Speaker
Description
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 property 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. In this talk, by taking a black hole surrounded by a gravitating thin disk as an example, we show that there seems to be a universal redshift relation for QNM spectrum in the presence of such environmental effects. The implications on testing GR through black hole spectroscopy will be discussed.
