SuperGiant Branch of HR diagram from MassLoss

[Widdekind]

On the HR diagram, the 'Super-Giant Branch' represents an "outgrowth", of super-massive MS stars ([math]\approx 30-60 M_{\odot}[/math]), at (roughly) constant Luminosity. Such suggests, that the fusing-and-radiating star-core is (largely) unaffected, by the outward swelling, of its outer envelope layers, as the star "puffs up". And, the onset of this stellar "super swelling" coincides closely, with (initial) star surface temperatures above the H-ionization threshold (i.e., T_surf> 1 eV).

 

Moreover, such stellar super-swelling may be much more extensive. For, super-massive stars, like Betelgeuse & Rigel, "are surrounded by shells of expelled gas", associated with stellar pulsations and extreme mass-loss, producing irregularly-varying Luminosities, "common to Super-Giants". In particular, Rigel's variability is "turbulent & energetic", exhibiting the characteristic complexity. So, perhaps all Super-Massive stars "Nebularize", above T_surf> 1 eV, corresponding to masses [math]> 30 M_{\odot}[/math], swelling into super-sized Super-Giants, after they reach, and as they then evolve back off of, the MS ?

 

 

 

Hyper-Novae (HNe) shock-shells always expand, into circum-stellar nebulae ?

 

Super-massive stars, like Betelgeuse ([math]\approx 20 M_{\odot}[/math]), cast off considerable amounts of material, into circum-stellar nebulae:

 

And, HN after-glows could be caused, by expansion of HN-generated shock-fronts, into surrounding materials (Bergstrom & Goobar. Cosmology & Particle Astrophysics, p.232):

 

Indeed, Rigel appears to pulsate, with a period of nearly a month, and an amplitude of up to 0.3 magnitudes (~30%). These pulsations push out expanding shells of off-cast material. And, afore-mentioned Betelgeuse also apparently pulsates, albeit with a longer period, of nearly 6 years; and, a correspondingly larger amplitude, of 1 magnitude (~3x). Such pulsations apparently arise when the:

 

... stellar atmosphere is inherently unstable. As the star contracts, it absorbs more and more of the energy that passes through it, causing the atmosphere to heat up, and expand. Conversely, as the star expands, its atmosphere becomes less dense, allowing the energy to escape, and the atmosphere to cool, thus initiating a new contraction phase.

Now, both Betelgeuse & Rigel have comparable masses ([math]\approx 20 M_{\odot}[/math]), even as indicated by their comparable luminosities. But, Betelgeuse has ballooned, to become much bigger. Having traveled (roughly) twice-as-far off of the MS; and, nearly to the "end of the line", on the SGB; then, perhaps Betelgeuse is twice as old, as Rigel -- 10 Myr vs. 5 Myr, say, if such stars are expected to live for the former amount of time ? If so, then Rigel resembles Betelgeuse, in its younger years. And, stellar cycles of pulsation would apparently, then, increase, in both period & amplitude, over star-evolutionary time. And more, even as stellar pulsations can be caused by contraction-induced "fusion flashes", perhaps SNe & HNe can be viewed, as "humongous pulsations", from a proposed star-destroying "final fusion flash", perhaps converting the core completely into iron ?? Perhaps, then, Betelgeuse is a candidate, for a near-future (<1 Myr) HNe & GRB ??

 

Note, too, that super-massive stars, living fast & furiously, and dying young & spectacularly, probably do not stray far, from their GMC 'hatcheries'. So, then, such super-massive stars, may often be surrounded, not only by their own off-cast nebulae, but also the nebular remnants, of their original SF region:

 

Edited August 1, 2011 by Widdekind