Astrophysics HL


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IBO Diploma Physics Option E

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Astrophysics HL

  1. 1. Astro - HL
  2. 2. Star Formation <ul><li>Dark Nebula -Birthplace of Stars </li></ul><ul><ul><li>Example- Horsehead Nebula </li></ul></ul><ul><ul><ul><li>In the constellation Orion. </li></ul></ul></ul><ul><ul><ul><li>The birthplace of stars </li></ul></ul></ul><ul><ul><ul><li>75% Hydrogen, 24% Helium, 1% dust (many different elements) </li></ul></ul></ul>
  3. 3. Star Formation <ul><li>Gravity begins to pull the gas and dust together. </li></ul><ul><li>They lose gravitational potential energy…this is converted into kinetic energy. </li></ul><ul><li>The temperature increases. </li></ul>
  4. 5. The Perfect Storm <ul><li>A small region in the Swan Nebula, 5,500 ly away, described as 'a bubbly ocean of hydrogen and small amounts of oxygen, sulphur and other elements'. </li></ul>
  5. 6. Ant Nebula <ul><li>Name is Mz3, lies within our galaxy between 3,000 and 6,000 ly from Earth. </li></ul>
  6. 7. Cone Nebula <ul><li>2.5 light years in length (the equivalent of 23 million return trips to the Moon) </li></ul>
  7. 8. Hour Glass Nebula <ul><li>8,000 light years away, has a &quot;pinched-in-the-middle&quot; look because the winds that shape it are weaker at the centre. </li></ul>
  8. 9. Star Formation <ul><li>Protostar </li></ul><ul><ul><li>High temperature leads to ionisation of elements. </li></ul></ul><ul><ul><li>E-M energy is emitted. </li></ul></ul><ul><ul><li>The star can have considerable Luminosity. </li></ul></ul><ul><ul><li>5000 times the surface area and 100 times as Luminous as our Sun. </li></ul></ul>
  9. 10. Star Formation <ul><li>Protostar- </li></ul><ul><ul><li>Temperature continues to increase… </li></ul></ul><ul><ul><li>Electrons stripped from the atoms in the core. </li></ul></ul><ul><ul><li>A plasma is formed. </li></ul></ul>
  10. 11. Star Formation <ul><li>Main Sequence Star- </li></ul><ul><ul><li>Nuclear Fusion starts up. </li></ul></ul><ul><ul><li>Temperatures now high enough to fuse Hydrogen into Helium. </li></ul></ul><ul><ul><li>Gravitational contraction will now stop as the Fusion process will offset the contraction. </li></ul></ul><ul><ul><li>“ Hydrostatic Equilibrium” </li></ul></ul>
  11. 12. You are not Required to Memorize these Reactions
  12. 13. Main Sequence Stars <ul><li>Where a star lands on the Main Sequence depends on its mass. </li></ul><ul><li>A star will </li></ul><ul><li>stay at this </li></ul><ul><li>place on the </li></ul><ul><li>main sequence </li></ul><ul><li>for its lifetime </li></ul><ul><li>as a Main Sequence </li></ul><ul><li>Star. </li></ul>
  13. 14. Main Sequence Stars <ul><li>The life of a Main Sequence star is determined by its mass. </li></ul><ul><li>High Mass = </li></ul><ul><li>Short Lifespan. </li></ul><ul><li>Sun (1M) - 10 Billion </li></ul><ul><li>Years. </li></ul><ul><li>15 M - 10,000 </li></ul><ul><li>Years. </li></ul>
  14. 15. Main Sequence Stars <ul><li>Once hydrostatic equilibrium is reached… the star will remain stable for as long as it is a Main Sequence Star (thousands to up to billions of years). </li></ul>
  15. 16. The Future of our Sun <ul><li>There is enough Hydrogen in our Sun’s core to produce fusion for another 5 billion years. </li></ul><ul><li>Eventually the core will be mostly Helium. </li></ul><ul><li>Hydrogen Fusion will then begin outside the core. </li></ul>
  16. 17. The Future of our Sun <ul><li>No fusion happening in the core to counteract the gravitational contraction. </li></ul><ul><li>The core will begin to collapse. </li></ul><ul><li>This raises the cores temperature. </li></ul><ul><li>Sun will start to expand. </li></ul><ul><li>Surface temperature will drop. </li></ul><ul><li>Sun enters RED GIANT STAGE. </li></ul>
  17. 18. The Future of our Sun <ul><li>Luminosity increases due to massive size. </li></ul><ul><li>Out to the orbit of Venus. </li></ul><ul><li>Core temperature now so high that Helium can be fused. </li></ul><ul><ul><li>Higher temperature required to fuse Helium as it has two positive charges. </li></ul></ul>
  18. 19. The Future of our Sun <ul><li>Helium fused into Carbon and Oxygen. </li></ul><ul><ul><li>This is where our carbon comes from. </li></ul></ul><ul><ul><li>Once the Helium is used up in the core, the star collapses due to the high mass core even more… this raises the temperature even higher! </li></ul></ul><ul><ul><li>Burning of Hydrogen in the outer layers causes further expansion. </li></ul></ul>
