Fermi's Large Area Telescope (LAT) resolved gamma rays with energies a billion times greater than that of visible light from supernova remnants of different ages and in different environments. W51C, W44 and IC 443 are middle-aged remnants between 4,000 and 30,000 years old. The youngest remnant, Cassiopeia A, is only 330 years old and appears to the LAT as a point source. The images bring astronomers a step closer to understanding the source of some of the universe's most energetic particles — cosmic rays. The emissions are likely the result of accelerated protons interacting with nearby gas clouds, but other possibilities have not been eliminated. Astrophysicists believe that supernova remnants are the galaxy's best candidate sites for cosmic-ray acceleration. These observations provide further validation to the notion that supernova remnants act as enormous accelerators for cosmic particles.
Fermi mapped GeV-gamma-ray emission regions (magenta) in the W44 supernova remnant. The features clearly align with filaments detectable in other wavelengths. This composite merges X-rays (blue) from the Germany-led ROSAT mission, infrared (red) from NASA's Spitzer Space Telescope, and radio (orange) from the Very Large Array near Socorro, N.M.