Quark star

Quark stars are truly strange -- some may have made a transition to a type matter known as "strange matter", consisting of phenomenally dense material in which the particles that make up atomic nuclei have fallen apart. They are intermediate between neutron stars and black holes in density. Quark stars can also be more compact and cool faster than neutron stars. In fact, some might even be ultra-compact -- so dense that light itself can orbit.

Strange stars in the Galaxy include RX J185635-3754 and 3C58.