Does Betelgeuse (and other giants) have a photosphere ?

[skysurfer]

I wonder whether such huge giants have a photosphere due to their extreme thinness (average 0.00061kg/m3: about that of air of 0.5 mbar at standard temperature), compared to the Sun's 1410 kg/m3: slightly heavier than water.
So large part of the body is semi-transparent so one can see background stars through it.
I think even bluish supergiants like Rigel, Deneb or Gamma Cassiopeiae are not completely opaque at their edges.

What are your ideas on this ?

My hypothetic idea is the attached image.

[DJDD]

Interesting question.

I wonder if the brightness of the star would obscure everything behind it?