
Astronomers have spotted the universe’s first molecule - pseudolus
https://www.sciencemag.org/news/2019/04/astronomers-have-spotted-universe-s-first-molecule
======
_bxg1
Clickbaity title. Should have been "Astronomers have spotted the universe’s
first _type of_ molecule", or "Astronomers have spotted _molecules like_ the
universe’s first".

~~~
jiveturkey
sorry to say so, but that seems rather obvious. _of course_ astronomers
haven't spotted the actual first instance of a molecule.

~~~
snakeboy
If you come from a non-technical background, where many physical discoveries
of varying difficulty all _seem_ impossible, it's an obviously misleading
headline.

~~~
subw00f
How often people of non technical background go to science magazine with so
little knowledge that they assume there's a way to find _the_ universe's first
molecule?

~~~
djakjxnanjak
I don’t know much about physics/astronomy. My rough understanding is that very
early in the Big Bang, all matter/energy was condensed into some really exotic
form and it turned into atoms and molecules as it expanded. When I read the
headline, I imagined that during the Big Bang a molecule was produced that
somehow had a lot of energy and emitted that energy in such a way that we
managed to detect some kind of echo of it today. I have seen images described
as images of radiation from the Big Bang, so this sounded impressive but not
unbelievable to me.

~~~
_bxg1
This was my impression too. I still thought it was _probably_ not what they
meant - maybe a 10% chance that it was - but it was misleading nonetheless.

------
ridgeguy
I’m curious why the helium hydride (HeH) would form before H2 (molecular
hydrogen). Hydrogen (single atomic form) should have formed a larger fraction
of post-bang elements than helium (and much more than lithium). I didn’t see
anything in the article about this.

HeH has a binding energy of 25.1 kJ/mole [1]. H2 has a dissociation energy of
104 kcal/mole [2]. Expressing these energies in eV per molecule, it’s ~0.26eV
for HeH and ~ 4.5eV for H2. So H2 would seem to be stable at higher
temperatures and should form first in a cooling gas mixture whose particle
kinetic energies are declining.

Or is “binding energy” different from “dissociation energy”?

Would like to understand a little of the thermodynamics that allow HeH rather
than H2 to be the primordial molecule.

[1]
[https://en.wikipedia.org/wiki/Helium_hydride_ion](https://en.wikipedia.org/wiki/Helium_hydride_ion)
[2] [https://en.wikipedia.org/wiki/Bond-
dissociation_energy](https://en.wikipedia.org/wiki/Bond-dissociation_energy)

~~~
mirimir
That was also my first reaction.

But TFA says that H+ reacted with neutral He. That gives you HeH+, which is
what they detected. And I see that the ionization energies of He are 2372.3
kJ/mol for the first electron, and 5250.5 kJ/mol for the second. But the
ionization energy of H is just 1312.0 kJ/mol. So neutral He would have formed
long before neutral H, and He plus H+ was the first possible combination.

Also, HeH+ is an extremely strong acid, so it would grab an electron from just
about anything else that it encountered. And neutral HeH is not stable.

~~~
logfromblammo
In the post-bang environment, you can flip those numbers around to see the
order in which the hot nuclei capture the hot electrons. A [He+2] nucleus can
grab hotter electrons than a [He+1] ion, which in turn can grab hotter
electrons than a [H+] proton.

So at a temperature cool enough for neutral He to exist and still hot enough
for [H+] ions, they were pretty much the only massive things around that could
react with each other.

If an [HeH+] caught a hot electron, it would fall apart into He and H, with no
further need to share electrons. A [H+] could glom onto that neutral H to make
[H2+] (which also forms when cosmic rays blast through an H2 cloud). If an
[H2+] caught another electron, the H2 and another [H2+] will react to make
[H3+] and H. So it turns out [H3+] is a pretty common hot cloud molecule, too.

Plain old H2 doesn't exist by itself until the temperature drops enough for
those positive ions to catch electrons and stop being an acidic plasma.

------
gus_massa
The article says "HeH", but tt's very important to notice that the molecule
they detected is HeH+ (the charged version), not HeH (the non charged
version).

I can't find the information now, but the non-charged version is probably not
stable (or the bound is extremely weak).

The title of the research paper is: Astrophysical detection of the helium
hydride ion HeH+

------
apo
> Helium hydride (HeH), a combination of helium and hydrogen, was spotted some
> 3000 light-years from Earth by an instrument aboard the airborne
> Stratospheric Observatory for Infrared Astronomy (SOFIA), a telescope built
> into a converted 747 jet that flies above the opaque parts of Earth’s
> atmosphere.

Not quite. The paper makes it clear that what was actually observed was HeH+:

> Here we report observations, based on advances in terahertz spectroscopy8,9
> and a high-altitude observatory10, of the rotational ground-state transition
> of HeH+ at a wavelength of 149.1 micrometres in the planetary nebula NGC
> 7027.

[https://www.nature.com/articles/s41586-019-1090-x](https://www.nature.com/articles/s41586-019-1090-x)

~~~
aeorgnoieang
I don't think it's _wrong_ , tho definitely (somewhat) less precise. An
ionized molecule is still that molecule.

~~~
gus_massa
If you forget to put the charge + or - in a chemistry exam, you will never
approve.

------
csallen
They've spotted the first type* of molecule, no? Not the actual first
molecule.

~~~
ncmncm
They're all interchangeable, right? Unless the first compound was really, for
some reason, between a deuterium and an H3. But the difference in energy
levels would be hard to detect.

In any case, the scarcity of signatures outside violent environments indicates
that no primordial HeH compounds survived, and these are recent re-
occurrences.

So, "the first type of compound". Less punchy, I guess.

~~~
coldtea
> _They 're all interchangeable, right?_

Only with respect to use (properties).

They still all have different histories (space/time lines).

If they indeed have found the first molecule, that would be a huge thing (and
a huge mystery, of how they've managed to (a) find it, (b) recognize it as
such, since all are interchangeable).

------
ncmncm
Why would this form before H2?

Or are they really talking about a first compound? And if they are, why not
say so?

~~~
gus_massa
Read the comment by mirimir, that is based in the research article instead of
the press article:
[https://news.ycombinator.com/item?id=19694140](https://news.ycombinator.com/item?id=19694140)

------
mirimir
Maybe this ought to be merged with
[https://news.ycombinator.com/item?id=19690167](https://news.ycombinator.com/item?id=19690167)

Using the phys.org link, because it's more substantive.

------
mito88
They found one only?

------
Jenz
HeH!

