After a star becomes a red giant, most if not all of the planets orbiting it are usually destroyed. However, the red giant is still quite huge and can be orbited. Let's say a solar system is divided into two parts, inner and outer, like the one we currently live in, though for the sake of this question, not identical. When the star swells, the inner system is, obviously, completely and totally destroyed and burned into nothingness. The outer system becomes the new inner system. At this point, over time, could new planets form and create a "new" solar system around the red giant?
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5$\begingroup$ "the inner system is, obviously, completely and totally destroyed and burned into nothingness." I challenge that assertion, mainly because neither physics nor it's subsidiary chemistry work that way. Because, really... how do you burn a giant chunk of iron in an oxygen-free environment? Vaporize it? Sure, but the iron still exists. And if it's a gas giant, the methane will just get blown away. But still exist. $\endgroup$– RonJohnCommented Aug 8 at 9:24
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1$\begingroup$ @RonJohn They might end up swallowed by the star and sink to its bottom, thus ceasing to exist as a planet? $\endgroup$– gerritCommented Aug 8 at 12:39
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$\begingroup$ @gerrit "sink to the bottom", as in the Sun's core? $\endgroup$– RonJohnCommented Aug 8 at 15:26
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1$\begingroup$ @RonJohn Yes. :) Or at least in that direction — I'm not sure if one can still speak of a planet the remains are physically within the star, nor of the physics in the interior of a (red giant) star. $\endgroup$– gerritCommented Aug 8 at 15:44
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1$\begingroup$ @RonJohn If a planet gets into the internals of an expanding star, it will obviously be slowed down by the viscosity of the expanding material. $\endgroup$– RuslanCommented Aug 9 at 12:24
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2 Answers
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Possibly.
Two reasons. Firstly, planetary debris and possible moon-like objects that appear to be being perturbed by a planet have been found very close to a white dwarf. The suggestion is that these are too close to have been present when the red giant progenitor of the white dwarf was "alive". So, these bodies have probably coagulated from debris after the white dwarf formed.
Secondly, a significant fraction of white dwarfs appear to have been polluted by rocky material that has fallen onto them from some sort of debris disk around them (see Swan et al. 2023 for recent JWST observations of such an object). Perhaps some of that material can form planetary bodies - see the first point.
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No.
To make planets you need raw materials. When a star is first forming from a cloud of dust and gas, some of the dust and gas can form into a disc around the proto-star and in that disc, planets can grow.
But when a star expands into a red giant it doesn't form a new disc: where would the dust and gas for the disc come from?
Now, the red giant is much more luminous than the main sequence star that it developed from, and so planets and moons that were frozen can become habitatable. It is even speculated that life could develop on one of the moons of the gas giants as the sun gets bigger and brighter. But the red giant phase of a star's life is fairly short, so it is unlikely that there would be time for complex life to evolve. Of course all that is very speculative.
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4$\begingroup$ Don't red giants expel lots of dust and gas, especially when they form a planetary nebula? $\endgroup$– AstrovisCommented Aug 7 at 23:24