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Stars

Stars . Life cycle of star http://www.youtube.com/watch?v=H8Jz6FU5D1A. http://aspire.cosmic-ray.org/labs/star_life/starlife_proto.html. 1. Nebula = cold, dark cloud of dust and gas [mostly H]. gravity pulls particles, to clump together. Accretion: accumulating more mass.

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Stars

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  1. Stars

  2. Life cycle of starhttp://www.youtube.com/watch?v=H8Jz6FU5D1A

  3. http://aspire.cosmic-ray.org/labs/star_life/starlife_proto.htmlhttp://aspire.cosmic-ray.org/labs/star_life/starlife_proto.html

  4. 1. Nebula = cold, dark cloud of dust and gas [mostly H]

  5. gravity pulls particles, to clump together

  6. Accretion: accumulating more mass

  7. Clumps increase in size [accretion]pressure and temperature increases [due to KE of particles]

  8. 2. Protostarwhen forces are in equilibrium : gravity collapses particles together, high temperature/pressure pushes particles apart.At equilibrium Gas pressure = gravity

  9. If protostar too small, becomes brown dwarf, never a real star.

  10. 4. STAR If enough mass, critical temperature protostar core begins to fuse H into He :star is born.

  11. The star is stable while the gravitation pulling the star together is balancedby the internal pressure pushing it apart.

  12. During lifetime, stars fuse Hydrogen into Helium and then fuse helium into Carbon.

  13. Massive stars can fuse carbon into heavier elements.

  14. 3. Main sequence

  15. 90% of stars spend majority of life on the Main Sequence

  16. On the main sequence, hydrogen is fused into helium H is fused into He..

  17. Main sequence is a grouping of stars by size, color, luminosity

  18. We compare other stars to the brightness [luminosity ] of the Sun:

  19. Temperature determines the color of a star

  20. Mass-luminosity relationship for Main Sequence StarsL = Lo[M/Mo]3.5Lo = luminosity of SunMo = mass of Sun

  21. The Herzsprung-Russell Diagram H-R diagramshows relationship of luminosity, temperature, size

  22. [ H-R diagram]

  23. Note the scales are log scales, not linear.

  24. Mo is the mass of the SunLow mass stars: 0.5Momedium mass stars: 0.5Mo – 3Momassive stars: >3 Mo

  25. Larger, hotter stars burn out very fast - in a few million years.Smaller, cooler stars burn slowly for billions of years

  26. The Sun is a medium yellow star.The surface temperature is about 6000KThe Sun has a life expectancy of about 10 billion years

  27. Try the interactive star lab: http://aspire.cosmic-ray.org/labs/star_life/starlife_sequence.html

  28. Wh

  29. After becoming red giantlow mass stars [mass of Sun] shrink into white dwarfs.Radius is close to radius of Earth.

  30. Medium mass stars [ 1.4 to 3 Mo] expand into Red Giants , collapse and then explode into a supernova

  31. Finally becomes a neutron star [about the size of Manhattan]

  32. Massive stars collapse and begin to fuse carbon.They explode as supernova and the core is crushed into a black hole .

  33. After all H is fused, star leaves the main sequence.

  34. Pressure increases, stars expand enormously and cool.

  35. Small stars expands and sheds outer layers

  36. Medium stars expand into red giants

  37. After about 100,000 years the protostar has drawn in enough dust and gas to become a star.

  38. When core temperature reaches 10 million degrees, H begins to fuse into He, releasing energy [heat]

  39. Most stars are Main Sequence Stars

  40. When core H has all fused to He,

  41. About 1 million Earth’s fit in the Sun

  42. http://www.youtube.com/watch?v=g4iD-9GSW-0

  43. Sun compared to largest star

  44. http://www.youtube.com/watch?v=Bcz4vGvoxQA

  45. HR diagramshttp://www.youtube.com/watch?v=Kqe6F-Qf9Tk

  46. Black hole swallows a starhttp://www.youtube.com/watch?v=O3Z5AS3TTS4

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