To be clear, processing is not faking the photograph, all of this is real. Processing involves basic steps to improve the image. You don't add anything that wasn't already there in processing, you are only enhancing the data that exists
For example, we color calibrate our images to have accurate colors to the true nebula. We stretch/brighten the image, to reveal the nebula and stars inside. We can saturate to bring out colors, and play with the histogram to add contrast between space and the nebula. Sharpen to add clarity to fine detail.
None of that is modifying the data, or what is already there. It's still all real, but the way we process enhances the image.
And, this is kind of the art aspect of Astrophotography. Deciding how your image should feel and look through processing.