by jsendak | Feb 9, 2024 | GR & QC Articles
Black hole superradiance has proven being very valuable in several realms of gravitational physics, and holds a promising discovery potential. In this paper, we show how it can sheed light on a long standing problem in physics, the quest for magnetic monopoles in the Universe. Placing them in the interior of primordial rotating black holes, which act as natural amplifiers, we show that massive charged bosonic fields in their vicinity exhibit a superradiant instability which surpasses significantly that of neutral Kerr black holes. Strikingly, this is true for black holes containing an order-one number of magnetic monopoles, or merely a single one, and possessing either low, moderate or large values of angular momentum. In particular, the instability is drastically faster than the radiative decay time of charged pions, thus making it physically relevant. Furthermore, our analysis identifies the most unstable modes as a class of monopole spheroidal harmonics, that we dub north and south monopole modes, whose morphology is markedly different from the usual superradiantly unstable modes since they extend along the rotational axis. We conclude by discussing implications of our results for primordial magnetic black holes, and their observational signatures as sources of cosmic rays and high-frequency gravitational waves.
Black hole superradiance has been proven to be valuable in various areas of gravitational physics and offers significant potential for discovery. In this paper, we focus on its application to the long-standing challenge of finding magnetic monopoles in the Universe.
We propose that primordial rotating black holes could serve as natural amplifiers for magnetic monopoles placed within their interiors. This amplification leads to a superradiant instability in the vicinity of these black holes, which is even more pronounced than that observed in neutral Kerr black holes. This instability is relevant for black holes containing just one or a small number of magnetic monopoles, regardless of their level of angular momentum.
An interesting finding is that the superradiant instability occurs at a much faster rate than the radiative decay time of charged pions, making it physically relevant. Additionally, our analysis reveals the existence of a specific class of monopole spheroidal harmonics known as north and south monopole modes. These modes differ from the usual superradiantly unstable modes as they extend along the rotational axis of the black hole.
In conclusion, our research has significant implications for understanding primordial magnetic black holes and their potential role as sources of cosmic rays and high-frequency gravitational waves. By exploring the phenomenon of black hole superradiance and its application to magnetic monopoles, we have opened up new avenues for investigation and future discoveries in gravitational physics.
Roadmap for Readers
- Introduction to black hole superradiance and its relevance in gravitational physics
- Discussion of the long-standing problem of finding magnetic monopoles in the Universe
- Explanation of the proposed use of primordial rotating black holes as amplifiers for magnetic monopoles
- Presentation of the superradiant instability observed in the vicinity of these black holes
- Comparison of the instability in black holes with different numbers of magnetic monopoles and levels of angular momentum
- Analysis of the faster rate of the superradiant instability compared to the decay time of charged pions
- Description of the unique monopole spheroidal harmonics known as north and south monopole modes
- Discussion of the implications for primordial magnetic black holes and their potential observational signatures as sources of cosmic rays and high-frequency gravitational waves
- Summary of the key findings and their significance in advancing our understanding of gravitational physics
Potential Challenges and Opportunities
While our research opens up exciting possibilities for further exploration, there are several challenges that need to be addressed:
- Experimental verification: The proposed phenomenon needs to be empirically tested in order to validate its existence.
- Data collection: Gathering observational data on primordial magnetic black holes and their characteristics poses technological and logistical challenges.
- Theoretical refinement: Further theoretical analysis is required to fully understand the underlying mechanisms and implications of the observed superradiant instability.
- Interdisciplinary collaboration: Collaboration between researchers from diverse fields such as astrophysics, particle physics, and gravitational wave astronomy is crucial for comprehensive investigations.
Despite these challenges, the opportunities presented by this research are immense:
- Potential discovery of magnetic monopoles: This research offers a new avenue for detecting elusive magnetic monopoles in the Universe.
- Advancement of gravitational physics: The study of black hole superradiance and its application to magnetic monopoles can significantly contribute to our understanding of gravitational phenomena.
- Expanded knowledge of primordial black holes: Investigating the role of primordial rotating black holes in amplifying magnetic monopoles can shed light on the formation and evolution of these mysterious objects.
- New observational tools: The identification of primordial magnetic black holes as potential sources of cosmic rays and high-frequency gravitational waves opens up new possibilities for detecting and studying these phenomena.
