I was planning on putting up an unadorned link to this spectacular view of iron projectiles piecing through a nebula from Scientific American (photo by Gemini). But the Astronomy Picture of the Day stole my thunder so now I'm going to use their explanation and then add an insightful complaint about something completely different in the post below this one.
Why are bullets of gas shooting out of the Orion Nebula? Nobody is yet sure. First discovered in 1983, each bullet is actually about the size of our Solar System, and moving at about 400 km/sec from a central source dubbed IRc2. The age of the bullets, which can be found from their speed and distance from IRc2, is very young -- typically less than 1,000 years. As the bullets rip through the interior of the Orion Nebula, a small percentage of iron gas causes the tip of each bullet to glow blue, while each bullet leaves a tubular pillar that glows by the light of heated hydrogen gas.