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What happens when a helium white dwarf accretes enough matter?

Say you have a white dwarf made of helium, what happens when it's core becomes dense enough to fuse helium and how massive would it have to be for this to happen?

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  • $\begingroup$ I don't know enough about white dwarf physics to write an answer, but your question might be addressed in Nomoto (1986), "The fate of accreting white dwarfs: Type I supernovae vs. collapse" (link to pdf). It includes some information regarding accretion onto helium white dwarfs. For a different approach to detonating a helium white dwarf, see The response of a helium white dwarf to an exploding type Ia supernova. $\endgroup$ Commented Sep 19, 2021 at 17:04
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    $\begingroup$ Is the white dwarf accreting helium? $\endgroup$
    – ProfRob
    Commented Sep 24, 2021 at 6:49

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If the white dwarf (WD) is accreting matter, whether or not it is composed of helium, it will undergo a type 1a supernova or form a cataclysmic variable.

The Chandrashekar limit (maximum mass for a stable white dwarf) is independent of the composition of the WD, what matters is the degeneracy pressure and the mass of the WD. So, when the accreted mass exceeds the Chandrashekar limit, it will either give rise to a type 1a supernova or form a cataclysmic variable.

If the accretion rate is high, then the helium white dwarf will undergo a type 1a supernova as a result of a runaway helium fusion. If the accretion rate is not high enough, then the white dwarf will occasionally give rise to novae, forming a cataclysmic variable.

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