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Main Sequence Lifetimes

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  1. Main Sequence Lifetimes • Time on Main Sequence • How much fuel it has (Core H) • How fast it consumes the fuel (Luminosity)

  2. Main Sequence Lifetimes

  3. Main Sequence Lifetimes • Our Sun M = 1 M() and L = 1 L() • tMS-lifetime = 1010 years = 10 billion years • Large Mass Bright Star M = 10 M() and L = 105 L () • tMS-lifetime = 1010 • tMS-lifetime = 106 years = 1 Million years

  4. Nuclear Fusion and Forces of Repulsion • For Hydrogen repulsion of 2 (1+) charges • At 1 Atomic radius Frepulsion= 2.3 x 10-8 N • For Helium repulsion of 2 (2+) charges • At 1 Atomic radius Frepulsion= 9.2 x 10-8 N • Ratio of forces 9.2/2.3~4x • For Hydrogen, we had 2 pairs of H fused to make 1 Helium. • For Helium, we need 3 pairs of He to fuse to make 1 Carbon  so ratio 3/2(4) = 6x  6x as much force

  5. Nuclear Fusion • Hydrogen Fusion requires temps ~ 7 Million K • Helium Fusion requires temps ~ 100 Million K • A bit more than 6x (~14x) • Energy from Helium fusion ~0.1 Energy released in Hydrogen fusion • All stars > 0.5 M() can create Helium burning Temps of 100 million K

  6. Nuclear Fusion • High Mass Stars create 100 Million K by contracting Core a little. • Low Mass Stars create 100 Million K by contracting Core a lot! • If a Low Mass Star contracts Core a lot, Core can become Degenerate!!

  7. Degenerate States of Matter • Normal Matter only one atom may exist in a particular energy state. This causes atoms to have some spatial separation. • Degenerate Matter many atoms may exist in the same energy state. This causes atoms to become quite close together.

  8. Degenerate Matter • Super-Fluids • Super-Conductors • Bose-Einstein Condensates

  9. Super-Fluid http://london.ucdavis.edu/~zieve/Research/creep.jpg

  10. Super-Conductor http://sci-toys.com/scitoys/scitoys/magnets/levitation_closeup.jpg

  11. Bose-Einstein Condensates http://math.nist.gov/mcsd/savg/vis/bec/3D.00007.jpg

  12. Bose-Einstein Condensates • http://science.nasa.gov/headlines/y2002/images/neutronstars/magnetar_huge.jpg

  13. Degenerate Core of a Star • Gas atoms so close act like Solid! • Heat a Gas, Changes in Both Volume and Pressure • Heat a Solid, Small Changes in both Volume and Pressure.

  14. High Mass Star (Normal Gas Core) • Fusion releases Energy  Heats Gas • Heated Gas  Gas Expands due to increase Pressure • Expanded Gas  Cools Gas • Cooling Gas decreases Nuclear Fusion rate • Decreased Nuclear Fusion Rate  Pressure drops • Gas Contracts  Increased Temps  Increased Fusion • Gas properties regulate Nuclear Fusion

  15. Low Mass Star (Degenerate Core) • Fusion releases Energy  Heats Gas (Solid) • Heated Solid  No Increase in Pressure • No Increase in Pressure  No Expansion • No Expansion  No Cooling • Increased Temperatures  Increased Nuclear Rate • Increase Nuclear Rate  Increased Release of Energy • Increased Temps etc…… • No Regulation of Nuclear Fusion  Helium Flash!!

  16. Helium Flash • Explosive release of energy • Usually restores Degenerate Core back to normal Core • Helium Flash Ends First Red Giant Phase of Low Mass Stars and start Yellow Giant Phase • High Mass Stars do not have a helium flash • High Mass Stars go originally to Yellow Giant Phase and then expand into Red Giants • Onset of Helium Burning often cause stars to become unstable (Variable Stars)

  17. Lagrange Points http://www.jwst.nasa.gov/orbit.html

  18. Mass Mystery??? • Both stars in a binary form about same time • More massive stars evolve faster • Red Giant star (on left) is less massive than Main Sequence star (on right) • Solution Mass Transfer!!!

