Research Highlight
November 24, 2009
VERITAS Discovers Evidence for the Origin of Cosmic Rays
by Simon Swordy and Scott Wakely
The VERITAS collaboration, an international team of astronomers from the US, Canada, UK and Ireland, including KICP senior members Simon Swordy and Scott Wakely, and KICP associate member Lucy Fortson, recently announced the discovery of very high energy (VHE) gamma rays emitted by the starburst galaxy M82 (the Cigar Galaxy). The observed gamma rays have energies more than a trillion times higher than the energy of visible light, and are the highest energy photons ever detected from a galaxy undergoing large amounts of star formation. The discovery was made from data taken over a two-year long observing campaign.

The starburst galaxy M82 (the Cigar Galaxy)
Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

This new detection points to the answer to a long-standing cosmic mystery - the origin of very high energy cosmic ray particles. Cosmic rays are subatomic particles such as protons that are boosted to very high energies by some type of cosmic accelerator. Scientists have been seeking the mechanism by which the most energetic of these particles are accelerated to energies in excess of 100 GeV - and these new data point to processes in active starburst regions such as those found in the center of M82.

VERITAS - Very Energetic Radiation Telescope Array; located at the Fred Lawrence Whipple Observatory near Amado, Arizona

The VERITAS data offer strong support to a long-held theory that supernovae and stellar winds from massive stars are responsible for producing high energy cosmic ray particles. Galaxies such as M82 that have a high rate of stellar formation should also produce a high number of cosmic rays, which will then collide with gas and radiation in the galaxy to produce the VHE gamma rays detected by VERITAS.

The high number of cosmic rays inferred from the VERITAS data is consistent with expectations based on the intense rate of massive star formation seen in M82, offering fundamental insight into the origin of cosmic rays.
Publication: A connection between star formation activity and cosmic rays in the starburst galaxy M82, The VERITAS Collaboration, Nature (1 November 2009) Letter

Additional references: NSF Press Release

VERITAS website