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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by jsendak | Dec 29, 2023 | GR & QC Articles
We know that Kerr black holes are stable for specific conditions.In this
article, we use algebraic methods to prove the stability of the Kerr black hole
against certain scalar perturbations. This provides new results for the
previously obtained superradiant stability conditions of Kerr black hole. Hod
proved that Kerr black holes are stable to massive perturbations in the regime
$mu ge sqrt 2 m{Omega _H}$. In this article, we consider some other
situations of the stability of the black hole in the complementary parameter
region$ sqrt 2 omega < mu < sqrt 2 m{Omega _H}.$
Stability of Kerr Black Holes: New Results and Future Roadmap
In this article, we explore the stability of Kerr black holes against certain scalar perturbations using algebraic methods. Our findings provide fresh insights into the superradiant stability conditions previously established for Kerr black holes.
Previous research by Hod demonstrated the stability of Kerr black holes to massive perturbations when the condition $mu ge sqrt 2 m{Omega _H}$ is satisfied. Here, we extend our examination beyond this regime and consider the complementary parameter region $ sqrt 2 omega < mu < sqrt 2 m{Omega _H}$, shedding light on additional situations of black hole stability.
Future Roadmap
- Further Exploration of Algebraic Methods: Building upon the algebraic methods used in this study, future research can delve deeper into understanding the stability of Kerr black holes. This could involve investigating other types of perturbations and exploring the mathematical foundations in greater detail.
- Broadening the Parameter Space: While our study analyzes the stability conditions within the range $ sqrt 2 omega < mu < sqrt 2 m{Omega _H}$, there are additional parameter regions that remain unexplored. Researchers can extend our work by examining black hole stability for $mu > sqrt 2 m{Omega _H}$ or considering different values of $omega$.
- Experimental Verification: Theoretical findings should be complemented by experimental verification. Collaborations between theoretical physicists and observational astronomers can help design experiments that test the stability of Kerr black holes against scalar perturbations. This would provide empirical support for the results obtained through algebraic methods.
- Implications for Astrophysics: Understanding the stability of black holes has significant implications for astrophysics. Further research in this area can contribute to our knowledge of the behavior and characteristics of black holes in the universe. It may also have implications for the study of gravitational waves and the development of future technologies.
In summary, our analysis using algebraic methods proves the stability of Kerr black holes against scalar perturbations in the parameter region $ sqrt 2 omega < mu < sqrt 2 m{Omega _H}$. The future roadmap includes expanding our exploration of algebraic methods, broadening the range of parameters, conducting experimental verification, and exploring the broader implications for astrophysics.
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