友善列印 - 4/16 12:30 Prof. Dimitrios Giataganas (NSYSU) Black Hole Mergers as the Fastest Scramblers on the Photon Ring (R521, 5F, General Building II, Nat'l Tsing Hua Univ.)

4/16 12:30 Prof. Dimitrios Giataganas (NSYSU) Black Hole Mergers as the Fastest Scramblers on the Photon Ring (R521, 5F, General Building II, Nat'l Tsing Hua Univ.)

******** CTCD/NTHU HEP Seminar ********

Speaker ： Prof. Dimitrios Giataganas (NSYSU)

Title ：Black Hole Mergers as the Fastest Scramblers on the Photon Ring

Time ：12:30-13:30, Thursday, 2026/4/16

Place ：R521, 5F, General Building II, Nat'l Tsing Hua Univ.

Host ： Prof. Kingman Cheung (NTHU) & Prof. Norihiro Iizuka (NTHU)

Abstract:
Since black holes are believed to be the fastest scramblers in nature, it is natural to ask whether this property is also encoded in the photon ring itself. We show that this is indeed the case and we find that the induced near-photon-ring geometry takes a local Rindler form. Then by mapping the instantaneous mass and angular momentum of two nonspinning black holes in a quasi-circular binary to those of an effective Kerr black hole, we find that the merger remnant corresponds to the configuration that maximizes the photon ring Lyapunov exponent. This points to a connection between the properties of black holes formed in binary mergers and the dynamics of their unstable null orbits.