What marks the definitive end of fusion for the core of a low-mass star ($\lesssim 2.2 M_\odot$) after the red giant phase?

Answer

The core leaves behind a white dwarf made primarily of helium and carbon nuclei.

For low-mass stars, the core never reaches the necessary temperature for subsequent fusion stages like carbon fusion; fusion stops permanently, leaving a cooling white dwarf remnant.

What marks the definitive end of fusion for the core of a low-mass star ($\lesssim 2.2 M_\odot$) after the red giant phase?

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