QUESTION:
Where did the carbon soot, sand and dust particles come from?

ANSWER from Scott Sandford on May 16:
The dust and ice in interstellar clouds comes from a variety of sources.
The soot-like particles and PAHs probably come from carbon stars.  Carbon
stars are stars that are approaching the ends of their lives and are losing
a lot of their mass in 'winds' that blow a lot of carbon into space.

Similarly, the silicates mostly come from old stars that are losing Si and O.
Some dust grains are also ejected into space when stars blow up as novae or
supernovae.  When these dust grains concentrate into an interstellar cloud,
they begin to block out star light and the temperature of the dust in the
cloud drops to very low temperatures.  Gas molecules that hit a dust grain
at these temperatures will stick and form ices, just as the water vapor in
your breath condenses on a cold window when you breathe on it.

Finally, some of the organic materials in the dust are formed when the ices
in the interstellar clouds are irradiated with ultraviolet light and cosmic
rays.  This radiation causes chemistry to occur which produces a complex
mixture of new, carbon-rich molecules.