Could accretion on a neutron star’s poles cause the jets?

[Jonathan Scott]

http://www.astronomy.com/news/2015/08/neutron-stars-strike-back-at-black-holes-in-jet-contest

OK, I see what you mean. I had interpreted that as a mismatch of strengths, but it does involve timing too.

Lets use symbol for URM for ultra-relativistic matter or quark gluon equivalent. What would happen to a star that was a mixture of neutrons and URM?

I don't know what your "ultra-relativistic matter" is meant to be if it isn't simply the same stuff under more pressure. And I don't know the mechanical properties predicted for the hypothetical quark gluon plasma.

Would it regulate its radius to 1.00 SR?

If you mean SR = Solar Radius, you're very confused, as the radius of a neutron star is about 35,000 times smaller than the sun.

 

[Bernie G]

OK, I see what you mean. I had interpreted that as a mismatch of strengths, but it does involve timing too.
I don't know what your "ultra-relativistic matter" is meant to be if it isn't simply the same stuff under more pressure. And I don't know the mechanical properties predicted for the hypothetical quark gluon plasma. If you mean SR = Solar Radius, you're very confused, as the radius of a neutron star is about 35,000 times smaller than the sun.

Suggestion: SR = Schwarzschild radius. SM = solar mass. URM = ultra-relativistic matter. NS = neutron star.
"Ultra-relativistic matter" are charged particles moving at close to c. Its mechanical properties are mostly determined by the equation (rho)(c^2)/3. It is affected by magnetic fields and radiates energy. What is called "quark-gluon plasma" also generates pressure of (rho)(c^2)/3 as does light. I think a magnetic field would redirect a lot or all of the pressure of URM in a neutron star along the magnetic axis.
URM is not just neutrons under greater pressure. Core neutrons would be low velocity or stationary and not having a net charge and would not be deflected much by a magnetic field compared to charged particles. Why can't neutrons and URM live side by side temporarily in a NS? The existence of one does not have to mean the destruction of the other. If a stationary neutron collapses to a much smaller net mass with ultra-relativistic velocities and the net mass-energy is the same, so what's the big deal if mc^2 is conserved.
If ultra-relativistic jets from neutron stars don't occur simultaneously with large accretion, then the jets are originating from inside the star.

 

[Jonathan Scott]

Any references for this "ultra-relativistic matter"? This isn't something I know about, but from basic physics principles I can't see any way that something deep inside a neutron star could somehow acquire additional energy, and if it changed state in some way because of the pressure, I would only expect it to be able to remain in existence within the conditions that created it.
I would have thought that the temperature would have meant that even if a neutron cannot move very far, it would be moving at extremely high speed anyway.

 

[Jonathan Scott]

Also, I still think that baryon number conservations means that a neutron cannot turn into a collection of bits with significantly more kinetic energy. Obviously, if it were possible for "fragments" to exist independently, then thermal effects giving the fragments similar energy to other particles would make them faster and the bits could be given more energy than the original. However, as quarks cannot be isolated and there is no antimatter around to cancel the baryon number, this doesn't seem to apply.

 

[Jonathan Scott]

On the SR abbreviation, I don't understand how you think a neutron star could have a radius equal to its Schwarzschild radius, as that ensures total gravitational collapse to a black hole (assuming standard GR anyway).

 

[Bernie G]

My info about URM or quark-gluon plasma or quark type matter was gleaned from various sources. Just google those terms and terms like "radiation pressure" and "ultra-relativistic pressure" and things like (rho)(c^2)/3 will pop up. If URM or other ultra-relativistic stuff briefly formed in a neutron star it would logically escape the star quickly or heat the star.

I probably shouldn't have brought up the possibility of a compact star that was a mixture of neutrons and URM regulating its radius, and am still formulating thoughts on that. Its probably too divergent from what might cause ultra-relativistic jets from a neutron star.

