Jonathan A. Rebouças

Spacetime is like a giant sheet of paper. Fold it, and distant corners come together. Poke a pencil through, and you get a wormhole, a short tunnel through the folds. But the paper wants to spring back flat, snapping the passage shut. To keep it open, you need a rare “gasket”—matter with negative energy.

Wormholes — tunnels through curved spacetime, allowed by general relativity. To be stable, they need repulsive energy — the kind that pushes apart rather than attracts.

A white dwarf is the cooling core of a Sun-like star. Its fate hinges on mass: there's a strict Chandrasekhar limit (about 1.4 solar masses) beyond which the star collapses further.