How do we explain relativistic jets given what we know about gravity?

[SRH]

Since all matter should be pulled in by gravity, (or spacetime warps into a well) uniformly around a sphere, how can matter and energy escape along the rotational poles as seen in relativistic jets?

Is there such a thing as anti-gravity at the rotational poles of AGNs with relativistic jets? If not, how do we explain matter and energy moving away from a massive object (and at very high velocity taboot)?

Thanks.

[antoniseb]

There have been quite a few simulations done on accreting black holes that take charge and magnetism into account that do result in relativistic jets forming in the environment of the black hole. No magic anti-gravity is needed. More observations are required to narrow the models to be really accurate, but the general structure comes from the nature we already know.

[SRH]

So relativistic jets are a magnetic phenomenon?
But the accretion is not a magnetic phenomenon but solely due to gravity, correct?

[antoniseb]

... solely due to gravity, correct?

Why do you insist on making misleading overly-simplistic statements, and then asking us to confirm their correctness?
Accretion and the relativistic jets are all a result of many physical phenomena working in chorus.

[Cougar]

So relativistic jets are a magnetic phenomenon?
But the accretion is not a magnetic phenomenon but solely due to gravity, correct?

That accretion is not just dropping into the black hole. It is spinning. The high velocity spinning and "rubbing" of the material in decaying orbits creates enormous magnetic fields that can fling (or beam) loose particles away at relativistic speeds. See http://en.wikipedia.org/wiki/Relativistic_jet

[Jeff Root]

There is no obvious mechanism for the jets, but they are
not generally presented in the media / popular literature
as being a great mystery. Instead, the mechanism is only
referred to in passing and only in the most extremely vague
terms. People are left guessing. Is it something scientists
all understand but I don't? Is it something they don't want
to bother explaining at my level? Or what?

The part about the gravity of a black hole pulling stuff in
from all directions is clear to any reader. Why anything
should then be shot out along the black hole's polar axis
is completely at odds with all previous information the
reader has.

TOEfetish's dependence on wild guesses is a result.

-- Jeff, in Minneapolis

[Shaula]

This paper has a review of the most likely mechansims and some info on the results from simulations.

It is no great mystery, the models and physics have been around since the late 70s. The details are harder to pin down, the contri9butions of the different factors and so on. But the core mechanism seems to be pretty well established. Got to that paper from Wikipedia, so it is not like the current mainstream is 'hiding it' or anything. The explanations are out there. The detailed models, though, are very complex bits of simulation work. So less accessible to anyone without a background in MHD.

[tusenfem]

There is no obvious mechanism for the jets, but they are
not generally presented in the media / popular literature
as being a great mystery. Instead, the mechanism is only
referred to in passing and only in the most extremely vague
terms. People are left guessing. Is it something scientists
all understand but I don't? Is it something they don't want
to bother explaining at my level? Or what?

This is nonsense, there is a mechanism, it is well explained, also in popular books.
No, you will not understand the details because you will have to be an expert in electrodynamics and plasma physics.

[Jeff Root]

There is no obvious mechanism for the jets, but they are
not generally presented in the media / popular literature
as being a great mystery. Instead, the mechanism is only
referred to in passing and only in the most extremely vague
terms. People are left guessing. Is it something scientists
all understand but I don't? Is it something they don't want
to bother explaining at my level? Or what?

This is nonsense, there is a mechanism, it is well explained,
also in popular books.

No, you will not understand the details because you will
have to be an expert in electrodynamics and plasma physics.

This is typical of numerous responses by a few posters
including some moderators to various comments by me
and some other posters. You complain that what I say
is wrong, then proceed to say the same thing yourself.
I might say that a bear is a carnivore, and you would
say "No, that's completely wrong, Jeff. Bears are not
carnivores, cats and dogs and bears are all carnivores.
You keep making this same error over and over. If you
do it again you'll get an inflection!"

What I said was exactly right. There is no obvious
mechanism for relativistic jets. That's why the Wiki
article uses the word "hypothesis" to refer to the
proposed possible mechanisms. It's why TOEfetish
had to ask what the mechanism is. If the mechanism
were obvious or widely discussed, he probably would
not have needed to ask here. I've never seen a
mechanism for it explained here in the forum, and I
suspect that it never has been. I'd like to see such
an explanation here, maybe in this thread, although
it would not be primarily for my benefit, but for that
of people like TOEfetish. But if it's well-written, it
might engage me, too.

However, the main reason it hasn't been explained
here appears to be that there is no widely agreed-on
explanation.

