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Cosmic Recycling

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Ken Tapping, December 13, 2006

In the sky this week...

> Saturn rises around 9 p.m.
> The Moon will reach Last Quarter on December 12, and will be New on December 20.


Not long ago, Chris Purton, a fellow astronomer at our observatory, gave an interesting public lecture. He pointed out that the atoms making up each one of us have their own histories. For the 14 billion years since the beginning of the universe they have been circulating around in the dust and gas clouds filling our galaxy, inside stars and planets, and then they came together in us. When we have finished with them, they will resume their separate wanderings, becoming parts of other things.

At the beginning, the universe contained only hydrogen and helium. Stars formed, and created energy by turning hydrogen into other elements, like oxygen, carbon, nitrogen and so on, and when those stars died, their material was returned to the cosmic dust and gas clouds. Big stars end their lives in huge explosions called supernovae, where, for a month or so, the dying star shines brighter than all the billions of other stars in its galaxy combined. There is so much energy released in these explosions that some of the material in the star is converted into gold, silver, lead and the other heavy elements. The gold in your wedding and engagement rings was forged in dying stars.

Very little of the hydrogen created at the beginning of the universe has been used up so far. Our telescopes show the star formation and star death are still going on all over our galaxy and in every other galaxy close enough for our telescopes to resolve detail. However, even though atoms get turned into other atoms inside stars, the raw material, hydrogen, is the one thing that is not being replaced. One day there won't be any hydrogen left. For a while there could be types of stars that get all their energy from converting other elements, but in the end all sources of energy will run out and the passage of atoms from one body to another and their transformation into other elements will stop.

Hydrogen is not only important as an energy source and a raw material for making other elements; it is an important ingredient in the chemistry of life. In the gas and dust clouds between the stars, it reacts chemically with other atoms to make water, ammonia, formaldehyde and countless other chemicals that are building blocks of the chemicals we all have at work in our bodies.

Since the 1950's, experiments have been done where these cosmic chemicals were put in a flask and electrical discharges – simulating lightning – were passed through them. The resulting gunk was found to contain amino acids, the building blocks of proteins. It has been found that hydrogen seems to be an important ingredient in getting this chemistry started along the path leading to life.

Hydrogen contains a lot of energy. When it undergoes nuclear fusion in stars, and turns into larger atoms, some of that energy is released. As we fuse those larger atoms into even larger ones, we get out some more energy. However, we cannot entirely reverse the process. To turn all those other atoms back into hydrogen atoms requires more energy than we obtained, so using up the cosmic hydrogen is like a one-way direction sign, pointing into the future. We'll just keep recycling our atoms until the hydrogen runs out.

Ken TappingKen Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,