English: Diagram of the Southern Crab Nebula Structure This diagram traces the hourglass structure formed by a pair of huge, bipolar gas bubbles ejected by a double star in the center of the Southern Crab Nebula. The gases are dispersed too thinly for the full shape of the hourglass to be photographed. Instead, the bubbles appear brightest at the edges, giving the illusion of crab leg structures. The stars are likely embedded inside a disk of material that constricts and directs the outflow of gas from the system. This disk apparently also launched twin jets of material that form knots far outside the system as they slam into interstellar material.