There is more chemistry and more important chemistry in space than you think

[old_eyes]

Last week, I was able to attend and online lecture organised by the Royal Society of Chemistry called "Astronomical Spectroscopy: understanding the complex chemistry hidden between the stars". Now I am a chemist with a keen interest in how the universe works, and did not expect to be surprised, but I was astonished by the latest research. Not only is there more chemistry going on than I suspected, but it is more important.

This event was based on a Faraday Discussion meeting held at STSI in Baltimore in June. You can download all the proceedings here in return for registering Faraday Discussions  Home-Discussion summary &amp;amp; research papers from discussion meetings that focus on rapidly developing areas of physical chemistry and its interfaces<br/><br/>Chair: Susan Perkin<br/>Impact factor: 3.4<br/>Time to first decision (peer reviewed only): 19 days (rsc.org)

Webinar speakers were:

• Martin McCoustra, Professor of Chemical Physics, Heriot Watt University
• Serena Viti, Professor of Molecular Astrophysics, Leiden Observatory
• Wendy Brown, Professor of Physical Chemistry, University of Sussex

It was a pretty dense hour, but I want to pick out a couple of fascinating things that were new to me.

We have now identified about 250 molecules in space using spectroscopy. from small radicals and ions like OH, through simple molecules like water, methane and ammonia, to complex things like amino acids - precursors to life. Unsurprisingly the biggest diversity is found in high density regions like collapsing dust and gas clouds where stars and planets are forming (Nice animation here: Exploring Star and Planet Formation (webbtelescope.org)). Most of the work is done at IR and radio frequencies using a variety of space and terrestrial telescopes, and JWST is a game changer. We can now study the molecular composition and distribution in distant galaxies.

The first amazing idea is that molecules are crucial in maintaining the rate of star formation. Atoms, yes, dust and gas and general stuff, yes, but molecules? Turns out that the collapse of a gas cloud under gravity is limited by the presence of charged ions that create magnetic fields that oppose the force of gravity. Carbon monoxide ice and water ice in space form solid crystals on dust particles that also have an electric field that can mop up the ions. Killing the magnetic field and allowing the cloud to continue to condense until a star can light up. And for small stars like the sun, thermal motion in the cloud can stop gravitational condensation. But molecules are great at radiating energy in the IR, so the excess thermal motion energy can be radiated away, the cloud cools, and the stars can form.

The second idea is that chemistry happens very effectively on the surface of dust particles, driven by starlight, stellar winds and cosmic rays, and shock fronts (pressure and temperature waves). This produces a chemical soup, that includes all the bits and pieces we need for the formation of life. Carbonaceous meteorites are known to contain such a chemical soup, and even more remarkably, the molecules have the same chirality (handedness) as found in life on earth. Many more complex molecules exist in mirror image forms, and life only uses one form (Getting it wrong can be very bad. Thalidomide was synthesised as a 50:50 mix of the two mirror forms. One was the active drug, and the other was toxic - leading to all those birth defects).

Another interesting idea is that different drivers are important at different points on the timeline towards formation of stars and planets. Cosmic rays are energetic enough to get chemistry going with simple molecules in a very cold dense gas cloud. As the star starts forming dust particles covered with a layer of ice have a catalytic surface that can form more complex molecules, and then as the star lights up it emits high energy jets (Herbig-Haro objects). These shocks allow high energy reactions to happen - increasing the range and complexity of molecules that can form.

I apologise if this is all horribly boring, but I was just fascinated and surprised by the range of molecules that can form in space, and just how important they are cosmologically.

[tomato]

Thanks for this, I am a Chemist by training but  mostly saw it as a means to an end of furthering my career. I sure I would have found it more interesting if I could have attended a few lectures like the one you have described.

[Zermelo]

Very interesting, thanks for posting.

It looks like we need to extend the list of "things that needed to be right, in order for us to be here".

[Gfamily]

If you read the book "First Light: Switching on Stars at the Dawn of Time" by Emma Chapman, one of the questions that needs to be determined about the very first stars (the Population III stars) is what was the Initial Mass Function of stars formed when the primordial gas clouds collapsed. As there's only Hydrogen and Helium (and possibly a very little Lithium), only 1 molecule (H₂) can exist to be implicated in the cooling required to allow collapse. 

The Initial Mass Function gives the size distribution of the stars that were produced - and the larger the stars that were formed in the first generation of stars, the more rapidly heavy elements can be created and (importantly) dispersed back into the interstellar medium to form the next generation of stars. 

[old_eyes]

On 11/11/2023 at 16:26, Gfamily said:

If you read the book "First Light: Switching on Stars at the Dawn of Time" by Emma Chapman, one of the questions that needs to be determined about the very first stars (the Population III stars) is what was the Initial Mass Function of stars formed when the primordial gas clouds collapsed. As there's only Hydrogen and Helium (and possibly a very little Lithium), only 1 molecule (H₂) can exist to be implicated in the cooling required to allow collapse. 

The Initial Mass Function gives the size distribution of the stars that were produced - and the larger the stars that were formed in the first generation of stars, the more rapidly heavy elements can be created and (importantly) dispersed back into the interstellar medium to form the next generation of stars. 

I have read "First Light: Switching on Stars at the Dawn of Time", and isn't it a great read? Thanks for pointing out the issue in the early universe. I did not immediately make that connection. I looked up a few papers (most of which were way beyond me) and gleaned a few points. Population 3 stars are often massive, and there is something called the Jean's density at which gravity overcomes any push back from thermal motion or magnetic fields. Models also suggest that there is enough energy dissipation from several processes involving H₂, H and ions to allow the cloud to reach the Jean's ratio. Some authors suggest that HD may have an important role to play as it has a dipole, which H₂ does not. Others say there is not enough D around to make this a viable process.

So as with much of the history of the very early universe, there is no agreed view yet.