In presence of DM-neutron interaction, DM particles can be captured inside a neutron star (NS), subsequently a dark core is formed inside the NS after thermalization. If DM is bosonic, then DM particles can form Bose-Einstein condensate (BEC), which has two major implications in NS observables. If DM is non-annihilating or feebly annihilating, the dark core can collapse due to the onset of  self-gravitation, leading to a minuscule black hole (BH) formation inside the NS.