This is more of a physics problem, 3

[trashcanman]

This is more of a physics problem, but deals with gas.
According to Astro Physics Scientists, a star is made when a huge cloud of H2 starts coming together by gravity. The gas packs in tighter and tighter, creating higher and higher pressure and temperature, till pressure/temperature reaches fusion conditions, then the start turns on.

How the heck does this happen? It seems to violate the gas laws I was taught. I was told that a gas will expand to fill the volume allowed. Well, in space volume = infinity. So, how can gas come together???

I will appreciate a real answer. Thanks.

 

[TugboatEng]

Until the star starts generating its own heat the temperatures are very close to absolute zero. The gas laws don't likely apply. At close to absolute zero there isn't a lot of energy available to scatter the gas molecules about.

 

[rb1957]

a gas will expand to fill a container ... on earth, within our gravity well (and probably within any other gravity well too).

I imagine that particles moving in space interact with each other and eventually coalesce.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[3DDave]

It's pretty clear that gravity holds the gas against the planet; the gas giants Jupiter and Saturn show that enough gas will hold together. Collect more gas and one gets a star.

 

[LittleInch]

Correction to the title maybe - This is more of an astro physics problem.....??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

Initially there isn't any gravity to contain the molecules of gas. Here on earth and even in our solar system the gas molecules are hot and moving very quickly. They tend to bounce off each other which causes them to scatter and fill their container.

In deep space at close to absolute zero there is very little energy in the gas molecules so instead of bouncing off of each other they are attracted to each other by their own gravitational forces.

 

[AZPete]

You will note that gas density decreases with altitude. Thus, the driving force is gravity, mutual pull to the cg. Molecular interaction (kinetic energy levels) occurs, but within a gravity field encompassing all of the interactions at large.

 

[TugboatEng]

Also note that at near absolute zero, hydrogen behaves as a metallic solid, not a gas.

 

[rb1957]

this is what happens when you try to apply a fact from our experience (gases fill their containers) to outer space "where's the container ?"

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[AZPete]

Perhaps a better way of thinking about it is to drop the word gas from the lexicon until things heat up. In a near absolute zero environment, best to think in terms of hard pieces of matter like marbles. Gravity, mutual attraction of zillions of marbles, bring them all together. As they coalesce, they will knock each other about, transferring the kinetic energies among themselves (which registers or is measured as temperature).

The attractive force X the distance traveled = energy, so as they all collide from millions of miles of travel, they impart their energies. At some point, you have measurable temperatures, lots of mass, and molecules banging around between high and low states of potential energy. Eventually, you find states relatable to the gas laws.

 

[Snickster]

I agree with Tugboat. In deep space there is no heat content of the H2 molecules therefore their kinetic energy and hence velocity is nearly zero. If they are not moving at any velocity and being able to pack very close together because of the temperature, then the intermolecular forces and gravity can bring the molecules together easily.

 

[fel3]

For more detailed information, the Wikipedia article on star formation (

https://en.wikipedia.org/wiki/Star_formation)

is very good and it has lots of links to published papers and books by professional astronomers. You can follow this up with Wikipedia's very good article on stellar evolution (

https://en.wikipedia.org/wiki/Stellar_evolution).

About twenty years ago I prepared a presentation for my astronomy club about stellar evolution and the then-current Wikipedia article was one of my two starting points for research (the other was a book on the subject by a professional astronomer).

As you can see from these two articles, star formation is a very simple physical process with a lot of nuances.

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--Winston S. Churchill