Little Green Men

Stars come and stars go. When our own Sun's nuclear fire goes out, billions of years in the future, alien astronomers (if any are looking) will hardly notice the loss. The Sun will contract to a dwarf the size of the Earth. First it will glow white. Then, as it cools, red, and then brown. Finally, it will be only a cinder. Not a dramatic event. But sometimes a star is so large that its end is catastrophic.

Seven thousand years ago, a huge star exploded. The light of this explosion was first seen in 1054, almost a thousand years ago. We can still see the remains of this explosion. Called the crab nebula, these remains can be seen in binoculars as a hazy patch of light south of the brilliant planet Mars, rising in the north-east at 10:00.

Not only can we see it, we can also hear it, with the tremendous amplification of radio telescopes. When first heard, the sound was like nothing heard before.

Astronomers were setting up one of the first radio telescopes in 1967. They heard a regular signal from the direction of the Crab Nebula. Thirty times a second. They called this L.G.M. radiation -- not really a scientific name. L.G.M. means Little Green Men. It was thought that only an alien civilization could produce signals so regular. But the explanation was simpler, and more profound, than that.

All stars rotate. Even our own Sun rotates, though it rotates only about once a month. When a star collapses, like a twirling skater drawing in her arms, it rotates faster. The smaller it gets, the faster it rotates. The dead heart of the star at the center of the Crab Nebula is only about the size of Burlington. It rotates thirty times a second. As it rotates it emits a beam of radiation, which we "hear" as a click thirty times a second. The star has become a pulsar. But there's more.

The core of the star contracted to an impenetrable ball of neutrons. The outer layers of the star, rushing inwards under the attraction of gravity, collided with this impenetrable ball in a fantastic supernova explosion. Simple atoms were forced together to form ever larger ones. The heavy elements, the elements of life, were born. In the crab nebula we see the remains of a star that once was much brighter than the Sun.

This, and millions of stars like it, gave us life. Keep looking up! In the stars onerhead you'll see our home.

(10/17/07)