The Hourglass Nebula:
A BIPOLAR WIND BLOWN BUBBLE
Nature makes extraordinary sculpture.  This is an image of MyCN18 also known as the hourglass nebula.  The amazing shape you see is actually a gravestone marking the death of sun-like star more than 1000 light years away. The two ends or lobes of the glowing hourglass  shown in this Hubble Space Telescope image are formed from of gas ejected by the star at the center more than 5,000 years ago.   As it the star ages it drives a sequence of powerful winds into space.  The older the star gets the faster the wind becomes.  For reasons astronomers still do not understand the star may eject an intial slow moving wind in a disk-like shape. The fast winds which come later overtake the slowly expanding disk. The disk is so dense that fast wind is almost halted. It can, however, escape in the directions above and below the disk. By squezzing the wind along the equator the disk makes the bubble which develops become elongated in the bright hourglass shaped shell  you see in this picture. There are other examples of bipolar wind blown bubbles around dying stars. Click on the images below to see some more.