Messier 17: Omega Nebula
Messier 17, the Omega Nebula or Swan Nebula, is a star forming region located about 5,500 light years away towards the constellation Sagittarius. It is one of the most active regions of star formation in the Milky Way, and its fascinating shapes are created by the young, hot stars it contains.
These stars carve away at surrounding dust and gas, stripping away some material and shaping the rest. The ultraviolet radiation also ionizes hydrogen gas. In this process, radiation energizes electrons, stripping them from their nuclei. The electrons recombine into atoms, and release a photon of light, creating the characteristic red glow.
Image from National Geographic, information from HubbleSite.