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Most matter is empty space. In atoms, a cloud of electrons orbit the nucleus. In neutron stars, they're stomped into it, negative electrons physically crushed into the positive protons to create an endless mass of neutral neutrons. No space, no charge, no elements, chemistry itself crushed out of existence by all-dominating physics.

The resulting neutronium is 40 trillion times denser than lead. If you stood with a spoonful of neutronium, it would fall through the spoon, cut a hole in your foot, and punch through the Earth until it shot through the core and out the other side. Then it would turn around and do it again, and again, and again and again, until it got thermodynamically bored (aka slowed down and stopped by friction). It's a material so solid that merely trying to weigh it shoots your home planet through the heart multiple times. It's as dense as anything can get without giving up on matter entirely and becoming a black hole.

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Black holes: The full stop at the end of everything.

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So we have white dwarfs, the densest thing you can get without breaking atoms, and neutron stars, the densest thing you can get without breaking the existence of matter, and PSR J0348+0432 has both. A binary system built out of the two densest anythings, ever, orbiting each other every two and a half hours. A system twice the mass of the sun whipping around in less time than it takes to watch The Hobbit. That's not an orbit, that's how you blend space-time. Large masses can bend space, but these are rippling it, jumping up and down on the fabric of reality so hard that they're sending out waves of existence-deformation.