A standard technique for astrophotography is to take what are called 'dark frames'. Not specifically applicable to your single exposure Milky Way photos, but still might be worth a try. works like this: A series of (let's say) 3 minute exposures are made of a galaxy/nebula/cluster or what have you. From 'several' images to hundreds - these are called 'light frames'. A series of dark frames are then taken by covering the lens and viewfinder and opening the shutter for the same amount of time used for the astrophotos - maybe 5, 7, or 9 frames. (I use odd numbers because folks tell me I'm odd....) The dark frames are averaged and that average image is then subracted from EACH of the light frames. There is more to it, but that's a brief description. Two free programs that automate much of the averaging, alignment and stacking are (my preferred) 'Deep Sky Stacker' and 'IRIS'. There are others at various price points. There are lots of variables to consider, for one, the temperature of your camera will gradually rise during an imaging session and plateau at some point - might take 30 minutes, might take two hours. In-camera noise reduction is not usually very good for astro.