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114 Cards in this Set
- Front
- Back
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1. What does evolution in biology describe?
In astronomy what does evolution describe? |
How the properties of POPULATION change overt time
How a SINGLE OBJECT changes over time |
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2. How do we describe the evolution of a star?
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Use a star's track through the H-R diagram
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3. What do we mean when we say a star "moves" through the diagram?
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It isn't physical motion
The characteristics of the star change SO the point on the diagram which corresponding to it changes (moves) |
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4. What do astronomers refer to fusion as?
What can the product be referred to as? |
Burning (even though its a nuclear process and not a chemical on like wood burning)
Say a star "burns" H when it is fusing H into He "Ash" |
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5. What are two different paths for fusing H into He?
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Proton-proton cycle
C-N-O (CNO) cycle: occurs at higher temperatures only (> 20 million K) *more efficient than P-P cycle |
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6. Briefly describe the CNO cycle?
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1. C12 + H1 -> N13 + gamma ray
2. N13 -> C12 + neutrino + positron 3. C13 + H1 -> N14 + gamma ray 4. N14 + H1 -> O15 + gamma ray 5. O15 -> N15 + neutrino + positron 6. N15 + H1 -> C12 + He4 Final Products: He4 and C12 |
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7. In the CNO cycle what is C12?
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A catalyst because it is not consumed in the reaction but it one of the final products
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8. Why does the CNO cycle require higher temperatures?
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**P-P cycle requires high temperature to overcome electromagnetic repulsion between protons
Electric force is proportional to the product of the charges involve SO, C has 6 protons so the repulsion between a C nucleus and a proton is 6x higher than repulsion between 1 proton and another |
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9. What is Helium burning?
What is another name for it? What does it require? |
Three H4 -> C12 + energy
"Triple alpha process" ('alpha particles' emitted in radioactivity are actually He4 nuclei) Still higher temperature (~10^8 K) |
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10. What can happen at even higher temperatures?
What happens with heavier elements? |
Possible to fuse C, O, etc.
Fusion gets harder and harder as charges of nuclei increase and less energy is yielded |
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11. Past what element is fusion basically useless in terms of energy yield?
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Iron (Fe56)
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12. Why is stellar evolution difficult to observe?
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Even with most massive stars evolution occurs over million of years
Cannot observe a single star go through its whole life cycle |
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13. How do we observe stellar evolution?
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Infer what's happening by observing differences between populations of stars of different ages
(**compare star clusters) Also through detail observations of stars in a given stage of their life (i.e. the Sun) |
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14. What is key to stellar evolution?
How is the star during its stay on the Main Sequence? |
Balance between outward pressure and inward gravity
Hydrostatic equilibrium |
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15. In equilibrium what does any change result in?
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A change in the stars structure (temperature/density/size) until equilibrium is restored
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16. From what two sources can pressure come from?
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1. Ordinary pressure
2. Degeneracy pressure |
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17. What is ordinary pressure?
For a typical gas or plasma how is pressure, temperature and density related? |
The force exerted by particles bouncing off each other
Pressure is proportional to both temperature and density |
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18. What does the Pauli Exclusion Principle state?
What is a result of the Exclusion Principle? |
No two identical particles of ordinary matter (like 2 electrons) can exist in the exact same state (position, velocity, etc)
We can only compress an electron rich plasma so far Otherwise multiple electrons would have to be in the same state |
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19. How does the plasma start to act?
What is this? |
Behave more like a liquid or solid (resists being compressed any further)
"Degeneracy Pressure" |
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20. How is degeneracy pressure related to temperature and density?
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INDEPENDENT OF TEMPERATURE
Dependent on density It becomes important at high densities/pressure in stars |
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21. When does the star to leave the Main Sequence?
How does evolution depend on mass? |
All the H in the core is consumed (still have H but not in core)
Low-mass stars (Sun) go quietly High-mass stars go out with a bang |
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22. As a star's life goes on what happens to the core?
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Composition changes steadily until H is only at outer core
Helium "ash" builds up in the core |
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23. What happens as the H fuel in the core is used up?
