Caleb A. Scharf writes:

It’s a relatively little-known fact outside of astrophysics that the key to the first stars in the universe, and the earliest structures condensing out of the primordial murk, was chemistry.

Specifically, the key was the formation of molecular hydrogen or H2. A pair of atoms bonded together and capable of rotating and vibrating. A few years ago I wrote about some of the details in this column. In brief, without the formation of molecular hydrogen it’s very hard for cosmic gas to cool off. If it can’t cool off it can’t condense to make stars, and for those stars to forge the first heavier elements that act as much more efficient coolants for subsequent generations of forming objects. (It could be argued that helium hydride, forming before molecular hydrogen, was also key, but more so for enabling the formation of molecular hydrogen in the first place).

Closely related to molecular hydrogen is the ‘mother molecule’ of protonated molecular hydrogen, H3+. Once this forms it unlocks an astonishing network of chemistry that includes (after such elements form) carbon, nitrogen and oxygen.

We’ve also long known that molecules form in the chill of interstellar space, especially in the great nebula or molecular clouds that dot our galaxy and others. We’ve furthermore seen that a majority of these molecules involve carbon. And over the years there’s been slow but steady progress in decoding the details of the chemical mix, including recent work that hints at the likelihood of biologically important nucleobases like cytosine and adenine forming in space. [Continue reading…]