Thanks for posting to the Astrophotography Forum.
The typical way to get darker blacks in images to adjust the histogram by moving the "Black Point" up to a higher value. The histogram of unprocessed images has a range from 0 to 255, with 0 representing black and 255 representing white. Moving the bottom of that range from 0 to higher values will increasingly darken the image.
The details for how to do this depends on the software you are using to process your images. Most of the software that I've seen have a tool called "Levels" for basic histogram adjustment using three points (Black Point, Grey Point, White Point) and a tool called "Curves" for more advanced multi-point histogram adjustments.
Keep in mind that those tools can usually be applied to the composite RGB channel or to the individual R, G, or B color channels.
Nice detail, I love the composition!
In September, my wife and I went camping near Cherry Spring (Lyman Run) and captured some Milky Way images from the campsite. I have been working to process them and was trying to figure out how to get darker blacks in the images.
I stacked 14 images of 10 secs at ISO1600 taken with a unmodified Canon Rebel T6i using a Rokinon 14mm f2.8 lens.