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1. Core contracts and heats up (increase efficiency)
2. When H is used up completely, core collapses 3. H begins fusing outside core (high temps in H-burning shell) |
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24. During "shell burning" what happens to the characteristics of the star?
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1. Surface temp decreases
2. Core increases in density and temperature 3. Radius and Luminosity increase 4. Outer layers of star puff up because of increase in temperature in H-burning shell |
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25. What is all of this?
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Beginning of evolution off Main Sequence
Sub-giant branch -surface temp decreases -central density increases -central temp increases -solar radii increases -longest period after leave Main Sequence |
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26. What happens on the Red-Giant Branch?
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1. Core shrinks
2. Outer layers of star expand and cool *Star is now red giant (extends out as far as orbit of Mercury) |
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27. How is the luminosity on the Red-Giant Branch?
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Luminosity increase enormously
-despite cooler temperature * L ∝ (R^2)(T^4) |
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28. Is there fusion in the core during on the Red Giant Branch?
What happens to the core? What does it result in? |
No fusion in core
Continues to contract and heat up It heat up the H shell increasing L and pressure |
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29. When the surface temperature reaches 3000-4000 K what happens?
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Core can't cool anymore
Star gets larger and larger but surface temperature stays constant |
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30. How long this process of contraction continue for?
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It continues until it is hot enough for H to fuse
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31. When does He fusion begin?
Why is extremely high temperature and densities necessary for He fusion? |
Core temp has risen to 100,000,000 K
The Be8 particle yield from fusion of 2 He4 is high unstable It will decay unless an alpha particle fuses with it first |
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32. In an ordinary gas what would the increased energy output lead to?
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An increase is pressure so the core puffs
It would expand and cool till equilibrium is reached |
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33. How is the He core different?
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It is so dense that pressure is almost totally due to electron degeneracy
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34. What is special about the degeneracy pressure?
What happens? |
Almost independent of temperature
When He starts fusing, pressure does not change significantly This means star doesn't expand and cool until an equilibrium fusion rate is reached |
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35. What does the sudden burst of energy?
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Instead of puffing up the core it raises the cores temperature
This increases rate of He fusion at the core still further |
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36. What is this called?
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Helium Flash
-release huge energy in short period of time -core expands -tip of Red Giant branch -core is as dense as it can be |
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37. What happens at the end of the He Flash?
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1. He fuses rapidly
2. Temp get high enough that ordinary gas pressure is significant 3. Core expands and cools 4. Star reaches equilibrium again on Horizontal Branch |
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38. What is the Horizontal branch?
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Place where burn He at steady state
-solar radii has decreased -central density decreases -surface temp increases -central temp increases |
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39. What happens on the Asymptotic Giant Branch?
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1. He core fuses to C and core becomes hotter and hotter
2. He burns faster and faster 3. Star is similar in structure to when it left Main Sequence EXCEPT has two shells burning |
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40. How is the star on the Asymptotic Giant Branch?
How long it it? How does this star end this branch? |
Red Giant (outer layers expands by pressure) again - even bigger - BUT it's as big as it'll get
Short stage so these are rare stars End with even denser core and outer layers that grow to a huge size |
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41. After the Asymptotic Giant Branch what are we left with?
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A carbon core supported by degeneracy pressure
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42. How is the core when it is a carbon core?
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No fusion
Core density reach to an equivalent of 10 tons in volume of a grape |
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43. Since there is not more fusion energy being generated in the core what happens?
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1. Core continues to contract
2. Series of He flashes occur on outside of degenerate core 3. Outer layers are repeatedly blown off and then they settle down and happens again |
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44. What happens to the outer layers eventually?
Why is it named a "planetary nebula"? |
Blown off
Ejected envelope expands into interstellar space forming a "planetary nebula" Look like disks - much like planets in early telescopes |
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45. What two parts has the star now split into?
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1. Small, extremely dense C core (white dwarf)
2. Envelope about the size of our solar system (planetary nebula) |
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46. What is the envelope rich in?
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Dust from C, O, etc. produced in last stages of fusion
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47. How does a planetary nebula end?
