At this point, without energy from fusion to hold it back, gravity quickly smashes the iron core. Gravity is so much stronger in the core of a massive star than inside the sun, that even electron pressure is not enough to stop the collapse. The force of gravity is so great that electrons are essentially shoved inside protons, creating a solid ball of neutrons about 15 kilometers across. Imagine, if you can, a mass equal to our sun's, squeezed into a ball the size of Manhattan!
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