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Author Topic:   Star Formation (Star Condensation)
Hoof Hearted
Junior Member (Idle past 4361 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 1 of 33 (390410)
03-20-2007 8:28 AM


I've got what should be a really simple question about star formation...

We are told that after the big bang, the universe expanded and eventually stars formed from the immense clouds of hydrogen and helium gas that stretched across the galaxy.

However, one of the fundamental properties of a gas, is that it attempts to expand as much as possible and will repel other molecules around it. This principal is what keeps the tyres inflated on our cars.

This being the case, I would have expected no star formation to ever have taken place. What force could act upon a body of dispersed gas and initiate the process of causing it condense into a liquid? I can understand perfectly that our sun now holds itself together by gravity. But I would have thought that this force only comes into being when a vast amount of matter is densely packed into an object such as our sun.

Is it possible that gravity can overcome a gas's attempt to expand even when there is initially no concentrated mass of matter?

Ian

Edited by Hoof Hearted, : No reason given.

Edited by Hoof Hearted, : No reason given.

Edited by Adminnemooseus, : Added the "(Star Condensation)" part to the topic title.


Replies to this message:
 Message 3 by fallacycop, posted 03-22-2007 1:27 AM Hoof Hearted has taken no action
 Message 4 by Taz, posted 03-22-2007 2:01 AM Hoof Hearted has replied

  
Hoof Hearted
Junior Member (Idle past 4361 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 7 of 33 (390816)
03-22-2007 4:11 AM
Reply to: Message 4 by Taz
03-22-2007 2:01 AM


Thank you for the involved reply. I accept now that a dispersed cloud of gas can indeed collapse and form a star. But would I be correct in assuming the following?:

1. A tiny amount of gas would always expand because of the lack of gravity.

2. Once seeded, a large cloud will contract because of the effect of gravity.

3. So presumably there is an intermediate size of cloud which causes an equilibrium. The two forces cancel each other out and a stalemate occurs.

Ian


This message is a reply to:
 Message 4 by Taz, posted 03-22-2007 2:01 AM Taz has taken no action

  
Hoof Hearted
Junior Member (Idle past 4361 days)
Posts: 24
From: Chorley, Lancs, UK
Joined: 03-20-2007


Message 10 of 33 (391027)
03-23-2007 7:08 AM
Reply to: Message 8 by CTD
03-23-2007 5:58 AM


Re: More info
I was just reading those articles and realised something quite fundamental in all of this...

When I mentioned the scenario of compressed air keeping my car tyres inflated. I was forgetting that the air in my car tyres is somewhere close to 300°K. If the same quantity of air was at the temperatures encountered in deep space, then I suspect that I would be running on my rims.

So of course a cold gas is relatively easy to compress, and it's a lot easier to for me to understand now how a star can be formed from gravity.


This message is a reply to:
 Message 8 by CTD, posted 03-23-2007 5:58 AM CTD has taken no action

  
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