Now here is update to my work.
Gimp:i do not found any good tutorial for realistic galaxy.But i found some free Photoshop galaxy brushes.
So first i made starfield (there is very good script for starfield)then i make galaxy with brushes.Next i use sparkle filter,then i added some supernovas.
And last i put my spaceship there-the ship is "wrong color"- i think.it should be more bluish color than grey....
And if you have some critics or suggestions,tell me!

That big chunk of blue right next to the ship really distracts me. I do appreciate the fact you took it a step further, but with all that blue, wouldn't the ship itself have a blue tint to it?

Yeah i know.... that blue chunk must be more transparent and more colors and that ship should be more bluish.
but now i have new space background under work

Very Nice again!

If you haven't already discovered it, deviantART (http://www.deviantart.com) has a huge collection of space art tutorials. One member, taenaron, was a gallery moderator of the science fiction & space art gallery for a long time and he has a collection of the 'best' space art tutorials in his favorites area.
http://taenaron.deviantart.com/favourites/9264622
The tutorials for Photoshop generally work equally well in GIMP.

If you search the tutorial section of deviantART, http://browse.deviantart.com/resources/tutorials/ you'll find a wide assortment of additional space art related tutorials.