Rigel Wide. Image Credit: Rheinhold Wittich
What are we seeing in today's APOD? It looks as if B8Ia-type blue supergiant Rigel is creating its own red hydrogen emission nebula.
But that's not possible. At spectral class B8Ia, the temperature of the photosphere (the outer visible layer or "edge") of Rigel is ~12,000 K. That's hot, and it is more than twice as hot as the Sun, but it is nowhere near hot enough to ionize hydrogen and make it glow as a red nebula. But Rheinhold Wittich's image shows us that there
is red nebulosity around Rigel. How can that be?
Well, as Stanislav Volskiy's image demonstrates, the red nebulosity near Rigel is an extension of Barnard's Loop, the very large red semicircular feature seen to the left (east) of the Orion Nebula and Orion's Belt.
Let's check out Barnard's Loop and the names of the principal stars of Orion:
Note in Stanislav Volskiy's image that Saiph does not seem to be involved much (or at all) with Barnard's Loop, because the red nebulosity of this large loop does not change its appearance in the vicinity of Saiph. And Bellatrix, the "other shoulder" of Orion, is a foreground star, and should have nothing to do with Barnard's Loop.
But Rigel
is affecting and interacting with a small part of Barnard's Loop:
Note how the blue light of Rigel turns the red nebulosity of Barnard's Loop into a magenta hue. But also note how Rigel seems to have "cleared a hole" in the red nebula around itself. This is very obvious in the APOD.
In my opinion, it is
the strong wind from Rigel that has blown this hole in the red nebula. Because we expect almost all supergiant stars to blow a strong wind.
The strong wind of Rigel has not only blown a hole in the red nebula around it, but it has sent red cloudlets of glowing hydrogen flying in all directions around itself, including above and below the supergiant star. So blue star Rigel attacks the red clouds that are coming its way.
Ann
Rigel Wide
