A high-energy photonic jet (white and blue) blasts through a collapsar with a black hole at its center. The red space around ...

Earth’s core could contain helium from the early solar system. The noble gas tucks into gaps in iron crystals under high pressure and temperature.

Much smaller amounts of iron-54 and 57 (still with 26 protons, or it wouldn’t be iron, but 28 and 31 neutrons) and a tiny ...