Wind-Blown Bubbles

As a star like the sun dies is drives a sequence of powerful winds into space. First the winds are relatively slow but very dense. Just before the star dies the wind becomes very fast. As the fast wind expands it sweeps the slow wind into a shell of gas that looks like a giant ``bubble''. For reasons no one yet understands, the slow wind sometimes takes on a dougnut shape with more gas in the equator than at the poles. The fast wind can't push through the walls of the dougnut but it can escape escape through from the holes (above and below the star). In this way, dense doughnut-shaped slow winds can lead to non-spherical bubbles. Sometimes these bubbles look like an hourglasses or figure-8.