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Sheperd Doeleman said in a TED video that the accretion disk is heated by friction. Is that correct? I thought it might be adiabatic heating from the compression of the gasses.

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It is mainly caused by:

  1. Thomson scattering (coherent)

  2. Compton scattering (decoherent)

Please see here:

https://arxiv.org/abs/1604.00070

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    $\begingroup$ That article is about Compton effects in radiation dominated accretion disks. Doeleman's remark is more general. $\endgroup$ – PM 2Ring May 15 at 17:51
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I see no reason why both effects could not contribute to the heating,one does not exclude the other. Collisions between particles in the accretion disc must make some contributon,but that probably comes under the heading of friction. If there are radioactive materials in the accretion disc,that must also make a contribution,however small.

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    $\begingroup$ I expect that Doeleman is using the term "friction" to cover all inelastic collision processes in the accretion disk. Some heat is generated when new infalling material hits the disk. That material has a lot of kinetic energy (converted from gravitational potential energy), but I guess it's ultimately friction that turns that KE to heat. $\endgroup$ – PM 2Ring May 17 at 7:41
  • $\begingroup$ @Michael Walsby - I'm sure there's lots going on in there. I'm more asking about what's the dominant source of heat. $\endgroup$ – Doradus Jun 16 at 13:26

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