Black Hole Spectroscopy
Listening to a Black Hole's Gravitational-Wave Ringing
Emanuele Berti
Simons Investigator, Bloomberg Center for Physics and Astronomy
Professor, William H. Miller III Department of Physics & Astronomy
Johns Hopkins University
About the Lecture
According to general relativity, a binary black hole merger results in a perturbed Kerr black hole that emits so-called “ringdown” radiation – a superposition of damped exponentials (“quasinormal modes”) with frequencies and damping times that depend only on the mass and spin of the remnant. As Steve Detweiler presciently pointed out when he completed the first calculation of the Kerr quasinormal mode spectrum, LIGO-Virgo-KAGRA observations of the gravitational radiation emitted by black hole mergers are now providing direct experimental evidence of black holes, just like the 21 cm line identifies interstellar hydrogen. The lecture will discuss some recent developments in this “black hole spectroscopy” program, including the modeling of nonlinearities in the ringdown, frequency-domain waveform models based on the black hole’s greybody factors, and the possibility of resonant mode excitation.
Reading & Media References:
1. How black hole spectroscopy can put general relativity to the test, E. Berti, M. H.-Y. Cheung, S. Yi, Physics Today 78 (5), 32–37 (2025)
https://doi.org/10.1063/pt.fvtp.lpxx
2. Quasinormal modes of black holes and black branes, E. Berti, V. Cardoso, A.O. Starinets, Class. Quantum Grav. 26, 163001 (2009)
https://iopscience.iop.org/article/10.1088/0264-9381/26/16/163001
3. Testing general relativity with present and future astrophysical observations, E. Berti et al., Class. Quantum Grav. 32, 243001 (2015)
https://iopscience.iop.org/article/10.1088/0264-9381/32/24/243001
4. Black hole spectroscopy: from theory to experiment, E. Berti, V. Cardoso, G. Carullo et al., Class.Quant.Grav. 43, 123001 (2026)
https://iopscience.iop.org/article/10.1088/1361-6382/ae59e2
About the Speaker
Emanuele Berti is Professor in the William H. Miller III Department of Physics and Astronomy at Johns Hopkins University. Before joining Johns Hopkins, he was a faculty member at the University of Mississippi and held a research professorship at Instituto Superior Técnico in Lisbon.
His research is in gravitational physics and gravitational-wave astronomy, with emphasis on black holes and neutron stars, tests of general relativity, modified theories of gravity, compact-binary astrophysics and cosmology, and the science of future observatories including LISA, Cosmic Explorer, and the Einstein Telescope.
Emanuele has made major contributions to the theory and observational use of black-hole quasinormal modes, the characteristic ringdown vibrations of black holes. This work underlies black hole spectroscopy, in which the frequencies and damping times of gravitational waves from a newly formed black hole are used to test whether it has the properties predicted by general relativity. He also studies black-hole populations and the formation history of merging binaries.
Emanuele is an author on more than 250 refereed scientific publications. He served as President of the International Society on General Relativity and Gravitation and as Chair of the Division of Gravitational Physics of the American Physical Society.
Among other honors and awards, he is a Simons Investigator and a Fellow of the American Physical Society, the International Society on General Relativity and Gravitation, and the American Association for the Advancement of Science. He has received the Richard A. Isaacson Award in Gravitational-Wave Science and a Frontiers of Science Award.
Emanuele earned a Laurea in Theoretical Physics and a PhD in Physics, both at Sapienza University of Rome.
Readings about the Speaker:
Johns Hopkins Physics & Astronomy: https://physics-astronomy.jhu.edu/directory/emanuele-berti/
Personal webpage: https://pages.jh.edu/eberti2/
Google Scholar: https://scholar.google.com/citations?hl=en&user=uurxA2QAAAAJ
Curriculum Vitae: https://pages.jh.edu/eberti2/EmanueleBertiCV.pdf
Speaker’s Social Media Pages:
Webpage: https://pages.jh.edu/eberti2/
LinkedIn Profile: https://www.linkedin.com/in/emanuele-berti-b987856/
Bluesky: https://bsky.app/profile/emaberti.bsky.social
Facebook page: https://www.facebook.com/emaberti
YouTube Channel: https://www.youtube.com/@EmanueleBerti1