Explosion in space I'm curious about what happens if an explosive substance detonates in space. On Earth, I guess a good chunk of the energy released is carried away by shock waves in the atmosphere. But in space, the medium that supported the propagation of the shock wave on Earth is much more rarefied, so how does that work? 
 A: What is a shock wave ?
It is a form of wave front arising from the scatter of the explosion parts. In the interaction with the medium, the average energy and momentum of the original particles/fragments is diminished transferring them to the wave front.
When there is no medium the particles/fragments/gas following momentum conservation disperse linearly until they meet an obstacle. If they are in a gravitational field they will follow the corresponding paths prescribed by the field instead of linearly, and one would have to solve for those the equations.
Supernovae, discussed in a comment by @JerrySchirmer create their own medium by the enormous amount of matter they have, thus shock waves are generated. That is a different story. If there is no medium there is no shock wave.
A: I am not a chemist but my understanding of a chemical explosion is that there is a very fast release of energy and PRODUCTS. So I would say that the products are accelerated and expand. Since there is no atmosphere to work against, the dynamics is quite simple. A couple of years ago NASA used an impactor to study a comet. Maybe there is a model of the plume in the published papers.
A: Some portion of energy is released as radiation, electromagnetic shockwave will travel in space far away.
Electromagnetic waves travel with a speed relative to medium specifications. When medium specifications are not constant over a distance, shockwaves occur.
A: I was just reading a sample of some random book that I came across ('Great Formulas Explained') and stumbled upon this formula that deals with 'Explosions' : Taylor-Sedov Formula . I then got reminded of this post on 'Stackexchange - Physics' and thought of posting here.
Here's a snippet pulled from this sample:

When a strong explosion takes place, a shock wave forms that
  propagates in a spherical manner away from the explosion. The shock
  front separates the air mass that is heated and compressed due to the
  explosion from the undisturbed air.
Using the concept of similarity solutions, the physicists Taylor and
  Sedov derived a simple formula that describes how the radius (in m) of
  such a shock sphere grows with time (in s). To apply it, we need to
  know two additional quantities: the energy of the explosion E (in J)
  and the density of the surrounding air D (in Kg/m3). Here's the
  formula:
r = 0.93 * (E/D) power 0.2 * t power 0.4

This formula is also used for modelling Supernova explosions. A search for 'Taylor Sedov formula for explosions' on any good search engine will lead you a good number of sources to read. Here are a couple of 'em:
1) Blast Wave
2) Supernova Remnant
3) Supernova Remnant Explained With Formulas
