Question About Energy Conservation Of Gas Clouds

[waht]

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?

 

[Teegvin]

The energy comes from the gravitational potential of the gas.

There is no energy created or destroyed.

Where's the conflict?

 

[waht]

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.

 

[Teegvin]

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.

 

[waht]

Thanks, that summed it up.

 

[FrigginGenius]

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.

 

[Teegvin]

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.

 

[KingNothing]

In other words, for it to 'spread out' again would require more energy, and often the energy that causes such an event is heat!