Gravitational waves produced by black holes colliding and merging provide a new way of testing existing scientific theories and uncovering new phenomena.
GW250114: Rotating Black Holes Collide (Credit: Aurore Simonnet (SSU/EdEon), LVK, URI; LIGO Collaboration)
Listening to the 'ringing’ produced by black holes after they collide and merge could allow scientists to test Einstein’s theory of General Relativity under the most extreme conditions in the Universe whilst unlocking the secrets of these mysterious objects.
Leading a major international review with the Institute of Physics, astrophysicists at the University of Birmingham, Johns Hopkins University and Intituto Superior Tecnico of Lisbon showcase how black hole ‘spectroscopy’ is rapidly evolving from a theoretical concept into powerful experimental science.
During the ‘ringdown’ phase following collision and merger, a newly formed black hole emits characteristic gravitational-wave vibrations known as ‘quasinormal modes’. By measuring these frequencies, scientists can determine the black hole's mass and how fast it is spinning, as well as investigating whether Einstein's theory is correct.
By listening to the ringing of newly formed black holes, we are turning gravitational waves into a tool for exploring some of the deepest questions in physics, from the nature of gravity itself to the possibility of discovering entirely new forms of matter and energy.
Since the first detection of gravitational waves in 2015, the LIGO-Virgo-KAGRA collaboration has observed hundreds of black hole mergers and measured tens of black hole ringing down according to their characteristic tones.
So far, every observed ringdown agrees with general relativity, but current detectors are limited. Future observatories - including the European-led Einstein Telescope, the US Cosmic Explorer and the space mission LISA - may find fresh evidence for new physics.
Review co-lead Dr Gregorio Carullo, from the University of Birmingham, said: “By listening to the ringing of newly formed black holes, we are turning gravitational waves into a tool for exploring some of the deepest questions in physics, from the nature of gravity itself to the possibility of discovering entirely new forms of matter and energy.”
Black hole collisions generate intense gravitational fields that cannot be recreated in laboratories on Earth. Researchers have discovered:
Multiple ringing overtones, analogous to harmonics in musical instruments,
in LIGO data.
Mode interactions, where vibrations influence one another.
Dynamical modes excitations.
Exceptional points, where modes merge and behave in unusual ways.
“Tails” of emission, amplified by mergers in crowded astrophysical environments.
The review identifies black hole ringdowns as potential ways of testing phenomena beyond the Standard Model of particle physics, including:
Beyond-Einstein gravity theories
Dark matter
Quantum-scale effects near black hole horizons
The review brings together more than 70 experts from institutions across the UK, Europe, North America, Asia and South America to provide the most comprehensive assessment yet of the field and was spurred by the largest international workshop dedicated to the topic, hosted by the Danish Architectural Center, Copenhagen, in 2024.
The next generation of detectors is expected to transform the field, giving scientists instruments that should detect many more black hole mergers and measure multiple vibration modes routinely. These future observatories should allow astrophysicists to uncover black hole formation mechanisms challenging current models, test Einstein's theory far more precisely and search for new particles and forces.
Reflecting on these upcoming advancements, Carullo said: "As gravitational-wave detectors become more sensitive, black hole spectroscopy promises to transform black holes from mysterious objects into precision laboratories to study challenging astrophysical processes and uncover new fundamental physics phenomena."
For more information, please contact Tony Moran, International Communications Manager or call +44 (0)7827 832312
'Black hole spectroscopy: from theory to experiment' - Emanuele Berti et al is published by the Institute of Physics.
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Participating institutions: University of Birmingham, UK; Johns Hopkins University, USA; Niels Bohr Institute, Denmark; Universidade de Lisboa, Portugal; Beijing Institute of Mathematical Sciences and Applications, China; University of Waterloo, Canada; Friedrich-Schiller-Universität, Jena, Germany; INFN sezione di Torino, Italy; Columbia University, New York, USA; Universidad Complutense de Madrid, Spain; Radboud University, Nijmegen, The Netherlands; Scuola Normale Superiore, Pisa, Italy; The Barcelona Institute of Science and Technology, Spain; Universitat de Barcelona, , Spain; Syracuse University, USA; University of Massachusetts Dartmouth, USA; University of Maryland, USA; Astroparticle Physics Laboratory, NASA/GSFC, USA; Center for Research and Exploration in Space Science and Technology, NASA/GSFC, USA; Universidade Federal do ABC, Sao Paulo, Brazil; Wake Forest University, Winston-Salem, USA; University of Illinois at Urbana-Champaign, USA; University of Southampton, UK; Universita di Pisa, Italy; Max Planck Institute for Gravitational Physics, Potsdam, Germany; Stony Brook University, USA; Flatiron Institute, New York, USA; California Institute of Technology, Pasadena, USA; and Université Paris Cité, France.
Assistant Professor
Staff profile for Dr Gregorio Carullo, School of Physics and Astronomy, University of Birmingham
