Sharing the stellar treasure

The nuclear treasures accumulated by stars are now complete and we may draw up an inventory. But treasure is only treasure if it can be shared. What would be the point of the stars unflagging labours if their fruits could not be redistributed Nature has resolved the distribution problem by explosion or wind ejection. The star throws everything it can overboard before it goes down. In the sky, winds, blasts and deflagrations are entirely beneficial. 

The explosion of a supernova is a very happy event. It results in the spherical propulsion of matter into the interstellar medium, matter that has been simmering over millions of years, spiced up in the final moments by a little explosion and radioactivity. In the medium that lies between the stars, temperatures and densities are much lower than in stellar objects themselves. The supernova matter is diluted and cools down. Nuclei in the expelled material capture electrons to form various atoms and molecules. The cycle 

But all this cannot happen without losses along the way. Stellar corpses and collapsed cores (white dwarfs, neutron stars and black holes) are permanently removed from the great flow of nuclear evolution. It is as though their substance has been conflscated, so that it can no longer take part in the ebb and flow of matter, entering the stars in one form and re-emerging in another. Almost all elements required for life are now present. 

At this point in the presentation, our picture of stellar evolution and the nucleosynthesis of naturally occurring chemical elements is almost complete. Many reflnements would be required to give a fuller view. In fact, many pieces of the jigsaw are still missing or inadequately understood, in particular with regard to the r process. Despite all this, we have tried to convince the reader that the nucleosynthesis model constitutes a fundamental opus of the human intellect. 

It is not therefore to the planets that we should associate the elements iron with Mars, lead with Saturn, mercury with Mercury. It is indeed the stars that have nurtured them. Some stars make carbon, others gold. Thermonuclear combustion modifies the composition of the hottest regions within stars. Each star is responsible for the confection and distribution of a particular batch of atoms, apart from hydrogen and a large part of the helium in the Universe which were synthesised in the Big Bang, and the lightweight trio lithium, beryllium and boron. 

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