Paolo Pani and colleagues solved a 50-year old problem in black hole physics. Their study is due to appear in the prestigious journal Physical Review Letters.

One of the most amazing predictions of Einstein’s General Relativity is the existence of black holes, regions of the spacetime that are disconnected from the rest of the Universe, as not even light can escape from them. Surprisingly, black holes are extremely simple objects and behave pretty much like elementary particles. Regardless the infinite ways they can be formed, all black holes in the Universe are described by only three physical quantities: the mass, the spin and the electric charge. Black holes with nonvanishing mass, spin and charge are called Kerr-Newman black holes and these solutions were discovered in 1965, after decades of theoretical labour.

Black holes possess characteristic frequencies of vibration, called quasinormal modes. These modes are associated to the emission of gravitational waves, pretty much like the vibrations of a guitar string are associated to acoustic waves. Thus, as the properties of an instrument can be traced back from the sound it produces, by studying the quasinormal modes of black holes one can “hear the sound of spacetime”. In his infamous monograph on black holes, Nobel laureate Subrahmanyan Chandrasekhar forecast that the computation of Kerr-Newman modes would require a major breakthrough.

Now, Paolo Pani and colleagues have developed a new technique to study the vibrations of black holes. Although restricted to slowly-rotating black holes, unexpected features were already uncovered, such as isospectrality between modes, which can have important theoretical implications for gravity and high-energy physics. For more details read the original article, to appear in Physical Review Letters.