Kepler to Investigate Newly Discovered Nebula 38
derGoldstein writes with an article in DigitalTrends: "An amateur astronomer recently discovered what has been confirmed to be one of the best looks yet at a planetary nebula, the last, gassy breath of a dying star. The nebula, named Kronenberger 61 after the enthusiast who discovered it, will offer insights into the future and death of our own sun."
Re:What you are seeing (Score:3, Interesting)
While that's a nice story, it's probably mostly incorrect. Most planetary nebulae like this are created when a massive Population II star (over 120 solar masses) that formed in a metal-poor region that was usually deposited by a population III star, explodes in a pair instability supernova [wikipedia.org]. This is a destructive explosion that usually completely obliterates the original star in one blast, having converted up to a fifth of its mass into iron or higher elements. It isn't some pulsing thing that happens over and over. If there's anything left at all it's likely another form of black dwarf [wikipedia.org] consisting of the heaviest elements of the original star's core visible only in the infrared as it can't sustain fusion and its fissibles decompose. The blown off mass is quite important, as that's where we come from. The densest parts of the shell eventually congeal to become stars in a globular cluster [wikipedia.org]. The globular form of the cluster is commonly seen orbiting galaxies rather than within them because the globular form is destroyed over time by tidal forces and interaction with surrounding masses.
This pulsing and contracting thing has been seen and is quite rare. It occurs when the mass of the star is much higher, and its gravity can recapture most of the mass that was thrown off. This would be visible as not one, but multiple shells of glowing gas.
The generations are given in reverse order. Generation I stars like our sun are the oldest, and are probably formed out of the peripheral debris of just such an explosion. Generation II stars are older, and we haven't yet spied a generation III star that formed of hydrogen and helium when more metallic elements didn't yet exist.