Magnetocentrifugal Mechanism of Pair Creation in AGN
Sergei Trushkin
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis is a theoretical paper attempting to explain jets from active galactic nuclei. There are issues I feel the authors need to address before acceptance.
- The idea that magnetic fields are strong around black holes is an assumption that flies in the face of much work dating back to the 1990’s (see Lubow, Ghosh, Pringle etc.). Please make contact with that plasma physics literature.
- Why do you cite reference [8] for the frozen-in condition? Blandford & Znajek assume it. They don’t motivate it in any detail. Again, need to refer to the appropriate MHD references.
- The frozen-in condition for magnetic fields is based on assumptions and simplifications that are difficult to motivate near black holes where magnetic fields are expected to be tangled up to the extreme. Ideal MHD likely breaks down. In astrophysics it has now become an article of faith but it should be used with caution. You should at least comment on the assumptions that go into it, if not attempt to alleviate the concerns near black holes where gravity ultimately dominates.
- In the Introduction you discuss the work done by the electric field. Work is a concept associated with forces. And the work is not “on” the wavelength but possibly “associated” with it. Work is done by forces on objects, not on wavelength. Your language is sloppy.
- Your references to black hole rotation are strange. You should probably reference Kerr himself and/or Bardeen et al 1973 as more fundamental references.
- The observations of AGN produce constraints on the mechanisms that are possible for the generation of strong jets. But you ignore the observations. In fact, you seem to be describing processes that are ubiquitous to accreting supermassive black holes but the consequence is that all AGN have jets, which is not observed. In fact, AGN with jets are the minority. What is the physical difference between radio loud AGN and radio quiet AGN in your model for jet formation? Black hole spin cannot be the answer because most black holes would have to be spinning, yet radio quiet AGN are 80% of AGN, which is the opposite of what you would get if spin were the discriminator. Magnetic fields cannot be the answer because of X-ray binaries. Please engage with this fundamental issue.
Author Response
We would like to thank an anonymous referee for interesting comments, which we have taken into account in revising the manuscript. The paper has been revised according to his/her suggestions, that can be seen below:
Referee-1
- The idea that magnetic fields are strong around black holes is an assumption that flies in the face of much work dating back to the 1990’s (see Lubow, Ghosh, Pringle etc.). Please make contact with that plasma physics literature.
Reply: Done, please see the third paragraph of introduction.
- Why do you cite reference [8] for the frozen-in condition? Blandford & Znajek assume it. They don’t motivate it in any detail. Again, need to refer to the appropriate MHD references.
Reply: Done.
- The frozen-in condition for magnetic fields is based on assumptions and simplifications that are difficult to motivate near black holes where magnetic fields are expected to be tangled up to the extreme. Ideal MHD likely breaks down. In astrophysics it has now become an article of faith but it should be used with caution. You should at least comment on the assumptions that go into it, if not attempt to alleviate the concerns near black holes where gravity ultimately dominates.
Reply: Done, please see the 3rd paragraph of introduction.
- In the Introduction you discuss the work done by the electric field. Work is a concept associated with forces. And the work is not “on” the wavelength but possibly “associated” with it. Work is done by forces on objects, not on wavelength. Your language is sloppy.
Reply: Done, please see the second paragraph of introduction.
- Your references to black hole rotation are strange. You should probably reference Kerr himself and/or Bardeen et al 1973 as more fundamental references.
Reply: Done, please see both references.
- The observations of AGN produce constraints on the mechanisms that are possible for the generation of strong jets. But you ignore the observations. In fact, you seem to be describing processes that are ubiquitous to accreting supermassive black holes but the consequence is that all AGN have jets, which is not observed. In fact, AGN with jets are the minority.
Reply: It is worth noting that we do not consider particular mechanisms of the formation of jets and we only explore the magneto-centrifugal excitation of pairs in AGN ambient, because of this one requires only two factors: rotation and the strong magnetic field.
- What is the physical difference between radio loud AGN and radio quiet AGN in your model for jet formation? Black hole spin cannot be the answer because most black holes would have to be spinning, yet radio quiet AGN are 80% of AGN, which is the opposite of what you would get if spin were the discriminator. Magnetic fields cannot be the answer because of X-ray binaries. Please engage with this fundamental issue.
Reply: We do not consider any model of jet formation, therefore any question related to it is irrelevant.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper brings interesting results that have to be published. However, some important extensions and comments are necessary before its publication.
1. The paper represents a direct extension of previous work of the authors on the case of pulsars to the case of magnetized BHs. However, the magnetic field of pulsars is related directly to them, while the magnetic field around BHs is considered to be external. The authors have to explain to what extend such a shift of the magnetic field character is reflectd in the nature of the considered processes.