Can a Sun-like star ever fuse C? Where does a star spend most of its life? |
Nebula continues to expand as dead core cools
Eventually the nebula dissipates into the interstellar medium No it never becomes hot enough (not even a star twice the mass of the Sun can burn C) On Main Sequence then as a Red Giant |
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48. How is a white dwarf born?
What is an example of a white dwarf? Are they easy to detect? |
Once the outer envelope is gone, remaining core is extremely dense and hot but small
Has high L only due to high temperature (no fusion) Sirius B who is a companion of large and brighter Sirius A Difficult to observe - Hubble has detected white dwarf stars in globular cluster |
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49. How is a black dwarf formed?
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White dwarf cools but size does not change significantly
It gets cooler and dimmer and finally ceases to glow significantly becoming a black dwarf |
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50. What will happen when the Sun becomes a Red Giant?
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It will expand beyond Earth's orbit
Despite its cooler surface temperature, its L has increased enormously |
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51. Do stars more massive than the Sun follow the same path?
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No, they follow very different path when leaving the Main Sequence
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52. When do high mass stars leave the Main Sequence
How are the first few events similar to those in lower mass stars? |
When there is no more H fuel in their cores
First a H shell, then a core burning He to C, surrounded by He and H burning shells |
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53. Is the evolution of high mass stars smoother?
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Yes! They evolve more smoothly
2.5 solar masses do not experience a He flash rather He burning begins gradually 4 solar mass stars makes no sharp moves, it moves smoothly back and forth |
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54. What is special about a star more than 8 solar masses?
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It can fuse elements beyond C in its core
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55. How is such as massive star's fate different?
How does such a star die? |
Its path across the H-R diagram is almost a straight line
Stays at about the same L as it cools off Dies in a violent explosion called a supernova |
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56. What complication does stellar winds add to the evolution of a star?
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All stars lose mass via some form of stellar winds
Most massive stars (O and B) have the strongest winds Stellar winds hollow out cavities in ISM surrounding giant stars It is the mass AFTER LOSSES TO WINDS that determines whether the core will get hot and dense enough to fuse He, C, etc. |
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57. How is the material ejected from an unstable red giant?
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Dusty
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58. In observations of star clusters, what are "blue stragglers"?
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Not typical Main Sequence stars
They must have formed more recently than most stars in a cluster Probably formed from the merger of smaller stars |
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59. In observing stellar evolution in star clusters what is seen after 10 million years?
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Most massive stars have already left the Main Sequence
Many of the least massive stars have not even reached the Main Sequence yet |
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60. What is seen after 100 million years?
What does this show? |
Main Sequence Turnoff begins to develop
The highest-mass stars that are still on the Main Sequence |
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61. What is seen after 1 billion years?
What about after 10 billion years? |
Main Sequence Turnoff is much clearer
Red-Giant, Sub-Giant, Asymptotic Giant, and Horizontal branches are clearly population White dwarfs, indicating that solar mass stars are in their last phases of life also appear |
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62. How does the spacing between stars in a binary-star system affect evolution?
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If they are widely separated, evolution proceeds much as it would if they were not companions
Close together, unusual evolutionary path because it's possible for material to transfer from one star to another |
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63. What surrounds each star in a binary star system?
How are the particles inside this? What is the Lagrangian point? |
Its own Roche lobe
Gravitationally bound the the central star Point where the gravitational forces from the two stars are equal |
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64. What are the types of binary-star systems?
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1. Detached Binary
-each star has its own Roche lobe 2. Semidetached Binaries -one star can transfer mass to the other 3. Contact Binaries -much of the mass is shared between the two stars |
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65. What is Algol?
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Binary star system with a 3.7 solar mass M-S star and 0.8 solar mass Red Giant
Began as a detached binary with 3 solar mass star and 1 solar mass star |
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66. What happened in the evolution of Algol?
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1. Blue-Giant star entered Red-Giant phase and expanded to where mass transfer occurred
2. Enough mass accredited onto smaller star that it became Blue Giant (other stars is a Red Sub-Giant) |
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67. What can happen in binaries w/ white dwarfs?
