Section 12.C Flashcards
The core contracts so much that temperatures may hit 100 million °K, hot enough to begin helium fusion suddenly.
That event is called what? __________________ (two words, abbreviated H. F.)
Recognize this as the end of the red giant phase of a star.
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After the helium flash, the star settles on the Horizontal Branch on the H-R diagram to burn helium to make what kind of atoms?
_____________. It also makes a little oxygen. This happens in the core.
Out of the periods of a star’s life, pick out the stable hydrogen-burning period as when it is on the Main Sequence. For comparison, the Horizontal Branch is the stable helium-burning period.
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When too much helium becomes carbon, diluting the remaining helium that’s fusing, the core again contracts
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- And the outer portions of the star again expand, and cool. This defines the Asymptotic Giant Branch,
- The star may become large enough to be a “red supergiant.”
For high-mass stars at least 5 times heavier than the Sun…
These stars have enough mass to make their cores hot enough to undergo additional stages of nuclear fusion burning.
In the further stages, these stars can burn carbon and oxygen to produce even heavier types of atoms.
See section 13 in this study guide for more on heavier stars and how they go supernova when they die.
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For low-mass stars like the Sun, core collapse and expansion of the surface continue until there is nearly no helium left.
The star becomes unstable, pulsates multiple times, then loses its outer layers.
The expelled outer layers become what kind of nebula? __________________________________.
And the core of that dying star becomes a small dead star called a ____________________.
Considering the two objects just mentioned on the two lines above, if you are asked about one of those kinds of objects, make sure you realize it is made at the same time as the other one is.
Know the difference between a white dwarf and neutron star (NS’s are covered later in section 13) and recognized their approximate sizes (earth-size white dwarfs vs. 10-20 mile-wide neutron stars).
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