Can Wormholes and Black Holes be Distinguished by Magnification? (Cosmology)

The enigmatic universe has long captivated the imagination of scientists and stargazers alike. Among its many profound phenomena, wormholes and black holes stand as cosmic mysteries that continue to beckon exploration. Recent research conducted by Ke Gao and Lei-Hua Liu delves deep into the intricate world of these celestial wonders, focusing on the rotational Simpson-Visser metric (RSV) as the key to unraveling their magnification effects.

The allure of wormholes and black holes lies not only in their perplexing existence but also in their ability to magnify the cosmos. Understanding the finite distance analysis of this magnification phenomenon has been the pursuit of many astronomers and physicists, and Gao and Liu’s work takes a significant step towards clarity.

By meticulously calculating the deflection of light within the RSV metric, the researchers were able to unveil the mesmerizing magnification effect. This groundbreaking approach enabled them to apply the RSV metric to specific examples, including the Ellis-Bronnikov wormhole, Schwarzschild black hole, and Kerr black hole (or wormhole), shedding light on their unique magnification characteristics.

The results of their study are as intriguing as the objects of their investigation. Notably, the Ellis-Bronnikov wormhole exhibited singular magnification peaks, a distinctive trait that sets it apart from its black hole counterparts. In contrast, Schwarzschild’s black hole, as the ADM mass increases, unfolds the astonishing spectacle of up to three peaks of magnification.

The story doesn’t end there; black holes with negative spin, known as Kerr Black holes, introduce a fascinating twist. As spin increases, these enigmatic entities transition from three magnification peaks to a solitary peak, a phenomenon that is mirrored in the case of positive spin. These findings open new vistas in our comprehension of black hole behavior.

Perhaps the most tantalizing revelation is the application of this research to the Central Black Hole of the Milky Way Galaxy. Here, the lensing effect showcases multiple peaks of magnification, offering a tantalizing glimpse into the cosmic wonders that lie at the heart of our galaxy. Regrettably, these captivating effects remain beyond the purview of observation from Earth, a testament to the vastness of the cosmos.

In essence, Gao and Liu’s research provides not only a discernible phenomenological difference in magnification between black holes and wormholes but also lays down a firm theoretical foundation for future explorations into the intricacies of these celestial enigmas. As humanity continues to gaze towards the heavens, such revelations bring us ever closer to unlocking the profound secrets of the universe, one cosmic puzzle at a time.

Reference: Ke Gao, Lei-Hua Liu, “Can wormholes and black holes be distinguished by magnification?”, Arxiv, 2023. https://arxiv.org/abs/2307.16627

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Unveiling Superradiant Instabilities: Exploring Black Hole Dynamics in the String Axiverse Scenario (Cosmology)

The axiverse scenario is a theoretical framework that proposes the existence of a large number of light axion particles in the universe. In this scenario, primordial black holes (PBHs) could be formed in the early universe and emit Hawking radiation, which is a process by which black holes gradually lose mass and energy over time.

Calza et al. have investigated the possibility that PBHs in the axiverse scenario can interact with light axions and undergo a process known as superradiance. Superradiance occurs when a rotating black hole interacts with a bosonic field (such as axions) and amplifies the energy of the field. In this case, the superradiant instability is triggered by the emission of a large number of light axions, which causes the black hole to spin up.

The researchers studied the coupled dynamics of superradiance and evaporation for these spinning black holes. They found that the mass and spin distribution of present-day black holes should follow a threshold condition dictated by the superradiance phenomenon, as long as the black hole mass is below the value at which the superradiant cloud forms, for a given heavy axion mass.

Additionally, Calza et al. showed that the decay of heavy axions within the superradiant cloud can produce photon pairs, resulting in a distinctive line in the black hole’s emission spectrum. This line would be superimposed on the black hole’s electromagnetic Hawking emission, providing a potential observational signature for the presence of superradiance in the axiverse scenario.

It’s important to note that these findings are based on a specific theoretical framework and involve several assumptions. Further observational and experimental studies would be necessary to confirm or refine these predictions.

