What Mechanism Creates the Jet Emanating From a Quasar?

  • #1

Summary:

What causes the high energy jet to emanate from a quasar -- magnetism, frame dragging, or both?
Given that a quasar is a super massive black hole with an accretion disk rotating at some significant percentage of the speed of light, what is the mechanism that generates the enormously luminous jet that emanates from the "poles" of the black hole that has become a quasar?

a. The magnetic field produced by the spinning accretion disk rotates at high velocity, accumulates energy from the disk and focuses the energy into an enormously luminous jet.

b. The frame dragging produced by the spinning accretion disk accumulates energy from the disk and focuses energy into an enormously luminous jet.

c. The rotating magnetic field accumulates energy from the disk and the frame dragging focuses the energy into an enormously luminous jet.

d. The rotating magnetic field and the frame dragging both contribute to accumulating energy from the disk and both combine to focus the energy into an enormously luminous jet.

e. The rotating magnetic field and the frame dragging should be considered the same phenomenon/mechanism that accumulates energy from the disk and focuses the energy into an enormously luminous jet.

My vote is d.

PS: "Accumulates energy from the disk" is, in my view, a simplification. In addition to energy gathered from the accretion disk, I believe that black hole evaporation (Hawking radiation) is likely to add to the energy that is accumulated and focused into the jet.
 

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  • #2
Vanadium 50
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f. Nothing to do with magnetic fields or frame dragging or Hawking radiation.
 
  • #3
PeterDonis
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what is the mechanism that generates the enormously luminous jet that emanates from the "poles" of the black hole that has become a quasar?
This question has been extensively studied by astrophysicists. Have you read any of what they have published? Parts of what you write look like possibly garbled versions of what astrophysicists believe to be the primary mechanisms involved, but other parts don't.

f. Nothing to do with magnetic fields or frame dragging or Hawking radiation.
For the last one, yes--Hawking radiation does not [Edit: fixed] play a significant role in the mechanisms astrophysicists believe to be at work.

Magnetic fields, however, do play a significant role in those mechanisms. Frame dragging also does to the extent that the behavior of magnetic field lines around a spinning black hole is significantly different from their behavior around a non-spinning black hole, and the difference is due to frame dragging.
 
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  • #5
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Hawking radiation does play a significant role in the mechanisms astrophysicists believe to be at work.
I find this hard to believe. Are you missing a not?

As far as the other two, the energy driver is accretion. Matter is falling and giving up energy as it does so. If you had no frame dragging and no magnetic fields, you would still have the energy. Indeed, as magnetic fields can do no work, they cannot be part of the power. The same argument can be applied to frame dragging.

Shut both of them off, and you still get jets. Perhaps they would look different, but you'd still get them.
 
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  • #6
PeterDonis
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Are you missing a not?
Yes, I was; fixed now.

the energy driver is accretion
Accretion is one driver, yes. Another is extraction of energy from the hole's spin.

However, to explain the jets, the energy source alone is not sufficient. You also have to account for the collimation of the jets--why they are emitted in two narrow beams along the hole's spin axis. Magnetic fields and frame dragging play critical roles in that.

Shut both of them off, and you still get jets.
No, you don't, because without magnetic fields and frame dragging, there is no collimation mechanism; you would just get radiation being emitted in all directions as matter accretes onto the hole and gets heated up by collisions.
 
  • #7
PeterDonis
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to explain the jets, the energy source alone is not sufficient. You also have to account for the collimation
And also the transfer of energy from the accreting matter to the outgoing jets. Magnetic fields play a critical role in that as well.
 
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There are physics based computer simulations which produce the jets:

but a computer simulation of a complex system might not tell you "what is the mechanism".
 
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  • #10
PeterDonis
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This article describes some of the recent ideas floating around and frame dragging doesn’t currently come into the mix.
Note that this article is about jets from spinning neutron stars, not spinning black holes. Frame dragging will be significantly weaker for the former than for the latter, because for spinning black holes, accreting matter can fall into the hole's ergosphere, where frame dragging has stronger effects. As the paper by Blandford that I linked to notes, those effects are believe to be significant for quasars.
 
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Note that this article is about jets from spinning neutron stars, not spinning black holes. Frame dragging will be significantly weaker for the former than for the latter, because for spinning black holes, accreting matter can fall into the hole's ergosphere, where frame dragging has stronger effects. As the paper by Blandford that I linked to notes, those effects are believe to be significant for quasars.
Provided that the black hole does spin rapidly.

Can you tell apart an accretion disk of a rapidly spinning black hole from the accretion disk of a black hole that is not spinning, spinning slowly or spinning in another direction?
 
  • #12
PeterDonis
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Provided that the black hole does spin rapidly.
If it doesn't, you won't see jets since there is nothing to direct energy or matter outflow strongly along a particular axis. A slow spin might bias outflow somewhat towards the spin axis, but that won't produce narrow, well-collimated jets.

