ASTRON 1F03 Lecture Notes - Lecture 19: Degenerate Matter, Photodisintegration, Sn 1987A
18 Dec 2015
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The total number of protons and neutrons always stays the same in nuclear reactions. Iron weighs less than any other combination of protons and neutrons. Fusion or iron or more massive elements require energy. Once the star has an iron core, any further reaction uses up energy! The core collapses: at these high densities, neutrinos repel (strong nuclear force and neutron degeneracy pressure). Shock waves take a mere few hours to rip through the star. Core steps, energy of collapse drives a shock wave through star. Outer layers blow off in tremendous explosion (type ii supernova), leaving core. Light energy emitted is that of billions of suns! 100x: 1044 joules, comparable to entire lifetime output of sun. Neutrinos carry off energy of 100 times larger still! (1046 joules) (we detected 13 neutrinos from sn1987a at sno! **massive stars create enormous core temperatures as red supergiants, fusing helium into carbon, oxygen, and even heavier elements.
