I'm not sure what you mean by "fusion". If two black holes come together, they merge to form a single black hole. There is no fusion involved. Whether or not it is super massive would depend on their original sizes but probably one of them would have to already be super massive.How can two Black holes fusion and consist a supermassive Black Hole ?!
ThanksThe OP is probably wondering about the details like when a sun comes to close to a black hole and theres a stream of material from the sun being sucked into the black hole.
For two black holes neither will give up material and so they'll act like two point masses coming together. The event horizon will look like two spheres merging into one larger one if you could even see it.
Thank you for information But i didn't understand 'Schwarzschild or Reissner black hole ' and 'Kerr or Newman black holes'Black hole singularities can simply collide only if both are Schwarzschild or Reissner black holes, AND they are colliding along straight line between the point masses. Then the result is also a Schwarzschild or Reissner black hole.
But what happens when two Kerr or Newman black holes merge? How do the two separate ring singularities evolve into one ring singularity?