Dragon's Egg by Robert L. Forward is a novel that has a species living on the surface of a neutron star.
Thank you! Did not realize there was a Lem book I had not read.
Star Maker, by Olaf Stapledon also touches on this.
this was amazing thank you! do you have a list of books you read or recommend (goodreads) to peek at?
Not at the moment, but it’s a good suggestion. I should start putting something together like that. Feel free to email me though if you want to talk about books. You can find my email at the link in my profile.