Reference: Marco Calzà, João G. Rosa, Filipe Serrano, “Primordial black hole superradiance and evaporation in the string axiverse”, Arxiv, 2023. https://doi.org/10.48550/arXiv.2306.09430

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How Microlensing by Black Holes Can Influence The Characteristics of the Shadow? (Cosmology)

Gravitational microlensing is a phenomenon that occurs when the light from a distant source is bent and magnified by the gravitational field of an intervening object. In the context of black hole shadows imaged by the Event Horizon Telescope (EHT), a recent analysis by Himanshu and Silk presents a detailed exploration of how microlensing by intervening compact objects can influence the center, size, and shape of the shadow. This article summarizes their findings, highlighting the dependence of the shadow on the Einstein angle and the implications for future observations.

Microlensing and Black Hole Shadows:

The concept of a black hole shadow refers to the dark region in the immediate vicinity of a black hole caused by its intense gravitational pull, as predicted by Einstein’s theory of general relativity. Himanshu and Silk demonstrate that microlensing effects can introduce significant modifications to the black hole shadow, resulting in observable changes in its characteristics.

Dependence on Einstein Angle:

The size of the shadow is found to be dependent on the Einstein angle, which is a measure of the angular scale associated with gravitational lensing. The authors show that the center, size, and shape of the shadow are influenced by the relative size of the Einstein angle to the true/unlensed shadow size. This dependency provides a valuable insight into the behavior of black hole shadows under the influence of microlensing.

Effects of Lens Location:

The location of the intervening lens plays a crucial role in the shift, size, and asymmetry of the black hole shadow due to microlensing. Himanshu and Silk’s analysis reveals that microlensing can create an asymmetry of up to approximately 8%, which is twice the asymmetry caused by the spin and tilt of the supermassive black hole (SMBH) relative to the observer. Additionally, the size of the shadow can be enhanced by approximately 50% compared to its true size.

Limitations and Future Prospects:

Presently, the terrestrial baselines of the EHT lack the resolution required to detect microlensing signatures in black hole shadows. However, the authors suggest that future expansions of the EHT, including space-based baselines at the Moon and L2, hold the potential to enable the detection of microlensing events. These advancements could open up new avenues for studying the dynamics of black holes and their surrounding environments.

Observing Microlensing Events:

While the event rate of microlensing phenomena near the supermassive black hole Sgr~A∗ is currently low (0.0014 per year), making them difficult to observe even with space-based baselines, continuous monitoring of the shadow of Sgr~A∗ could provide valuable insights into the compact object population surrounding the galactic center. By tracking potential microlensing events, researchers may gain a deeper understanding of the distribution and properties of these compact objects.

Conclusion:

In conclusion, the work by Himanshu and Silk offers a comprehensive analysis of gravitational microlensing effects on black hole shadows imaged by the EHT. The study highlights the dependence of the shadow’s center, size, and shape on the Einstein angle and demonstrates the significant impact of intervening compact objects on the asymmetry and size of the shadow. Although current observational capabilities limit the detection of microlensing signatures, future expansions of the EHT, including space-based baselines, could unlock the potential to observe these events and provide further insights into the nature of black holes and their surroundings.

Reference: Himanshu Verma, Joseph Silk, “Microlensing Black Hole Shadows”, Arxiv, 2023. https://arxiv.org/abs/2306.02440

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The Great Disguise: Magnetic Fields Rendering Black Holes Invisible (Cosmology)

Black holes, formed through the collapse of magnetized progenitors, possess magnetic fields that extend beyond their event horizons. The interaction between black holes and magnetic fields has significant implications for the surrounding environment and the detectability of these cosmic entities. In a recent study, Chandrachur presented an intriguing finding suggesting that a test particle’s geodesic motion is disrupted by an intense magnetic field surrounding a black hole, rendering it unable to maintain a regular orbit. These findings have significant implications, as they suggested that, this can impede the formation of accretion disks and altering the motion of surrounding stellar objects. Moreover, the shielding effect of certain magnetic field strengths may render black holes virtually undetectable, providing an explanation for the unexpectedly weak magnetic fields observed in some supermassive black holes. This article explores Chandrachur’s theoretical investigation and examines the implications for the detectability and magnetic field limits of black holes.

