Question About Energy Conservation Of Gas Clouds

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Discussion Overview

The discussion revolves around the energy conservation of a collapsing hydrogen gas cloud in space, specifically focusing on the dynamics of gravitational potential energy, heat generation, and radiation as the cloud compresses. Participants explore the implications of energy loss and transformation in the context of the gas cloud not evolving into a star.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant posits that as the gas cloud collapses, pressure and heat increase due to decreased volume and gravitational trapping, leading to heat radiation into space.
  • Another participant asserts that the energy involved comes from the gravitational potential of the gas, emphasizing that energy is neither created nor destroyed.
  • A question is raised about whether the gravitational potential energy decreases over time as heat is radiated away, given that mass remains constant.
  • It is noted that the potential energy of the gas decreases as it becomes denser, with the change in potential energy equating to the work done in compressing the gas.
  • Participants discuss whether the gas continues to radiate heat even when it reaches maximum density, questioning if potential energy would be exhausted at that point.
  • One participant suggests that the gas will continue to radiate until it reaches thermal equilibrium with incoming radiation, indicating a balance of energy loss and gain.
  • Another participant adds that for the gas to expand again, additional energy would be required, often in the form of heat.

Areas of Agreement / Disagreement

Participants express differing views on the implications of energy conservation in the context of the gas cloud's behavior, particularly regarding the fate of gravitational potential energy and the conditions under which heat radiation occurs. No consensus is reached on these points.

Contextual Notes

The discussion includes assumptions about the nature of energy transformation and the conditions under which the gas cloud operates, which may not be fully defined or agreed upon by all participants.

Who May Find This Useful

This discussion may be of interest to those studying astrophysics, thermodynamics, or energy conservation principles in astrophysical contexts.

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Suppose in space you have a hydrogen gas cloud that is collapsing into a sphere under its own gravity. Pressure and heat rises due a decreased volume and gravity trap.

Let's say the gas cloud is not going to reach fission and won't become a sun, so it's a gas giant.

My question is under such pressure, heat is radiated back into space. According to conservation of energy something has to be lost from the gas giant. What is it?
 
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The energy comes from the gravitational potential of the gas.

There is no energy created or destroyed.

Where's the conflict?
 
Teegvin said:
The energy comes from the gravitational potential of the gas.

There is no energy created or destroyed.


So if the energy is coming from the gravitational potential energy, does than mean that over time the gravitational potential energy decreases? Since heat as friction is released into space as an electromagnetic wave? and mass is constant.
 
Yes, the potential energy of the gas at the outside decreases.

When the cloud is spread out, the gas closer to the outside has more gravitational potential energy with respect to the centre than it does when it is dense. The change in potential energy in going from spread out to dense is equal to the work done in moving and compressing the gas.

Compression causes heating, so the gas heats up and radiates some of that heat into space as electromagnetic radiation, yes. :cool:
 
Thanks, that summed it up.
 
When it compresses and becomes as dense as its going to get, does it still radiate heat? Seems like the potential energy would run out - having all been converted to heat from the compression - when it hits that state.
 
It will continue to radiate until it reaches equilibrium with whatever radiation is hitting it. After that it still loses energy, but it gains energy at the same rate.
 
In other words, for it to 'spread out' again would require more energy, and often the energy that causes such an event is heat!
 

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