Depending on the density reached in the cores of neutron stars, such objects
may contain stable phases of novel matter found nowhere else in the Universe.
This article gives a brief overview of these phases of matter and discusses
astrophysical constraints on the high-density equation of state associated with
ultra-dense nuclear matter.Comment: 16 pages, 11 figures, Contribution to Proceedings of the 3rd
International Workshop on Astronomy and Relativistic Astrophysics (IWARA),
3-6 October 2007, Joao Pessoa, Brazi