Princeton University Gravity Group Lunch Seminar

Black holes (BHs) can be described as astrophysical particle accelerators because finite-energy particles in free fall can collide with diverging center-of-mass (CM) energy near the horizon. Here we examine the case of high energy collisions which occur near a rapidly rotating (near-extreme Kerr) BH. Firstly, we show the conditions to produce a high energy collision around a rapidly rotating BH: at least one particle must approach the superradiant bound slower than the collision radius approaches the horizon. When both particles are ingoing or outgoing, it is additionally required that the particles approach the superradiant bound at different rates. Secondly, we examine the specific case of a collision between an infalling particle and a particle on a circular orbit. We find the escape probability and energies of ejecta from such collisions, showing that they can be observable by observers far from the BH.