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/