Cosmic rays likely powered by exploding stars and stellar "winds"
3 Nov 2009, 1415 Hrs

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Washington, November 3 In a new research, astronomers have solved a 100-year old mystery of the origin of cosmic rays, by finding evidence which indicates that cosmic rays are likely powered by exploding stars and stellar "winds".

Astronomers came across the evidence using the VERITAS telescope array.

VERITAS 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.

VERITAS could not detect M82's cosmic rays directly because they are trapped within the Cigar Galaxy. Instead, VERITAS looked for clues to the presence of cosmic rays: gamma rays.

Gamma rays are the most energetic form of light, far more powerful than ultraviolet light or even X-rays.

When cosmic rays interact with interstellar gas and radiation within M82, they produce gamma rays, which can then escape their home galaxy and reach Earthbound detectors.

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 xceptionally 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 ackground noise. Although the signal is only a tiny fraction of the data, we made many checks for possible bias and we are onfident that the signal is genuine," he added. (ANI)

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