-- Jeff, in Minneapolis

[Shaula]

However, the main reason it hasn't been explained here appears to be that there is no widely agreed-on explanation.

Wrong. The main reason that it has not been explained on here is because it is so complex. There is a widely agreed on mechanism and some interesting effects the magnitude of which are not fully mapped out (Penrose's frame dragging for example).

See the first bit of section 1.3 in the paper I linked for several references.

[quotation]

I don't see how it couldn't have been covered here before. A quick search of "relativistic jets" returns close to 300 entries witin the threads of this forum. This is a link Nereid provided some months ago that might still help (plasma astrophysics workshop):
http://www.pppl.gov/conferences/2010...T-webFINAL.pdf

[korjik]

This is typical of numerous responses by a few posters
including some moderators to various comments by me
and some other posters. You complain that what I say
is wrong, then proceed to say the same thing yourself.
I might say that a bear is a carnivore, and you would
say "No, that's completely wrong, Jeff. Bears are not
carnivores, cats and dogs and bears are all carnivores.
You keep making this same error over and over. If you
do it again you'll get an inflection!"

What I said was exactly right. There is no obvious
mechanism for relativistic jets. That's why the Wiki
article uses the word "hypothesis" to refer to the
proposed possible mechanisms. It's why TOEfetish
had to ask what the mechanism is. If the mechanism
were obvious or widely discussed, he probably would
not have needed to ask here. I've never seen a
mechanism for it explained here in the forum, and I
suspect that it never has been. I'd like to see such
an explanation here, maybe in this thread, although
it would not be primarily for my benefit, but for that
of people like TOEfetish. But if it's well-written, it
might engage me, too.

However, the main reason it hasn't been explained
here appears to be that there is no widely agreed-on
explanation.

-- Jeff, in Minneapolis

Actually Jeff, we tell you you are wrong because you say things that are incorrect. If this case it is 'There is no obvious mechanism for relativistic jets'. That statement is just plain wrong. There are obvious mechanisms involved with relativistic jets. The problem is that describing them requires a very good understanding in general relativity and plasma physics to even begin to make a real description. Even then, to make the problem calculable, there are simplifications required that can change the outcome of the calculation by quite a bit. Add on top of that that when looking at a jet you are trying to see very dim details on a very bright object many light years away when you are trying to pin down the characteristics of a jet, and you get a very poorly described set of parameters for the jet you are trying to figure out how it works.

So, what is actually happening is that the mechanism is probably the best known thing about relativistic jets, but without a really good look at the details of a jet, the particulars of how a jet works is not known.

[quotation]

...but without a really good look at the details of a jet, the particulars of how a jet works is not known.

Well, there have been some really interesting laboratory simulations over the past couple of years that do go into details such as magnetic bubble collapse, by creating hydrodynamic jets from conical wire arrays, so that today, we can say, for example, that the evolution of jets is dominated by current-driven instabilities:

http://amrel.obspm.fr/~ciardi/docs/c...31-50_2010.pdf

Overall, the experiments demonstrate that magnetic acceleration and collimation, occurring within a framework of strongly episodic outflow activity, can be effective in producing well-collimated and heterogeneous jets.

Or, http://amrel.obspm.fr/~ciardi/pages/...sodicjets.html

The experimental results show the periodic ejections of magnetic bubbles naturally evolving into a heterogeneous jet propagating inside a channel made of self-collimated magnetic cavities. The results provide a unique view of the possible transition from a relatively steady-state jet launching to the observed highly structured outflows.

[Jeff Root]

Actually Jeff, we tell you you are wrong because
you say things that are incorrect. In this case it is
'There is no obvious mechanism for relativistic jets'.
That statement is just plain wrong.

Okay, got it: There *is* an obvious mechanism for
relativistic jets.

There are obvious mechanisms involved with
relativistic jets.

Okay, mechanisms, rather than mechanism, and
those mechanisms are "involved with" relativistic
jets rather than actually explaining them, but at
least they are obvious.

The problem is that describing them requires a
very good understanding in general relativity and
plasma physics to even begin to make a real
description.

Okay, so they aren't the least bit obvious at all.

So what you're saying is that there is no obvious
mechanism for relativistic jets. Got it.

Even then, to make the problem calculable, there
are simplifications required that can change the
outcome of the calculation by quite a bit.

So you are saying that the descriptions resulting
from such calculations are uncertain. Different
researchers may come to different conclusions,
depending on the choices they make in defining
the problem.