Magnetic Fields and Circular Orbits:

Chandrachur’s study focused on a Schwarzschild black hole with mass M immersed in a uniform magnetic field B. By analyzing the frequencies associated with equatorial circular orbits of test particles, the study revealed a critical threshold. When the radius of the orbit exceeds a specific value, specifically rB > 2/B, all three frequencies become imaginary. This discovery indicates that a test particle’s geodesic motion is disrupted beyond or at r > rB, preventing the formation of an accretion disk and potentially causing the absence of motion for surrounding stellar objects.

The Concealment of Black Holes:

The detection of black holes typically relies on observing their effects on nearby stars and gas. However, Chandrachur’s findings suggest that a black hole surrounded by a magnetic field of the order B ~ M¯¹ can shield itself from detection. This intriguing phenomenon implies that the presence of a sufficiently strong magnetic field can render a black hole effectively invisible to observational techniques.

Constraining Magnetic Field Strengths:

Motivated by these theoretical insights, researchers have sought to determine the limits of magnetic field strengths that can maintain the undetectability of a magnetized black hole. This is achieved by considering the sphere of magnetic influence around an astrophysical black hole, characterized by its radius rf. For instance, a black hole with a mass of 10⁹ times that of the Sun (M = 10⁹ M) could remain undetectable if it is surrounded by a magnetic field stronger than 10⁶ Gauss (G) and has a sphere of influence with a radius of approximately 10⁵ times its mass (rf ~ 10⁵ M). Similarly, a black hole with a mass of 10 times that of the Sun (M = 10M) could remain undetectable with a surrounding magnetic field stronger than 10¹⁴ G and a sphere of influence with a radius of approximately 10⁵ times its mass (rf ~ 10⁵ M). These findings provide insights into the puzzlingly weak magnetic fields observed in some supermassive black holes.

Conclusion:

The interplay between magnetic fields and black holes has far-reaching consequences for their detectability and astrophysical environments. Chandrachur’s study revealed that intense magnetic fields can disrupt the geodesic motion of nearby test particles, leading to the absence of accretion disks and altered motion of surrounding objects. Furthermore, a black hole surrounded by a sufficiently strong magnetic field can effectively cloak itself, evading detection. Further exploration of this fascinating phenomenon will deepen our understanding of the complex relationship between magnetic fields and black holes, unlocking new insights into the nature of these enigmatic cosmic entities.

Reference: Chandrachur Chakraborty, “Black holes shielded by magnetic fields”, Arxiv, 2022. https://doi.org/10.48550/arXiv.2211.11356

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Unraveling the Mystery: Ultra Cold Black Holes Defy Cosmic Censorship (Cosmology)

Black holes have long captivated the imagination of scientists and the public alike with their mysterious and extreme nature. These enigmatic cosmic entities are known for their immense gravitational pull, which traps anything, including light, within their event horizons. However, recent research by Shahar Hod has unveiled a surprising revelation: the existence of dangerously cold black holes (10^-108 °K) that defy our understanding of their behavior. By examining the emission spectra of highly charged black holes, scientists have discovered a potential violation of the cosmic censorship principle, suggesting a fundamental lower bound on their temperatures.

The Bekenstein-Hawking Temperature and Quantum Physics

To comprehend the concept of dangerously cold black holes, we must first understand the Bekenstein-Hawking temperature (TBH). This temperature is associated with black holes and arises from the interplay of quantum physics and general relativity. According to the principles of quantum mechanics, black holes are not completely devoid of energy and possess a temperature that causes them to emit thermal radiation.

The cosmic censorship principle, proposed by physicist Roger Penrose, is a foundational concept in general relativity. It suggests that singularities within black holes, characterized by infinite density and curvature, are hidden from the outside universe by the event horizon. This principle acts as a safeguard, preventing the existence of naked singularities, which could disrupt our understanding of spacetime.

Analyzing Emission Spectra and Naked Singularities

Recent investigations by Shahar Hod into the emission spectra of highly charged black holes have revealed a peculiar phenomenon. Black holes that approach extreme charge levels exhibit Bekenstein-Hawking temperatures (TBH) in the regime TBH ≲ m⁶/e³, where {m, e} represent the electron’s proper mass and electric charge, respectively. If these near-extremal black holes emit a photon with a thermal energy of ω = O(TBH), a startling possibility emerges: they could transform into horizonless naked singularities.