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by jsendak | Jan 20, 2024 | GR & QC Articles
Adiabatic binary inspiral in the small mass ratio limit treats the small body
as moving along a geodesic of a large Kerr black hole, with the geodesic slowly
evolving due to radiative backreaction. Up to initial conditions, geodesics are
typically parameterized in two ways: using the integrals of motion energy $E$,
axial angular momentum $L_z$, and Carter constant $Q$; or, using orbit geometry
parameters semi-latus rectum $p$, eccentricity $e$, and (cosine of )
inclination $x_I equiv cos I$. The community has long known how to compute
orbit integrals as functions of the orbit geometry parameters, i.e., as
functions expressing $E(p, e, x_I)$, and likewise for $L_z$ and $Q$. Mappings
in the other direction — functions $p(E, L_z, Q)$, and likewise for $e$ and
$x_I$ — have not yet been developed in general. In this note, we develop
generic mappings from ($E$, $L_z$, $Q$) to ($p$, $e$, $x_I$). The mappings are
particularly simple for equatorial orbits ($Q = 0$, $x_I = pm1$), and can be
evaluated efficiently for generic cases. These results make it possible to more
accurately compute adiabatic inspirals by eliminating the need to use a
Jacobian which becomes singular as inspiral approaches the last stable orbit.
Mapping Orbit Integrals to Orbit Geometry Parameters
This article discusses the development of mappings from orbit integrals (energy E, axial angular momentum L_z, Carter constant Q) to orbit geometry parameters (semi-latus rectum p, eccentricity e, and inclination x_I). These mappings are essential for accurately computing adiabatic inspirals where a small body moves along the geodesic of a large Kerr black hole.
Current Understanding
The community has long been able to compute orbit integrals as functions of the orbit geometry parameters. However, the reverse mappings, i.e., functions that express p, e, and x_I in terms of E, L_z, and Q, have not yet been developed in general.
New Developments
In this article, the authors present generic mappings that translate E, L_z, and Q into p, e, and x_I. These mappings are particularly simple for equatorial orbits (Q = 0, x_I = ±1) and can be efficiently evaluated for generic cases.
Potential Opportunities
- Accurate Computation: The developed mappings provide a more accurate method to compute adiabatic inspirals, eliminating the need for a singular Jacobian as the inspiral approaches the last stable orbit.
- Improved Understanding: By bridging the gap between orbit integrals and orbit geometry parameters, researchers can gain a deeper understanding of the dynamics of small bodies moving in the vicinity of Kerr black holes.
Potential Challenges
- Validation: The newly developed mappings need to be validated through further research and comparison with existing methods. This will ensure their reliability and accuracy in various scenarios.
- Complex Scenarios: While the mappings are efficient for generic cases, there may be complex scenarios or extreme conditions where their applicability needs to be further studied.
Roadmap for Readers
- Understand the current state of knowledge regarding the computation of orbit integrals and their dependence on orbit geometry parameters.
- Explore the limitations and challenges faced in the absence of reverse mappings from orbit integrals to orbit geometry parameters.
- Examine the new developments presented in this article, focusing on the generic mappings that allow for accurate computation of adiabatic inspirals.
- Consider the potential opportunities stemming from these developments, such as improved accuracy and a deeper understanding of small body dynamics around Kerr black holes.
- Recognize the potential challenges in validating the mappings and their applicability in complex scenarios.
- Stay updated on further research in this field to gain insights into the refinement and expansion of the developed mappings.
In conclusion, this article presents a significant advancement in understanding adiabatic inspirals by developing mappings from orbit integrals to orbit geometry parameters. While offering opportunities for accurate computation and improved understanding, these mappings need validation and careful consideration of their applicability in various scenarios.
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by jsendak | Jan 18, 2024 | GR & QC Articles
Motivated by the first image of a black hole captured by the EHT, there has
been a surge of research using observations of black hole shadows to test
gravity theories. In this paper, we carry out the related study about shadow of
Kerr black hole surrounded by a cloud of strings in Rastall gravity, which
deviates from the Kerr black hole due to the presence of the string parameter
$a_0$ and the parameter $beta$. The horizons, ergospheres, and photon region
of the black hole are shown. Moreover, we explore the shadow and observations
of the black hole, which are closely linked to the parameters $a_0$ and
$beta$. Treating M87* as Kerr black hole surrounded by a cloud of strings
under Rastall gravity, we constrain the black hole parameters by the EHT
observations. For a given $beta$, the circularity deviation of the black hole
obeys $Delta Clesssim0.1$ in all regions. The angular diameter
$theta_{d}=42pm3mu as$ can give the upper bound of parameters $a$ and $a_0$
for fixed $beta$. The shadow axis ratio satisfies the observation data of EHT
($1<D_xlesssim4/3$) in the whole space for a given $beta$. These results are
consistent with the public information of EHT. In other words, candidates for
real astrophysical black holes can be Kerr black holes surrounded by a cloud of
strings in Rastall gravity.
Conclusions
The research presented in this paper focuses on the shadow of a Kerr black hole surrounded by a cloud of strings in Rastall gravity. The study examines the horizons, ergospheres, and photon region of the black hole, as well as the parameters $a_0$ and $beta$ that affect its properties. The observations of the black hole shadow are closely linked to these parameters.
