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Author Topic: What happens when the last star burns out?  (Read 1526 times)

Offline bizerl

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What happens when the last star burns out?
« on: 26/11/2012 23:18:07 »
This is more a conservation of energy question than anything else. If, say, a rogue planet is in interstellar space, cooling gradually as the molten material inside slowly hardens, what happens to the energy that was keeping it warm? I understand that energy can't disappear, it just changes form. Does the mass of the planet very slightly increase in step with E=mc2?

If you then extrapolate that question to the eventual loss of all heat in the universe due to the increasingly expanding universe, what happens to the thermal energy that was providing that heat? again, does it change in to mass?

If so, could the process of the big bang be described as the gradual conversion of pure energy, to pure mass?


 

Offline evan_au

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Re: What happens when the last star burns out?
« Reply #1 on: 27/11/2012 10:31:36 »
The energy of a rogue planet comes from its initial temperature, supplemented by sources such as gravitational collapse and radioisotope decay  (if the body were large enough to sustain some hydrogen fusion, it would be classified as a brown dwarf rather than a rogue planet).

This heat is radiated off into interstellar space, which at present has a typical temperature about 2.7 degrees Kelvin (very cold!).

Because the planet is radiating energy, and energy is equivalent to mass (according to Einstein), the rogue planet will be losing mass, but very slowly (this is the opposite to the suggestion that cooling increases mass).
Against this, a rogue planet will sometimes collide with and absorb atoms of the thin gas and dust grains in interstellar space, so overall it will probably be slowly gaining mass.

Because the universe is expanding at an increasing rate (due to an unknown that we call dark energy), there is an increasing amount of space through which this heat is diluted, and it will become increasing red-shifted to even lower energy than its current 2.7K, allowing such a rogue planet to eventually cool even closer to absolute zero.

Quote
could the process of the big bang be described as the gradual conversion of pure energy, to pure mass?

I think that our current description of the Big Bang would better be summarised as "the gradual conversion of pure energy, to empty space".

 

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Re: What happens when the last star burns out?
« Reply #1 on: 27/11/2012 10:31:36 »

 

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