A shroud of grainy particles veils the heart of most galaxies, helping to make stars, planets and even us. But where did it all come from? Stuart Clark investigates
HE universe, it seems, has the same
problem I have. Dust, everywhere.
Looking round as I type this, I find myself
wondering where on earth it all comes from.
Just how does it accumulate without invitation
on every surface, in every nook and cranny?
Increasingly, astronomers can be heard
muttering something similar. Unlike my
bothersome but insignificant pilings, cosmic
dust is important stuff. Its wispy grains,
mainly formed of amorphous carbon,
carbonate and silicate, are just fractions of a
micrometre across – about the size of a smoke
particle. If it weren’t for them, though, the
night sky would be much brighter, with
thousands of extra stars on view. Not that stars
could exist in such numbers without dust: its
presence cools down clouds of interstellar gas
and aids their collapse into stars. In addition,
small molecules meet and bind on the grains’
surfaces, allowing more complex chemicals to
form than would be possible through chance
encounters in the cosmic outback. Cosmic
dust is the starting point for building whole
planets and more besides. Go back far enough
in time, and dust is the stuff that made us.
Yet we have a problem with cosmic dust, one
so big we can’t just sweep it under the carpet:
we don’t know what made it.
Not so long ago, we thought we did. Longlived stars in their final stages of existence were the dust factories. When a star like the
sun ages, changes in its internal chemistry
cause it to bloat and turn into a red giant many
times its original size. Once the sun goes that
way, it will be curtains for Mercury, Venus and
possibly Earth, but a happy day for dust fans.
Our swollen star’s tenuous outer atmosphere
will provide a perfect environment for solid
grains to condense from hot gas,...
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