After Mission of Gravity
Dragon's Egg by Robert L. Forward
If Mesklin's crushing gravity made you crave even more extreme physics, Dragon's Egg throws you onto a neutron star where cheela aliens think a million times faster than humans and entire civilizations rise and fall between human heartbeats. Forward builds intellectual challenges from relativity and plasma dynamics, turning nuclear forces into survival puzzles that demand your full attention—no apologies, no dumbing down, just rigorous science as the beating heart of alien contact.