PROLOGUE
THE BIRTH AND DEATH OF A STAR
The star was a relative newcomer to the galactic scene. It had begun life as a vast cloud of interstellar hydrogen which over the millennia had collapsed in upon itself, pulled together by gravitational attraction. As the cloud coalesced, the gas at its center grew hotter. After a while, the interior began to glow with a visible light. Then one day, the temperature at the cloud’s center reached the level where hydrogen fuses into helium. On that day, a new star blazed forth to illuminate the blackness of the interstellar night.
For millions of years the star shone with a luminosity equal to that of several thousand of its lesser brethren. Indeed, the star’s radiance made it a beacon visible across the length of the galaxy. However, such profligacy is not without its costs. Where smaller suns took as long as 10 billion years to consume their available supplies of fusible hydrogen, the giant star managed the same feat in less than a single gigayear. About the time the first apelike prehumans ventured forth onto the savannas of Africa, the star ran low on hydrogen fuel, and as quickly as it had flamed alight, the nuclear fire at its heart was snuffed out.
The end of fusion brought with it a resumption of the contraction that had molded the primordial cloud. As the core fell inward, its temperature rose precipitously. Within seconds, the temperature at the star’s center reached the point where helium fuses into carbon. The nuclear fire flamed anew, this time powered by the helium ash of the previous cycle. Since the new fire was hotter than the old, the star wasted energy even more lavishly than before. It expanded as well, providing a larger surface area from which to radiate the vigorous new energy to surrounding space. Along with the expansion came cooling of the star’s outermost layers, and a change in color. Where before the star had radiated a brilliant blue-white light, its visible surface was now a bright yellow-green color.
The star continued on the quick burning helium-carbon cycle until the time when the first agricultural settlements began to appear on Earth. Then, having depleted its supply of helium, the inner fire failed, triggering yet another cycle of contraction and heating. This time it was the turn of the carbon atoms to provide the star’s new source of energy. Once again, the new fuel produced more energy than previously, forcing the star’s surface to expand to provide sufficient area to radiate the heat. By the time the star stabilized at 400 solar diameters, its hue had shaded down from yellow-green to a deep red-orange.
The star was well into its dotage when the first human telescopes were turned its way. The first starships to arrive at the star made note of this fact a few centuries later when they recorded more neutrinos than expected pouring forth from the star’s fiery interior. It was obvious even then that the star had not long to live. Still, a stellar lifetime is a very long time, and no one truly expected the end to come as quickly as it did.
At 17:32 hours on 3 August 2512, the star exhausted the last of its carbon fuel. Within seconds, the old cycle of contraction and heating began again. This time things were different, however. For now, the star’s core was rich in iron, and iron cannot be fused to produce energy. Rather, fusing iron nuclei rob energy from their surroundings. With its core hopelessly chilled by iron fusion reactions, the star gave up its ages-old fight with gravity. The core began its final collapse.
As billions upon countless billions of tons of matter fell inward, they gave up the potential energy they had stored through the millennia. This “energy of position” reappeared as heat, causing the temperature at the center of the star to rise rapidly toward infinity. Some of this heat was radiated into the middle layers of the star’s atmosphere; which, unlike the core, were still rich in unburned hydrogen. A furious thermonuclear reaction resulted. In the blink of an eye, the star began to produce as much energy each second as it had previously radiated away in its entire lifetime.
The end came quickly as the star exploded in the most titanic explosion ever witnessed by human beings.