Astro Mid Term Sem. 2 (Book 2/7) Flashcards
if a M-S mass [M(sun)] is < 0.25, what is its evolution?
Red Giant -> He White Dwarf
if a M-S mass [M(sun)] is 0.25 - 0.8 what is its evolution?
Red Giant -> Planetary Nebula -> C White Dwarf
if a M-S mass [M(sun)] is > 8 (core < 3) what is its evolution?
Red Giant -> Supernova -> Neutron Star
if a M-S mass [M(sun)] is > 20 (Core > 3) what is its evolution?
Red Giant -> Supernova -> Black Hole
A star remains on the M-S as long as it can what?
As long as it can fuse hydrogen into helium in its core
The mass of a main sequence star determines its what?
It determines its core pressure and temperature
Stars with higher mass have higher core temperatures and more rapid fusion rates, making these stars what?
These stars will be both more luminous and shorter-lived
Stars with lower mass have cooler cores and slower fusion rates, making these stars what?
These stars will have smaller luminosities and longer lifetimes
What is the structure of an average, mature star? (like our sun)
- Hydrogen Fusion reactions occur in the core which releases;
- Gamma and X-ray Radiation. This radiation moves through the radiation zone from particle to particle, eventually heating gases at the bottom of the convection zone.
- Convection Cells carry energy to the surface, where it is emitted to space as Visible light, Ultraviolet Radiation, and Infrared Radiation
What is the life of the sun? (diagram in book 2 middle of page 2)
- Interstellar cloud; Protostar; Average, mature sun; Red Giant; Yellow Giant; Red Giant; Ejected Gas Shell w/central star; Planetary Nebula; White Dwarf is what is left
Thought Question: What happens when a star can no longer fuse hydrogen to helium in its core? A) Core cools off B) Core shrinks and heats up C) Core expands and heats up D) Helium Fusion immediately begins
Answer is B, the core shrinks and heats up
Thought Question: What happens as a star’s inert helium core starts to shrink?
A) Hydrogen fuses in shell around its core
B) Helium fusion slowly begins
C) Helium fusion rate rapidly rises
D) Core pressure sharply drops
Answer is A, hydrogen fuses in shell around its core
What happens as a star contracts?
Hydrogen (H) begins fusing very rapidly to helium (He) in a shell around the core.
Luminosity will also increase because the fusion rate is higher.
The size will increase: red giant phase
What happens as a star contracts?
Hydrogen (H) begins fusing very rapidly to helium (He) in a shell around the core.
Luminosity will also increase because the fusion rate is higher.
The size will increase: red giant phase
See middle of book 2 page 3 for slide
- Helium fusion requires higher temperatures than hydrogen fusion
- Helium fusion combines 3 He nuclei to make Carbon (C)
The expansion of a star to a giant or super giant size does what to the outer layers?
It cools the outer layers and moves towards the upper right in the H-R diagram
What is the evolution of a gas cloud onto the M-S? (as described in book 2)
- The star shrinks from a large cloud to a spinning ball of gas
- protostar heats up slightly
What happens to a new star once on the M-S? (as described in book 2)
- star burns hydrogen in its core
- star settles down onto the M-S
- slight increase in temp. and luminosity
What happens to a M-S star as it is becoming a giant? (as described in book 2)
- the hydrogen in the star’s core begins to run out
- the star leaves the M-S and swells to become a Red Giant
- the temp. drops
- the luminosity increases because the star is so much bigger
What happens to a M-S star as it is becoming a giant? (as described in book 2)
- the hydrogen in the star’s core begins to run out
- the star leaves the M-S and swells to become a Red Giant
- the temp. drops
- the luminosity increases because the star is so much bigger
What are the basic characteristics of a White Dwarf? (as described in book 2 bottom of page 5)
- The core of the star is left
- No more burning in the core
- The star will continue cooling until it can no longer be seen
What happens when the star ends fusion? (White Dwarf)
- C and O from core helium burning
- Thin layer of He (the product of shell hydrogen burning)
- Typical mass less than half a solar mass to more than 1 solar mass
- ## Same size as Earth
What happens when the star ends fusion? (White Dwarf)
- C and O from core helium burning
- Thin layer of He (the product of shell hydrogen burning)
- Typical mass less than half a solar mass to more than 1 solar mass
- Same size as Earth
- Compact (a spoonful of its matter weighs between 10-100 tons)
- In the final stages of the formation of a Planetary Nebula nuclear burning in the central star ceases
When a White Dwarf cools down enough, what does it form?
It forms a huge crystal - a Degenerate Diamond
- This is the fate of the sun
