Dimethylmercury ((CH3)2Hg) is an organomercury compound. This colorless liquid is one of the strongest known neurotoxins. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous.
The formation of a star begins with gravitational instability within a molecular cloud, caused by regions of higher density-often triggered by shock-waves from nearby supernovae (massive stellar explosions), the collision of different molecular clouds, or the collision of galaxies (as in a starburst galaxy).
A promising way of getting this process going is the traveling compression wave, or density wave, which astronomers believe is responsible for the Galaxy's spiral arm structure (Figure 20.14). As the wave moves past a cool molecular cloud, it compresses the cloud, driving the particles closer together.