What is PSR J1748–2446’s claim to weirdness fame? Simple. It’s the universe’s fastest-spinning celestial object. It’s also a star whose surface is not just solid, but harder than a diamond. Its density is 50 trillion times greater than lead. Its magnetic field sizzles a trillion times more intensely than our Sun’s. In a nutshell, it’s the most extreme example of a neutron star.

A neutron star forms when the core of a heavy sun, with the mass of about a few million Earths, collapses into a tiny sphere while the rest of its body hurtles outward during a supernova explosion. When this occurs, the inverse-square law of gravity goes into its demo-mode with a vengeance. Because this star no longer has a fusion generator, and thus no outward-pushing pressure to keep it from collapsing, gravity has a free hand. When the collapsing star gets five times smaller, its inward-pulling surface gravity becomes 25 times fiercer. When the star shrinks to 100 times smaller than it was before, its surface gravity now sucks inward with 100 x 100 (i.e., 10,000) times more force — and it keeps going. The smaller the star becomes, the more violent its collapse.

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Normal 1-solar-mass stars stop collapsing when they’re the size of Earth. Then, electron degeneracy pressure halts the show because each electron needs a bit of breathing room. But if a star’s mass is more than 1.4 Suns — the famous Chandrasekhar limit — as PSR J1748–2446 originally was, then electrons get squeezed into the protons and the collapse continues. At this point, the previously separate atomic particles lose their identities. Everything becomes a neutral ocean of ultra-dense goo, and a few million Earths now pack into a ball less than 20 miles (30 kilometers) wide — a star that could barely cover Los Angeles.