Stable quark stars beyond neutron stars: Can they account for the missing matter?

The structure of a spherically symmetric stable dark 'star' is discussed, at zero temperature, containing (1) a core of quarks in the deconfined phase and antileptons, (2) a shell of hadrons in particular n, p, Λ and ∑^- and leptons or antileptons and (3) a shell of hydrogen in the superfluid phase. If the superfluid hydrogen phase goes over into the electromagnetic plasma phase at densities well below one atom/(10 fm) ³, as is usually assumed, the hydrogen shell is insignificant for the mass and the radius of the 'star'. These quantities are then determined approximately: mass = 1.8 solar masses and radius = 9.2 km. In contrast, if densities of the order of one atom/(10 fm)³ do form a stable hydrogen superfluid phase, we find a large range of possible masses from 1.8 to 375 solar masses. The radii vary accordingly from 9 to 1200 km.