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What is the difference between Supernova Type Ia and Nova? Base on a web search, they seem to have a similar formation process, as they are both white dwarfs in a binary system who absorb masses from their companions. But they result different in mass ejection, brightness and lasting time.

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In a nova, a layer of hydrogen is pulled from a regular star, forming a kind of dense atmosphere around the white dwarf. This atmosphere is heated by the white dwarf, until a critical temperature is reached, and fusion begins in the atmosphere. The white dwarf is rather unaffected by this, and the process of forming a hydrogen atmosphere can restart. Recurrent novae are well known.

In a type 1a supernova, the mass of the white dwarf increases towards the Chandrasekhar mass, of about 1.44 sun-masses. At this point, the degenerate carbon and oxygen, which the white dwarf is mostly composed of, begins to fuse. The energy released is enough to completely unbind the white dwarf.

In a nova it is only the hydrogen atmosphere that explodes. In a supernova it is the whole carbon-oxygen star.

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    $\begingroup$ "This atmosphere is heated by the nova", should this be "This atmosphere is heated by the white dwarf"? As at this stage, the star should still be classified as a white dwarf? $\endgroup$ Jul 20, 2021 at 7:37

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