Using a high ISO setting to capture starry skies is a pretty common practice when shooting astrophotography, though such an ISO setting can result in a fair amount of noise in your image. This tutorial takes you through several processes in Photoshop to reduce the amount of noise in your final image.
Of course, there are several different software options out there for removing noise from images and still other applications that are designed specifically for processing night sky images. But if you're like me, having the ability to use multiple tools that already exist within Photoshop to accomplish the same result is preferable. Everyone has their own methodology for handling the post-production of their images, but I have found it to be helpful to continually check out ways that other photographers go about editing their shots.
Even though I've been processing my own Milky Way shots for years, I still learned some new things from this video by Justin Majeczky. Especially with programs like Adobe Photoshop, where there are constantly updates to the software that result in new tools and capabilities, there are always new and improved ways to go about handling your images for even better results than what was possible before. So, check it out, you might just add a new tool to your library of post-production capabilities.