If there trualy are blakc holes in the wh 40k universe then that is what it is, and as for not only black holes, i dotn think anyone has gone close enough to look. That wuld after all be increadably stupid because of time dialation and massive tidal forces because of the high gravity. Even the squat wordls are out of the galaxtic habitable zone. By modern science they should not be able to support any life.