  19. 20. The Future of our Sun <ul><li>At this point the Sun’s surface will reach out to the Earth’s Orbit! </li></ul><ul><li>10,000 times as luminous as today. </li></ul><ul><li>The sun will start to shed layers… these layers are called planetary nebula. </li></ul>
  20. 21. The Future of our Sun <ul><li>The core will now be exposed. </li></ul><ul><li>The core is called a White Dwarf. </li></ul><ul><ul><li>About the size of the Earth. </li></ul></ul><ul><ul><li>Very hot, very small. </li></ul></ul><ul><ul><li>Not luminous. </li></ul></ul><ul><ul><li>Will eventually cool into a cold, “dead” star called a brown dwarf. </li></ul></ul>
  21. 26. The Future of our Sun <ul><li>Our Sun will eventually make Hydrogen, Helium, Carbon and Oxygen. </li></ul><ul><li>The production of these new elements from Hydrogen is called Nucleosynthesis . </li></ul>
  22. 27. Mass – Luminosity Relationship <ul><li>There is a relationship between the luminosity of a star and its mass </li></ul><ul><li>  L = M 3.5 </li></ul><ul><li>  Where L is luminosity, M is mass in solar units and applies to all main sequence stars </li></ul><ul><li>The power (3.5) can be any value between 3 and 4 as it is itself mass dependant.  </li></ul>
  23. 28. The Chandrasekhar Limit <ul><li>If the initial solar mass of a star is greater than 8 solar masses… then the star will become a… </li></ul><ul><ul><li>Supergiant Star and eventually collapse to a… </li></ul></ul><ul><ul><li>Neutron Star or a Black Hole. </li></ul></ul>
  24. 29. The Chandrasekhar Limit <ul><li>A star greater than 8 solar masses (1 solar mass is the mass of our Sun)… will collapse to a core… </li></ul><ul><ul><li>With a mass of greater than 1.4 Solar Masses. </li></ul></ul><ul><ul><li>A neutron star or a black hole </li></ul></ul><ul><ul><li>If the core is less than 1.4 solar masses the star will become a White Dwarf. </li></ul></ul>
  25. 30. The Chandrasekhar Limit <ul><li>This 1.4 solar mass of the core boundary is called the Chandrasekhar limit. </li></ul><ul><ul><li>Famous Indian astronomer. </li></ul></ul><ul><ul><li>Less than 1.4 solar mass for the core… electron degeneracy prevents further collapse. </li></ul></ul><ul><ul><ul><li>Electrons cannot be packed together any further. </li></ul></ul></ul>
  26. 31. THE OPPENHEIMER-VOLKOFF LIMIT <ul><li>is the equivalent to Chandrasekhar but applies to neutron stars. </li></ul>
  27. 32. The Supergiants <ul><li>Stars with masses greater than 8 solar masses initially will evolve into a Supergiant star… </li></ul><ul><ul><li>Eventually collapse to a core greater than 1.4 solar masses. </li></ul></ul><ul><ul><ul><li>Become a Neutron Star or a Black Hole. </li></ul></ul></ul>
  28. 33. The Supergiants <ul><li>The star will undergo the same process as a Red Giant… </li></ul><ul><ul><li>Fusion of Helium in the inner core. </li></ul></ul><ul><ul><li>Fusion of Hydrogen in the outer layers. </li></ul></ul><ul><ul><li>Expansion. </li></ul></ul><ul><ul><li>Cooling at the surface of the star. </li></ul></ul><ul><ul><li>Subsequent fusion of Oxygen and Carbon in the core. </li></ul></ul>
  29. 34. The Supergiants <ul><li>The difference is that the star is massive enough to continue to… </li></ul><ul><ul><li>Collapse after the Oxygen and Carbon fusion. </li></ul></ul><ul><ul><li>Further gravitational collapse leads to further temperature rises. </li></ul></ul><ul><ul><li>Capable of beginning the fusion of silicon. </li></ul></ul>
  30. 35. The Supergiants
  31. 36. The Supergiants <ul><li>The fusion of silicon makes iron. </li></ul><ul><li>Supergiants are the brightest stars visible due to their enormous size. </li></ul><ul><li>Betelgeuse in the constellation Orion. </li></ul>
  32. 37. The Supergiants <ul><li>Iron cannot undergo fusion due to its very high coulombic repulsion (26 protons). </li></ul><ul><li>It would need astronomical temperatures. </li></ul><ul><li>The star has reached a critical state. </li></ul>
  33. 38. The Supergiants <ul><li>The star will once again begin to collapse into the core. </li></ul><ul><li>But no more fusion will take place to counteract the gravitational collapse. </li></ul><ul><li>Incredibly high temperatures lead to the combining of electrons and protons. </li></ul>
