As The Doctor would say, “The Universe is big. It’s vast and complicated and ridiculous. And sometimes, very rarely, impossible things just happen…” That’s the theory, anyway. The interesting thing about studying, frankly, any kind of science is that you start to realise that more and more of the things that your teachers in school told you were impossible, well… they aren’t quite so impossible after all. Consider Helium, for instance…
We were all taught in school about the noble gasses, and how they don’t form chemical compounds. But that isn’t quite true. I’ve waxed lyrical about Xenon compounds before, but what about the lightest noble gas, Helium? Even most scientists would merrily argue that it’s far too small and exciteable to form any kind of compound. It’s like the exuberant puppy of the periodic table, always dashing about, bouncing into things and causing a ruckus, but never content to stay still. Helium doesn’t even like to stay still with itself. At normal pressures, it will never even form into a solid, no matter how cold you make it. Curious.
But Helium can actually partake in chemistry. Enter the Helium Hydride ion, HeH+. It’s not hugely different to the H3+ ion which makes so many interstellar chemical reactions tick. It’s even fairly easy to make, from a little gas phase reaction:
H2+ + He → HeH+ + H
Yes, it can actually be that simple. It only works if it’s a gas, mind you. This, one of the simplest molecules that can exist, is also the strongest acid known, and it would rapidly react with anything that came into contact with it. Some astrochemists believe that HeH+ will exist naturally in interstellar space. Some cosmologists believe that HeH+ was actually the very first molecule to be created after the Universe was born.
Chemistry was simple in the early Universe. There was nothing but Hydrogen and Helium, with a miniscule amount of Lithium thrown in for good measure. Logically then, with enough Helium atoms and enough H+ ions drifting about, some of them must have formed into HeH+ molecules. So then, the first stars that lit up the Universe would have contained HeH+, and how exactly this would have affected their formation and evolution is anyone’s guess. Perhaps HeH+ could have helped radiate away excess energy, helping the early stars to collapse, the same way carbon monoxide does in the Universe we see up in the sky at night.
While any HeH+ that may exist in the Universe today has yet to be actually detected, quite a few places are currently being considered as hunting grounds. Dense young planetary nebulae (like NGC 7027), star forming regions, white dwarf stars, luminous blue variables… The list goes on.
While no one’s found it yet, like with many predicted things out in space, it’s only a matter of time. There’s a lot of ground to cover. As I was saying before, the Universe is big…