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Ian Howarth star.ucl.ac.uk/~idh/

UCL Science Centre ‘Science Lectures for Schools’ 2010 Nov 26. Ian Howarth http://www.star.ucl.ac.uk/~idh/. The Hertzsprung-Russell Diagram: Stars Struggle Against Gravity. The Hertzsprung-Russell Diagram: Stars Struggle Against Gravity. What’s this got to do with supernovae?

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Ian Howarth star.ucl.ac.uk/~idh/

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  1. UCL Science Centre ‘Science Lectures for Schools’ 2010 Nov 26 Ian Howarth http://www.star.ucl.ac.uk/~idh/

  2. The Hertzsprung-Russell Diagram: Stars Struggle Against Gravity The Hertzsprung-Russell Diagram: Stars Struggle Against Gravity

  3. What’s this got to do with supernovae? Normal stars are in a state of equilibrium between gas pressure pushing outwards and gravity pulling inwards (just like our atmosphere). However, to maintain the gas pressure we need a heat source. When that source is exhausted, gas pressure is removed, and the star will collapse. A big star will undergo a big collapse: a supernova SN 1994D in NGC 4526

  4. RCW 86: remnant of “Guest Star” from 185 1054, Crab Nebula SN 1006: brightest star ever seen

  5. “Tycho’s Star” (1572) De nova [et nullius aevi memoria prius visa] stella

  6. Kepler’s Star (1604)

  7. SN 1885 in M31

  8. Fritz Zwicky (1898-1974) (coined Supernova)

  9. SN 1937A NGC 4157

  10. Tom Boles

  11. M51

  12. Nuclear ‘burning’: HHe ~1x107K

  13. ~3x107K

  14. Helium burning: ~108K The continuing struggle against gravity... Carbon burning: ~109K

  15. Then what...? Gravity’s victory!

  16. Collapse!! Timescale ~1s Velocities ~1/4 c Cooling by photo- disintegration γ+56Fe↔134He+4n and electron capture p++e-→n+νe Most energy comes out in neutrinos Shock wave propagates out over a day or so  observed SN

  17. SN 1987A (Feb 23)

  18. 25 neutrinos = all extragalactic neutrino astronomy...confirms core-collapse model (and limits neutrino mass)

  19. To recap: Stellar evolution is the struggle of pressure against gravity. Gravity always defeats gas pressure, eventually For solar-type stars, the last defence is electron degeneracy pressure (the sun will end its life as a white dwarf). For more massive stars, the final fate is a neutron star, or a black hole, formed in a supernova explosion On the way, massive stars make pretty much all the elements heavier than oxygen (and quite a lot of the lighter ones): “we are stardust” http://www.star.ucl.ac.uk/~idh/

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