Relativistic Jets from Supermassive Black Holes?

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Discussion Overview

The discussion revolves around the phenomenon of relativistic jets emitted from supermassive black holes, exploring the mechanisms behind their formation and the nature of their emission. Participants consider whether these jets originate from the black hole itself or from the surrounding accretion disk, and they delve into the implications of various theoretical models.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question how relativistic jets can be emitted if nothing escapes from black holes, suggesting that jets must originate from the accretion disk instead.
  • There is uncertainty regarding the exact mechanism of jet formation, with some proposing that magnetic fields play a role in accelerating particles from the accretion disk.
  • Participants express curiosity about the shape of the jets, wondering if they are cylindrical or conical, and whether current imaging techniques can resolve this.
  • Some contributions mention that jets are often observed to have a conical shape, while helical structures may arise from periodic processes related to the accretion disk.
  • Concerns are raised about the composition of jets, particularly whether an electrically neutral jet can be collimated by magnetic fields, and the implications of this for the presence of charged particles.
  • There is discussion about the apparent one-sidedness of some jets, with relativistic effects like beaming being suggested as explanations for this phenomenon.
  • Participants note that energy may escape from a black hole, but there is confusion regarding mass-energy equivalence and the implications for the jets.

Areas of Agreement / Disagreement

Participants generally agree that jets originate from the accretion disk rather than the black hole itself, but there is no consensus on the specific mechanisms involved in their formation or the nature of their structure. Multiple competing views and uncertainties remain throughout the discussion.

Contextual Notes

Limitations include unresolved questions about the exact mechanisms of jet formation, the dependence on definitions of jet structure, and the implications of relativistic effects on observations.

Islam Hassan
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If nothing can escape black holes, how are relativistic jets of particles and radiation emitted from the supermassive variety of the same? Are they emitted from the BH proper or from something else?


IH
 
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Drakkith said:
See post number 13 in this thread: https://www.physicsforums.com/showthread.php?t=223661


Thanx for the reference; so it remains something of a 'mystery'.

Perhaps one thing that can be said is that if the jets are not emitted from the BH proper -and classic BH theory would preclude that- they must be emitted from the accretion disk. I fail to see by what possible mechanism though.

It just seems impossible even to speculate as to how this may be achieved...


Faro
 
Discussion as to the possible ways of emission shouldn't be a problem. Inventing your own theory based on little to no evidence or understanding of astrophysics and other related areas would be a very big problem and would be against PF rules. As I like to put it, asking questions is fine. Proposing solutions isn't. Those are for papers and peer review.

The particles must almost assuredly come from the accretion disk initially, as they wouldn't be able to escape from beyond the event horizon. I believe that a similar problem with the jets from neutron stars exists as well. Perhaps they occur for the same reasons.
 
Drakkith said:
Discussion as to the possible ways of emission shouldn't be a problem. Inventing your own theory based on little to no evidence or understanding of astrophysics and other related areas would be a very big problem and would be against PF rules. As I like to put it, asking questions is fine. Proposing solutions isn't. Those are for papers and peer review.

The particles must almost assuredly come from the accretion disk initially, as they wouldn't be able to escape from beyond the event horizon. I believe that a similar problem with the jets from neutron stars exists as well. Perhaps they occur for the same reasons.


I wonder is there any evidence as to how the jet forms initially? Do we know for example whether the initial jet (presumably emitted from the accretion disk) is cylindrical or conic in shape? Do we have sufficient resolution in imaging to do this?


IH
 
Islam Hassan said:
I wonder is there any evidence as to how the jet forms initially? Do we know for example whether the initial jet (presumably emitted from the accretion disk) is cylindrical or conic in shape? Do we have sufficient resolution in imaging to do this?


IH

My understanding is that it is conical. And I'm not sure the beams are "emitted by the accretion disk", I think that the source of the particles is from the disk but they are believed to be accelerated by magnetic fields or something which results in the jets.
 
Indeed, the emission is often seen to be conical. A helical structure is often seen on large scales, though, for example in 3C 273 and S5 0835+710:

Anatomy of Helical Extragalactic Jets: The Case of S5 0836+710

I haven't sifted through too much of the literature on the structure of jets proper, but the helical structure is often thought to be due to some periodic process like possible precession of the source of the jet, which is assumed to be the accretion disk. The disk amplifies any magnetic field and twists and collimates the field along the axis of rotation.

The wiki article on relativistic jets, while short, mentions a couple of mechanisms, though is not an exhaustive review.
 
SpiffyKavu said:
The wiki article on relativistic jets, while short, mentions a couple of mechanisms, though is not an exhaustive review.

The wiki article say that " it is hypothesized that the jets are composed of an electrically neutral mixture of electrons, positrons, and protons in some proportion." If this is the case, can a relativistic jet be collimated by magnetic fields if it is electrically neutral?

Would it be easier to propose a mechanism if the jets were composed of radiation only without any massive particles?

Can we today somehow simulate a 'mini-accretion disk' in the laboratory?IH
 
Last edited:
Islam Hassan said:
If this is the case, can a relativistic jet be collimated by magnetic fields if it is electrically neutral?

The jet is neutral but the single particles are charged.
 
  • #10
DrStupid said:
The jet is neutral but the single particles are charged.


But then one would expect to have two jets jutting out from opposite poles of a BH/accretion disk, one with positively charged particles and another with negatively charged particles. How then does one explain single-jet occurrences like in this pic:

http://en.wikipedia.org/wiki/File:Onde-radioM87.jpg


IH
 
  • #11
  • #12
Islam Hassan said:
But then one would expect to have two jets jutting out from opposite poles of a BH/accretion disk, one with positively charged particles and another with negatively charged particles. How then does one explain single-jet occurrences like in this pic:

http://en.wikipedia.org/wiki/File:Onde-radioM87.jpg


IH

Magnetic fields will deflect charged particles in the same direction in some cases. The technique is used in magnetic confinement for plasmas. I assume whatever is happening with the magnetic fields doesn't separate the particles from each other.
 
  • #13
SpiffyKavu said:
The wiki article on relativistic jets, while short, mentions a couple of mechanisms, though is not an exhaustive review.


Very interesting that the two proposed mechanisms in the wiki article both involve energy transfer from the BH to the jet.

What about mass-energy equivalence? Energy may escape from a BH but not mass? But then photons are massless and they cannot escape either...very confusing...


IH
 
  • #14
Nothing is escaping the event horizon, the particles and energy observed orginate outside the event horizon.
 

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