Relativistic Jets from Supermassive Black Holes?

Islam Hassan

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

Drakkith

See post number 13 in this thread: http://www.physicsforums.com/showthread.php?t=223661

Islam Hassan

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

Drakkith

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.

Islam Hassan

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

Drakkith

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.

SpiffyKavu

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.

Islam Hassan

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

DrStupid

The jet is neutral but the single particles are charged.

Islam Hassan

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

SpiffyKavu

M87 has evidence of an antipodal jet, I believe. The one-sided jet is typically explained away as a relativistic effect, due to beaming:

http://en.wikipedia.org/wiki/Relativistic_beaming

Basically, there just isn't enough light being emitted towards us to be seen with previous observations. Special relativity also explains the observed apparent superluminal motion seen in some of these jets, M87 included:

http://en.wikipedia.org/wiki/Superluminal_motion

Drakkith

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.

Islam Hassan

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

Chronos

Nothing is escaping the event horizon, the particles and energy observed orginate outside the event horizon.