The sun is a continuous explosion. The reason we cannot hear the sun is because of the vacuum separating us.

If that space was to be filled with air, would the sun be audible?

  • $\begingroup$ techly.com.au/2015/04/30/… $\endgroup$ – user198207 Jun 27 '18 at 10:02
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    $\begingroup$ Continuous explosion? $\endgroup$ – Kyle Kanos Jun 27 '18 at 11:00
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    $\begingroup$ A constant exothermic reaction with shards of matter flying around all over the place? Explosion seems like a fitting word $\endgroup$ – Ben Crossley Jun 27 '18 at 11:07
  • $\begingroup$ See also physics.stackexchange.com/q/107195/25301 $\endgroup$ – Kyle Kanos Jun 27 '18 at 11:19
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    $\begingroup$ "Continuous explosion" is a self-contradictory phrase. A thing is said to "explode" when it suddenly flies apart into many (possibly, uncountably many) pieces. No phenomenon can be both "continuous" and "sudden." And a thing that flies apart can't do so continuously. $\endgroup$ – Solomon Slow Jun 27 '18 at 13:41

Setting aside your hypothetical premises, as well as the complications of MHD, there is a way to shed some light on your question. Here’s a sketchy answer:

The Sun is a boiling cauldron of turbulent convection. The kinetic energy of fluid motions can be characterized statistically by the well-validated Kolmogorov spectrum. Kolmogorov’s arguments apply straightforwardly to incompressible fluids, but sound waves involve compression. Unless the ratio of length to time scales in turbulent motions were to approach the speed of sound, little energy would couple into compression modes. The cauldron would simmer quietly.

Kolmogorov predicted the distribution of kinetic energy with respect to spatial frequency $(k\sim {{L}^{-1}})$ via glorified dimensional analysis, starting with the driving power per unit mass $(W\sim {{L}^{2}}{{T}^{-3}})$, which is applied at long length scales but ultimately dissipated by viscosity at short length scales. The total kinetic energy per unit mass $({{L}^{2}}{{T}^{-2}})$ distributes as ${{W}^{2/3}}\int{dk\ {{k}^{-5/3}}}$, with an unknown coefficient and long and short length cutoffs set by the radius of the system and viscosity, respectively. The persistence time of an eddy with length scale $1/k$ should scale as ${{k}^{-2/3}}{{W}^{-1/3}}$. Only large-scale eddies have high velocities, but even they don’t get close to the speed of sound.

How to find the parameter W in convective transport? The heat flux (i.e., luminosity per unit area) has units of power per unit area, rather than volume. When a blob of fluid absorbs heat, it becomes buoyant, and the heat will be converted to kinetic energy as the blob rises through a distance determined by gravity and the ratio of thermal expansion to specific heat capacity.

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