Near-extremal Kerr-like ECO in the Kerr/CFT Correspondence

Abstract

The Kerr/CFT correspondence has been established to explore the quantum theory of gravity in the near-horizon geometry of a extreme Kerr black holes. The horizon can be replaced by partially reflective membrane due to quantum gravitational corrections on the near-horizon region. Because of this modification, black holes now can be seen as a horizonless exotic compact object (ECO). In this work, with Kerr/CFT correspondence we study the properties of Kerr-like ECO in near-extremal condition. We compute the quasinormal modes and absorption cross-section and compare the results with CFT computation. The dual CFT one needs to consider finite size/finite N effects in the dual CFT terminology. We find consistency between properties of the ECOs from gravity side and from CFT side. The quasinormal mode spectrum is in line with non-extreme case with differences in the length of the circle where the dual CFT lives, and phase shift of the incoming perturbation. The absorption cross-section has oscillatory feature that start to vanish in near extremal limit. We also show that the echo time-delay depends on the position of the membrane and extremality of the ECOs.