Comment Get me one with a really short period! (Score 5, Interesting) 19
I'd really love to see the discovery of a Quark Star.
Black Holes have two modes of creation.
One - observed and well-documented, Supernova explosion, with the core collapsing directly into a black hole.
The other is only known in theory. A neutron star obtaining enough mass through accretion to collapse either from interstellar gas or by connecting with another star (possibly also neutron). Before that happens though, there is a phase hypothesized between the neutron star and the black hole, where the matter degenerates enough that the neutron structure collapses and the star is composed of unstructured quarks. A little more and it collapses into a Black Hole.
No such star has been observed, and we don't know what other effects accompany it. The mass window is very narrow, somewhere between 3 and 4 solar masses, but the exact boundaries are not known. Dual systems with neutron stars of very short period are the candidates for this to happen. Hulse-Taylor binary binary will merge within next 300mln years, but I really hope we can observe one within our lifetimes.