Dragon's Egg from Robert L. Forward. I heard about it on the fediverse, and I am really glad I did. It's a hard sci-fi book about the interactions between humanity and a highly intelligent alien species that lives on a neutron star with 67Billion Gees.
I loved it! Haven't seen many people talk about it outside of whatever initial recommendation list I had heard it from. I really enjoyed the mix of hard sci-fi and socio-political commentary. Really reminiscent of Heinlein's best in that aspect, from what I recall.