Wait a minute, you say. Nothing moves faster than light, that's a physical limit, right?
Yes and no. What's true is that nothing moves faster than light in a vacuum. But light slows down in other substances, such as air. It is thus possible for particles with extraordinarily high energy to move faster than light through the Earth's atmosphere, for example – a phenomenon with some interesting consequences.
Particles that travel faster than light through the atmosphere produce radiation that scientists liken to the sonic boom produced by faster-than-sound travel. This effect, called Cerenkov Radiation, can provide some clues about the composition of the original particles. That's proved to be particularly interesting to scientists studying cosmic rays.
Cosmic rays are particles from outer space, often protons or complete atomic nuclei, that frequently strike the Earth's atmosphere with enough energy to fall into this faster-than-light category, emitting
Cerenkov radiation.
Scientists are still unsure about the origin of most cosmic rays. One recent study tracked a small percentage back to the centers of distant galaxies. But most are believed to originate inside the Milky Way, possibly thrown off by exploding stars.
A number of different methods of observing these rays' Cerenkov signatures have been devised, ranging from very precise balloon-based detectors to large ground-based facilities. Now researchers at the
University of Chicago are using a National Science Foundation grant to build a new kind of detector that combines the advantages of both methods, with an eye towards detecting the presence of iron atomic nuclei – ideally gaining enough data to help shed new light on the exploding-star theory.
"They're raining down on the atmosphere of the Earth, tens of thousands of particles per second per square meter," said University of
Chicago assistant professor Scott Wakely, who will be running the experiment, in a statement. "(From) where exactly, we don't know."
Radiation flashes may help crack cosmic mystery [University of Chicago]
(Image: A double supernova viewed by NASA's Swift observatory. Possibly a source of cosmic rays? Credit: Stefan Immler NASA/GSFC, Swift Science
Team.)
