2
$\begingroup$

A black hole, neutron star or any object that has accumulated an accretion disc, sometimes features opposing jets, positioned perpendicular to the accretion disc.

I understand that these jets are produced by magnetic fields created by the enormous amount of electrically charged plasma located on the "equator" of the gravity source. Please correct me if I have this either plain wrong or under-simplified it.

My question is: where does the material, either electron-ion jets or electron-positron jets, come from?

  1. If it comes from the accretion disc itself, is it made up of particles that have a slight velocity vector component inwards, normal to the gravity source, which then get caught up in the central magnetic field and forced into the outrunning jet?

  2. Alternatively, is it matter that is preexisting around the poles of the gravity source. Assumption 1 seems far more likely to me, but I would appreciate any explanation.

EDIT: There are duplicate type questions listed below but 1. The answer to my question postulated the possible creation of material at the base of the disc, and 2. I wanted to know could the jets occur from existing material in the jet region? Neither of these points, in my opinion, were dealt with in the previous questions. END EDIT

Improve this question
$\endgroup$
3

1 Answer 1

Reset to default
3
$\begingroup$

Any matter that was just sitting at the poles would quickly get caught up in the jet, so this won't provide a lasting source of material. If you have a solid surface like in the case of a neutron star, you can imagine ripping material off the poles of the object, but since we also observe jets around black holes this clearly isn't necessary.

You might also imagine matter forming at the base of the jet. With high enough radiation you could produce matter-antimatter pairs from energetic photons. Once there is some matter, it is easy for incoming photons to produce more. Note, though, that a single photon in vacuum can't spontaneously pair produce (energy and momentum cannot be conserved). This isn't actually a problem, though, since a photon can scatter off a strong magnetic field to pair produce while conserving both energy and momentum.

The fact is, though, that is not necessary either. The accretion disk itself can very well feed the jet. In fact, many simulations that produce jets around black holes are done with ideal magnetohydrodynamics, where mass is neither created nor destroyed. The accretion disk has some thickness, and even if it did not particles could still be deflected out of the midplane by magnetic fields such that they wound up in the polar region.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thanks Chris, I didn't really think the assumption 2 could be true, I was trying to think of the path a particle would follow, other than to fall out of the disc and right into the source. Obviously the jets are there, so that can't be right. I don't have the background to even think of matter forming at the base of the jet or to follow how a particle could end up perpendicular to its original path in such a strong gravity gradient, in a spherically symmetrical space, but for example if magnetic fields can do it, then that could be it. Thanks again. $\endgroup$
    – user81619
    Commented Jun 2, 2015 at 0:11
  • $\begingroup$ Several duplicates are available - the jets likely form from material in the disk getting hooked and accelerated by twisting magnetic fields. $\endgroup$
    – ProfRob
    Commented Jun 2, 2015 at 6:29