Naked singularities are singularities that lack an event horizon, which would ordinarily conceal their infinite density and curvature from the external universe. The existence of naked singularities contradicts the cosmic censorship principle and challenges our understanding of the nature of black holes.

The Conjecture and Implications

Based on these findings, a conjecture arises that pertains to the yet-unknown quantum theory of gravity. It suggests that the temperatures of well-behaved black hole spacetimes must adhere to a lower bound, namely TBH ≳ m⁶/e³. This conjecture indicates a fundamental restriction on the temperatures of black holes, preventing them from becoming dangerously cold.

If this conjecture is verified, it would have profound implications for our understanding of black holes and the laws of physics. It would establish a minimum temperature threshold, providing insights into the underlying mechanisms governing the behavior of these celestial entities. Furthermore, it could potentially reconcile the cosmic censorship principle with the existence of highly charged black holes.

Conclusion

The existence of dangerously cold black holes challenges our preconceived notions of these cosmic behemoths. By scrutinizing the emission spectra of highly charged black holes, researchers have uncovered a potential violation of the cosmic censorship principle, which may indicate a fundamental lower bound on black hole temperatures.

Further investigations and theoretical developments are necessary to test and validate the conjecture proposed in this essay. The study of quantum gravity, yet to be fully understood, holds the key to unraveling the mysteries of black holes and their behavior at extreme temperatures.

As scientists continue to explore the frontiers of knowledge, it is through such revelations and conjectures that we inch closer to unlocking the secrets of the universe and broadening our understanding of the fundamental laws that govern it.

Reference: Shahar Hod, “Black holes that are too cold to respect cosmic censorship”, Arxiv, 2023. https://arxiv.org/abs/2305.08918

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The Multiverse Unveiled: Exploring The Karch-Randall Braneworld (Quantum / Cosmology)

In the realm of theoretical physics, understanding the concept of a multiverse has been a subject of great interest and speculation. Gopal Yadav, a prominent physicist, has proposed an intriguing model based on wedge holography that offers insights into the nature of the multiverse. By considering gravitating baths with varying degrees of gravity, Yadav’s model delves into the composition, lifespan, and communication between universes within the multiverse. Additionally, the model addresses the possibility of obtaining the Page curve of black holes and even offers a resolution to the famous “grandfather paradox.” In this article, we will delve into the key findings and implications of Yadav’s model, shedding light on the exciting implications for our understanding of the multiverse.

Wedge Holography and Multiverse Construction:

Yadav’s model of wedge holography revolves around the consideration of two gravitating baths, one with strong gravity and the other with weak gravity. By embedding 2n Karch-Randall branes in the bulk, which may or may not contain black holes, the model describes the multiverse in various scenarios.

In the first case, the multiverse is constructed using d-dimensional Karch-Randall branes embedded in anti-de Sitter branes. Notably, Yadav found that once created, the multiverse consisting of AdS branes persists indefinitely. In contrast, the second case involves d-dimensional Karch-Randall branes embedded in de Sitter branes, resulting in a multiverse composed of de Sitter branes with a short lifespan. These branes are created and annihilated simultaneously. Furthermore, Yadav highlights the incompatibility of describing a multiverse as a mixture of d-dimensional de Sitter and anti-de Sitter spacetimes within the same bulk due to the different intersecting characteristics of these branes.

Exploring Black Holes and Radiation:

Within Yadav’s model, the possibility of obtaining the Page curve of black holes is also investigated. By employing two Karch-Randall branes, one serving as a black hole and the other as a bath, the model encounters challenges in defining the island surface and identifying the nature of the radiation emitted. For instance, when a Karch-Randall brane consists of a black hole and cosmological event horizons, such as a Schwarzschild de-Sitter black hole on the brane, the observer collecting radiation faces difficulty in distinguishing between Hawking radiation and Gibbons-Hawking radiation.

