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Luka Klikovac
When the dust unsettles
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
T
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,
When the dust unsettles
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
T
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,