A closer look at the universe's most energetic particles - cosmic rays - which are mostly protons travelling at the speed of light. Young supernovae have been observed to have the strongest magnetic fields and the highest-energy cosmic rays. Cosmic rays produce gamma rays when they encounter interstellar gas. This image shows where these remnants emit radiation a billion times more energetic than visible light.

Cassiopeia A, a supernova remnant, has been found to have extremely bright gamma rays, shown here in magenta. The supernova is about 10 light years across and is located about 11,000 light years from Earth in the constellation Cassiopeia. Cas A was formed by a massive starburst in our galaxy about 340 years ago.

Image description:

In the background, the darkness of space is sparsely littered with bright yellow stars of all sizes. In the centre of the image, covering most of the photo, is a supernova containing blue, yellow, orange and green gas and dust. To the upper right of the supernova is a magenta smear of bright gamma rays.