The Integral Trees

Blurb

The Integral Trees is a 1984 science fiction novel by Larry Niven. Like much of Niven's work, the story is heavily influenced by the setting: a gas torus, a ring of air around a neutron star. A sequel, The Smoke Ring, was published in 1987.
It was nominated for the Nebula Award for Best Novel in 1984 and the Hugo Award for Best Novel in 1985.