Thor's Helmet: Pre-Supernova with Emissions Nebula?”

[Stratosphere]

I read that Thor's helmet (NGC 2359) is in a pre-supernova stage, but there is an emissions nebula around it. How this possible if the star is hasn't gone supernova?

 

[mgb_phys]

Don't know the specific object but giant stars lose their outer envelopes in the late stages of evolution.

 

[negitron]

Don't know the specific object but giant stars lose their outer envelopes in the late stages of evolution.

Right. See Eta Carinae as an example of just such a pre-nova star.