As far as I know exotic stars are composed of degenerate matter created by the balance between gravity and pressure of exclusion principle and as the mass of the star grows it goes into more compressed stages. At the same time with growing density of the star gravitational pull rises and so does its escape velocity.
The thing I don't understand is why the point at which escape velocity reaches the speed of light is the same point as the one at which star becomes a black hole? Why there are no "black stars" which hadn't collapsed? Is there some connection between exclusion principle and the speed of light?