Long story short, if you put too much fissionable material in one place, you’re asking for trouble. If it gets to that critical point and the chain reaction starts, it’s going to release a ton ...

The payoff in nuclear energy comes when a mass of fissionable material “goes critical,” i.e., when it begins to support a nuclear chain reaction. In the early days of the Los Alamos atom-bomb ...

Many stars are variable. The "novae" flash into sudden brilliance and then fade back to dimness. Others wax & wane regularly every few days. In a letter to Britain's Nature ...