Once, someone had asked two interesting (though absolutely hypothetical) questions: 1) What should happen during the collision of two BHs, one consisting of matter (BH+) and the other consisting of antimatter (BH-)??? Should they form a larger BH or should they be annihilated??? My personal opinion is that -probably- the EH of the new BH is formed before the singularities (of the original BHs) will meet each other. So, as the mass of a BH is concentrated on its center (i.e. on its singularity), the annihilation of their masses will take place after the formation of the new EH (and the vast amount of photons that will be produced from the annihilation will never manage to escape). As a 2nd thought, we cannot really know what will happen when the two singularities will meet each other, as we don't know the "form" of the mass on a singularity or even the laws of Physics that govern it. What's your opinion??? 2) Suppose that there are two neutron stars (NS), one consisting of matter (NS+) and the other consisting of antimatter (NS-), and each of them having a mass somewhat lower than the critical mass for the formation of a BH. What should happen during their collision??? Should they form a BH or should they be annihilated??? My personal opinion is that -probably- there will be an annihilation right on the contact point and this will lead to the gradual annihilation of the whole mass of the two objects before an EH has the chance to be formed. What's your opinion???