My question is regarding Hawking Radiation and its effect on black hole. Now as we know that particle and particle pairs create at every place in space and it is true near black hole horizon. Then why it is like that each time gravity of black hole sucks antimatter particle and its mass decreases . Is it true to think that on average black hole sucks an equal amount of particle and antimatter particle in some given time and its mass remains constant?
Both matter and antimatter particles increase the black hole mass. The reason why black hole is losing mass is much more complicated and its precise description is rather technical, but in simple terms: the particle that flies away is carrying away some energy. That energy cannot be creared from nothing; it is taken off the black hole itself. Thus the event horizon shrinks a bit.
The in-falling particle with negative energy is just a picturesque way of saying that a positive energy particle is flying away.
The outgoing particles are both matter and antimatter particles.