Deep in space, NASA's Fermi Gamma-ray Space Telescope has collected evidence that the massive explosion of stars long ago is responsible for the cosmic rays that bombard the surface of the Earth.
Cosmic rays are high-energy charged particles that zip through the universe. About 90 percent of cosmic rays are protons, the rest being electron and atomic nuclei — all shooting through the galaxy near the speed of light.
Scientists have sought the source of high-energy cosmic rays since their discovery a century ago. During the cross-galaxy flight, the cosmic rays happen upon magnetic fields that send the highly charged particles rocketing off in another direction. The scrambled paths have made it nearly impossible for researchers to unravel and trace cosmic rays to their origin.
Now, NASA scientists have determined that supernovae are one progenitor of cosmic rays.
The Large Area Telescope on the Fermi Gamma-ray Space Telescope collects and maps the gamma-ray light from supernovae explosions, millions and billions times the energy of visible light.
One defining feature of cosmic rays is the incredible speed at which these charged particles hurdle through the universe. In 1959, the physicist Enrico Fermi suggested that magnetic fields in interstellar clouds were likely responsible for accelerating cosmic rays to their high speeds.
When stars violently explode in a supernova, they produce an enormous shock wave as debris slams against the gas and magnetic fields surrounding the star. When charged particles wander across the supernova remnant's outermost wave, they are accelerated by the strong changing magnetic field at the wavefront. After hundreds of years of encounters with the supernova remnant wave front, the particles eventually zip out of the supernova remnant shock wave, released as cosmic rays.
When the cosmic rays interact with the interstellar gas, they release gamma rays. Protons and electrons release gamma rays at similar energies but through different processes when they slam into the interstellar gas. By studying the fingerprints of the gamma rays collected by the Fermi telescope, the researchers were able to determine that supernova remnants produce cosmic rays of protons.
The details of the research was published on February 15, 2013 in the journal Science.