Gravitational Waves, Event Horizons and Black Hole Observation: A New Frontier in Fundamental Physics

Abstract

The observation of supermassive black holes by the Event Horizon Telescope Collaboration and the detection of gravitational waves emitted during the merging phase of compact binary objects to stellar-mass black holes by the LIGO–Virgo–KAGRA collaboration constitute major achievements of modern science. Gravitational wave signals emitted by stellar-mass black holes are being used to test general relativity in an unprecedented way in the regime of strong gravitational fields, as well as to address other physics questions such as the formation of heavy elements or the Hawking Area Theorem. These discoveries require further research in order to answer critical questions about the population density and the formation processes of binary systems. The detection of supermassive black holes considerably extends the range of scientific investigation by making it possible to probe the structure of spacetime around the horizon of the central mass of our galaxy as well as other galaxies. The huge amount of information collected by the VLBI worldwide network will be used to investigate general relativity in a further range of physical conditions. These investigations hold the potential to pave the way for the detection of quantum-mechanical effects such as a possible graviton mass. In this paper we will review, in a cursory way, some of the results of both the LIGO–Virgo–KAGRA and the EHT collaborations.