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

Speaker ：Dr. Che-Yu Chen (RIKEN iTHEMS)

Title ：Is black hole spectroscopy reliable in testing GR?

Time ：12:30-13:30, Thursday, 2025/5/1

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

Host ： Prof. Po-Yen Tseng (NTHU)

Abstract:
The ringdown phase of gravitational waves emitted by a perturbed black
hole is described by a superposition of exponentially decaying
sinusoidal modes, called quasinormal modes (QNMs), whose spectra depend
only on the properties of the black-hole geometry. The extraction of QNM
frequencies of an isolated black hole thus allows for testing GR, the
so-called black hole spectroscopy program. However, astrophysical black
holes are not perfectly isolated. It remains unclear whether the
validity of black hole spectroscopy would be affected when environmental
effects surrounding the black holes are taken into account, such as
accretion disk, dark matter halo, etc. Can we lift the degeneracy
between the environmental effects and putative non-GR physics? In this
talk, I’ll demonstrate how we address this important issue by
considering the QNM spectrum of a black hole surrounded by a gravitating
thin disk. There seems to be a universal redshift effect on the spectrum
induced by the environment, hence it seems possible to lift such
degeneracy.