Earth is constantly bombarded by cosmic rays - electrically charged particles from the depths of space. Yet almost none of them reach the surface - they’re blocked by the atmosphere. Instead, they create showers of other particles that do reach the ground. These particles reveal details about the cosmic rays and about the objects that created them.
Most cosmic rays come from exploding stars. A few others appear to come from disks of hot gas around supermassive black holes or other powerful objects.
When they reach Earth, they strike atoms in the atmosphere, producing a shower of other types of particles. Those particles decay in a tiny fraction of a second, producing still other types of particles.
The most common of these particles are muons. They’re similar to electrons - the negatively charged parts of atoms. They’re much heavier than electrons, though.
Muons are so energetic that they go through just about anything. In fact, several hundred of them zip through your body every minute. Fortunately, they don’t do any damage - they just keep going. They can penetrate deep into solid rock before they’re finally absorbed.
Detectors can trace the paths of muons that pass through them. That reveals where the cosmic rays that gave them birth came from, helping astronomers piece together their trip through the cosmos.
The end of that trip can illuminate not just the mystery of cosmic rays, but mysteries right here on Earth. More about that tomorrow.
Script by Damond Benningfield, Copyright 2013
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