The Helium See

Hui Yang (University of Illinois) and NASA/ESA Hubble Space Telescope image of a vast nebula called NGC 604, which is rich in helium. In the early moments of the Big Bang, two elements were forged: hydrogen and helium. Technically, the tiniest traces of light elements such as lithium were produced as well, but nothing of consequence. The early Universe was about 3 parts hydrogen to 1 part helium. All the heavier elements, from the oxygen in your lungs to the iron in your blood, were created through astrophysical processes. Fused in stars, formed in supernovae, or scattered by the collisions of neutron stars. Even in the present cosmos, heavier elements are so cosmically rare that astronomers group them all as metals. One of the ways astronomers study the Big Bang is through the relative abundance of different elements. In particular, the primordial abundance of hydrogen and helium. That might seem easy, since they were the two elements formed by the Big Bang, but there is a catch.…