equilibrium is reached between...
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the red giant branch and the Helium flash branch.
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Stage 10
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Helium-to-Carbon burning occurs stably in core, with Hydrogen-to-Helium burning in shell…
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Once helium runs out at the core, the temperature... and the size....
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cools slightly ; gets larger (now a supergiant)
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During a red supergiant stage, the carbon moves to... while helium burns in the...
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Core ; shell
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Then what?
-carbon does what... -surface layers... -forming a what... -WHAT APPEARS? |
carbon continues to compact and heat.
Surface layers are ejected Bright center = WHITE DWARF! A planetary nebula with the white dwarf in the center. |
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planetary nebulas
-planets? -emit radiation.. -the source of what... |
nothing to with planets
emit radiation that is much smaller than H II discussed in Chapter 11 Higher elements in stars (C, N, O) |
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White dwarfs
-size -density -luminosity |
small (about the size of earth)
VERY DENSE (1 million g/cm^3) very dim |
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What happens to white dwarfs?
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they continue to lose mass and temperature and eventully fade away.
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Some white dwarfs form
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Novas
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Nova
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a star and a white dwarf pair.
Material is lost to the dwarf and hydrogen burning ignites again. |
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what happens to higher mass stars?
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they form an onion level layer of burning elements from hydrogen to iron. The core becomes iron and that is the end of the road.
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Why is iron the end of the road?
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With no more sources of energy, and Fe fusion taking energy from the gas, pressure support in the star’s core is lost…
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There are actually two classes of super nove what are they?
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Type II- massive star explosion (already discussed)
Type I- Carbon burns on the WD everywhere simultaneously and the star explodes in a CARBON DETONATING SUPERNOVA. |