2. Around the magnetized BHs usually the Blandford-Znajek process (MNRAS 1977, 179, 433-456; MNRAS 2004, 350, 427; MNRAS 2018, 478, L89), the magnetic Penrose processes (JApA 1985, 6, 85; Universe 2020, 6, 26; Universe 2021, 7, 416) or the magnetic reconnection process (PRD 2021, 103, 023014) are considered. The authors have to comment on the relation of their process to the three mentioned processes, especially to the magnetic Penrose process and B-Z process having clearly similar origin as the process considered in the paper.
3. The authors have to exactly specify definition of velocities introduced in their paper; they have to give to which observer the velocities are related. The notion of "absolute" space is not defined in relativistic situations.
4. The case of the radiative back-reaction forces has to be treated in the relativistic form, considered e.g. in (ApJ 2018, 861:2; Universe 2021, 7, 416). The authors have to comment on the reflections of the relativistic model on their estimates.
5. The authors should comment the energy-source for the created electron-positron pairs.
Comments on the Quality of English LanguageSmall corrections of English Language are welcome.
Author Response
We would like to thank an anonymous referee for interesting comments, which we have taken into account in revising the manuscript. The paper has been revised according to his/her suggestions, that can be seen below:
Referee-2
- The paper represents a direct extension of previous work of the authors on the case of pulsars to the case of magnetized BHs. However, the magnetic field of pulsars is related directly to them, while the magnetic field around BHs is considered to be external. The authors have to explain to what extend such a shift of the magnetic field character is reflected in the nature of the considered processes.
Reply: The studied mechanism requires two important factors strong magnetic field and rotation. Although the origin of magnetic field in neutron stars and black holes are different, the result is the same. In the case of BHs the co-rotation of the magnetic field lines is guaranteed by the accretion disk, which is the origin of the magnetic field and therefore, the centrifugal mechanism will take place there.
- Around the magnetized BHs usually the Blandford-Znajek process (MNRAS 1977, 179, 433-456; MNRAS 2004, 350, 427; MNRAS 2018, 478, L89), the magnetic Penrose processes (JApA 1985, 6, 85; Universe 2020, 6, 26; Universe 2021, 7, 416) or the magnetic reconnection process (PRD 2021, 103, 023014) are considered. The authors have to comment on the relation of their process to the three mentioned processes, especially to the magnetic Penrose process and B-Z process having clearly similar origin as the process considered in the paper.
Reply: Please see the last paragraph of section 3.
- The authors have to exactly specify definition of velocities introduced in their paper; they have to give to which observer the velocities are related. The notion of "absolute" space is not defined in relativistic situations.
Reply: All velocities are defined in the frame of the zero angular momentum observer at large distances. Please see the 3rd paragraph of introduction
- The case of the radiative back-reaction forces has to be treated in the relativistic form, considered e.g. in (ApJ 2018, 861:2; Universe 2021, 7, 416). The authors have to comment on the reflections of the relativistic model on their estimates.
Reply: Please see the last paragraph of section 3.
- The authors should comment the energy-source for the created electron-positron pairs.
Reply: The energy source of the pairs is the electric field, which in turn pumps energy from rotation. Please see a sentence before Eq. 20.
Small corrections of English Language are welcome.
Reply: Done
Reviewer 3 Report
Comments and Suggestions for AuthorsThe of light cylinder for NS an BH brings very different character - if in neutron stars it is the clear edge of wave zone, in BH the concept is not so definite. You should explain your model more clear - for Fig 1. It would be worth to do more detail introduction refered not only you papers but the most cited papers , for ex. Meier+ 2001, Shu at al. 1994-1995 and so on.
I think the paper could be published after addition more clear and detailed introduction with needed references on the (a lot of) papers about magnetocentrifugal mechanism in cosmic jets.
Author Response
We would like to thank an anonymous referee for interesting comments, which we have taken into account in revising the manuscript. The paper has been revised according to his/her suggestions, that can be seen below:
Referee-3
The of light cylinder for NS an BH brings very different character - if in neutron stars it is the clear edge of wave zone, in BH the concept is not so definite. You should explain your model more clear - for Fig 1.
Reply: Done, please see the third paragraph of introduction
It would be worth to do more detail introduction refered not only you papers but the most cited papers, for ex. Meier+ 2001, Shu at al. 1994-1995 and so on.
Reply: Done, please see the third paragraph of introduction
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsChanges have been made. Recommend acceptance.
Author Response
An anonymous reviewer did not have any comments, therefore, we just improved the manuscript a bit.
