Some quick research tends to indicate that by the time the white-dwarf stage has been reached, any planetary nebula blown-off by the star has long-since ceased to glow as the gas has re-combined. The planetary nebula is produced from a helium flash when the star is structurally an asymptotic giant branch star <http://en.wikipedia.org/wiki/Asymptotic_giant_branch_star>. Planetary nebula are very short-lived, on the cosmic timescale, lasting only about 10,000 years. On Sat, Jan 24, 2009 at 5:43 PM, Chuck Hards <chuck.hards@gmail.com> wrote:
Not sure, Joe. I know that the Crab Nebula remnant is a pulsar, or spinning neutron star- which is what happens to stars more massive than white dwarves. But I suppose many planetary nebula central stars could be white dwarves- do you know of any that are easily observed visually with an amateur telescope?