The centers of black holes and quasars often have jets coming out the two poles of an accretion disk, say north and south. Is it known if the two jets spin in the same direction or opposite directions to each other?

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    $\begingroup$ what makes you think the jets spin? $\endgroup$ Sep 10, 2013 at 10:40
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    $\begingroup$ I think the question is what makes you think they don't spin... not a whole lot out there with zero angular momentum. I'm no relativistic jet expert, though. Have no idea on the answer to this question. $\endgroup$
    – Kyle Oman
    Feb 16, 2014 at 2:59
  • $\begingroup$ It all depends on what mechanism for jet formation you pick. If it's just the geodesic model, then they will certainly spin -- angular momentum in equals angular momentum out, minus what is exchanged with the star. $\endgroup$ Jan 25, 2015 at 20:18

2 Answers 2


The Blandford-Znajek process and variants are leading contenders for explaining black hole jets. The driving energy for the jets is extracted from the black hole spin and transferred to the outgoing plasma by twisted magnetic fields. Along with energy, the jets must contain the lost angular momentum from the black hole, which then ultimately comes from material being accreted from the disk.

Thus I would expect that the angular momentum vector in the jets (in both directions) is in the same sense as the black hole angular momentum. i.e. the material spirals away from the black hole in the same sense in both directions. e.g. If the black hole spins clockwise looking down on its "north rotation pole", then the angular momentum vector points south. Material travelling towards you and away from you will also spin clockwise.

See also models for astrophysical relativistic jets from compact objects and Why are polar jets emitted along the axis of rotation?


Looking at Earth's spin down upon the north pole, it is counter-clockwise. Looking at Earth's spin down upon the south pole, it is clockwise. The sense of helicity depends upon the observer's position. (If the spin is relativistically propagating, the observer only has one POV. Beta-rays are chiral left-handed until they are slowed.)

Looking down in one direction all the way through, there is a problem with angular momentum disk vs. jets if the mirror-direction jets are not spinning in the same sense while traveling in opposite directions. Choose your nomenclature to define the relative directions of spin.

This is not a frivolous problem! Chemical optical rotation is "coming toward," viewed through a polarimeter. Geometric rotation is "going away," whether clockwise rotation drives the screw into wood (if yes, right-handed). Optically left-handed quartz is observed to be crystallographic space group P3(1)21, which is a right-handed 3(1) screw axis (and 3(2) left-handed). It gets worse! P3(1)21 quartz and P3(2)21 berlinite are both levorotatory, as optical rotation is not sourced by physical atomic mass distribution, J. Appl. Crystallogr. 19, 108 (1986).

When you say "same direction of rotation," define it very carefully.

  • $\begingroup$ Yes, I did mean "Looking down in one direction all the way through". I can conceptualize and agree with your comment "there is a problem with angular momentum disk vs. jets if the mirror-direction jets are not spinning in the same sense while traveling in opposite directions." but close to a black hole there is a lot going on with a lot of energy. Mostly wondering if observations have provided a proof of this and I would be very interested in any research in this area. Your crystallographic comments and analogy are also very interesting, thank you. $\endgroup$ Feb 15, 2014 at 8:12
  • $\begingroup$ If you label the orbit of the matter in the accretion disk "prograde", would that help define terms for the answer? i.e. are both jets in prograde rotation, both retrograde, one prograde and the other retrograde...? $\endgroup$
    – Anthony X
    May 19, 2014 at 20:46

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