find me similar background as on a hoodie

hi i have this design with an astronaut and behind there is a background with a galaxy half green half red. i already have the astronaut side, all i want is to find if possible or if not using existing galaxy hd photo re-create the background same as on the hoodie design example hope this is clear. note: this design has involved 2 photos mixed together in photoshop, one photo in one layer in the back and one photo another layer on the front on top of this background. i need the layer in the back. thank you hope it makes sense