Kerr Black Hole as a Pevatron at the Galaxy Center

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the paper which is submitted for publication, for the Kerr black holes (BH) it is supposed concentration of the masses on the spherical surface of event horizon. Such placement of massive components of the BH which is uniform on its surface not in its volume is analogous with the behavior of charged particles on the ideal conductor surface in electromagnetic field (the authors use the term “a perfect mass conductor” for the BH considered).

Placing particles on a spherical surface of a certain (gravitational) radius allowed estimating an average distance between particles, which turns out to be significantly smaller than for the distribution throughout the BH volume. Then, an average energy of particles by order of magnitude is evaluated as PeV.

So, the confining of the Kerr BH massive components to the surface of horizon by strong gravity allows considering the central BH in the Galaxy as the source of very-high energy cosmic rays (protons with energies up to PeVs). The authors beleive, their idea and numerical estimations are supported by HAWC Collaboration registration of very high-energy photons from the Galaxy center (GC).

It seems these sufficiently simple macroscopic estimations of the BH basic (thermodynamic) parameters and average characteristics of particles distribution over the BH horizon can present an interesting model of hypothetical PeVatron at the GC.

From my point of view, more detailed analysis of (microscopic) dynamics and possible processes at the (blurry) BH horizon surface and in the surrounding matter is not only important but necessary especially if in the model it is planned more careful analysis of high-energy particles evaporation, their further movement and interactions. Besides, interactions of these radiated particles with the ambient matter including dark matter components can impact on the DM distribution with spike near GC and also can result to some specific astrophysical manifestations or signals, not only high-energy photons.

Obviously,  the quantified developing of this model will be more cumbersome than estimation of an order of magnitudes, however, at least a some (brief?) discussion of directions, methods and possible applications of analysis of the model would be appropriate in the text of this paper.

Please, also enumerate (with number 4) the formula for the density of flux in the beginning of the Section 4.

With the above noticed minor modifications and additions the paper can be published in the journal “Universe”.

Author Response

Dear Referee,

please find in the attachment our reply.

Thanks a lot.

Best regards,

Simone for the Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This article is the journal version of the same article that the author deposited in arXiv earlier this year. 

The article is well written. It contains new ideas and is of interest of both researchers in black hole physics and astro-particle physics. When the presentation up to the discussions of the existence of peV particles on the event horizon of 2D BH are logical, linking to the HAWC observation is very weak.

The presence of energetic particle in the PeV range does not implies that the systems are PeV sources as viewed by distant observers. For instance, the plasma that emit the CMB are not 3K but CMB observed today is 3K. Any emission, in photons or in particles, from the event horizon would suffer infinite time dilation, leading to the infinite shift to lower energies. So, unless the PeV particles are not at the event horizon, then it can retain the PeV energy. The argument that the authors use to derive the PeV energy particles is based on the undertainty principle of how much one can pack the Fermion on the surface of the Event horizon, not a small region near the event horizon. Thus, the author will need to clarify why the particles when evaporated from the event horizon can retain the PeV energies when reaching the observer, i.e. imprinting PeV signatures as what we see in HAWC observations.

The next issue is the life span of stellar black hole is too short, which is an issur realised by the authors. The authors put this issue under the carpet claiming that it will be accounted in their future work. The author should at least describe how the issue is resolved. It is acceptable to show the rigorous "proof" in the future work, but it is unacceptable to give an empty statement hoping that the readers believe that the authors can resolve this issue. It is unaccepatble if this issue is not probably addressed in a transparent manner.  

I recommend a major revision, because of these two issues. 

The authors would need to address them properly and explicitly. Otherwise, the paper is unrelated to the HAWC observations of the mysterious PeV source near the Galactic Centre. Without the linking to interpretation of HAWC PeV observation, the article is simply an academic exercise rather than a scientific article with excellent merits. 

If the authors could address these two issues, it would be a very excellent paper, well written and containing new science and very interesting aspects of linking fundamental physics and current observations in astro-particle physics. At that stage I will not hesitate to highly recommend the publication of the article. 

Author Response

Dear Referee,

please find in the attachment our reply.

Thanks a lot.

Best regards,

Simone for the Authors

     

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I recommend the publication. 

Author Response

Dear Editor,

please find our reply in the attachment.

Best regards,

Simone

Author Response File: Author Response.pdf