Resolving the “Grandfather Paradox”:

Figure 1: Different universes Q−1,−2,−3,1,2,3 where different people are living. © Gopal Yadav

Perhaps one of the most intriguing implications of Yadav’s model is its potential to resolve the well-known “grandfather paradox.” In this setup, where universes communicate through transparent boundary conditions at the interface point, the paradox can be circumvented. Suppose an individual, Bob, resides on Q1 while his grandfather lives on Q-1. To avoid the paradox, Bob cannot travel to Q-1, where he could potentially prevent his own existence. However, he can travel to Q-2, Q-3, and so forth, where he can meet other individuals like Robert and Alice. Thus, within this model, the “grandfather paradox” finds resolution.

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Reference: Yadav, G. Multiverse in Karch-Randall Braneworld. J. High Energ. Phys. 2023, 103 (2023). https://doi.org/10.1007/JHEP03(2023)103

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What Let Neutron Star Rotate? (Cosmology)

Introduction:

Neutron stars, the dense remnants of core-collapse supernovae, are known for their extreme physical properties and play a vital role in understanding the dynamics of stellar evolution. These fascinating celestial objects are born with a unique characteristic – natal kicks. These kicks are a consequence of asymmetric ejection of matter and possibly neutrinos during the supernova explosion, imparting both linear and rotational motion to the neutron star. Recent research by Loeb and colleagues delves into the intriguing possibility that these natal kicks may occur off-center, leading to a natal rotation. The paper explores the correlation between observed pulsar spin and transverse velocity in our galaxy and develops a model to constrain the natal rotation imparted to neutron stars.

The Nature of Natal Kicks and Rotation:

During a core-collapse supernova, the asymmetric expulsion of matter and neutrinos generates a recoil force, propelling the newly formed neutron star away from its birthplace. If this force is exerted even slightly off-center, it imparts a rotational motion to the neutron star. As a result, neutron stars born with off-center kicks may possess a certain degree of rotation.

Exploring the Pulsar Population:

Loeb and colleagues’ study aims to investigate the implications of off-center natal kicks on the population of pulsars in our galaxy. Pulsars, rapidly spinning neutron stars emitting beams of radiation, provide valuable insights into the physics of these stellar remnants. By analyzing the spin properties and transverse velocities of pulsars, the researchers seek to establish a correlation that can shed light on the presence and characteristics of off-center natal kicks.

Modeling Natal Rotation:

To examine the effects of natal rotation, Loeb and colleagues developed a comprehensive model that incorporates the observed population of pulsars in the galaxy. By comparing the model’s predictions with the available data on pulsar spin periods, transverse velocities, and ages, the researchers were able to constrain the location of the off-center kick.

Key Findings:

After thorough analysis and modeling, the study by Loeb and colleagues presents a significant finding. The researchers determine, with a confidence level of 90%, that the location of the off-center kick, referred to as Rkick, is approximately 1.12 kilometers. This result suggests that the off-center kicks responsible for imparting natal rotation to neutron stars tend to occur at a consistent distance from the center of the star.

Implications and Future Directions:
The findings of this study hold considerable implications for our understanding of core-collapse supernovae and the resulting neutron stars. By constraining the location of off-center natal kicks, this research provides valuable guidance for future simulations of massive star core-collapse, aiding in the refinement of models that replicate the complex dynamics of these cataclysmic events.

Moreover, the observed correlation between pulsar spin and transverse velocity offers insights into the mechanisms governing the formation and evolution of neutron stars. This knowledge contributes to our understanding of stellar astrophysics and the intricate processes that shape the behavior and properties of these enigmatic cosmic objects.

Reference: Giacomo Fragione and Abraham Loeb, “Neutron star kicks and implications for their rotation at birth”, Astro, 2023. https://astro.paperswithcode.com/paper/neutron-star-kicks-and-implications-for-their

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Moon Emerges As Superior Dark Matter Detection Site (Cosmology)

Neutrinos, elusive particles that interact weakly with matter, have long captured the imagination of scientists. These subatomic particles, produced in various astrophysical processes, can provide valuable insights into the mysteries of the universe.

Recent research done by Gaspert and colleagues has revealed an intriguing possibility: the Moon could serve as an ideal platform for detecting dark matter through neutrino flux. While this opens up exciting avenues for scientific discovery, practical challenges must be overcome to realize this ambitious endeavor.

