Originally discovered by Australian scientists Michael Burton and David Allen, the bullets are huge masses of molecular hydrogen tipped with iron atoms.
How big is 'huge'? Roughly ten times the size of Pluto's orbit. Harvesting just one would meet our iron needs forever, according to Burton. Apart from the size of the bullets, the fact that they are 1500 light years away presents certain problems.
The nebula is a mass of hydrogen and the bullets travel at up to 400 kilometres (250 miles) per second. The resulting impacts generate heat, causing the bullets to glow brightly and leave wakes of excited hydrogen that are clearly visible in infrared images.
Astronomers at the Gemini Observatory in Hawaii obtained impressively sharp images of the structures thanks to adaptive optics. Adaptive optics uses a deformable mirror to correct for distortions caused by the Earth's atmosphere.
Sodium ions in the upper atmosphere glow when stimulated with a laser, and their twinkling provides a reference source for the real-time adjustment of the telescope's adaptive optics.