February 11, 2016, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the detection of gravitational waves for the first time. As predicted by Einstein’s general theory of relativity, these waves result from the fusion of massive objects, causing ripples in spacetime that can be detected.
Since then, astrophysicists have theorized countless ways to use gravitational waves to study physics beyond standard gravity and particle physics models and advance our understanding of the Universe.
To date, gravitational waves have been proposed as a way to study dark matter, the interiors of neutron stars and supernovae, mergers between supermassive black holes, and more.
What’s new – In a recent study, a team of physicists from the University of Amsterdam and Harvard University proposed a way to use gravitational waves to search for ultralight bosons around rotating black holes. This method could not only offer a new way to discern the properties of binary black holes, but could lead to the discovery of new particles beyond the Standard Model.
The research was conducted by researchers at Gravitation Astroparticle Physics Amsterdam (GRAPPA), University of Amsterdam, with support from the Center for Theoretical Physics and the National Center for Theoretical Sciences at the University of Taipei (Taiwan) and from Harvard University. . The paper describing their work, titled “Sharp Signals of Boson Clouds in Black Hole Binary Inspirals”, recently appeared in the Physical examination letters.
It is a well-known fact that normal matter will fall towards black holes over time, which will form an accretion disk around its outer edge (aka. Event Horizon). This disk will be accelerated to incredible speeds, causing the material inside to overheat and release huge amounts of radiation as it slowly accretes onto the face of the black hole. However, over the past few decades, scientists have observed that black holes lose some of their mass through a process called “superradiance.”
This phenomenon was studied by Stephen Hawking, who described how rotating black holes would emit radiation that would appear “real” to a close observer, but “virtual” to a distant observer. In the process of transferring this radiation from one reference frame to another, the acceleration of the particle itself would make it go from virtual to real. This exotic form of energy, known as “Hawking Radiation”, will form clouds of low-mass particles around a black hole. This leads to a “gravitational atom”, so named because it looks like ordinary atoms (clouds of particles surrounding a nucleus)
Although scientists know that this phenomenon occurs, they also understand that it can only be explained by the existence of a new ultralight particle that exists beyond the Standard Model. That was the focus of the new paper, where lead author Daniel Baumann (GRAPPA and University of Taipei) and his colleagues examined how superradiance causes the spontaneous formation of unstable clouds of ultralight bosons around black holes. Moreover, they suggest that the similarities between gravitational and regular atoms go deeper than their structure.
In short, they suggest that binary black holes could cause particles in their clouds to ionize via the photoelectric effect. As described by Einstein, it happens when electromagnetic energy (such as light) comes into contact with a material, causing it to emit excited electrons (photoelectrons). When applied to a binary black hole, Baumann and his colleagues show how clouds of ultralight bosons could absorb “orbital energy” from a black hole companion. This would cause certain bosons to be ejected and accelerated, as evidenced by the gravitational wave signals associated with the black hole.
Finally, they demonstrated how this process could dramatically alter the evolution of binary black holes by reducing the time it takes for objects to merge. As they say:
“The orbital energy lost in this process can exceed the losses due to GW emission, so that ionization drives inspiration rather than just disturbing it. We show that ionization power contains sharp features that lead to distinctive “folds” in the evolution of the transmitted GW frequency.
These “flaws,” they claim, will be noticeable to next-generation gravitational-wave interferometers like the Laser Interferometer Space Antenna (LISA). This process could be used to discover a whole new class of ultralight particles and provide direct information about the mass and state of “gravitational atom” clouds. In short, ongoing studies of gravitational waves using more sensitive interferometers could reveal exotic physics that will advance our understanding of black holes and lead to new breakthroughs in particle physics.
This is one of the many possibilities that have been ventured through the ongoing revolution with gravitational wave astronomy. In the years to come, 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 primordial gravitational waves will reveal things about the early Universe, help solve the mystery of the matter/antimatter imbalance, and lead to a quantum theory of gravity (aka a theory of everything).
This article was originally published on Universe today by Matt Williams. Read the original article here.