Where Does the Radiated Energy Come From in a Gravitational Collision?

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Discussion Overview

The discussion revolves around the source of radiated energy during a gravitational collision between two massive bodies. Participants explore the conversion of gravitational potential energy to kinetic energy and subsequently to thermal energy during the collision, considering both Newtonian and relativistic perspectives. The conversation touches on concepts of mass, energy conservation, and the implications of binding energy.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that the radiated energy comes from the gravitational potential energy of the bodies when they were in space, which is converted to kinetic energy as they move towards each other.
  • Another participant suggests that the kinetic energy could be released as heat energy during a partially inelastic collision, indicating uncertainty about their understanding of the mechanics involved.
  • A later reply mentions that some kinetic energy might be used to deform the masses upon merging, implying that not all gravitational potential energy converts to radiated energy due to losses.
  • One participant asserts that energy associated with the gravitational field is part of the mass and is accounted for after the particles merge, questioning the clarity of the original inquiry.
  • Another participant challenges earlier claims by stating that the mass of any bound system is less than the mass of its unbound constituents, introducing the concept of mass deficit and binding energy.
  • There is a reiteration of the idea that while energy is radiated away, the total mass-energy equivalence remains intact, suggesting a complex interplay between energy forms.

Areas of Agreement / Disagreement

Participants express differing views on the source of radiated energy and the implications of mass-energy relationships. There is no consensus on the correctness of the claims made, and multiple competing views remain throughout the discussion.

Contextual Notes

Some participants acknowledge their lack of expertise in the area, which may affect the reliability of their contributions. Additionally, there are unresolved assumptions regarding the nature of the collision and the specifics of energy conversion processes.

dtfroedge
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Presume there are two massive bodies in open space, having zero relative velocity, and having the same space ambient temperature. That is, the incoming and out-flowing black body radiation is balanced and the temperature is unchanging. Presume these bodies become gravitationally attracted, and fall together. On impact the temperature will rise, and then the excess thermal energy will be radiated away, returning to the ambient state. By both Newtonian and Relativistic mechanics, the total rest mass is equal to the sum of the rest mass of the two combined bodies. (Black Hole theory depends on it.)
The question is, from whence did the radiated energy come?
 
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From the gravitational potential they had when in space.
This was converted to kinetic energy when they started to move towards each other.
The k.e. was converted into heat in the inelastic collision, and the heat was radiated away.
 
This is certainly not my area of expertise and I am quite probably wrong, but it would seem that the kinetic energy of the bodies, built up as they fell toward each other through the force of gravity could be released as heat energy if this were considered a partially inelastic collision. It's a good question, and I'd love to be corrected on this if I'm wrong...
 
Update: Stonebridge, you beat me to it, but at least it looks as if I was thinking along the correct lines...
 
I should have added that some of the (kinetic) energy could have been used to deform the masses when they merged; depending on how they actually did that. So that the original source was the gravitational p.e. - though it won't have all been converted into the radiated energy. There would be some losses on the way!
 
Remember, any energy associated with the gravitational field is part of the mass, and is all accounted for after the particles are merged.
 
dtfroedge said:
Remember, any energy associated with the gravitational field is part of the mass, and is all accounted for after the particles are merged.
I don't see a question in there (and it doesn't sound right anyway...)...what are you getting at?
 
There was a quantity of energy radiated away, yet the entire e=mc^2 is still there
 
dtfroedge said:
the total rest mass is equal to the sum of the rest mass of the two combined bodies.
dtfroedge said:
Remember, any energy associated with the gravitational field is part of the mass, and is all accounted for after the particles are merged.
dtfroedge said:
There was a quantity of energy radiated away, yet the entire e=mc^2 is still there
Actually, all of this is incorrect. The mass of any bound system is always less than the mass of the unbound constituents. This is called the "mass deficit" and is related to the binding energy of the system. It is really only significant for nuclear binding, but it applies to the other forces also. Your specific scenario is described in the 3rd paragraph in the Mass Deficit section of the Wikipedia article on Binding Energy: http://en.wikipedia.org/wiki/Binding_energy
 
  • #10
DaleSpam said:
Actually, all of this is incorrect. The mass of any bound system is always less than the mass [/url]

DaleSpam
You're right, very good.
 
  • #11
I am impatiently waiting for a point here, dtfroedge.
 

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