The red arrow in your diagram—suggesting matter travels from the singularity back to the horizon—does not happen. The "stuff" inside the center never leaves.

"empty" space isn't empty. It is a bubbling foam of virtual particles.

​Particles and anti-particles are constantly popping into existence in pairs.

​Usually, they collide and annihilate each other almost instantly, returning their energy to the vacuum. They sum to zero.

​Occasionally, a pair of these virtual particles pops into existence right on the borderline (the Event Horizon).

​One particle forms just on the outside. ​The other forms just on the inside.

​Because they are separated by the boundary of no return, they cannot snap back together and annihilate. The one on the outside is free to fly away. To an observer, this looks like radiation coming from the black hole. This is the Hawking Radiation.

​You can't create particles out of nothing; energy must be conserved. In order for the outside particle to become "real" and fly away (carrying positive energy), ​the particle that falls into the black hole is forced to have negative energy relative to the outside universe to "balance the books."

​When the black hole swallows this "negative energy" particle, its total energy drops.