  We consider a process where two identical massive particles fall inwards,
starting from rest at infinity towards the extremal Kerr black hole, collide
outside the event horizon in its vicinity and produce two massless particles.
The center of mass energy of collision between the two particles diverges if
one of the particle admits a specific critical value of the angular momentum
and if the collision takes place at a location arbitrarily close to the event
horizon. Assuming the isotropic emission of particles in the center of mass
frame we show that one of the massless particles produced has divergent
conserved energy comparable to the center of mass energy with probability
slightly less than half. This particle enters the black hole event horizon
which coincides with the Cauchy horizon, turns back, and emerges through the
white hole event horizon into another asymptotic region in the maximal
extension of Kerr spacetime. Since conserved energy is preserved in this
process, it is perceived as a particle with divergent energy by the observer
when it reaches infinity. Thus the extremal white hole appears to be a source
of ultra high energy particles. Similar processes wherein collision takes place
slightly inside the black hole event horizon or just outside or inside of white
hole event horizon also produce high energy particles.
