Finite-size effects in extreme mass ratio inspirals

Vojtěch Witzany

10.12.2018 14:00

Extreme mass ratio inspirals are gravitational-wave inspirals of compact, stellar-mass objects into supermassive black holes that are expected to be detected by the space-based mission LISA. The motion of the compact object is modeled as the motion of a particle in the space-time of the supermassive black hole perturbed by the particle itself. However, additional corrections due to the finite size of the compact object must be included in an accurate waveform model. I will first discuss the scaling of these contributions to the orbital motion and show that it seems that we only need first order finite-size corrections to meet the LISA precision requirements. I will then proceed to present recent results on the analytical solution of the orbital motion under the first-order corrections.

Self-similar accretion in thin discs around near-extremal black holes

Roberto Oliveri

11.02.2019 14:00

Near-maximally spinning black holes display conformal symmetry in their near-horizon region, which is therefore the locus of critical phenomena. In this talk, we revisit the Novikov–Thorne accretion thin disc model and find a new self-similar radiation-dominated solution in the extremely high spin regime. Motivated by the self-consistency of the model, we require that matter flows at the sound speed at the innermost stable circular orbit (ISCO). We observe that, when the disc pressure is dominated by radiation at the ISCO, which occurs for the best-fitting Novikov–Thorne model of GRS 1915+105, the Shakura–Sunyaev viscosity parameter can be expressed in terms of the spin, mass accretion rate and radiative efficiency. We quantitatively describe how the exact thin disc solution approaches the self-similar solution in the vicinity of the ISCO and for increasing spins.