Seeking the Source of Cosmic Rays
The rarest cosmic rays carry more than 100 billion times as much energy as generated by any particle accelerator on Earth. ("Cosmic ray" is a historical misnomer because they are individual particles, not a ray or beam.) Astronomers have devised methods for detecting cosmic rays that hit Earth's atmosphere. However, detecting cosmic rays from a distance requires more effort.
VERITAS has found new evidence for cosmic rays in the Cigar Galaxy (M82), which is located 12 million light-years from Earth in the direction of the constellation Ursa Major
"This discovery has been predicted for almost 20 years, but until now no instrument was sensitive enough to see it," said Wystan Benbow, an astrophysicist at the Smithsonian Astrophysical Observatory. Benbow coordinated this project for the VERITAS collaboration.
The VERITAS observations strongly support the long-held theory that supernovae and stellar winds from massive stars are the dominant accelerators of cosmic-ray particles. Galaxies with high levels of star formation like M82, also known as "starburst" galaxies, have large numbers of supernovae and massive stars. If the theory holds, then starburst galaxies should contain more cosmic rays than normal galaxies. The VERITAS discovery confirms that expectation, indicating that the cosmic-ray density in M82 is approximately 500 times the average density in our Milky Way Galaxy.
"This discovery provides fundamental insight into the origin of cosmic rays," said Rene Ong, a professor of physics at the University of California, Los Angeles, and the spokesperson for the VERITAS collaboration.