Energy | Pages 110-111 | See Linked Version

Nearly 170,000 years ago a giant star blew up in the Large Magellanic Cloud, the galaxy closest to our Milky Way. Silver, gold, lead, and other heavy elements rifled into space, forged by the fires of the star's spectacular death. Its remnants flew outward at millions of miles per hour to form a hot nebula of glowing gas. Fierce shock waves may have triggered nearby clouds of gas and dust to collapse into baby stars, just as loud noises can set off an avalanche on a snowy mountain slope. The aftermath of the blast rippled through the star's cosmic neighborhood for tens of thousands of years.

Beyond this maelstrom of matter and motion, the star also made a spectacle of itself far and wide with an enormous burst of pure energy. Some of this energy took on a familiar form: visible light, like the light we see from our Sun. This light streamed across the gulf between the Large Magellanic Cloud and the Milky Way, covering nearly 6 trillion miles per year. On February 23, 1987, a tiny fraction of the star's light finally reached Earth. The Canadian astronomer Ian Shelton took a photograph of the Large Magellanic Cloud that night from an observatory in Chile. He noticed a bright spot in the image that hadn't been there the night before. When he went outside, Shelton became the first person in more than a century to simply look up in the sky and see a star blowing itself to bits.

The explosion, named Supernova 1987A, was the brightest supernova seen from Earth since one recorded in 1604 by Johannes Kepler. Outside of the Sun, Moon, and planets, it quickly became one of the most intensely studied astronomical objects in history. Within a few hours it shone as brightly as if it drew its power from 200 million suns. Other forms of light, invisible to our eyes, also taught us about the workings of the supernova. For instance, high-energy x-rays and gamma rays revealed that the inner and outer layers of the star mixed together when it exploded, instead of expanding in smooth shells. Radio waves opened a window into the turbulent heart of the supernova, where a spinning neutron star--a pulsar--may lurk. Despite some tantalizing hints, astronomers have not yet spotted the pulsar's telltale repeating signal.

Supernova 1987A's impressive visual impact landed it on the cover of many magazines. However, most people don't realize that light was just a tiny fraction of the supernova's prodigious output of energy. The doomed star shed 30,000 times more energy in the form of ghostly subatomic particles called neutrinos. In the first 10 seconds of its explosion, the star unleashed 10 billion trillion trillion trillion trillion neutrinos. That's 1 followed by 58 zeros. During those 10 seconds, the detonation produced more power than the combined output of all the stars in the visible universe.

The neutrinos flashed into space in all directions, at or near the speed of light. Because they rarely interact with other matter, the neutrinos zipped through almost everything in their paths--including our planet, once they got here 167,000 years later. Indeed, every square inch of your body was pierced by about 300 billion neutrinos shortly before Ian Shelton spotted Supernova 1987A. Astronomers managed to stop 19 of those fleeting particles in their tracks with two giant underground vats of water, where the neutrinos made tiny flashes. This marked the first detection of neutrinos from an event beyond our solar system. There's an infinitesimal chance that a similar flash occurred within the vitreous humor in one of your eyes at the moment the neutrinos struck Earth.

Supernova 1987A was a nearby example of how energetic our cosmos can get. Supernovas may seem rare, but the universe contains so many stars and galaxies that one pops off somewhere about once every second. In our Milky Way we can expect a star to die in this fashion once or twice a century. A thick pall of dust across the galaxy's center hides many of these stellar bombs. But if one of the stars we see in the night sky exploded, it would outshine Venus at its brightest and might rival the full Moon. Gamma rays from a very close supernova could even strip away the protective ozone layer in Earth's atmosphere and eradicate life on the planet. That would be the ultimate irony, since generations of long-ago supernovas seeded our cosmic neighborhood with the ingredients that eventually gave rise to life on Earth.

ENERGY Powers the Universe

When it comes to energy, you probably don't think of gamma rays and neutrinos from exploding stars. Rather, energy has other meanings during everyday life. When you have no energy, it's an excuse to lie on the couch and watch television. In an energy crisis, it's wise to drive less and turn down the thermostat. A high-energy rock concert makes your ears ring. Our common concepts of energy add seemingly unscientific twists to motion, power, loudness, or some physical activity. (continued)