Cosmic dust is fuel for future generations of stars

At this time of year, if the night sky is clear, dark and hopefully smoke-free, the Milky Way crosses the sky like a great arch, diving down to the southern horizon, to the left of the red supergiant star Antares.

Starting almost overhead and broadening as we head south, there is a dark rift in the Milky Way. This rift is cold, dark dust, blocking out the light of the countless stars lying beyond.

There is a lot of hydrogen out there too, dating back to the beginning of the universe. This is the fuel for future generations of stars. The dust is important too. In addition to being the raw material for making new planets, it is also the site where the basic chemicals for life as we know it are built.

The sort of dust with which we are familiar consists of fibres, skin cells, soil particles and grit from broken up stone. Cosmic dust is very different. As far as we know, it contains no fibres or pet hairs. It is formed when ageing giant stars start blowing off their material, including the waste products from a lifetime of energy production—all the elements other than hydrogen and some helium.

A lot of these atoms continue to float around in space as single atoms. However some of them combine to form particles up to around a tenth of a millimetre in diameter. Under some conditions, these clouds of particles can be persuaded to form much bigger bodies, such as planets. In mostly empty space, the atoms do not form hard lumps; they form "fluffy" lumps, with strings of atoms sticking out.

Empty space has no temperature; the temperature of stuff in space depends on the balance between the energy it receives, which is mainly starlight, and the efficiency with which it radiates this energy away. The less efficient a body is at radiating energy away, the hotter it has to be in order to do so. These fluffy dust particles are very efficient at radiating off the energy hitting them, which makes them very cold. They are also well shaped for making large molecules, including complex, organic (carbon-based) ones.

Imagine a carbon atom wandering around in space. It just happens to collide with a single atom of oxygen. They could form a molecule of carbon monoxide. However, when wandering around alone in space, they usually hit each other too hard to hang together, so they wander off to continue their single existences.

However, an atom hitting one of these fluffy dust particles bounces between the fluffy bits sticking out, losing energy to the dust particle, which is very cold. Finally, it just sticks on.

It can just sit there until an oxygen atom happens to come by. A methane molecule consists of one carbon atom and four hydrogen atoms. The chance of one carbon atom drifting around in space colliding simultaneously with four hydrogen atoms is close to zero. Building the molecules on a dust grain, one atom at a time, works. The large amounts of methane in the atmospheres of the planets Saturn, Uranus and Neptune show this.

Amino acids are the building blocks of proteins, and important for life as we know it. They have been detected in cosmic dust clouds. Glycine is one of those detected. It is the simplest amino acid, containing one nitrogen atom, five hydrogen atoms, two carbon atoms and two oxygen atoms.

The only way significant amounts of glycine or larger amino acids and other biologically important compounds can form in any quantity is on the surfaces of those cold, dust grains, with a trickle of starlight to stir up the chemical reactions.

Our radio telescopes are picking up the signatures of so many organic and other molecules in those dark clouds that we have not yet identified most of them. When new planets form, they get a ration of these biological precursors. If conditions are suitable, they could help life get started.

This is something to think about when gazing at those dark lanes along the Milky Way,

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• Saturn rises soon after sunset, with Jupiter following three hours later.

• The Moon will be new on Aug. 16.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, near Penticton.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.