Just like regular clouds here on Earth, it's easy to see shapes in the interstellar clouds of dust and gas that make up nebulae. But this waterfall-shaped nebula is particularly spectacular... and nobody quite knows why it looks like that.

Located in the Great Orion Molecular Cloud Complex, nebula HH-222 is considered one of the most mysterious objects in known galaxy. A NASA astronomer explains why:

The elongated gaseous stream stretches about ten light years and emits an unusual array of colors. One hypothesis is that the gas filament results from the wind from a young star impacting a nearby molecular cloud. That would not explain, however, why the Waterfall and fainter streams all appear to converge on a bright but unusual non thermal radio source located toward the upper left of the curving structure.

Another hypothesis is that the unusual radio source originates from a binary system containing a hot white dwarf, neutron star, or black hole, and that the Waterfall is just a jet from this energetic system. Such systems, though, are typically strong X-rays emitters, and no X-rays have been detected. For now, this case remains unsolved. Perhaps well-chosen future observations and clever deductive reasoning will unlock the true origin of this enigmatic wisp in the future.

Via NASA.