  19. More Massive Star is Dimmer?? • Β Lyrae • More Massive Star is Dimmer • Solution – Accretian Disk blocks some of light!!

  20. Stellar Evolution in a Globular Cluster In the old globular cluster M55, stars with masses less than about 0.8 M are still on the main sequence, converting hydrogen into helium in their cores. Slightly more massive stars have consumed their core hydrogen and are ascending the red-giant branch; even more massive stars have begun helium core fusion and are found on the horizontal branch. The most massive stars (which still have less than 4 M ) have consumed all the helium in their cores and are ascending the asymptotic giant branch.

  21. Dredges • 1rst – After Core H ceases • Relative abundance of Carbon, Nitrogen and Oxygen changed at surface • 2nd – After Core He ceases • Again Relative abundance of C, N, and O changed • 3rd – After during AGB (if M > 2 M() ) • Prominent Carbon compounds. C2, CH, CN • Strong C absorption lines in spectra • Carbon Star!!

  22. TT Cygni is an AGB star in the constellation Cygnus that ejects some of its carbon-rich outer layers into space. Some of the ejected carbon combines with oxygen to form molecules of carbon monoxide (CO), whose emissions can be detected with a radio telescope. This radio image shows the CO emissions from a shell of material that TT Cygni ejected some 7000 years ago. Over that time, the shell has expanded to a diameter of about ½ light-year.

  23. Later Stage of Low Mass Stars • Helium Shell burning decreases as its fuel is used up • Dormant Helium Shell provides insufficient pressure to support Dormant Hydrogen Shell • Hydrogen Shell contracts, Heats up, Re-ignites! • Helium produced in Hydrogen Shell adds to Helium Shell Fuel • Hydrogen Burning re-heats Helium Shell, Small Helium Flash!! • Helium Shell Burning Pushes Star out again • Outer layers detach!! Planetary Nebula!!

  24. Planetary Nebulae • Thermal Pulses happen in increasingly shorter intervals over time • 1 M() loses about 40% of its mass this way • As outer layers are ejected, hot core exposed • Core Temp ~ 100,000 K emits UV radiation • Radiation ionizes gas creating Fluorescence glows • Radiation also propels gas outward in increasingly larger rings • Non-symmetric radiation creates hour-glass shapes

  25. 1980’s • Two “Neutrino Telescopes” went into operation • Kamiokande (U-Tokyo and U-Penn) detector in a zinc mine in Japan • IMB (U-Cal at Irvine, U-Michigan, and Brookhaven) detector in a salt mine in Ohio • Neutrinos interacts with a proton in the water creating a supersonic positron • Positron moves faster than the speed of light in water creating a shockwave effect known as Cerenkov radiation

  26. http://ncas.sawco.com/condon/text/s6c06f1b.htm

  27. http://www.pbs.org/wgbh/nova/barrier/boom/images/cone.jpeg

  28. http://www.sonicbooms.org/T38/T38c3.jpg

  29. http://www.simulationinformation.com/sonic%20boom.jpg

  30. http://www.anomalies-unlimited.com/Odd%20Pics3/Images/shuttlesonic.jpghttp://www.anomalies-unlimited.com/Odd%20Pics3/Images/shuttlesonic.jpg

  31. http://www.physlink.com/Education/AskExperts/ae219.cfm

  32. http://dept.physics.upenn.edu/balloon/cerenkov_radiation.htmlhttp://dept.physics.upenn.edu/balloon/cerenkov_radiation.html

  33. http://www.physlink.com/Education/AskExperts/ae219.cfm

  34. Solar Neutrinos Vs Supernova Neutrinos?? • Energy • Solar Neutrinos ~<1 MeV • Supernova Neutrinos ~>20 MeV • Measuring Properties of Cerenkov radiation, the speed of the e+ which created the radiation can be found • Speed of e+ gives originally energy of neutrino which collided with proton that created the e+