Using the EHT observations of M87*, the paper also discusses how the black hole parameters can be constrained. The circularity deviation of the black hole is found to be $Delta Clesssim0.1$ in all regions for a given $beta$. The angular diameter $theta_{d}=42pm3mu as$ provides an upper bound for the parameters $a$ and $a_0$ with fixed $beta$. The shadow axis ratio is also found to be consistent with the EHT observation data (
Based on these findings, it is concluded that Kerr black holes surrounded by a cloud of strings in Rastall gravity can serve as candidates for real astrophysical black holes.
Future Roadmap
Building on this research, there are several potential challenges and opportunities on the horizon:
- Further observational verification: It is important to continue gathering observational data of black holes to further verify the consistency of the parameters and properties discussed in this study. This could involve utilizing data from future EHT observations or other telescopes and instruments.
- Refining parameter constraints: The current constraints on the black hole parameters are based on a fixed $beta$ value. Future research could explore how the constraints vary with different values of $beta$ to provide a more comprehensive understanding of the underlying physics.
- Exploring other gravity theories: While this study focuses on Rastall gravity, there are several alternative theories of gravity that could also be investigated. Comparing the results across different theories can help shed light on the fundamental properties of black holes.
- Investigating the nature of the string cloud: The presence of a cloud of strings around black holes is an intriguing concept. Further research could delve into the nature and behavior of these strings, potentially revealing new insights into the interactions between gravity and quantum physics.
By addressing these challenges and opportunities, future research in this field can contribute towards a more comprehensive understanding of black holes and their role in the universe.
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by jsendak | Jan 12, 2024 | GR & QC Articles
Recent observational data from the Event Horizon Telescope (EHT)
collaboration provide convincing realistic evidence for the existence of black
hole rotation. From a phenomenological perspective, a recently proposed stable
rotating regular (SRR) black hole circumvents the theoretical flaws of the Kerr
solution. For the purpose of obtaining observational signatures of this black
hole, we study its gravitational lensing effect. In the strong field limit, we
calculate the deflection angle of light, the radius of the photon sphere, and
other observables. The observables include the relativistic image position,
separation, magnification, and time delays between different images. Then, by
modeling M87* and Sgr A* as the SRR black hole, we compute their observables
and evaluate the deviation of the observables from the Kerr case. In the weak
field limit, we calculate the light deflection angle of M87* and Sgr A* via the
Gauss-Bonnet theorem (GBT). With the growth of deviation parameter $e$, the
gravitational lensing effect in the weak field limit intensifies monotonically,
and the gravitational lensing effect in the strong field limit changes
dramatically only at high spins. Our research may contribute to distinguish
between SRR black holes from Kerr black holes under higher-precision
astronomical observations.
Future Roadmap:
Introduction
In recent years, the Event Horizon Telescope (EHT) collaboration has provided compelling evidence for the existence of black hole rotation. However, a new stable rotating regular (SRR) black hole has been proposed to overcome some theoretical flaws of the previous Kerr solution. This article aims to explore the gravitational lensing effects of the SRR black hole and differentiate it from the Kerr case.
Observables and Calculations
The study focuses on several observables that can be used to distinguish between the SRR black hole and the Kerr black hole. These observables include:
- Relativistic image position
- Separation between images
- Magnification of images
- Time delays between images
To calculate these observables, the deflection angle of light, the radius of the photon sphere, and other factors need to be determined in both the weak field limit and the strong field limit. In the weak field limit, the Gauss-Bonnet theorem (GBT) is used for light deflection angle calculations for M87* and Sgr A*.
Deviation Parameter and Gravitational Lensing
The article explains that the intensity of the gravitational lensing effect in the weak field limit increases with the growth of the deviation parameter $e$. On the other hand, in the strong field limit, significant changes in the gravitational lensing effect are only observed at high spins. This information can aid in distinguishing SRR black holes from Kerr black holes under higher-precision astronomical observations.
Conclusion
This research on the gravitational lensing effects of stable rotating regular black holes provides a potential method for differentiating them from previous Kerr black holes. By calculating various observables, including relativistic image positions, separations, magnifications, and time delays, it is possible to evaluate the deviation of the observables from the Kerr case. However, further astronomical observations and higher precision measurements are required to fully understand and confirm these distinctions.
Potential Challenges and Opportunities:
The road ahead presents some challenges and opportunities:
- Challenge: Obtaining higher-precision observations: Accurate measurements and observations will be crucial to identify the differences between SRR black holes and Kerr black holes.
- Challenge: Theoretical validation: The proposed SRR black hole must undergo further theoretical scrutiny to confirm its stability and resolve any potential flaws.
