Image of the Day: A Spectacular 20,000-Year-Old Supernova Remnant



Thought to be about 20,000 years old — middle-aged for a such a structure — the W44 supernova remnant is located 9,800 light-years away in the constellation Aquila. The Fermi  Large Area Telescope (LAT) not only detected W44, it actually revealed super-energetic gamma-rays coming from places where the remnant's expanding shock wave is known to be interacting with cold, dense gas clouds, providing clues to the origin of cosmic rays, the particles, primarily protons, that move through space at nearly the speed of light. Magnetic fields deflect the particles as they race across the galaxy, and this interaction scrambles their path and masks their origins.

Scientists can't say for sure where the highest-energy cosmic rays come from, but they regard supernova remnants as perhaps their likliest origin.

In 1949, the Fermi telescope's namesake, physicist Enrico Fermi, suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of gas clouds. In the decades that followed, astronomers showed that the magnetic fields in the expanding shock wave of a supernova remnant are just about the best location for this process to work.

So far, LAT observations of W44 and several other remnants strongly suggest that the gamma-ray emission arises from accelerated protons as they collide with gas atoms.

The Daily Galaxy via NASA

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