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

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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? - PowerPoint PPT Presentation

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

  • Ian Howarthhttp://www.star.ucl.ac.uk/~idh/UCL Science CentreScience Lectures for Schools 2010 Nov 26

  • The Hertzsprung-Russell Diagram: Stars Struggle Against GravityThe Hertzsprung-Russell Diagram: Stars Struggle Against Gravity

  • Whats 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

  • RCW 86: remnant of Guest Star from 185SN 1006: brightest star ever seen1054, Crab Nebula

  • Tychos Star(1572)De nova [et nullius aevi memoria prius visa] stella

  • Keplers Star (1604)

  • SN 1885 in M31

  • Fritz Zwicky (1898-1974)(coined Supernova)

  • SN 1937ANGC 4157

  • Tom Boles

  • M51

  • ~1x107KNuclear burning: HHe

  • ~3x107K

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

  • Then what...? Gravitys victory!

  • Lifetimes (yrs)Burning StageSun9M25MH burning10102x1077x106He burning1082x1067x105C burning380160Ne burning1.11.0Si burning0.0040.003

  • Collapse!!

    Timescale ~1s

    Velocities ~1/4 c

    Cooling by photo-disintegration+56Fe134He+4nand electron capturep++e-n+e

    Most energy comes out in neutrinos

    Shock wave propagates out over a day or so observed SN

  • SN 1987A (Feb 23)

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

  • 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 thanoxygen (and quite a lot of the lighter ones): we are stardusthttp://www.star.ucl.ac.uk/~idh/