On February 11, 2016, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the first-ever detection of gravitational waves. According to Einstein’s Theory of General Relativity predictions, these waves result from the merging of massive objects, causing ripples in spacetime that can be detected.
Since then, astrophysicists have theorized countless ways in which gravitational waves can be used to study physics beyond the standard models of gravity and particle physics, thereby enhancing our understanding of the universe. Gravitational waves have been proposed as a means to study dark matter, the interiors of neutron stars, supermassive black hole mergers, and more.
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In a recent study, a group of physicists from the University of Amsterdam and Harvard University proposed a method by which gravitational waves could be used to search for super-light bosons (one of the two fundamental particles in nature) around spinning black holes. This approach not only offers a new way to discern the properties of binary black holes but also holds the potential for the discovery of new particles beyond the Standard Model.
The subsequent research was carried out by scientists at the Gravitational Physics and Astrophysics group Amsterdam (GRAPPA) at the University of Amsterdam, with support from the Center for Theoretical Physics and the National Center for Theoretical Sciences at the University of Taipei, and Harvard University. The results of the study were published in the journal “Physical Review Letters” under the title “Sharp Signals from Boson Clouds in Binary Black Hole Inspiral.”
A well-known fact is that ordinary matter will fall into black holes over time, forming an accretion disk around its outer edge (also known as the event horizon). This disk will be accelerated to tremendous speeds, causing the inner matter to become superheated and release an enormous amount of radiation while slowly accreting onto the black hole’s surface. However, over the past few decades, scientists have observed that black holes can shed part of their mass through a process called “superradiance.”
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Superradiance, also known as superradiant scattering, is a phenomenon of enhanced radiation in various contexts, including quantum mechanics, astrophysics, and general relativity.
Thіѕ рhenomenon wаѕ ѕtudіed by Steрhen Hаwkіng, who deѕсrіbed how rotаtіng blасk holeѕ would emіt rаdіаtіon thаt аррeаrѕ “reаl” to аn obѕerver neаrby but “vіrtuаl” to а dіѕtаnt obѕerver.During the transmission of radiation from one reference frame to another, the particle’s acceleration itself causes the particle to transition from virtual to real. This peculiar form of energy, called “Hawking radiation,” forms clouds of low-mass particles around a black hole. This leads to the formation of “gravitational atoms,” named as such because they resemble ordinary atoms (clouds of particles surrounding a core).
While scientists know that this phenomenon occurs, they also understand that it can only be explained through the existence of a new ultra-light particle beyond the Standard Model. This is the focus of the new paper, in which the primary author Daniel Baumann (GRAPPA and University of Taipei) and his colleagues examine how superradiance generates naturally unstable clouds of ultra-light bosons around black holes.
Additionally, they argue that the similarity between gravitational atoms and ordinary atoms goes deeper into their structure. In summary, they propose that binary black holes can cause the particles within their clouds to become ionized through the photoelectric effect. As Einstein described, this occurs when electromagnetic energy (such as light) interacts with a material, causing it to emit excited electrons (photoelectrons). When applied to a binary black hole, Baumann and his colleagues have outlined how the clouds of ultra-light bosons can absorb the “orbital energy” of a “companion” within the black hole. This would result in the ejection and acceleration of some bosons.
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Gravitational waves are oscillations caused by the curvature of spacetime, propagating outward from gravitational sources, and carrying energy in the form of gravitational radiation.
Finally, they have demonstrated that this process can significantly alter the evolution of binary black holes. As they state:
“The lost orbital energy in this process can overwhelm the losses from gravitational wave (GW) emission, so the ionization process propels the evolution not only by stirring. We demonstrate that the ionization strength features a pronounced ‘kink’ in the emitted GW frequency evolution.”
They argue that these “kinks” would be observable in next-generation gravitational wave interferometers like the Laser Interferometer Space Antenna (LISA). This process could be used to explore an entirely new class of ultra-light particles and provide direct information about the mass and state of “gravitational atom clouds.” In conclusion, ongoing research on gravitational waves using increasingly sensitive interferometers may unveil peculiar physical phenomena that enhance our understanding of black holes and lead to new breakthroughs in particle physics.
In the coming years, astrophysicists hope to use them to probe the most extreme environments in the universe, such as black holes and neutron stars. They also hope that primitive gravitational waves will reveal insights into the early universe, helping solve the mysteries of matter/anti-matter imbalance and leading to a new quantum theory of gravity.
(Reference: Inverse)