  34. 39. The Supergiants <ul><li>Neutrons and neutrinos are formed in large quantities. </li></ul><ul><li>High energy neutrinos form an outward pressure wave. </li></ul><ul><li>This wave hurtles outward. </li></ul>
  35. 40. The Supergiants <ul><li>This shock wave rips the outer layers off of the star. </li></ul><ul><li>The inner core is now exposed. </li></ul><ul><li>Huge amount of radiation floods into space. </li></ul>
  36. 41. Supernova <ul><li>The star has become a Supernova. </li></ul><ul><li>The luminosity for a brief moment is greater than the whole luminosity of a galaxy (1 billion stars)! </li></ul><ul><li>96% of the stars mass is lost to space. </li></ul>
  37. 42. Supernova <ul><li>The explosion has enough energy to fuse all of the elements with atomic number greater than iron. </li></ul><ul><li>The gas and dust flung into space will form a dark nebula . </li></ul><ul><li>The star cycle is ready to begin again. </li></ul>
  38. 43. Eskimo Nebula <ul><li>NGC 2392, a ring of comet-shaped objects flying away from a dying star.  Eskimo is 5,000 ly from Earth. </li></ul>
  39. 44. Cats Eye Nebula
  40. 51. Neutron Stars <ul><li>The combination of protons and electrons due to the enormous temperatures produce a neutron core. </li></ul><ul><li>A Neutron Star has been formed. </li></ul><ul><li>Very small, radius of less than 30 km! Extremely dense. </li></ul><ul><li>Oppenheimer-Volkoff Limit- upper limit for the mass of a neutron star beyond which it must collapse to become a black hole . Its value is not known exactly because the properties of neutron degenerate matter can only be estimated, but it is generally thought to be about 2 or 3 solar masses. </li></ul>
  41. 53. Mass-Luminosity relation <ul><li>There is a relationship between the luminosity of a star and its mass </li></ul><ul><li>L = M 3.5 </li></ul><ul><li>Where L is luminosity, M is mass in solar units and applies to all main sequence stars </li></ul><ul><li>The power (3.5) can be any value between 3 and 4 as it is itself mass dependant. </li></ul>
  42. 54. Pulsars <ul><li>A Pulsar is a Neutron Star that is rotating very rapidly. </li></ul><ul><li>Can rotate once every 2 seconds! </li></ul><ul><li>Pulsars have a large magnetic field. </li></ul><ul><li>This produces radio waves. </li></ul><ul><li>These radio waves are emitted in bursts as the star rotates. </li></ul>
  43. 56. Quasars <ul><li>Incredibly luminous objects found in our most distant galaxies. </li></ul><ul><li>12 Billion light years away. </li></ul><ul><li>Embryonic galaxies. </li></ul><ul><li>10,000 times brighter than our Milky Way Galaxy. </li></ul><ul><li>Radio wave emission. </li></ul><ul><li>Very large redshifts due to their enormous distance from Earth. </li></ul>
  44. 58. Black Holes <ul><li>Black Hole - a neutron star so dense that… </li></ul><ul><ul><li>Gravitational Forces are enormous. </li></ul></ul><ul><ul><li>Even light cannot escape its gravitational pull. </li></ul></ul><ul><ul><li>We therefore cannot see a Black Hole! </li></ul></ul>
  45. 59. Black Holes <ul><li>Light near a Black Hole will be bent. </li></ul><ul><li>Close to a Black Hole, the light bends back on itself. </li></ul><ul><li>Relativity tells us that time will cease at this point. The Event Horizon. </li></ul><ul><li>More on this in the Relativity Option. </li></ul>
  46. 60. Black Holes <ul><li>Evidence for Black Holes… </li></ul><ul><ul><li>Some stars have their gases being pulled away funnel like into space… </li></ul></ul><ul><ul><ul><li>Being pulled into a “Binary Star” that is a Black Hole. </li></ul></ul></ul>
  47. 61. Cygnus X-1 Black Hole <ul><li>15 times the mass of the Sun in orbit with a massive blue companion star. </li></ul>
  48. 62. Life Cycle Summary <ul><li>From Chandra X-Ray Observatory </li></ul>
  49. 63. Galaxies <ul><li>Our Milky Way Galaxy is a Spiral Galaxy. </li></ul><ul><ul><li>All spiral galaxies have a central bulge, a thin disc and a halo. </li></ul></ul>
  50. 66. Sombrero Galaxy <ul><li>28 million ly from Earth. Officially called M104, it has 800 billion suns and is 50,000 light years across. </li></ul>
  51. 67. Galaxies <ul><li>The central bulge </li></ul><ul><ul><li>Greatest density of stars </li></ul></ul><ul><ul><li>Youngest stars </li></ul></ul>
  52. 68. Halo - Made up of globular clusters. Very old stars. Up to 12 Billion years old.
