By Sally Morem
So begins a classic science fiction tale, Arthur C. Clarke’s “The Star.” 1,000 years from now, a Jesuit priest and astrophysicist, is a member of a starship crew that has made a heart wrenching discovery. They were investigating the Phoenix Nebula, the remains of an exploded star. One distant planet—that star system’s Pluto—survived the inferno. And on that planet, the crew found the carefully preserved remnants of a once glorious alien civilization.
But wait, it gets worse. The priest has determined, through careful dating methods and study of star charts, that the light of that brilliant supernova reached Earth in the eastern sky 3,000 years earlier—over Bethlehem.
Religious science fiction fans have strongly denounced this story as an anti-Christian diatribe, insisting that Clarke used traditional elements of science fiction storytelling merely for ideological purposes. But, what is really going on here? Clearly, Clarke did indeed set up an artificial situation. Aside from the obvious fact that there are no starships and that no human had ever visited another star system, Clarke has made it plain elsewhere that he doesn’t believe in the story of Christmas. So, what is he getting at? He conjoined space travel and Bethlehem in an effort to do what scientists do when they conduct “thought experiments.” He is reasoning his way through a difficult theoretical problem by constructing an elaborate metaphor.
Christians may be pleased to know that the events described in “The Star” are impossible, according to our present-day understanding of stellar evolution.
An ordinary stellar explosion—a nova—occurs only in a close binary star system. As the smaller star “strips” some of the larger star’s mass, occasionally it gets too much at once and “burps,” actually undergoing a powerful thermonuclear explosion. We see this from Earth as a brightening of the star—hence “new star” or the Latin “stella nova,” or just plain “nova.”
It’s extremely unlikely that any planet could settle into a stable orbit around two stars. The planet would be much more likely to lurch and loop about it in strange patterns with a good chance of being flung by centrifugal force into interstellar space. In order for life to have a chance to evolve, the planet in question must settle into a nice, regular orbit in the “water zone” around a star—that distance from the star in which liquid water can form on a planet and remain in the liquid state during most of the year. No star that can become a nova is capable of fostering such a stable planet.
So, Clarke’s star clearly could not have been a nova. But, in his story, he did hint at the possibility that the Phoenix Nebula was caused by a supernova. But the class of stars that are capable of going supernova are saddled with their own set of troublesome instabilities. A very massive star will build up a large amount of heavy elements during its lifetime of fusion reactions. Our own Sun is far too small to do this. At a certain point, the heavy elements bear down on the core, creating immense pressures, relieved finally by a massive explosion. In a few seconds, the supernova puts out more energy than a galaxy of stars. Sometimes the star is completely destroyed. It’s a good thing that none have occurred near our own Solar System or we wouldn’t be here to talk about it. The heavy radiation from such an explosion, even from a distance of many light years, would have destroyed all life on Earth.
Why can’t such a star harbor life-bearing planets? Because it wouldn’t be around long enough. Even though larger stars contain much more fuel than Sun-like stars, they undergo fusion at such prodigious rates that they burn themselves out in a few hundreds of millions of year, hardly enough time for microscopic life to form, let alone intelligent life. Clarke’s brave aliens could never have come into being in such a star system.
Stellar evolution was not so nearly well understood in the Fifties when Clarke wrote “The Star.” But this error in stellar physics only reinforces our earlier view that “The Star” is not so much a commentary on real life than it is a metaphor for dealing with a very difficult concept.