The making of a magnetar

Last year I pondered magnetar creation. Only about 31 were known as of March 2020; that May a 32^nd might have been spotted in the act of creation, a kilonova.

Now Tomer Shenar et al. may see their origins before creation (pdf). HD 45166 used to be a ternary; now, it is known as a binary but one of its stars had been a merger of two helium-rich stars. Thus amalgamated, A is a 43 kilogauss (= 4.3 T) magnet. By contrast Jupiter is low-teen gauss (1 mT); Earth's field isn't even one gauss. HD 45166's stars are far-enough apart that micronovae likely don't happen (on A).

As only two-star-mass, normally HD 45166A would just redgiant like our star will. But... the helium. Instead this paper predicts the electron-capture scenario, type Ib or IIb depending on the amount of hydrogen retained. Thus, although it will redgiant; the concurrent implosion won't go into a white-dwarf, but into a neutron-star. That star will keep its field, and upon implosion will spin even faster. That's a recipe for magnetars.