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I know that the radius is directly porportional to mass, but this result seams crazy.

Would be this effect responsible for the universe accelerated expansion?

May I say that this effect is black energy?

Editing made after the first answer:

I would want to say this: If you have 2 volumes at the beginning, and this results 8 volumes after merger, the inflation was 4 times. If this same merger coult built one result with 100 volumes (for example), every people could to surprise itself this result, but the difference (only 4 Times) isn´t so much, so it is more dificult to realize to many people.

This effect or phenomenon would occurs (hypothesis) with the terrestrian GPS orbits (for example) if the Earth could get double mass. This orbit would have to move away double the atual distance. The final imaginary volume under this orbit is 8 times the atual volume. I'm referring only to the imaginary volume defined by the orbit. and not to Earth volume, because each orbit has its well-defined escape velocity, as one events horizon has too.

If this happens, so always the universe expands when masses merge themselfs.

(Sorry my Google English)

João Bosco
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The event horizon radius of a black hole is proportional to the mass. Specifically the horizon radius is:

$$ r_s = \frac{2GM}{c^2} $$

Assuming you merge the two black holes without any mass loss due to gravitational radiation then the mass of the merged black hole will be double the masses of the two black holes. That means it will have double the event horizon radius and therefore eight times the volume, not four times. The density will therefore be only one quarter of the densities of the two black holes.

What you've discovered is that the density of a black hole decreases with size. This has been discussed before, for example in What is exactly the density of a black hole and how can it be calculated?

John Rennie
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