Add on top of that that when looking at a jet you
are trying to see very dim details on a very bright
object many light years away when you are trying
to pin down the characteristics of a jet, and you get
a very poorly described set of parameters for the jet
you are trying to figure out how it works.

So you are saying that the data on which the
proposed mechanisms are based is poor.

So, what is actually happening is that the mechanism
is probably the best known thing about relativistic jets,
but without a really good look at the details of a jet,
the particulars of how a jet works is not known.

So you are saying that because you can't see the
phenomenon clearly, you understand the phenomenon
better than you can describe it.

Interesting.

As I said, there is no obvious mechanism for relativistic
jets. I expect that the hypothesized mechanisms come
fairly close to being right, but there is nothing obvious
about them, so there is as yet no widely-agreed on
mechanism, which is why the hypotheses have not yet
reached the level of theory.

-- Jeff, in Minneapolis

[Frog march]

scientists have never really had the opportunity to study black holes themselves properly, so I don't see that even the theories about black holes have actually been validated.
Science without actual experimental data, and mainly just paper theories, isn't really science.

[korjik]

Okay, got it: There *is* an obvious mechanism for
relativistic jets.


Okay, mechanisms, rather than mechanism, and
those mechanisms are "involved with" relativistic
jets rather than actually explaining them, but at
least they are obvious.


Okay, so they aren't the least bit obvious at all.

So what you're saying is that there is no obvious
mechanism for relativistic jets. Got it.


So you are saying that the descriptions resulting
from such calculations are uncertain. Different
researchers may come to different conclusions,
depending on the choices they make in defining
the problem.


So you are saying that the data on which the
proposed mechanisms are based is poor.


So you are saying that because you can't see the
phenomenon clearly, you understand the phenomenon
better than you can describe it.

Interesting.

As I said, there is no obvious mechanism for relativistic
jets. I expect that the hypothesized mechanisms come
fairly close to being right, but there is nothing obvious
about them, so there is as yet no widely-agreed on
mechanism, which is why the hypotheses have not yet
reached the level of theory.

-- Jeff, in Minneapolis

Spoken like someone who has never actually done the science. Still wrong too

[Shaula]

so there is as yet no widely-agreed on mechanism

Wrong. Again. Unless you are now defining widely-agreed on to take into account the opinions of people who don't know anything about the physics. In which case you may as well say there are pretty much no widely agreed upon theories of physics at all.

[noncryptic]

Since all matter should be pulled in by gravity

Not all matter; only the matter that is on a trajectory that will bring it below escape velocity of the black hole.
Only behind the event horizon is escape velocity larger than c so that no escape is possible, but the accretion disk is outside the event horizon, so some of the matter/energy in the accretion disk can get an ecape trajectory .

[Cougar]

scientists have never really had the opportunity to study black holes themselves properly, so I don't see that even the theories about black holes have actually been validated.

And this claim is based on your exhaustive and comprehensive study of all peer-reviewed publications about black holes? Wow, google scholar returns over half a million papers. When did you find the time?

[Jeff Root]

I'd say the claim in the second clause of his sentence
is based on the factual statement in the first clause,
not on study of papers.

-- Jeff, in Minneapolis

[noncryptic]

I suppose it depends on your definition of "really".

I think it's a lot more factual to say that cosmologists do have the opportunity to study black holes, and do study black holes.

Also i'd say there aren't so much "theories" about black holes as there are mathematical models that are based on the theory of relativity and quantum theory.

[Frog march]

but the ones that are studied are quite a long way away, so there is a limit on what one can learn about them, and one can't do actual experiments on them.

It would be nice to be able to drop things into a black hole, and see what happened, close up, for example. I don't see how one could do that without travelling to one. I had thought that maybe mini-black holes could be used to study them, but I read that the LHC hadn't produced any mini black holes, and anyway they might not be that useful. Maybe one could see what happened when they evaporated.

[Hornblower]

I suppose it depends on your definition of "really".

I think it's a lot more factual to say that cosmologists do have the opportunity to study black holes, and do study black holes.

Also i'd say there aren't so much "theories" about black holes as there are mathematical models that are based on the theory of relativity and quantum theory.

My bold. If I am not mistaken, such mathematical models are valid examples of theories.

[noncryptic]

My bold. If I am not mistaken, such mathematical models are valid examples of theories.

I think models that are specific implementations of fundamental theories are in a different league than those fundamental theories.

but the ones that are studied are quite a long way away, so there is a limit on what one can learn about them, and one can't do actual experiments on them.

By that logic we also don't "really" study stars, galaxies and a bunch of other things. There's always a limit on what can be learned from observation, with or without experimentation.