Atmospheric pressure inside a protoplanetary disc

[Galexy]

Summary:: Could there be a place in a newly forming protoplanetary disc where the gas pressure and temperature would be anywhere close to survivable? I am writing a fiction story that takes place there, and I want to know how far from reality this premise would be.

When a protoplanetary disc is forming, presumably there would be a level where the gas (hydrogen/helium) pressure reaches about one bar. The question is; would this level inevitably be to hot (or cold) to accommodate a human presence? I have read through as many related astronomy research papers as I can find and have not come anywhere near answering this question.

 

[anorlunda]

Regardless of pressure, do you consider hydrogen/helium to be a life sustaining atmosphere?

 

[Bandersnatch]

The disks are extremely rarefied. As far as I understand, sufficiently so that their modelling can assume no effective pressure. Take a look at fig.5 here: https://astro.caltech.edu/~lah/review/protoplanetary_disk_theory.armitage.pdf

It estimates temperature vs density conditions in a disk around a young main sequence star (I.e. after it has ignited fusion, which means it's >less< luminous than during earlier stages). The blue line is for the densest, central plane.

For Earth-like 1 bar conditions you're looking for around 300 on the temperature scale, and around 10E-3 on the density scale. From the ideal gas law it follows that you can keep the same pressure by trading an order of magnitude of density for an order of magnitude of temperature. The graph suggests that you don't reach 1 bar until you are effectively well within the star.

 

[Melbourne Guy]

I want to know how far from reality this premise would be.

Are you writing a really hard sci-fi novel, @Galexy? It can be hard to write an engaging story if you are focused on describing accurate physics, and given our knowledge of forming protoplanetary discs, you can bend events and circumstances in whatever way you like. Esp. as your story either involves aliens or us in the far future, because we're not getting anywhere a forming protoplanetary disc without new physics or a radical technology overhaul.

 

[Galexy]

Regardless of pressure, do you consider hydrogen/helium to be a life sustaining atmosphere?

When I say "human presence" I don't mean completely unprotected (although my story characters happen to be naked, except for oxygen masks). LOL

 

[Galexy]

The disks are extremely rarefied. As far as I understand, sufficiently so that their modelling can assume no effective pressure. Take a look at fig.5 here: https://astro.caltech.edu/~lah/review/protoplanetary_disk_theory.armitage.pdf

It estimates temperature vs density conditions in a disk around a young main sequence star (I.e. after it has ignited fusion, which means it's >less< luminous than during earlier stages). The blue line is for the densest, central plane.

For Earth-like 1 bar conditions you're looking for around 300 on the temperature scale, and around 10E-3 on the density scale. From the ideal gas law it follows that you can keep the same pressure by trading an order of magnitude of density for an order of magnitude of temperature. The graph suggests that you don't reach 1 bar until you are effectively well within the star.

Thank you very much for your reply. In my story, I was assuming that the protoplanetary disk had not compressed to the extent that nuclear ignition had taken place. So little is known about the interior of such a beast that I figured I had lots of room to exercise my imagination. If the conditions are really as rarified as the graph indicates, I may have to think of a special case that makes the premise work. Thanks again!

 

[Bandersnatch]

Just to clarify the point about fusion ignition - it might be tempting to play with the idea that before the star ignites there are somewhat more balmy conditions in the centre of the cloud. But there aren't. The gas heats up as it falls down the gravity well, and it has to radiate all that energy to keep contracting. The effect is that the central part of the disk is always hot and luminous, even if the conditions for fusion are not there yet in the initial stages.