Term
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Definition
The internal structure of a star depends on:
– the balance of
→ gravity pulling inward
→ pressure pushing outward |
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Term
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Definition
| Conduction, Convection, or Radiation |
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Term
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Definition
flow of material (and energy)
from hotter regions to cooler regions
→ driven by density change |
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Term
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Definition
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Term
| Post Main Sequence - Low Mass |
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Definition
These stars are fully convective
– Fusion only occurs in the core
– all mass cycles though the core.
– the star uses almost all of its hydrogen (H)
and fusion eventually slows and stops
– the star just fades away.
None of these stars are old enough to die. |
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Term
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Definition
These stars have radiative cores and convective
envelopes
– as the core depletes its H, no new H is mixed
in
– as the core H becomes exhausted, fusion
slows, and the core begins to contract.
The core contracts
– contraction heats the core and the material
surrounding it
– the material surrounding the core (which still
contains H) gets hot enough to start fusing
H → He
– “shell fusion” begins at the bottom of the
giant branch ... the star becomes a giant
As the shell converts H to He, the He “piles-up”
in the core:
– the core increase in mass
– causing it to contract further and become
hotter
– hotter core causes shell to fuse faster
increasing L as the star moves up the giant
branch
“helium flash”
– star has a new energy source
– re-organizes its insides
– becomes a “horizontal branch” star (still a
giant) |
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Term
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Definition
| Stellar remnant left over at the center of a planetary nebula. Mass of the sun, radius of the earth. |
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Term
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Definition
| Giant collection of dust and particles; stars are created here. |
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Term
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Definition
| P ~ p; when added to a white dwarf, more mass is added but the star gets smaller because the gravity pulls everything inwards. |
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Term
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Definition
| White dwarf steals matter from closer mass source. After exceeding 1.4Msun, the gravity collapses in on itself in only a few seconds. Gas undergoes nuclear reactions, star goes BOOM. White dwarf and separate mass are destroyed, gas goes back into space. |
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Term
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Definition
| PMS - High mass star starts to fuse its shell; stars with Fe, Si and S -> O, Ne, Mg -> C and O -> He -> H. Fe piles up in the core, creating more density. Fe core exceeds 1.4Msun, causing star to implode. |
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Term
| Neutron Stars and Pulsars |
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Definition
| Neutron star = very small, very dense. Pulsars = pulsating radio service. An object that emits frequent pulsations as they rotate. |
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