For sound to travel, it has to have a medium. In space, there is no medium for it to travel. It has to be made of matter, like a solid, liquid or gas. Sound waves, unlike electromagnetic waves (ie, light waves, radio waves, etc.) have to have something in which the waves can travel through. That is why you can see stuff in space, but not hear it. So, if a Super Nova occurred in space, you could see it because light is an electromagnetic wave and can travel without a medium, but you could not hear it because sound waves cannot travel without a medium.