Nova, supernova

Supernovae get all the press, but there's a reason for that prefix. The baseline is the "nova", the "new star" that fades away. To that, Hillman, Shara, and Prialnik: doi 10.1038/s41550-020-1062-y offers a lifecycle for the average nova.

(h/t Science Daily, itself h/t this presser. These constitute the most inept summary of a paper I've read in some time. Our sun is not a red dwarf; it's yellow - as we all learnt from reading Superman comics at age seven, or from watching the cartoon at six. Also, the link is a mailto. And is Shara really "the lead" if Hillman is so noted in the paper? Be better.)

Think of the nova as a Type 1 supernova. (Type 2 is the single-star blazeout.) Two stars orbit each other: one white-dwarf; one main-sequence "dwarf" or maybe giant. The white dwarf, being more compact (henceforth called, "the dwarf"), keeps its integrity. The main-sequencer loses its outer layers to the dwarf. Eventually the dwarf has acquired a shell of hydrogen. That stolen hydrogen undergoes fusion like the good ol' days. But now, the fusion happens really fast. That's a hydrogen bomb visible from Earth - the nova.

Type 1 happens when it's so violent that it rips the dwarf to pieces. Those follow the same template such that they can be used to calibrate the distance from Earth; we use them to track the time-space distance to various galaxies. UPDATE 7/23: Those aren't well understood either.

But back to normal nova. These don't rip the dwarf. Some mass is lost into space, and I guess it might jostle the stars around some; but rarely enough to disassociate the pair. So the thinning star is still there and the dwarf is back to where it was. That means the process can happen again.

Shara / Hillman (and Prialnik, fetching coffee perhaps) ran some simulations and explains how. They go nova and nova-like and nova and ... Later, nova / novalike / dwarf-nova. Much later, nova / novalike / dwarf-nova / detached. We catch them at their brightest, and when we catch them; therefore, the novae we see here are usually the former, soon after the binary first forms. The Eta Cancri system may form as such after its red-giant collapses.

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