Hot answers tagged

65 votes
Accepted

Is it dark inside the Sun?

No, it's not. The radiation field in the interior of the Sun is very close to a blackbody spectrum. If you look in any particular direction the brightness (power per unit area) you see is $\sigma T^4$,...
user avatar
  • 115k
15 votes

Is it dark inside the Sun?

Coming from a different direction as @Rob's, Opacity and Thermal Radiation are orthogonal properties of a material. The photon flux at the interior of the sun is very high, so it is definitely not ...
user avatar
  • 259
9 votes

Why does metallicity increase the opacity inside stars?

Both free-free and bound-free absorption are strongly dependent on the atomic number $Z$ of nuclei in the gas. For free-free absorption it is simply that the emissivity per unit volume of electrons ...
user avatar
  • 115k
5 votes
Accepted

What class of elements are providing the many electrons needed to make the H- ion?

Easily ionised ones like sodium and potassium. Not much from lithium because that is rare. You don't need many free electrons. The fraction of H$^{-}$/H is very small, something like $10^{-7}$ in the ...
user avatar
  • 115k
4 votes

Are any supergiants translucent?

Although I will only tackle one part of the question, I find the following part of a picture from NRAO/AUI/NSF, S. Dagnello, cited from space.com worth sharing: You see the radial structure of ...
user avatar
  • 5,294
4 votes
Accepted

How far can you see in solar plasma at just under 1 solar radius?

If you have a look at the top-left panel of Fig.11 in these lecture notes by Rob Rutten, you will see that the continuum opacity at optical wavelengths at the photosphere is about $10^{-6.7}$ cm$^{-1}$...
user avatar
  • 115k
1 vote
Accepted

What is the meaning of grain opacity and why does it affect the formation time of gas giants?

The cooling of a gas giants outer envelope (which in turn cools the convective interior) is dominated by radiative transport. The radiative flux at the photospheric boundary is $$F_{rad}\propto- \frac{...
user avatar
1 vote

Are any supergiants translucent?

No mass blob of stellar mass is transparent at any wavelength of interest. Opacities $\kappa_{\nu}$(inverse transparency) as function of wavelength becomes really high and broad band at pressures ...
user avatar
1 vote
Accepted

What leads to increase in opacity in kappa mechanism?

It's a bit subtle, the key thing the partial ionization does is to keep the temperature from changing much. What you really want is an increase in density, not temperature. The reason the kappa ...
user avatar
  • 5,142

Only top scored, non community-wiki answers of a minimum length are eligible