Jets, Disks and Winds from Spinning Black Holes: Nature or Nurture?

Round 1

Reviewer 1 Report

The authors presented a viable alternative to the current assertion by the EHT consortium for the interpretation what powers jets in accreting black hole such as those in M87. The scenario proposed by the EHT researchers that suppose to explain their imaging observations of M87 is far from definitive. It is important that other viable scenario should be presented, so to maintain a balance of view. Otherwise, the community could be led to wilderness by a scenario from a consortium with reputation. This work serve the purpose to put into an equally viable scenario, from phenomenological arguments which is based on the authors' understanding of MHD. The authors brought into concepts such as currents, which is usually hidden under the carpets when dealing with MHD, in particular, in AGN and accretion physics researchers.

While the paper has excellent scientific merit, the authors so far presented only heuristic arguments without actually giving a solid quantitative analysis. I understand that it is a paper about idea, and so I would not nitpick with this. However, as a theorist myself, I would personally wish that the authors could show some solid calculations, so to strengthen the argument. 

The paper can however be improved by the following. 

(1) Referencing. There are places the authors tend to talk it as it is. There are issues which may be obvious to the authors but not to other researchers not exactly in the field but wish to know the subject more so to appreciate the authors' scenario and to compare with other scenarios including those proposed by the EHT consortium on M87 and other fields, such as those pointed out by the authors, e.g. solar physics, PWN etc. Here I list some places where some references should be added. 

Line 83: Rotational energy can amount to up to ~0.3 of the black hole mass. 

Line 118: By contrast, the magnetic flux which thread the horizon of spinning black hole is through to be slowing varying. 

Line 116: The black hole space time acts like a modest electric conductor with an effective resistance of ~100 Ohm. [I understand this is known among black hole electrodynamic researchers, but I would bet that 99% of black hole astrophysicist would not give this number without a thought.] 

Lines 140-143: The minimum value of the ratio of the electron pressure .... Larmor radius to the length scale which in turn is of the order of the .... , which is 1e-13.

Line 149: Instead, sufficient disk plasma may be transported across the magnetic field by small scale magnetic interchange instabilities. [This is a very hand waving argument. The authors should show some quantification or give some references to support their proposal.] 

Line 197: There may be magnetic flux tubes that connect the inner disk to the rapidly rotating black hole event horizon. [Like Line 149, this is another hand waving argument. The authors should elaborate more or give some references to support their proposal.] 

(2) Regarding other sources as discussed in Sec 4. 

It seems that the authors are not aware of relativistic jets were observed from accreting neutron stars. One particular example is Cir X-1, which was reported by Fender, R et al. 2004, Nature, 427, 222. Some of the finding of this work is relevant to some essence of the scenario put forward in this paper. The presence of a field with polarity and energy is extracted from the spinning some spinning object with an accretion disk, though the paper Fender et al. emphasis relativistic jets can be launched from objects without an event horizon. I think this work would be more directly related than some of those mentioned such as GRB and TDE or proto-stars.  

Author Response

We thank the referee for her/his thoughtful comments. In response let us start by explaining that this article was solicited as a guest essay in a compendium of such articles. It is not a regular research paper. Much of its content summarizes a paper already published in MNRAS with more formal arguments and more references. We have made this clear on l 37. We have added a few more references yes but as we have been thanked by several observers for writing a simplified version, we hope that we can continue in this spirit.  

l 83 have added reference for rotational energy 

l 118 fixed

l 116 reference added

l 140, 149, 197refs added.

Thanks for reminding us that neutron stars can make jets in X-ray binaries.

We have added a comment and a reference.

Reviewer 2 Report

The authors described their new ideas on the interaction between the central black hole and the accreting gas. Their original methods are physically reasonable and concisely summarized. Thus, I can recommend this essay for publication in Galaxy. I have only a few comments.

(1) The leading actors, "nature and nurture," appear only in the figure caption (as long as I looked for). Please let them appear earlier e.g., in the introduction, so that the readers may find the meaning of these keywords as early as possible.

(2) Please define $\varpi_{\rm out}$ and $\varpi_{\rm jet}$ in the final paragraph in section 2. Also, please briefly explain why "Even if $B_\phi \propto \varpi^{-1}$, the radial magnetic stress associated with it will be $(\varpi_{\rm out} / \varpi_{\rm jet})^2$ ..."

(3) In the 4th paragraph in section 2

Even if the plasma inertia is negligible compared to the magnetic field, the magnetosphere may not be force-free because of a charge deficit. Also, their inertia could change the boundary condition at the horizon qualitatively because of causality. It would be nice if such arguments are briefly mentioned. 

Typo: in the 5th paragraph in section 2, "constanbt"

Author Response

We thank the referee for her/his helpful comments.

We have added an explicit explanation of nature/nurture.

We have defined the cylindrical radius.

We have added an explanation of what we intend by force-free electrodynamics which may be different from the referee's viewpoint.

typo fixed