Can't make it up wrote:I thought that a planetary nebula was formed at the red giant phase during the transition from hydrogen fusion to helium fusion in the core, not when fusion stopped. I wasn't aware that main sequence core fusion stopped until a large iron core had been created. Nice, deep exposure though. I didn't even recognize it.
I can never remember the sequence of events during the death throes of a star. However, in the medium-mass stars that create planetary nebulae, an iron core
never forms. Stars that are massive enough to form iron cores end with supernova explosions. I have heard the nebulae created by Wolf-Rayet stars (which
do generate iron cores) referred to as planetary nebulae, but M27 is not in that category.
Notwithstanding my first sentence, I do remember that the iron core doesn't develop until well after the star has left the main sequence.
Doctor: You've developed an iron core.
Type O/B/WR patient: OMG, how much time have I got?
Doctor: Ten...
Patient: Ten what? Months? Weeks?
Doctor: Nine...
[quote="Can't make it up"]I thought that a planetary nebula was formed at the red giant phase during the transition from hydrogen fusion to helium fusion in the core, not when fusion stopped. I wasn't aware that main sequence core fusion stopped until a large iron core had been created. Nice, deep exposure though. I didn't even recognize it.[/quote]
I can never remember the sequence of events during the death throes of a star. However, in the medium-mass stars that create planetary nebulae, an iron core [i]never[/i] forms. Stars that are massive enough to form iron cores end with supernova explosions. I have heard the nebulae created by Wolf-Rayet stars (which [i]do[/i] generate iron cores) referred to as planetary nebulae, but M27 is not in that category.
Notwithstanding my first sentence, I do remember that the iron core doesn't develop until well after the star has left the main sequence.
Doctor: You've developed an iron core.
Type O/B/WR patient: OMG, how much time have I got?
Doctor: Ten...
Patient: Ten what? Months? Weeks?
Doctor: Nine...