Magnetized Black Holes: Interplay between Charge and Rotation

Round 1

Reviewer 1 Report

In the paper the authors treat the problem of magnetized black hole and its

influence on particle acceleration. They consider strong magnetic field case (mainly discussion) and focus on weak magnetic field and problem of particle movement. They alsodescribe the so-called magnetic Penrose process.

In my opinion the article is interesting and points the aims for future investigations. I recommend it for the publication.

 

Author Response

We thank the referee for very encouraging words!

The authors

Reviewer 2 Report

This manuscript reviews the magnetized black holes and particle acceleration near the horizon. The authors clearly revisit  aspects of rotation and charge within the framework of exact (asymptotically non-flat) solutions of  mutually coupled Einstein-Maxwell equations that describe magnetized, rotating black holes. The manuscript is well written and can be accepted only need one issue corrected: 'MKN' should be explained when it appears in the title of the second section.

Author Response

We thank the referee for very encouraging words and for the suggestion. The acronym MKN has been now spelled out at the first use.

The authors

Reviewer 3 Report

The paper is written in an appropriate way and I suggest publication. 

The level of English is adequate. 

Author Response

We thank the anonymous referee for very encouraging words.

The authors

Reviewer 4 Report

1. This paper reviews an idea that many think is astrophysically irrelevant and cannot be made astrophysically relevant because electric forces dominate over gravitational forces even near black holes. Although it is mentioned in the paper that its astrophysical application is likely unrealistic, the paper proceeds to discuss the astrophysical implications such as the nature of cosmic rays. There seems to be logical incoherence here.

 

2. Deeper in the paper, you discuss the Blandford & Globus idea as if it were some novel energy extraction mechanism. There is nothing deep or new about this mechanism. And, therefore, nothing deep or new about its application. Adding it to this review gives the illusion of progress in the field. The fact of the matter is that the Blandford-Znajek mechanism and related ideas for energy extraction from black holes are simplified analytic solutions that allowed us to develop a first stab at how energy might be extracted from black holes in order to explain the observations of jets across the black hole mass scale and particle acceleration. But it is time to move beyond these simplified prescriptions and deal with detailed plasma astrophysics near black holes in full general relativity. In short, a good motivation for this review is lacking.  

 

3. If there is anything worth pursuing in this space, it seems to be limited to understanding better the theoretical solutions associated with Einstein-Maxwell fields regardless of their real-life applications. In other words, an answer to the following question: what have we learned about solutions to Einstein-Maxwell from this and how does this help us in extending these mathematical solutions to more complex cases?

 

Author Response

This contribution has been conceived as an invited write-up of a talk presented at a meeting on the occasion of R.Ruffini birthday anniversary. We thus briefly summarize various viewpoints that has been discussed during the evolving history of the field with some emphasis on electromagnetic phenomena in strong gravity of black holes, where R.Ruffini with his collaborators had achieved significant discoveries. Some of these direction have been closed in the meantime whereas, e.g., electromagnetic acceleration of particle to very high energy assisted by black hole rotation are an active field of current research. We try to formulate the background of the present contribution more clearly.

The reference to Globus and Blandford has been removed.

Indeed, the section dealing with exact solution, albeit viewed as rather academic, is the focus of the contribution, which has thus been accompanied by the figure illustrating the interplay between the total charge and angular momentum that have rather different interpretation (as the MKN solution is not asymptotically flat, unlike the "classical" definition of isolated non-magnetized black holes. We attempt to clarify this viewpoint in the revised version.

Reviewer 5 Report

This is a good and interesting paper, concerning magnetized black holes and their charges and their rotations etc. This paper is generally very well written and it seems to me to be mathematically correct, thus this is a paper, which eventually deserves to be published. 

 

However, my main objection against this paper, is that the middle of this paper is bad organized, i.e. at page 4 and 5, there are 8-10 equations without any numbers, thus it is almost impossible for the innocent readers to inquire about this paper. I must insist that all equations are clearly numbered in the revised version of this paper!

 

 

Further revision is necessary. 

 

Author Response

We thank the referee for encouraging comments. We have revised the manuscript and enumerated all equations as required in the report. We also included additional minor ameliorations (indicated by boldface letters) and we updated the list of bibliography.

Round 2

Reviewer 4 Report

Ok. I find your responses reasonable. 

Reviewer 5 Report

The authors of this paper, have answered all my questions and comments, which I raised in my first report, in a very satisfying way and they have improved their paper in many different ways, so I can now clearly recommend this paper for publication in the Universe Journal.