A bosonic field impinging on a rotating black hole can be amplified as it scatters off the hole, a phenomena known as superradiant scattering. If in addition the field has a non-zero rest mass μ, the mass term effectively works as a mirror, reflecting the scattered wave back towards the black hole. In this physical system, known as a black-hole bomb, the wave may bounce back and forth between the black hole and some turning point, amplifying itself each time. Consequently, the field grows exponentially over time and is unstable. In this paper we study analytically for the first time the phenomena of superradiant instability (the black-hole bomb mechanism) in the regime Mμ=O(1) of great instability. We find a maximal instability growth rate of τ-1=1.7x10-3M-1 . This instability is 4 orders of magnitude stronger than has been previously estimated.
Download the paper in PDF format |