Question regarding Supernova SN1987

[Oblivion]

I have a question regarding Supernova SN1987A. I was wondering if anyone could tell me if the gas ring that surrounds it was the result of the explosion itself, or if it was there prior to it?

 

[Chronos]

It's the result of the star going supernova. As the core collapses, the outer layers of the star are ejected.

 

[Oblivion]

Ok that's what I figured, but this brings up another question: the gas ring is supposed to become more visible as the shockwave approaches. However, I was wondering how the gas ring got outside the shockwave in the first place, and why is there a difference in velocity between the two?

 

[Chronos]

When the core collapses, there is a recoil effect. In a supernova, this gives the gas shell a huge jolt of energy. Bear in mind, the initial collapse basically leaves the outer atmosphere as an abandoned child [when the core of the sun collapses, the outer shell will be outside the orbit of the Earth and the collapsed core will be about the same size as earth]. The aftershock of the core collapse propels the atmosphere.

 

[Labguy]

Ok that's what I figured, but this brings up another question: the gas ring is supposed to become more visible as the shockwave approaches. However, I was wondering how the gas ring got outside the shockwave in the first place, and why is there a difference in velocity between the two?

This site here: http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit3/supernova.html gives a good explanation of Type II supernovae (like 1987A) and even explains the expanding gass shells and shockwave as you are discussing.

Lower down the page, SN 1987A in particular is discussed.