The dark ridge running across the middle is the surface of a molecular cloud that’s being taken apart from above. A few million years ago the first stars in the Ara OB1 association switched on right at that boundary, and their ultraviolet light and stellar winds have been eroding the gas ever since, carving the ridges and hollows you see along the edge. The name comes from the shape: with a bit of imagination, two dragon heads face each other along that rim. Around 4,000 light-years away in Ara, far enough south that it never rises for most observers in Europe or North America.
