I feel a bit sheepish saying this as I have not had a go at processing astro images yet, and don't want to cause any offence, so feel free to ignore me completely if you disagree:
It looks a little over sharpened to me, this is clearly visible as black rings around the stars.
This over processing is visible in a lot of terrestrial images too:
http://www.phototakers.com/articles/articles/34.html