STELLAR CHEMISTRY

by Staff Writers
Menlo Park CA (SPX) Feb 15, 2013


Finding evidence for the acceleration of protons has long been a key issue in the efforts to explain the origin of cosmic rays. This pair of spectra from two supernova remnants (also shown visibly with data from various satellites and wavelengths) are the “smoking gun” that researchers have been looking for. The Fermi Large Area Telescope’s observations fit very neatly with predictions of neutral pion decay. Credit: NASA/DOE/Fermi LAT Collaboration, Chandra X-ray Observatory, ESA Herschel/XMM-Newton. For a larger version of this image please gohere.

A new study confirms what scientists have long suspected: Cosmic rays – energetic particles that pelt Earth from all directions – are born in the violent aftermath of supernovas, exploding stars throughout the galaxy.

A research team led by scientists at the Kavli Institute for Particle Astrophysics and Cosmology at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory sifted through four years of data from NASA’s Fermi Gamma-ray Space Telescope to find the first unambiguous evidence of how cosmic rays are born.

Reporting in the Feb. 15 issue of Science, the team identified two ancient supernovas whose shock waves accelerated protons to nearly the speed of light, turning them into what we call cosmic rays. When these energetic protons collided with static protons in gas or dust they gave rise to gamma rays with distinctive signatures, giving scientists the smoking-gun evidence they needed to finally verify the cosmic-ray nurseries.

Protons make up 90 percent of the cosmic rays that hit Earth’s atmosphere, triggering showers of particles that reach the ground and creating radiation for air travelers. Scientists have theorized that two of the most likely sources for the protons are supernova explosions within our Milky Way galaxy and powerful jets of energy from black holes outside the galaxy. But in neither case had the necessary evidence been nailed down.

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