Save guides, add subjects and pick up where you left off with your BBC account. Protons and neutrons are the heaviest particles in an atom and as a result they make up most of its mass.

Astronomers have discovered a likely explanation for a fracture in a huge cosmic "bone" in the Milky Way galaxy, using NASA's Chandra X-ray Observatory and radio telescopes.

Astronomers have discovered a likely explanation for a fracture in a huge cosmic "bone" in the Milky Way galaxy, using NASA's Chandra X-ray Observatory and radio telescopes.