8. Supernovae

Neutron stars are formed by stars with masses greater than eight times the mass of our sun. In these stars there is enough fuel to produce larger quantities of carbon and oxygen. If the carbon and oxygen core has a mass greater than 1.4 times the mass of our Sun, the gravitational forces are strong enough to collapse the core beyond the white dwarf stage. The carbon and oxygen will fuse to produce neon, sodium and magnesium.

All of these fusion processes have emitted energy to keep the star burning. But the silicon and sulphur in the core produce iron when they fuse together. Iron is the most stable form of nuclear matter, and the fusion of iron does not emit energy. In fact, iron requires energy for fusion to take place. The result is that fusion stops at the very centre of the star.

With no radiation from the core, the outer layers of the star begin to collapse in towards the centre, drawn by a gravitational attraction. The iron core is pushed together so tightly that nuclei of iron begin to touch, before emitting an immense shockwave.

This shockwave of very high energy particles spreads outwards through the star and holds enough energy to fuse elements together into isotopes of every imaginable element, including very heavy substances like uranium. The shockwave also spreads inwards through the core with enough energy to convert the protons and electrons of the iron into neutrons. The explosion is so powerful that the supernova will outshine the rest of the galaxy for a month.

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