In a groundbreaking development in the field of astrophysics, researchers have uncovered evidence of vibrations from the largest black-hole merger ever detected. Contrary to some established theories, the study reveals that the merger may have produced a black hole approximately 150 times the mass of the Sun. This finding not only defies existing beliefs but also provides a unique opportunity to rigorously test Albert Einstein’s theory of general relativity.
The study, led by physicists including Badri Krishnan, represents a significant leap in our understanding of black-hole mergers and their aftermath. The researchers, affiliated with institutions such as the University of California at Santa Barbara and Radboud University in the Netherlands, detected the long-sought vibrations emitted by the resulting black hole as it settled into a spherical shape.
The massive black-hole merger, named GW190521 after its discovery on May 21, 2019, presented a distinctive feature that set it apart from other events. Its merging frequency was so low that it entered the sensitivity range of gravitational wave observatories, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo observatory, only during its final two orbits.
Traditionally, the study of black-hole mergers involves analyzing the frequency of gravitational waves emitted during the spiraling orbits leading up to the merger. However, the researchers delved into uncharted territory by examining the vibrations occurring immediately after the merger.
When two black holes merge, the resulting black hole initially adopts a lopsided shape. However, black holes are stable only when they assume a spherical or spheroidal form, especially if they are rapidly spinning. Within milliseconds of the merger, the black hole stabilizes into its lowest-energy, symmetrical shape.
The groundbreaking aspect of this study lies in the detection of these post-merger vibrations, known as ‘ringdown.’ Much like a bell produces specific frequencies based on its shape, the stabilizing black hole emits gravitational waves with frequencies determined by its mass and spin.
Reanalyzing data from the GW190521 event, the researchers identified two distinct ringdown frequencies. These frequencies point to a resulting black hole with a mass of approximately 250 times that of the Sun, challenging the initial analysis by the LIGO-Virgo collaboration.
This discovery not only expands our knowledge of black-hole mergers but also provides a new avenue for testing the principles of general relativity. As the scientific community continues to explore the cosmos, this breakthrough marks a crucial step towards unraveling the mysteries of the universe.
Reference: https://www.nature.com/articles/d41586-023-03813-w
