User:Tohline/Appendix/Ramblings/OriginOfPlanetaryNebulae
On the Origin of Planetary Nebulae
This chapter — initially created by J. E. Tohline on 19 November 2016 — is intended primarily to provide a summary of the research that has been undertaken following a discussion that took place on 3 July 2013 with Kundan Kadam (an LSU graduate student, at the time) regarding the stability of bipolytropes.
|
|---|
| | Tiled Menu | Tables of Content | Banner Video | Tohline Home Page | |
Context
Why do stars become red giants? In particular, why does a star on the main sequence — whose internal density profile is only moderately centrally concentrated — readjust it internal structure to become a red giant — which has a highly centrally condensed structure — at the end of the core-hydrogen-burning phase of its evolution? It seems likely that this evolutionary transition is triggered by an instability associated with the Schönberg-Chandrasekhar mass limit. The inert helium core that is "left behind" is approximately isothermal — because the helium, itself, is not hot enough to burn — and this is not good from a structural or stability standpoint because self-gravitating, isothermal structures are notoriously unstable. Henrich & Chandraskhar (1941) and Schönberg & Chandrasekhar (1942)) discovered that a star with an isothermal core will become unstable if the fractional mass of the core is above some limiting value.
Treating as bipolytrope with <math>~(n_c, n_e) = (\infty, 3/2)</math> SC showed that this evolution is accompanied by a structural change toward a more centrally condensed structure. Faulkner et al. showed this more cleanly with analytic bipolytropic structures with <math>~(n_c, n_e) = (5, 1)</math>. We wondered whether mass-transfer in a binary system might accelerate the process. What type of instability results from exceeding the SC mass limit? Is it secular, or might it be dynamical? And what is the consequence; does the core collapse on a dynamical time scale; or does the envelope get "kicked off" to form a planetary nebula; or both?
See Also
|
|
|---|
|
© 2014 - 2021 by Joel E. Tohline |