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Tycho’s star shines in gamma rays

In early November 1572, observers on Earth witnessed the appearance of a “new star” in the constellation Cassiopeia, an event now recognized as the brightest naked-eye supernova in more than 400 years. Now, years of data collected by NASA’s Fermi Gamma-Ray Space Telescope reveal that the Tycho’s supernova remnant shine in high-energy gamma rays.

This detection gives astronomers another piece of evidence supporting the notion that supernova remnants can accelerate cosmic rays. The highest-energy cosmic rays are accelerated in the magnetic fields of interstellar gas clouds, and supernova remnants may be the galaxy’s best candidate sites for this process.

Astronomers conclude that a process called pion production best explains the emission. First, a proton traveling close to the speed of light strikes a slower-moving proton. This interaction creates an unstable particle — a pion — with only 14 percent of the proton’s mass. In just 10 millionths of a billionth of a second, the pion decays into a pair of gamma rays. [watch animation]

If this interpretation is correct, then somewhere within the remnant, protons are being accelerated to near the speed of light, and then interacting with slower particles to produce gamma rays, the most extreme form of light.

Above: This portrait of Tycho’s supernova includes gamma rays (magenta), X-rays (yellow, green, and blue), infrared (red) and optical data. »