Living Flashes

Blasts of Life and Death

I have always been fascinated by supernovae explosions. These mysterious flashes, some close and brilliant and others faint and remote, suggest that the universe, whether or not it is teaming with life, is still somehow alive. Some people, of course, must have dreaded and hated them. When they were seen in ancient China, the official astronomers were all too likely to be executed for having failed to predict them. And yet, despite these rare occasions when they brought death, supernovae have created life. Our bodies are part of the universe. The very atoms that composed them were forged in the nuclear furnaces of a giant star that burst forth into a supernova millions of years before the Sun was formed.

But for that primordial explosion, the Earth could not exist, for there would be no elements heavier than hydrogen and helium with which to form it. Nor could we exist anywhere else in the solar system. There would be no carbon to sustain life, no iron for our blood, no calcium for our bones, no oxygen to breathe, no zinc or manganese for our cells, no chlorine for our salt, no nitrogen for our agriculture, and no neon for our advertising. Nor would there be any Sun, or any main-sequence stars. For it needed the shock-wave of a supernova explosion to push great clouds of gas and dust into spherical shapes that eventually collapsed under their own weight and grew hot enough to undergo nuclear fusion. It is fascinating to speculate how frequently supernovae explosions occur in the universe. It is generally reckoned that there is about one per galaxy per century. Since there are believed to be around 100 billion galaxies, this means that, each century, somewhere out there, 100 billion stars explode and totally destroy themselves. And this, unless my arithmetic is at fault, means in turn that there are one billion explosions per year, three million per day, approximately 100,000 per hour, 2000 per minute or around 30 each second. Thirty per second! What a sight to see if only our telescopes were sufficiently powerful. But perhaps it is fortunate that the cosmos is so vast that no supernova has yet exploded sufficiently close to us to threaten our existence. The closest known supernova occurred about 35,000 years ago, at the height of the last Ice Age. From a distance of only 150 lightyears, it must have ripped away the ozone layer without which, so environmentalists tell us, life cannot continue. But life went on as usual. There is no sign that anyone was aware of any catastrophe. No cave painting recorded this extraordinary event. (Scientists only learned of it in modern times when studying ice cores.) People went on hunting and there continued to be sufficient game for them to hunt. So how near to Earth does a supernova have to be to wipe out life? Nobody knows; less than 50 to 100 1ight-years are popular guesses. My own fear is that Sirius, only nine lightyears from us, will one day blow. And if that happens we shall get a brief but terrible glimpse of the fascination of supernovae.