Chuck, You wrote: " I'm not sure that planetary nebula are illuminated by the central star" That was what the professor form Ohio States' Astronomy Department stated. Again I am no Phd, but Perhaps the idea that the Universe is 13.5 billion years old needs rethinking or perhaps that it takes 13 billion years for white dwarfs to exhaust themselves, I read mention that in some cases it takes 2 billion. She writes: "The ejected outer layers, heated by the hot new white dwarf, form an emission nebula. An emission nebula of this sort - ejected gas which is being excited by a hot white dwarf - is called a planetary nebula. " Erik --- chuck.hards@gmail.com wrote: From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Subject: Re: [Utah-astronomy] White dwarfs and YOU Date: Sun, 25 Jan 2009 20:18:05 -0700 No, I didn't mention that. Jerry was the one who posted about the visibility of white dwarfs in a cataclysmic variable system, not Bishop. I was attempting to distance that from Bishop and try to underline the differences. In my post, Bishop's comments were in quotes, mine were not. Sorry for the apparent confusion. On Sun, Jan 25, 2009 at 8:05 PM, <zaurak@digis.net> wrote:
You also mention that he is talking about white dwarfs from cataclysmic double stars. Perhaps in the case of planetary nebula (I believe most of these are not from cataclysmic doubles), that there is nothing to see until the "life" of White Dwarf is turned on, to illuminate the gases expelled from the red giant. Simply the intermediate period is before the nebula is visible. Again, I imagine most white dwarfs are not the product of double star systems gone wrong.
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