November 3, 2009
Shooting through space with the greatest of ease, cosmic rays can careen through the universe at nearly the speed of light. (Cosmic ray is a bit of a misnomer. The term really describes subatomic particles, but using an umbrella term like “cosmic thing” would just be aggravatingly vague.)
But what is the driving force behind these little bits-n-pieces? Scientists suspected that shock waves from supernovae and massive stars were propelling the superspeedy particles, but they couldn’t prove it in part because they could only observe cosmic rays that hit the Earth’s atmosphere. The VERITAS telescope—which is partially funded by the Smithsonian Institution—however, has allowed scientists to see indirect evidence of cosmic rays much farther away in the universe. While observing the M82 galaxy—which resides about 12 million light-years away from the Earth—VERITAS produced evidence that may shed some light on the matter.
M82 is a “starburst” galaxy, meaning that it is rich with newborn stars. Although VERITAS cannot observe cosmic rays directly, it can detect gamma rays—a form of radiation that is produced when cosmic rays interact with interstellar gas. It took more than two years of data collection, but VERITAS was ultimately able to detect gamma radiation emanating from M82. “The detection of M82 indicates that the universe is full of natural particle accelerators, and as ground-based gamma-ray observatories continue to improve, further discoveries are inevitable,” said Martin Pohl, a professor of physics at Iowa State University who helped lead the study. This evidence supports the theory that supernovae and massive stars are the universe’s predominant accelerators of cosmic rays.
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