At the same time.
At the scene of the colossal collision between the Galaxy Nebula and the Andromeda Nebula.
The Wandering Alliance employed all of their detection equipment to observe the process of the black hole collision and fusion.
They hoped to seize this rare opportunity to capture some black hole material and thereby unveil the mysteries of black holes.
At the moment of their meeting after thousands of light-years of travel, the two black holes merged eagerly like newlyweds, forming a larger super black hole.
Moreover, due to the black holes' own immense gravity binding them, it was as if a veil had been drawn over this "newlywed couple," keeping the interior changes of the black holes from being known to anyone.
One could only tell from the material in the surrounding accretion disk that the black hole was spinning rapidly; the internal conditions were unobservable.
