An extremely dense stellar remnant composed almost entirely of neutrons, formed when a massive star's core collapses during a supernova explosion. These objects pack more mass than the Sun into a sphere only about 20 kilometers across.
The concept was first proposed in 1934 by Walter Baade and Fritz Zwicky, shortly after the neutron's discovery in 1932. The name directly describes the star's composition - it's essentially a giant atomic nucleus made almost entirely of neutrons.
Neutron stars are the densest objects in the universe besides black holes - they're so dense that all of humanity could fit into a volume the size of a sugar cube! Their magnetic fields are trillions of times stronger than Earth's, and they can spin up to 700 times per second.
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