Since the Sun's mass isn't high enough it won't go supernova being a red giant but instead release a planetary nebula. So that seems to be kind of a substitute for a supernova. Would ejecting the planetary nebula be any dangerous for the planets of this system or maybe even other planetary systems close to the Sun?

I mean, the Sun releases its outer layers forming a planetary nebula. What remains is essentialy the Sun's core and will collapse to a white dwarf. What if the released matter (outer layers of the Sun) collides with a planet or moon?

  • $\begingroup$ The Sun's final act will happen more than 5 billion years from now. At that time, Alpha Centauri and the Sun would have performed 21 rotations around the galactic center, mixing with other stellar neighbourhoods across the galaxy. And Andromeda is expected to collide with the Milky Way in this time-frame probably mixing even more and dispersing some of the stars of our galaxy. Even in just 35,000 years (0.0007% of the time until the solar planetary nebula) Alpha Cen will cease to be our closest neighbour. So there's probably no chance for the Sun messing with this system in particular. $\endgroup$
    – Swike
    Feb 7 '20 at 13:39
  • 1
    $\begingroup$ @Swike I see, I'll adjust my question. $\endgroup$
    – user30007
    Feb 7 '20 at 14:49
  • $\begingroup$ Probably most "dangerous" to the planets in this solar system is the increasing brightness of the sun before it becomes a planetary nebula. The sun's brightness will gradually increase over the next 2 billion years or so, then increase dramatically as the sun leaves the main sequence and becomes a red giant. $\endgroup$
    – antlersoft
    Feb 7 '20 at 15:47
  • $\begingroup$ @antlersoft It depends on the distance of the planet or moon. Also, with the Sun becoming a red giant the planets and their orbits would go farther away from the Sun. On the peak of the red giant phase the Earth is said to be there where Jupiter is now. $\endgroup$
    – user30007
    Feb 7 '20 at 16:38
  • $\begingroup$ The mass loss would be more of an issue than the nebula itself - expansion of the planetary orbits may make the system become (much more) unstable, e.g. leading to planet-planet scattering. $\endgroup$
    – user24157
    Feb 8 '20 at 9:44

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