Are you thinking about Robert Forward's "Dragon's Egg"? The aliens live on the surface of a neutron star passing through the Solar System, and the "chemistry" o

Are you thinking about Robert Forward's "Dragon's Egg"? The aliens live on the surface of a neutron star passing through the Solar System, and the "chemistry" on the surface of the neutron star is much faster than our chemistry, consequently the aliens' society evolves much quicker.