A Black Hole that Behaves Like an Atomic Nucleus
A black hole that behaves like an atomic nucleus – what sounds like a scenario from the pen of an overzealous science fiction writer could actually be reality. As early as 1980, physicist Steven Detweiler recognized that the galactic monsters could be surrounded by a cloud of light particles resembling electrons in an atomic shell. It is still unclear whether these gigantic quantum objects, so-called gravitational atoms, really exist. The particles in the shell would have to be extremely light, lighter than any elementary particle known to date, such as axions, which are also candidates for dark matter. But there is still no trace of these either.
However, this situation might soon change. A team led by physicist Giovanni Maria Tomaselli from the University of Amsterdam has theoretically shown that gravitational atoms leave clear traces in binary systems comprised of two black holes, which could be detected by precise gravitational wave detectors. The results were published in September 2024 in the journal Physical Review Letters.
“Black holes are the most perfect macroscopic objects in the universe,” physicist Subrahmanyan Chandrasekhar (1910–1995) once said. These gigantic cosmic vacuum cleaners are created when matter is compressed to such an extent that nothing can escape their gravity within a certain distance—not even light. More than 40 years ago, Detweiler investigated how black holes could affect quantum fields, drawing on the groundbreaking work of Stephen Hawking.
Detweiler made a surprising discovery: If there were extremely light elementary particles of a certain class called bosons, they could surround the black hole like a cloud reminiscent of an atomic shell of electrons. “The term ‘gravitational atom’ is not an exaggeration,” writes physicist Caio F. B. Macedo in »Physics Magazine«. “The temporal evolution of the cloud is described by the Schrödinger equation, and the energy levels are similar to those of hydrogen.”
Interacting Gravitational Atoms
Tomaselli and his colleagues ventured beyond a single gravitational atom and focused on double systems of black holes. Their objective was to understand how a boson cloud would affect such binary systems. What they uncovered is astonishing.
Binary systems of ordinary black holes moving through empty space (without the hypothetical ultralight boson cloud) have been extensively studied. Due to their enormous mass, these celestial giants orbit each other while emitting gravitational waves. As they lose energy during their interactions, their orbits gradually tighten and become more circular. According to established theory, older binary systems exhibit orbits that are smaller and more circular.
However, Tomaselli’s team examined rotating pairs of black holes surrounded by a boson cloud. The particles in this cloud have a mass ranging from 10-20 to 10-10 electron volts—millions of times lighter than the lightest known neutrinos. This ultra-light boson category potentially includes dark matter candidates like axions. Notably, the research team discovered that the rotation of the black holes could excite the boson cloud—essentially “ionizing” it.
“This result is in stark contrast to the simpler picture of a binary star in a vacuum,” Caio F. B. Macedo, physicist.
The kinetic energy of the entire system would transfer into the cloud, subsequently affecting the trajectory of the black holes. As a result, the binary system would have a less circular and more eccentric orbit. “This offers an interesting possibility: the existence of the bosons—and possibly decoding their nature—could be deduced from the orbital parameters of the binary systems,” says Macedo. Essentially, binary systems of black holes could hold keys to previously hidden secrets in particle physics.
Potential Detection Methods of Gravitational Atoms
With gravitational wave detectors becoming increasingly sophisticated, there exists a promising avenue for the detection of these elusive gravitational atoms. Advanced gravitational wave observatories, such as LIGO and Virgo, are equipped to detect minute distortions caused by the passage of gravitational waves generated by massive cosmic events, including the merging of black holes.
- Gravitational Wave Signals: If gravitational atoms surround binary black holes, the emitted gravitational waves would carry information related to their properties, such as mass and energy levels.
- Orbital Eccentricity: Analyzing the orbital traits of detected black holes could reveal deviations from established models based on a vacuum scenario.
- Spectrum of Detection: Gravitational wave signals might possess distinct spectral characteristics associated with the presence of ultralight bosons in the vicinity of black holes.
Implications for Dark Matter Research
This groundbreaking research not only opens new avenues for understanding black holes but also interlinks with the larger quest for clarifying the nature of dark matter. The potential alignment of gravitational atoms and ultra-light bosons could provide insights into dark matter, a mysterious substance that constitutes a significant portion of the universe yet remains undetectable through classical means.
Studying gravitational atoms may unlock the mysteries surrounding axions and other elementary particles considered dark matter candidates. Gravitational wave observations could bridge fundamental physics and cosmology, integrating knowledge from black hole mechanics into particle physics investigations.
Future Research Directions
Researchers may follow various pathways to explore gravitational atoms further:
- Conducting simulations that model various configurations of gravitational atoms alongside black hole mergers.
- Investigating the compatibility of current dark matter models with findings regarding gravitational atoms.
- Collaborating with astronomers using observational data to narrow down the parameters concerning the existence of ultralight bosons.
Insights from Gravitational Physics
To fully appreciate the implications of gravitational atoms, it’s beneficial to explore some foundational principles of gravitational physics. Black holes represent the end-stage remnants of massive stars, collapsing into singularities surrounded by event horizons, beyond which no information can escape. The study of their interactions and surrounding environments presents a unique opportunity to unlock mysteries across multiple domains in physics.
Table: Comparison of Conventional Black Holes and Gravitational Atoms
| Characteristic | Conventional Black Holes | Gravitational Atoms |
|---|---|---|
| Nature | Singularities surrounded by event horizons | Clouds of ultralight bosons surrounding black holes |
| Mass | Star remnants with significant mass | Potential dark matter candidates |
| Detection | Gravitational waves and electromagnetic signals | Potential signatures in gravitational wave patterns |
| Research Implications | Stable astrophysical phenomena | Teasing apart dark matter mysteries |
This understanding of the universe—its constant evolution, intricate mechanics, and the interplay of light and dark matter—is not merely academic. It has profound implications for our grasp of the cosmos, unveiling layers to reality that have remained concealed for centuries.
