Black holes admit quantum mechanical bound states of ultra light particles such axions or neutrinos. These states can undergo quantum transitions absorbing or emitting gravitons. We are interested in considering the quantum mechanical system acting as a lasing medium for gravitons. Graviton trajectories, in the particle picture, in principle can correspond to gravitons that orbit the black hole arbitrarily many times before finally escaping to infinity. This allows for the possibility that the graviton passes through the lasing medium for an arbitrarily large amount of time, or equivalently, for an arbitrarily large distance. Quantum mechanically, such graviton trajectories correspond to graviton-black hole scattering states which exhibit an arbitrarily large time delay before they emerge at infinity. The spontaneous emission of such graviton states coupled with their subsequent stimulated emission as the graviton circles around the black hole through the lasing medium, can in principle give rise to significant amplification. The observation of intense beams of coherent gravitons would then be a confirmation of the existence of ultra light massive particles and of the existence of black holes. As the coupling of gravitons to matter is so small, that trajectories of the order of 1030 m would be required for significant amplification. This then corresponds to 1013 years. It has only been at most 14 ×109 years since the big bang. Hence in a few years particularly harmful, amplified graviton death rays will start to be emitted from black holes all over the universe, they are in this sense a time bomb. To be in the path of such a ray will not be pleasant.