What's the Deal with Astrophysical Jets?

[SHISHKABOB]

Jets in space seem like a really common thing, they're found associated with active galaxies, protostar accretion disks, and around neutron stars and stuff. But from what I understand, no one really knows how they work. Or rather, there's no... "equation" for them. The process that forms these jets is still quite a bit of a mystery, right?

I am wondering what makes explaining this process so difficult. Is it because we can't see the start of the jet directly, and so it's actually impossible for us to figure out exactly what's going on? Or is it because the process itself is very complicated?

 

[codex34]

Yep, they are a mystery, we currently don't have any model that produces jets, except for 'black holes', but even that doesn't give any real mechanism.
What about jet knots?
Do some jets have knots and some don't? or do they all have knots?

The main problem with them is you get a Schwarzschild radius and singularity before they can be worked out, it's a problem with the assumptions made, when you change the assumptions the singularity resolves itself but there will be serious objections in doing that, because black holes become redundant.
The solution is a model that is so simple, yet so alien in concept that it can't possibly be correct anyway, so there's no point in discussing it.

An interesting question is, why don't some things have jets?
Why doesn't the sun have jets?
Spherical objects don't produce jets?
Globular clusters?
Do the jets simply stop?, or could they continue inside spherical objects once the object goes from disc to spherical?


Try my very first post, (it's a partial solution to Shapiros' naked singularity - just don't tell anyone, sorry mods)

 

[Solon]

I was trying to find out how they determine the direction of flow in the 'jets', and have these two links, an older one and what seems to be the most recent. The full pdf file for the newer paper is available for free at the site.

M87 VLBA Movie at 43 GHz
http://www.aoc.nrao.edu/~cwalker/M87/index.html

MEASUREMENT OF THE ELECTRIC CURRENT IN A kpc-SCALE JET

We present radio emission, polarization, and Faraday rotation maps of the radio jet of the galaxy 3C303. From these data we derive the magnetoplasma and electrodynamic parameters of this 50 kpc long jet. For one component of this jet we obtain for the first time a direct determination of a galactic-scale electric current (~3 × 10^18 A), and its direction—positive away from the active galactic nucleus. Our analysis strongly supports a model where the jet energy flow is mainly electromagnetic.

http://iopscience.iop.org/2041-8205/741/1/L15

 

[codex34]

From observation they are always flowing outward away from the center, the knots/flares in the jets can be easily tracked over a number of years.
http://www.nasa.gov/images/content/582595main_hh34jet-seq.jpg

Which leads to another good question, what causes the knots/flares?
http://blackholes.stardate.org/images/editorial/ss433jimovie.gif

CRL 618, could that be caused by rare highly energetic knots/flares ejected deep into space? Same with parts of the eagle nebula?

DRAGNs, AGNs, Quasars, Nebulae, herbig haro objects.

Some jet stuff here:-
http://www.obs.u-bordeaux1.fr/yerac07/presen_agalnone/Elena Bannikova.pdf
(http://www-physics.univer.kharkov.ua/en/pers_pages/bannikova_e_y.html)
(from what I gather, the jet is caused by the 'vortex pair', where the hell did the 'vortex pair' come from? Vortex pair is horrible terminology, the toroidal flows are a lot more complex than simple vortex mechanics.

Jets should be formed along the paths of least resistance in rotating discs, material sucked into the center either accelerates to a halt (singularity), OR collides and is ejected along the paths of least resistance, you can fill in the rest...

 

[SHISHKABOB]

thank you very much for the information

 

[Astrofan]

Jets in space seem like a really common thing, they're found associated with active galaxies, protostar accretion disks, and around neutron stars and stuff. But from what I understand, no one really knows how they work. Or rather, there's no... "equation" for them. The process that forms these jets is still quite a bit of a mystery, right?

I am wondering what makes explaining this process so difficult. Is it because we can't see the start of the jet directly, and so it's actually impossible for us to figure out exactly what's going on? Or is it because the process itself is very complicated?

I have to admit that there definitely is no 'equation' to them, but on the other hand, they are being handled with a handful of equations. Simulations using MHD, GRMHD, RGRMHD have made lots of progress on the understanding of these jets in general.
It is generally thought that AGN jets are the result of strong magnetic fields ejecting plasma from the accretion disk and if you are concerned about the reality they have in simulations, then the answer is "YES" they are already being realized in various simulations.

The real mystery now is how exactly to match the simulations to the observation data.
And indeed the process is very very complicated, MHD simulations only capture general features of the jet flow, whereas the exact details of shocks, high energy particle ejections are reliant on simulations of the very microscopic scales. The complexity partly arises from the fact that in this area they deal with scales ranging many orders of magnitude. (Which obviously is something very useful to crash codes with...)