Can you tell apart an accretion disk of a rapidly spinning black hole from the accretion disk of a black hole that is not spinning, spinning slowly or spinning in another direction?
If you're close enough, sure, you'll be able to see the difference in the motion of the disk.

From very far away, like us observing distant pulsars or quasars, no, we can't see the accretion disk directly, we only see the X-ray emissions from it, and those don't give very good information about the details of motion of gas in the disk. The best indicator of spin from far away is the presence or absence of jets, as above.
 
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If it doesn't, you won't see jets since there is nothing to direct energy or matter outflow strongly along a particular axis. A slow spin might bias outflow somewhat towards the spin axis, but that won't produce narrow, well-collimated jets.
The spin, and indeed the presence, of the accretion disc itself?
How do you tell apart the case of a relatively light but collisionally thick accretion disc around a massive black hole that does not rotate along with the accretion disc, vs. the accretion disc around a black hole that rotates in the same plane and direction as accretion disc, and rapidly?
 
  • #14
PeterDonis
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The spin, and indeed the presence, of the accretion disc itself?
No, the spin of the massive body that is accreting the accretion disk.

How do you tell apart the case of a relatively light but collisionally thick accretion disc around a massive black hole that does not rotate along with the accretion disc, vs. the accretion disc around a black hole that rotates in the same plane and direction as accretion disc, and rapidly?
The latter case will have jets, the former won't.

If you're close enough, I believe you will be able to see that the latter case will have an accretion disk--infalling matter is preferentially driven into the equatorial plane of the rapidly spinning hole--whereas the former will have something more like an accretion cloud--no particular preferred plane for infalling matter. But from far away I don't think this difference will be observable; the key observable difference will be the presence or absence of jets.
 
  • #15
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The latter case will have jets, the former won't.

If you're close enough, I believe you will be able to see that the latter case will have an accretion disk--infalling matter is preferentially driven into the equatorial plane of the rapidly spinning hole--whereas the former will have something more like an accretion cloud--no particular preferred plane for infalling matter. But from far away I don't think this difference will be observable; the key observable difference will be the presence or absence of jets.
What about the preferred plane of the infalling matter itself?

If a nonrotating black hole lies at the centre of uniform mass distribution radially symmetrically infalling from all directions, there is indeed no preferred plane.

If the infalling particles do not collide with each other, whether because of their low cross-section (as might be the case for dark matter falling in the hole) or because of their low density (as might be the case for a hole in empty outskirts of a galaxy), then there still is no accretion disc. Infalling particles approach the hole on hyperbolic orbits and either fall in if the hyperbole enters event horizon, or escape if they pass event horizon.

If the infalling particles do collide with each other and the distribution of such particles possesses axial symmetry then there is still no accretion disc, because no preferred plane. Infalling particles that collide with particles falling in from opposite direction lose tangential speed (because of symmetry) and fall in along axis, forming no disc.

However, if there is more matter falling in from one specific side of a plane, then the particles falling in from opposite direction, or along other planes, will slow down, but not stop the infalling matter - allowing the infalling matter to slow down to a bound orbit of an accretion disc.

And that is an accretion disc whose plane is caused purely by angular momentum of infalling matter, irrespective of the angular momentum of black hole.
 
  • #16
PeterDonis
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What about the preferred plane of the infalling matter itself?
There might or might not be one, depending on where the infalling matter is coming from. If there is, a non-spinning hole won't affect it; a slowly spinning hole might affect it some; a rapidly spinning hole will force infalling matter into its own equatorial plane as it gets close to the hole.

that is an accretion disc whose plane is caused purely by angular momentum of infalling matter
Do you have any references for all this? Or is it just your own personal speculation?
 
  • #17
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Do you have any references for all this? Or is it just your own personal speculation?
Personal speculation. But look at the reasoning - these seem to be from quite simple first principles.

Do you agree with the reasoning that angular momentum of infalling matter - provided the infalling matter is liable to collisions, which is common - would cause an accretion disc in the absence of any frame dragging from central body rotation?

References have not been easy to find. For example this:
https://en.wikipedia.org/wiki/Accretion_disk
introduces the matter abruptly:
In the 1940s, models were first derived from basic physical principles.[6] In order to agree with observations, those models had to invoke a yet unknown mechanism for angular momentum redistribution. If matter is to fall inwards it must lose not only gravitational energy but also lose angular momentum. Since the total angular momentum of the disk is conserved, the angular momentum loss of the mass falling into the center has to be compensated by an angular momentum gain of the mass far from the center.
What it omits is the origin of disc having any angular momentum at all. Logically, it might be because infalling matter introduces some angular momentum when joining the accretion disc; but the article does not state that.
 