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A white dwarf that is part of a semidetached binary system can also accrete matter
Matter from other star settle into "accretion" disk around white dwarf Due to friction, material in disk falls onto white dwarf building it up Temp and density of in falling material can get extremely hot |
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68. What happens when enough material has accreted?
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Fusion can reignite suddenly burning off new material
Material keeps being transferred to the white dwarf and process repeats |
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69. What is a nova?
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A star that flares up very suddenly and then returns slowly to its former luminosity
These are actually outbursts around white dwarfs *Nova can happen again and again |
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70. What are the results of a nove?
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Can see ejected material expanding away from a star after a nova explosion
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71. What is a type I supernovae?
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"Carbon Detonation"
Binary star system with a white dwarf |
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72. What pressure supports white dwarfs?
What does the cause? |
Degeneracy pressure
More massive dwarfs will be smaller than less massive one |
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73. What happens if a white dwarfs mass exceeds 1.4 solar masses?
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Electron degeneracy cannot support it at all and it will start to collapse
As dwarf collapses, it heats up |
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74. As the white dwarf collapses and heats up, what begins?
What does this cause |
Carbon fusion begins throughout the star almost simultaneously
A huge rapid energy release and hence an EXPLOSION |
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75. Up to what element can a high mass star fuse up to?
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Can fuse elements in its core right up to iron in a succession of shells in its centers
Each higher element requires a higher temperature and yields smaller returns from fusion |
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76. What is special about iron?
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It's the most stable nucleus
It requires energy to be added for either fission or fussion |
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77. How are the reactions of heavier elements?
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Their reactions must go faster to provide a star's L
Each successive stage is over more quickly |
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78. What supports the iron core?
Once it's more massive than 1.4 solar masses what happens? |
Degeneracy pressure
Electron degeneracy can no longer support and core begins to collapse and heat up |
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79. What happens to the photons emitted by blackbody radiation at temps of ~10 billion K?
Why is this important? What does cooling the core and reducing its pressure support further? |
Photons are energetic enough to split nuclei
Splitting iron or lower elements requires energy input Collapse accelerates |
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80. At the end what happens?
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Inward pull of gravity is enormous (due to high mass)
Nothing is there to stop the star from collapsing further It does collapse very rapidly in a giant IMPLOSION |
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81. As the core becomes more and more dense what happens to the protons?
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Protons and electrons combine w/ one another to become neutrons
Neutrons are more massive than protons so this takes energy thus cooling the core more, reducing pressure, and accelerating the collapse |
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82. What happens to the neutrons?
What happens to degeneracy pressure? What happens to the neutron core? |
Mostly escape
All electrons have merged into neutrons so electron degeneracy pressure is not a factor Continues to collapse until it has the density of an atomic nucleus |
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83. At this point, what keeps in?
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Neutron degeneracy pressure
Acts just like electron degeneracy pressure but becomes important only at a higher density (core refuses to compress further) |
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84. What happens to the imploding outer layers?
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Rebound off the neutron-rich core in an enormous explosion (supernova)
Most of the star is blown up |
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85. What is a type II supernova?
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"Core-Collapse"
Explosion of massive star |
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86. How bright are supernova?
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Incredibly luminous
More than a million times as bright as a nova (as bright as many galaxies) |
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87. How many times does a supernova occur?
How common are each type of supernova? |
ONE TIME event, once it happens little or nothing left of the progenitor star
Two types are roughly equally common |
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88. What remnant does a supernova leave?
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The expanding clouds of material from the explosion, coming from the outer layers of the star
Crab nebula is remnant of supernova 1800 PC away in the year 1054 |
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89. What is the most recent known supernova in our galaxy?
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Kepler's Supernova in 1604
This is most recent even though we expect ~1 per 50 years |
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90. What is Supernova 1987A?
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Supernova in the Large Magellanic Cloud, a neighboring galaxy in 1987
It's atypical (light didn't peak for 100 days) |
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91. What is visible in Supernova 1987A?
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A cloud of glowing gas is now visible around it
The small central object (supernova remnant) is becoming discernible |
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92. What elements were formed in the Big Bang?
