Thank you everybody 

You've all given me plenty to think about with regards to technique and depiction, all extremely useful stuff.

I will clarify that this is in fact a drawing. I used graphite dust applied with cotton wool pads to hot press paper for the background. This accounts for it being on the grey side. Even though I managed to get it quite dark it's highly reflective and unfortunatly the scanner picked this up. The Brown dwarf itself was done in pastels with some graphite dust applied with cotton buds (they're for more than sticking in ears ).

I must admit I have been concerned about the graphite dust as this is a technique more used in scientific illustration because of the prescision that you can get with it.