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(617) 495-7462
Christine Pulliam
(617) 495-7463
pubaffairs@cfa
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Release No.: 2009-21For Release: Monday, November 02, 2009
These findings were published in the Nov. 1 online issue of the journal Nature, and are being featured today in a press conference at the Fermi Science Symposium in Washington, DC.
Seeking the source of cosmic rays
VERITAS has found new evidence for cosmic rays in the "Cigar Galaxy," also known as Messier 82 (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 Very Energetic Radiation Imaging Telescope Array System (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 Galaxy, the Milky Way.
"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.
Using gamma rays to infer cosmic rays
It took two years of dedicated data collection to tease out the faint signal coming from M82.
"We knew that the detection of M82 would have important scientific implications. As a result, we scheduled an exceptionally long exposure immediately after the experiment became fully operational" said Benbow. "The data needed to be meticulously analyzed to extract the gamma-ray signal, which is over a million times smaller than the background noise. Although the signal is only a tiny fraction of the data, we made many checks for possible bias and we are confident that the signal is genuine."
"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. A next-generation VHE gamma-ray observatory, the Advanced Gamma-ray Imaging System (AGIS), is already under development.
VERITAS is operated by a collaboration of more than 100 scientists from 22 different institutions in the United States, Ireland, England and Canada. To learn how it works, visit http://veritas.adlerplanetarium.org/project/. VERITAS is funded by the U.S. Department of Energy, the U.S. National Science Foundation, the Smithsonian Institution, the Natural Sciences and Engineering Research Council of Canada, the Science Foundation Ireland and the STFC of the U.K.
VERITAS Telescopes Help Solve 100-Year-Old Mystery: The Origin of Cosmic Rays
Cambridge, MA - Nearly 100 years ago, scientists detected the first signs of cosmic rays - subatomic particles (mostly protons) that zip through space at nearly the speed of light. The most energetic cosmic rays hit with the punch of a 98-mph fastball, even though they are smaller than an atom. Astronomers questioned what natural force could accelerate particles to such a speed. New evidence from the VERITAS telescope array shows that cosmic rays likely are powered by exploding stars and stellar "winds."
For more information, contact:
David A. Aguilar
Christine Pulliam
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu
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