by Ann » Tue Oct 09, 2012 2:51 am
zbvhs wrote:I'm a little confused. I thought sun-like stars went through a red-giant stage before collapsing to a white dwarf. The collapse blows off the star's outer layers and leaves behind a planetary nebula. Has that already happened in this case?
Yes, sun-like stars will expand to become red giants before they die. They will eventually become very unstable and shed their outer atmospheres, finally leaving just their exposed cores, surrounded by a glowing shell, a planetary nebula. (They don't collapse, however.)
It is interesting, as starsurfer pointed out, that Abell 39 is so perfectly round. This suggests a much gentler "expulsion process" than is generally found in planetary nebulae. Compare Abell 39 with this (false color) picture of a famous planetary nebula, the
Cat's Eye Nebula. You can see how ragged the outer parts of the nebula are, bearing witness to the "labor pains" of the progenitor of this planetary as it was going through its transitory phase.
Ann
[quote="zbvhs"]I'm a little confused. I thought sun-like stars went through a red-giant stage before collapsing to a white dwarf. The collapse blows off the star's outer layers and leaves behind a planetary nebula. Has that already happened in this case?[/quote]
Yes, sun-like stars will expand to become red giants before they die. They will eventually become very unstable and shed their outer atmospheres, finally leaving just their exposed cores, surrounded by a glowing shell, a planetary nebula. (They don't collapse, however.)
It is interesting, as starsurfer pointed out, that Abell 39 is so perfectly round. This suggests a much gentler "expulsion process" than is generally found in planetary nebulae. Compare Abell 39 with this (false color) picture of a famous planetary nebula, the [url=http://www.astro.uni-bonn.de/torino2014/20080303-Cat-Eye-Nebula.jpg]Cat's Eye Nebula[/url]. You can see how ragged the outer parts of the nebula are, bearing witness to the "labor pains" of the progenitor of this planetary as it was going through its transitory phase.
Ann