New Delhi: When two smaller black holes merge into a single, larger black hole, the resulting objects rings like a plucked guitar string or a bell before
settling into its final, stable shape. Instead of producing sound waves, the newly formed black hole rings in gravitational waves, ripples in the fabric of spacetime first predicted by Albert Einstein. The newly formed black hole vibrates at a specific set of frequencies known as qausinormal modes, depending on the mass and spin of the object. Studying quasinormal modes allows scientists to better understand about the objects that collided to form the black hole.
These quasinormal modes are fingerprints of black holes, allowing scientists to test Einstein’s theory of relativity in the most extreme gravitational environments in the universe. Researchers from the University of Cambridge have developed a new method to identify and catalogue these quasinormal modes with greater accuracy than before. The researchers sifted through sophisticated computer simulations of black hole mergers, and identified a fundamental note that black holes ring at, as well as overtones or fainter harmonics that fade away more quickly. The loudest mode is routinely observed in gravitational wave data, but the quieter modes are more difficult to detect.
Unusual nonlinear modes
The research provides a reference for theoretical studies as well as real observations. The study was based on Bayesian analysis, a statistical technique that systematically weighs evidence to determine the most probable explanation for a given dataset. Apart from the fundamental notes and overtones, the researchers also discovered unusual nonlinear modes, that are produced when two or more of the fundamental frequencies interact with teach other. These are similar to the complex tones produced by an electric guitar with heavy distortion. The research is expected to guide future interpretations of black hole merger events. A paper describing the research has been published in Physical Review Letters.
