Neutron stars are the densest objects in the universe outside of black holes, packing more than a Sun’s worth of mass into a ball just 20 kilometers wide. But here’s what’s crazy: they’re also among the roundest objects ever measured. Scientists calculated that the tallest “mountains” on a neutron star are just a few millimeters high. That’s because their intense gravity flattens everything into near-perfect spheres. So while Earth has Everest, neutron stars have… tiny, sub-millimeter bumps. For something that can spin 700 times a second and crush atoms into neutrons, it’s surprisingly smooth.
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