- Opportunity: Advancements in observational techniques: Technological advancements in observational tools and telescopes may enable researchers to obtain the necessary data to distinguish between these two types of black holes.
- Opportunity: New insights into black hole physics: Understanding the nature and characteristics of SRR black holes could provide new insights into the behavior of rotating black holes and the fundamental principles of general relativity.
With continued progress in observational capabilities and theoretical investigations, future studies can build upon this research to enhance our understanding of black hole rotation and potentially revolutionize our knowledge of astrophysics.
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by jsendak | Jan 10, 2024 | GR & QC Articles
We investigate the amplification of the genuine tripartite nonlocality (GTN)
and the genuine tripartite entanglement (GTE) of Dirac particles in the
background of a Schwarzschild black hole by a local filtering operation under
decoherence. It is shown that both the physically accessible GTN and the
physically accessible GTE are decreased by the Hawking effect and decoherence.
The “sudden” death of the physically accessible GTN occurs at some critical
Hawking temperature, and the critical Hawking temperature degrades as the
decoherence strength increases. In particular, it is found that the critical
Hawking temperature of “sudden death” can be prolonged by applying the local
filtering operation, which means that the physically accessible GTN can exist
for a longer time. Furthermore, we also find that the physically accessible GTE
approaches to the nonzero stable value in the limit of infinite Hawking
temperature for most cases, but if the decoherence parameter p is less than 1,
the “sudden death” of GTE will take place when the decoherence strength is
large enough. It is worth noting that the nonzero stable value of GTE can be
increased by performing the local filtering operation, even in the presence of
decoherence. Finally, we explore the generation of physically inaccessible GTN
and GTE of other tripartite subsystems under decoherence, it is shown that the
physically inaccessible GTN cannot be produced, but the physically inaccessible
GTE can be produced, namely, GTE can pass through the event horizon of black
hole, but the GTN cannot do it. In addition, we can see that the generated
physically inaccessible GTE can be increased by applying the local filtering
operation, even if the system suffers decoherence.
Conclusions:
- The genuine tripartite nonlocality (GTN) and genuine tripartite entanglement (GTE) of Dirac particles in the background of a Schwarzschild black hole are decreased by the Hawking effect and decoherence.
- The “sudden” death of the physically accessible GTN occurs at a critical Hawking temperature, degraded by increasing decoherence strength.
- The critical Hawking temperature of “sudden death” can be prolonged by applying a local filtering operation, allowing the physically accessible GTN to exist for a longer time.
- The physically accessible GTE approaches a nonzero stable value in the limit of infinite Hawking temperature, but “sudden death” of GTE occurs when the decoherence strength is large enough for certain cases.
- The nonzero stable value of GTE can be increased by performing the local filtering operation, even in the presence of decoherence.
- The generation of physically inaccessible GTN is not possible under decoherence, but physically inaccessible GTE can be produced, passing through the event horizon of a black hole.
- The generated physically inaccessible GTE can be increased by applying the local filtering operation, even in the presence of decoherence.
Future Roadmap
The findings from this study provide insights into the behavior of genuine tripartite nonlocality and entanglement of Dirac particles near a Schwarzschild black hole under the influence of decoherence. Moving forward, there are several potential challenges and opportunities on the horizon:
- Exploration of other black hole backgrounds: It would be valuable to investigate how genuine tripartite nonlocality and entanglement behave in the presence of different types of black holes, such as Kerr black holes or charged black holes. This could offer a more comprehensive understanding of the effects of different black hole properties.
- Quantifying the impact of other decoherence models: The current study focused on decoherence caused by local filtering operations. It would be interesting to explore the effects of other types of decoherence models, such as environmental noise or interaction with additional particles. Understanding how different decoherence mechanisms affect the physical accessibility of GTN and GTE could shed light on their robustness in practical scenarios.
- Experimental verification: Conducting experimental tests to validate the theoretical predictions made in this study would be a crucial next step. This would involve designing and implementing experiments that can simulate the behavior of Dirac particles near a black hole under controlled conditions of decoherence. Such experiments could provide evidence for the observed phenomena and contribute to the development of quantum technologies.
- Applications in quantum information processing: The study highlights the importance of GTN and GTE in the context of quantum information processing. Further research could explore how the manipulation and control of GTN and GTE near black holes could be harnessed for quantum communication, cryptography, and computation. Understanding the potential applications of these phenomena could enable advancements in quantum technologies.
Overall, the study sets a foundation for future investigations and opens up new avenues for exploration in the field of quantum physics and black hole dynamics. By addressing the challenges and opportunities outlined above, researchers can continue to deepen our understanding of these fascinating phenomena and potentially unlock groundbreaking applications in the field of quantum mechanics.
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