Basically, the Down Quark is involved in the creation of gravity, because the gravitational field around a neutron star is greater than the gravitational field around normal matter, as there is a higher proportion of Down Quarks in the matter of a neutron star than in ordinary matter. If the gravity is even stronger, as in a black hole, that matter might contain an even higher proportion of Down Quarks, or might be almost completely made of Down Quarks.
Not all black holes are "perfect" with an event horizon and a singularity. The event horizon might not form around an area of dark matter, which is a black hole without an event horizon. Singularities only form in the largest black holes and they have a radius equal to the Planck length and experience Planck time. When a singularity is compressed to less than the Planck length radius, it explodes to form a new universe.