Subject: Shockwaves in Space

When a fission or fusion explosion occurs on Earth, it generates a 
shockwave that is pretty formidable.
I would think that an explosion in space, such as a nova or an 
exploding sattelite, should also generate a shockwave. But will it 
actually do it?
The reason I am suspicious is that on Earth there are a lot of 
mediums (such as air, water and ground) that shockwaves can be 
carried on. There are no such mediums in space. So if a shockwave 
does occur, what carries it? At what speed would the shockwave be 
carried (I am assuming that it will not be faster than c, the speed 
of light)?
All of the stellar explosions we've seen are both distant and far in 
the past -- the most recently acclaimed supernova took place twelve 
billion years ago, twelve billion light-years away. A shockwave 
didn't carry that far or that long.

Re: Shockwaves in Space