http://news.yahoo.com/s/space/20051205/sc_space/newanimationhubblespotscosmictrafficjam
Superheated gas called plasma, spewing from a newborn star, travels in clumps that move at different speeds. Fast-moving, recently ejected clumps sometimes catch up with slower batches that had been sent out previously.
The resulting traffic jams create massive shock waves that travel trillions of miles across the cosmos.