Black holes and material interaction
Electrons and protons do not annihilate each other, since protons have a much greater mass than electrons. Only matter and antimatter does, since a particle and its antimatter counterpart have the exact same mass.

However, under the right conditions, an electron and proton can combine. This forms a neutron, since the charges will cancel each other out. This process is called electron capture, and it's the reason why neutron stars form.

I'm not an expert on black holes (I haven't studied GR), but I know that a lot of black holes form from neutron star collapses.