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I did not take this photo, but I have taken similar like it.
This would be my best guess. I’ve found that going beyond 20 seconds will cause streaking with the stars. The high iso will create some grain, but Canon cameras have a setting buried in the menu called high iso noise reduction; it takes a second photo with the shutter closed and uses info from both images to remove noise. I’m not sure if Nikon has something similar. Photoshop also does wonders removing more noise. The image will be slightly underexposed at these settings if there’s no moon in the sky, but if you shoot in RAW then you should be able to bring shadows back. I wont lie though, the better your lens and camera body are, the better the final results will be.