The “ Nessie ” Nebula is a filamentary infrared dark cloud ( IRDC ) with a large aspect ratio of over 150:1 ( 1.5 ^ { \circ } \times 0.01 ^ { \circ } , or 80 pc \times 0.5 pc at a kinematic distance of 3.1 kpc ) .
Maps of HNC ( 1–0 ) emission , a tracer of dense molecular gas , made with the Australia Telescope National Facility Mopra telescope , show an excellent morphological match to the mid-IR extinction .
Moreover , because the molecular line emission from the entire nebula has the same radial velocity to within \pm 3.4 km s ^ { -1 } , the nebula is a single , coherent cloud and not the chance alignment of multiple unrelated clouds along the line of sight .

The Nessie Nebula contains a number of compact , dense molecular cores which have a characteristic projected spacing of \sim 4.5 pc along the filament .
The theory of gravitationally bound gaseous cylinders predicts the existence of such cores , which , due to the “ sausage ” or “ varicose ” fluid instability , fragment from the cylinder at a characteristic length scale .
If turbulent pressure dominates over thermal pressure in Nessie , then the observed core spacing matches theoretical predictions .
We speculate that the formation of high-mass stars and massive star clusters arises from the fragmentation of filamentary IRDCs caused by the “ sausage ” fluid instability that leads to the formation of massive , dense molecular cores .
The filamentary molecular gas clouds often found near high-mass star-forming regions ( e.g. , Orion , NGC 6334 , etc . )
may represent a later stage of IRDC evolution .