How many elements exist on our planet? |
He, Li, Be, and H
H and He are most abundant in elements in universe 81 stable and 10 radioactive |
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93. What can C fuse with?
In what stars can C fuse? |
C or He to form more nuclei
In stars >~2.5 times as massive as the Sun |
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94. Which elements are more abundant?
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Those that can be formed through successive "alpha-particle" (He4) fusion
Causes jagged pattern at left of graph (O is more common than N) |
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95. What is the last element in the alpha particle chain?
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Nickel-56
This is unstable and quickly decays to Cobalt-56 and then to Iron-56 Iron-56 is most stable nucleus |
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96. What happens in neutron capture?
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In cores of massive stars, free flying neutrons are present
Since neutrons have no charge they can be "captured" onto a nucleus by the strong force |
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97. Up to what element can neutron capture form?
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Heavier elements (gold, silver, copper) up to
Bismuth-209 Heavier elements will break up spontaneously faster than they can accumulate more neutrons even in massive stars |
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98. From where are the most massive elements formed?
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Supernova
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99. Where does most of the light we see from supernova come from?
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Radio active decay
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100. How is the cycle of stellar evolution?
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Star formation is cyclical: stars form, evolve, and die
1. Start with gas and dust making up ISM 2. Star forms out of coolest, densest region (molecular clouds) 3. Star ages: turn H and H into C,N,O 4. Low mass stars eject their atmospheres including 'heavier' elements 5. High mass stars die explosively as supernova (heavier elements) 6. Explosive events trigger star formation while elements created in/ejected by dying star help make up new star |
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101. What remains after a Type I supernova?
What remains after a Type II supernova? |
Little or nothing of original star
Part of core may survive - call it a neutron star |
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102. What is a neutron star like?
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1. As dense as or denser than an atomic nucleus
2. 1-3 solar mass 3. Very small 4. Composed of unique form of matter Existence was theorized in 1933 and discovered in 1967 |
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103. What is special about the rotation of neutron stars?
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As the parent star collapses, the neutron core spins more and more rapidly
Typical periods are fractions of a second |
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104. What is the magnetic field of a neutron star?
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As the star collapses, the neutron star's magnetic field becomes more and more concentrated
Hence, enormously strong Powerful magnetic field can accelerate particles and produce radiation *has strong gravitational field as well |
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105. When was the first pulsar discovered?
What did it emitt? |
1967
Emitted extraordinary regular pulses of radio waved (nothing like seen before) |
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106. What was this pulsar found to be?
What causes the pulses? |
It was a neutron star, spinning very rapidly
'Lighthouse effect" |
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107. What is the 'lighthouse effects'?
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Strong jets of radiation are emitted at the magnetic poles of a neutron star
We see a pulse from when the beam points at us |
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108. What is the evolution of a pulsar like?
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1. Radiate energy away quite rapidly
2. Radiation weakens and stops in a few tens of millions of years 3. Neutron star is virtually undetectable 4. Pulsars will also not be visible on Earth if their jets are not pointing our way |
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109. In what ranges to pulsars radiate?
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Gamma-ray spectrum
Radio Visible Matter is accelerated to high energies by a pulsar's magnetic field |
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110. What happens to neutron stars at high velocities?
From where are x-ray bursts seen in our galaxy thought to originate? |
It can be ejected from their supernova
Originate on neutron stars that have binary partners The process is similar to a nova - occasional fusion flareups |
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110. What are millisecond pulsars?
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Most pulsars have periods between 0.03 and 0.3 seconds
1980 discovered millisecond pulsars spinning almost 1000 times per second |
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111. How are millisecond pulsars though to originate?
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Thought to be "spun-up" by matter falling in from a companion
That material's radius drops by a large factor, so it is orbiting quickly by the time it joins the pulsar |
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112. What is a neutron-star planet system?
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Pulsar whose period had regular variations
Variations consistent with being due to the gravitational influence of 2 planets (must have been picked up or formed after neutron star was formed) |
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113. What are gamma ray bursts?
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First spotted by satellites looking for violations of treaties banning above ground nuclear tests
Gamma ray burst spread uniformly over the sky Suggests they are far away from us |