  • #18
PeterDonis
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Personal speculation.
Then it's off topic here.

look at the reasoning
No, you need to go look at the literature to see if, just by chance, someone else, someone with more knowledge of physics than you have, has already looked at the cases you are looking at--or, better yet, has done a computer simulation of them. (Hint: they have.) Then you need to look at the results they obtained. Then you need to give references to some of those treatments in the literature in a thread like this one--but probably an "A" level thread, not an "I" level one.

these seem to be from quite simple first principles
Sure, conservation of angular momentum is a simple first principle. But it only applies to a closed system. The infalling matter by itself is not a closed system. It can interact with the gravitating mass (neutron star or black hole), and it can emit radiation. Those interactions can transfer angular momentum.

Also, as you note later in your post, there is the question of where the initial angular momentum of the infalling matter comes from. That is going to depend on the details of specific cases.

Treatments in the literature of scenarios like this will take these issues, and many more, into account.

References have not been easy to find.
That's because they aren't going to be the sort of references you find in Wikipedia articles. They're going to be "A" level papers in the literature, and might not be easily findable by anyone who is not a specialist in the field. Possibly preprints of them are on arxiv.org and might come up in a search.
 
  • #19
PeterDonis
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Do you agree with the reasoning that angular momentum of infalling matter - provided the infalling matter is liable to collisions, which is common - would cause an accretion disc in the absence of any frame dragging from central body rotation?
I agree that frame dragging is not necessary for the formation of an accretion disc. However, that does not mean frame dragging, if it is present, does not affect the dynamics of an accretion disc, or that such effects might not vary significantly with the strength of the frame dragging, and therefore with both the spin of the gravitating mass and the distance from it.
 
  • #20
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Accretion discs that are strongly warped because they sustain a large angle between the plane of the outer parts (determined likely by infalling matter) and inner parts (determined by the quadrupole and Lense-Thirring precessions due to central body) are recognized phenomena:
https://academic.oup.com/mnras/article/441/2/1408/1074705
 
  • #21
PeterDonis
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Accretion discs that are strongly warped because they sustain a large angle between the plane of the outer parts (determined likely by infalling matter) and inner parts (determined by the quadrupole and Lense-Thirring precessions due to central body) are recognized phenomena
Yes, they are. But note the "likely" in your first parenthesis, and its absence in the second.

Also note that "determined by infalling matter" is not just one thing; the abstract of the article you reference gives at least two causes that are attributable to the infalling matter: viscous angular momentum transport (which is present in previous models) and self-gravity (which the model proposed in the paper adds as a new factor). The abstract also mentions effects of a companion star (if present) as being significant in the model it is proposing.

Note further that neither of the causes attributable to the infalling matter are as simple as "the angular momentum of the infalling matter causes an accretion disc".

(Edit: The paper itself also gives two causes attributable to the central body: Lense-Thirring torque, i.e., frame dragging, and quadrupole torque. So the central body effect on the disc shape is not as simple as "frame dragging" either.)
 
  • #23
stefan r
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Accretion is one driver, yes. Another is extraction of energy from the hole's spin.

However, to explain the jets, the energy source alone is not sufficient. You also have to account for the collimation of the jets--why they are emitted in two narrow beams along the hole's spin axis. Magnetic fields and frame dragging play critical roles in that.



No, you don't, because without magnetic fields and frame dragging, there is no collimation mechanism; you would just get radiation being emitted in all directions as matter accretes onto the hole and gets heated up by collisions.
Suppose the question was "what causes the water jets in the hot tub"? I feel that the best answer is that the motorized centrifugal pump creates the jets. You could argue that the nozzles and the pipe leading to the nozzles are critical components to the jet effect. We could also claim that the electric power plant 20 miles down the road is creating the energy/power which produces the jets. Without the magnetic fields in the motor that drives the centrifugal pump the pump would not produce any jets. Connecting the power grid to the nozzle will not produce a proper hot tub jet. You also need water and an atmosphere and a gravity field to keep the water liquid and in the tub.

The images of jets from Hubble space telescope that we see are created by ionized gas/plasma in the interstellar medium. A glow discharge lamp containing the same gas mix as M87 should make a similar color to the M87 Jet but with a redshift adjustment in frequencies. So "glow discharge" is the mechanism.
 
  • #24
PeterDonis
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Suppose the question was "what causes the water jets in the hot tub"? I feel that the best answer is that the motorized centrifugal pump creates the jets.
And I disagree with you. All of the elements of the system are necessary to create the jets. The pump by itself just pumps water; it doesn't direct it into jets.

The images of jets from Hubble space telescope that we see are created by ionized gas/plasma in the interstellar medium.
By ionized gas/plasma that falls towards a supermassive, rapidly spinning black hole, where it gets heated up and produces X-rays, and some of it gets redirected by the magnetic field of the hole into jets that come out along the hole's spin axis.

There's a lot more there than just "ionized gas/plasma in the interstellar medium". Ionized gas/plasma by itself just glows. It doesn't create jets.
 

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