  35. February 23, 1987 • 12 second burst of neutrinos detected • Kamiokande detected 11 Neutrinos • IMB detected 8 Neutrinos • The Earth was subjected to a neutrino flux of approximately 1016 neutrinos • Supernova emitted 1058 neutrinos in about 10 seconds 160,000 years ago • Approximately 100x the Energy the Sun has emitted in its entire lifetime!! • About 100x the amount of light energy the Supernova emitted • Approximately 10x the total luminosity of the stars in the entire observable universe at the moment

  36. February 23, 1987 • 3 hours later Light arrived from Supernova 1987 ???? • Neutrinos not blocked by gas layers of the star • Light created only after shockwave reached the outer-most layers of the star

  37. Why was SN 1987A Unusual? • Peak Intensity about 0.1 of intensity of other observed Supernovas • Confusion over whether progenitor star was a Red Supergiant or a B3 I Blue Supergiant? • Pop I or Pop II star? • Possible Pop II meaning it oscillated between Red and Blue Supergiant.

  38. Supernova 1987A • In Blue Supergiant phase, radius is about .1 of size than when in Red Supergiant phase • When explosion occurred more mass closer to core, more energy needed to push outer layers away, less available for creating brighter light • Type II Supernova *****

  39. Types of Supernovas • Type II do have prominent Hydrogen Lines • Type I do not have prominent Hydrogen Lines in their spectra • Type I further subdivided into • Type Ia which has strong absorption lines of Si • Type Ib which does not have Si but does have absorption lines of He • Type Ic which has neither

  40. http://csep10.phys.utk.edu/guidry/violence/sn87a-rings.html *****

  41. http://apod.nasa.gov/apod/image/0402/sn1987a_acsHubble_full.jpghttp://apod.nasa.gov/apod/image/0402/sn1987a_acsHubble_full.jpg *****

  42. http://physics.uoregon.edu/~courses/BrauImages/Chap21/FG21_08A.jpghttp://physics.uoregon.edu/~courses/BrauImages/Chap21/FG21_08A.jpg

  43. Type II, Ib, Ic are found near sites of new star formation. • Type Ia found in galaxies where there are no ongoing star formations

  44. Supernova leftovers • Remnants • Gasses and elements • Core Relics • Neutron Stars • Black Holes

  45. Why More Supernovas in other Galaxies?? • Ought to see about 5 per century based on what we see in other galaxies (~100 remnants seen with radio in other galaxies) • Last Supernova in our Galaxy 1604 – Kepler • 1572 Brahe • 1054 China • Interstellar dust blocks best star forming regions from our view

  46. Neutrons form : • Supernova’s Create many reactions • Neutrons first discovered in 1932 Chadwick • Zwicky (Caltech) and Baade (Mt. Wilson Obs) Proposed parallel to White Dwarf, Neutron Star • White Dwarf uses Degenerate e- pressure to sustain outer layers weight • Neutron Star uses Degenerate n pressure • Neutrons can with stand more force, hence 1.4 M() limit no longer applies

  47. Improbabilities for a Neutron Star • Thimbleful would weigh 100 million tons Density 1017 kg/m3 • Recall 1 teaspoon of White Dwarf weighs ~ 5.5 tons!! Density 109 kg/m3  1 M() White Dwarf would have a diameter of 10,000 – 12,000 km, Size of Earth!!  1 M() Neutron Star would have a diameter of 30 km (19 miles), Size of large city!!

  48. http://www.astro.umd.edu/~miller/nstar.html

  49. 1960’s Cambridge England • 1967 Anthony Hewish’s Research Group from Cambridge University finish 4 ½ acre radio telescope array • Jocelyn Bell, Graduate Student, discovers regular pulses of radio noise from one location in the sky. • Period of Pulses was 1.3373011 seconds