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 while 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 Instituto Superior Técnico of Lisbon show how black hole “spectroscopy” is rapidly evolving from a theoretical concept into a powerful experimental science. The work is published in the journal Classical and Quantum Gravity.

During the “ringdown” phase following a 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 investigate whether Einstein’s theory is correct.