Some cameras have a 'long exposure noise reduction' setting which should eliminate hot pixels and reduce digital noise. Two exposures are taken in immediate succession, the first with the shutter open with your image in view, the second with the shutter closed. The latter will consist only of black, hot pixels and noise. This second exposure is 'subtracted', so-to-speak, from the actual image removing some of the excess noise and hot pixels.
As you will have probably already figured out, this setting means that it will take twice as long to take the photo: X seconds for the first exposure with the shutter open and X seconds for the subsequent exposure with the shutter closed. Whether waiting double the time is something you want to do will obviously be a function of the results so if you have the setting, try it out.
Opinions vary as to the effectiveness. Personally I always use it and don't mind the extra wait time (although I went through a phase of taking ~15-30 min exposures and that was a real pain!).
Scroll to the bottom of my post here and you'll see an example: https://photo.stackexchange.com/a/114106/88874
This was a 10 minute exposure (i.e. 20 minutes with long exposure noise reduction activated) at 2am and there is no noise in the dark areas. FYI the red sky was light pollution from a nearby town that was invisible to the eye. I was stumbling about in a pitch black field.