  53. 69. Galaxies <ul><li>Types of Galaxies … </li></ul><ul><ul><li>Spiral </li></ul></ul><ul><ul><li>Elliptical </li></ul></ul><ul><ul><li>Irregular </li></ul></ul>
  54. 71. Spiral Galaxies <ul><li>Consist of a rotating disk of stars and </li></ul><ul><li>interstellar medium, along with </li></ul><ul><li>a central bulge of generally older stars. </li></ul><ul><li>Extending outward from the bulge are relatively bright arms. </li></ul>
  55. 72. Elliptical Galaxies <ul><li>They range in shape from </li></ul><ul><ul><li>nearly spherical to </li></ul></ul><ul><ul><li>highly flattened ellipsoids and </li></ul></ul><ul><ul><li>in size from hundreds of millions to over one trillion stars. </li></ul></ul><ul><li>In the outer regions, many stars are grouped into globular clusters. </li></ul>
  56. 73. Irregular Galaxies <ul><li>Have no specific structure. </li></ul><ul><li>The Large and Small Magellanic Clouds, the nearest galaxies to us, </li></ul><ul><ul><li>are an example of irregular galaxies. </li></ul></ul>
  57. 74. Galaxies <ul><li>All galaxies must rotate, otherwise they would collapse due to gravitational attraction. </li></ul>
  58. 75. Galactic Clusters <ul><li>A Galactic Cluster is a system of galaxies containing several to a thousands of members. </li></ul><ul><li>They all reside in the same area. </li></ul><ul><li>Clusters can be grouped into Superclusters . </li></ul>
  59. 77. Two Galaxies Colliding <ul><li>114 million ly away are two merging galaxies, NGC 2207 & IC 2163 in the distant Canis Major constellation. </li></ul>
  60. 78. Galactic Motion <ul><li>We learned earlier that most Galaxies are moving away from each other. </li></ul><ul><li>Expansion of the Universe. </li></ul><ul><li>Evidence- Red Shift of stellar spectra. </li></ul><ul><ul><li>Further away… greater the Red Shift. </li></ul></ul>
  61. 79. Galactic Motion <ul><li>A method of determining the recessional speed of a galaxy away from Earth is determined using the equation… </li></ul><ul><li>Where  = the difference between the spectral line from a stationary source and the spectral line from the receding galaxy. </li></ul><ul><li> = spectral line of the stationary source. </li></ul>
  62. 80. Example <ul><li>A characteristic absorption line often seen in stars is due to ionized helium. It occurs at 468.6 nm. If the spectrum of a star has this line at a measured wavelength of 499.3 nm, what is the recession speed of the star? </li></ul>
  63. 81. Solution
  64. 82. Hubble’s Red Shift Law <ul><li>We have just seen how we can determine a galaxies recessional velocity from its Redshift. </li></ul><ul><li>We can also determine the galaxies distance. </li></ul>
  65. 83. Hubble’s Red Shift Law <ul><li>Hubble discovered a relationship between a galaxies distance and its recessional velocity. </li></ul>
  66. 84. Hubble’s Red Shift Law <ul><li>Distant galaxies were receeding very fast. </li></ul><ul><li>This fits with the expanding Universe Theory. </li></ul>
  67. 85. Hubble’s Red Shift Law <ul><li>v ≈ d </li></ul><ul><li>v = H d </li></ul><ul><li>Where H is </li></ul><ul><li>Hubbles </li></ul><ul><li> Constant </li></ul><ul><li>It is the </li></ul><ul><li>slope of the graph. </li></ul>
  68. 86. Hubble’s Red Shift Law <ul><li>Hubble’s Constant is estimated to be around 65 km s -1 Mpc -1 </li></ul><ul><ul><li>Much debate on the accuracy of this value. </li></ul></ul><ul><li>Try this Raisin Bread analogy animation </li></ul>
  69. 87. The Big Bang <ul><li>You are required to know the basic theory behind the stages of development of the Universe. </li></ul><ul><li>Detailed accounts are not necessary. </li></ul><ul><li>Just a general explanation. </li></ul>
  70. 88. The Big Bang <ul><li>At the start, the Universe would have been very hot. </li></ul><ul><li>As it expanded, the Universe cooled to a temperature where atoms could be formed. </li></ul>