Many neutrino fluxes on the Moon are nearly the same as on the Earth, but a few are radically different. For direct detection of electroweak scale dark matter on the Earth, the most important flux sources are solar neutrinos, diffuse supernova background neutrinos (DSNB) & atmospheric neutrinos.

Surprisingly, the solar and DSNB neutrino fluxes on the Moon closely resemble those on Earth. However, it is the flux of atmospheric neutrinos that exhibits a stark contrast due to the Moon’s unique characteristics. Unlike the Earth, the Moon lacks a substantial atmosphere, and cosmic rays bombarding its surface undergo direct collisions, generating a distinct neutrino spectrum.

This key difference has prompted Gaspert and colleagues to estimate the total flux and spectrum of neutrinos near the lunar surface. Their findings suggest that a large-scale liquid xenon or argon detector stationed on the Moon could offer significantly enhanced sensitivity to dark matter with masses above and approximate to 50 GeV, surpassing the capabilities of a comparable detector on Earth. This heightened sensitivity could even extend to detecting the elusive mχ = 1.1 TeV thermal Higgsino dark matter.

While these results fuel the motivation for lunar-based dark matter direct detection experiments, it is important to acknowledge the practical challenges associated with realizing such an apparatus. Several factors need to be considered, including transportation logistics, cosmic activation concerns, local background interference, infrastructure requirements, and the allocation of human resources. These obstacles must be addressed and overcome for the vision of Moon-based dark matter detection to become a reality.

Transporting a large-scale detector to the Moon is a formidable task that requires careful planning and execution. Launching and safely landing such a sensitive instrument without compromising its functionality poses significant engineering challenges. Additionally, the issue of cosmic activation arises, as prolonged exposure to cosmic rays during transit could lead to unwanted activation of detector components. Addressing this concern necessitates shielding measures and thorough safety protocols.

Local backgrounds, originating from lunar materials and natural radioactivity, could introduce unwanted noise into the dark matter signal. Rigorous studies and mitigation strategies are required to ensure that these local sources do not overshadow the sought-after signatures. Infrastructure development on the Moon, such as establishing power supply systems and maintaining a stable environment for the detector, presents further logistical hurdles that must be overcome.

Lastly, human resources play a vital role in the success of lunar-based experiments. Skilled personnel will be needed to operate and maintain the detector, troubleshoot issues, and analyze the vast amount of data collected. Collaborative efforts among scientists, engineers, and astronauts will be necessary to tackle the intricacies of such an ambitious scientific endeavor.

Despite the practical challenges, the current momentum towards lunar exploration offers an opportune moment to consider the potential applications of Moon-based experiments for scientific discovery. The quest to unravel the mysteries of dark matter, one of the most enigmatic aspects of our universe, is a formidable task that requires innovative approaches. The unique neutrino flux on the Moon, with its reduced backgrounds, provides an enticing opportunity for advancing our understanding of this elusive cosmic entity.

Reference: Reference: Andrea Gaspert, Pietro Giampa, Navin McGinnis, David E. Morrissey, “Dark Matter Direct Detection on the Moon”, Arxiv, 2023.

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What Aliens Utilising In Quantum Computers? (Cosmology)

Recently, Dvali revealed that quantum field theory places a universal limit on the information storage capacity of devices composed of quanta. These maximum capacity objects, known as “saturons,” are highly efficient in storing quantum information.

Now, Dvali and Osmanov have highlighted that due to universality of gravitational interaction, black holes possess the highest information storage capacity among all saturons.

Consequently, it is anticipated that advanced civilizations will utilize microscopic black holes (of size R ≤ 10¯¹⁸ cm) in their quantum computing systems.

The emitted Hawking radiation from these alien quantum computers is indiscriminate, consisting of ordinary particles like neutrinos and photons, detectable within the range of our current detectors such as IceCube’s VHE.

This presents an exciting opportunity for SETI to explore the potential presence of civilizations composed of hidden particle species that solely interact with our world through gravity.

Reference: Gia Dvali and Zaza N. Osmanov, “Black holes as tools for quantum computing by advanced extraterrestrial civilizations”, Arxiv, 2023.

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