[Red Badger]

Here’s my theory:

Once the last of the stars are extinguished, and nothing is left but Black Holes where entire galaxies once reigned, the Black Holes themselves will coalesce through their enormous gravity wells, combining and merging and eventually becoming one ULTRA BLACK HOLE, of unimaginable size and mass of sextillions of sextillions of Suns, become unstable, and a silent ‘new’ Big Bang starts the cycle all over again........................

[SuperLuminal]

Only Doctor Who knows for sure...
Will have to check with him, the next time he is here...