A classical nova
Following the discovery, quick follow-up work by additional astronomers indicates the event is a classical nova, which occur in binary systems housing a white dwarf (the remnant of a Sun-like star) and a main sequence, hydrogen-burning star. If the two are in a tight enough orbit, the white dwarf can pull material off its companion. This transferred mass — mainly hydrogen — piles onto the white dwarf’s surface. Eventually, enough accumulates that the temperature and pressure at the surface rise, sparking a thermonuclear reaction. The reaction causes the built-up hydrogen to rapidly undergo fusion into heavier elements, releasing immense amounts of energy in a blast we see from Earth as a nova.
This is a bit like what happens during a Type Ia supernova, but there’s a key difference: Type Ia supernovae destroy their white dwarf progenitors, while classical novae do not. That’s because the runaway reaction happens
within the white dwarf during a supernova, blasting it to bits. During a nova, the reaction only happens on the white dwarf’s surface, leaving the rest of the star intact. So, a Type Ia supernova can only happen once, but a classical nova can reoccur numerous times.
Observers have noted that Nova Reticuli 2020’s position in the sky is close to a previously discovered object, MGAB-V207, which astronomers classify as a VY Scl-type cataclysmic variable — meaning it has previously undergone sudden drops in brightness that astronomers associate with episodes of mass transfer from a companion to a white dwarf. According to an
Astronomer’s Telegram, the coincident positions, coupled with the follow-up observations indicating that this particular outburst is a classical nova, suggest Nova Reticuli 2020 may be the third ever classical nova observed in a star system previously known to contain a white dwarf.
If you’re a Southern Hemisphere observer interested in adding your data to the mix, you can
submit observations to the American Association of Variable Star Observers using the object name MGAB-V207 or N RET 2020.
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