 

[Jonathan Scott]

Although I consider it implausible that massive particles could escape from the surface of a neutron star, electromagnetic radiation can escape, in particular X-rays. Note that infalling material seems to land preferentially at the magnetic poles (which are not generally aligned with the rotation axis, hence pulsars) and cause local high-temperature spots which emit strong X-rays.
I've not done any calculations, but I could speculate that perhaps intense X-rays from recently fallen material could push some of the following material away from the magnetic poles. This would mean that matter which ended up near the rotation axis as a result would be pushed in the same direction all the time as the magnetic poles rotated, creating a polar jet, whereas material in other directions would probably end being dispersed back towards the equatorial plane.
This might give a possible direction to explore for an explanation of jets, although I don't know whether enough information is available to check the viability, and that's a different idea from the current thread. Note that no similar explanation could apply for black holes, as there would be no radiation from the surface.

 

[Bernie G]

Maybe the origin of powerful neutron star jets can be determined from observational analysis instead of mathematical analysis. (1) If all neutron stars with powerful jets have high spin rates also, that's a pretty good indication that spin rate (and hence a twisted magnetic field) is an important factor in powering (and not just directing) the jets. (2) If powerful jets from neutron stars sometimes don't occur simultaneously with accretion, that indicates the jets are not directly originating from the accretion.

 

[Jonathan Scott]

The snag with your statement (2) is that accretion isn't a single-stage process anyway, as I mentioned before. If a burst of stuff arrives in the vicinity, some of it may well produce immediate flares, but I think some of it can hang around in orbit as an accretion disk or rings for an extended period, only gradually working its way in over time.
Good luck with your investigations! If you find any relevant information in acceptable references, let us know, but to comply with the forum guidelines please try to limit any speculation to ideas which are firmly based on established science.

 

[Bernie G]

Although I consider it implausible that massive particles could escape from the surface of a neutron star, electromagnetic radiation can escape, in particular X-rays.

An ultra-relativistic particle would easily escape. The escape velocity from a 2 solar mass, 12-km radius neutron star is only about 0.7(c)

 

[Jonathan Scott]

An ultra-relativistic particle would easily escape. The escape velocity from a 2 solar mass, 12-km radius neutron star is only about 0.7(c)

As I have pointed out before, you have failed to explain or provide any references as to what any such ultra-relativistic particle could be or by what physical means it could get enough additional kinetic energy when at or near the surface to escape. Please do not continue this speculation unless you can provide relevant acceptable references.

 

[DrAupo1]

IMHO:
In the very center of a neutron star,where mass is equal in all directions there should be an area of zero gravity.
This would allow circulation of particles in a small area of the core.
In-falling matter would disturb this area,causing great stress as the particles are forced into a different arrangement.
This stress would create a domino effect,focused by the magnetic field,causing the emission of energy from the surface.

 

[Jonathan Scott]

IMHO:
In the very center of a neutron star,where mass is equal in all directions there should be an area of zero gravity.
This would allow circulation of particles in a small area of the core.
In-falling matter would disturb this area,causing great stress as the particles are forced into a different arrangement.
This stress would create a domino effect,focused by the magnetic field,causing the emission of energy from the surface.

Although there is zero field at some point, this is essentially irrelevant, as the pressure is at a maximum at the same location.
The rest sounds like the sort of "techno-babble" used in Star Trek, and doesn't belong in Physics Forums.

 

[Bernie G]

The snag with your statement (2) is that accretion isn't a single-stage process anyway, as I mentioned before. If a burst of stuff arrives in the vicinity, some of it may well produce immediate flares, but I think some of it can hang around in orbit as an accretion disk or rings for an extended period, only gradually working its way in over time.

Yes, but could a large mass of accretion material build up around a neutron star for months without radiating, and then suddenly form an ultra-relativistic jet?

 

[Jonathan Scott]

Yes, but could a large mass of accretion material build up around a neutron star for months without radiating, and then suddenly form an ultra-relativistic jet?

Why do you have this fascination with the term "ultra-relativistic"? Surely merely "relativistic" is enough in this context.
I don't know how long accreting material can stay in orbit, but I wouldn't be surprised if some material could remain around for an extended period before its orbit became unstable for some reason.
Another problem I think I previously forgot to mention with your alternative idea about material being emitted from the magnetic poles is that the jets are along the spin axis, not from the magnetic pole.
You can find out a lot more about neutron star jets from Googling. I see that it is commonly assumed that neutron stars produce jets only when they have a relatively weak magnetic field. I just spotted a paper from some time ago (2003) explaining a specific possible mechanism: "FORMATION OF SEMIRELATIVISTIC JETS FROM MAGNETOSPHERES OF ACCRETING NEUTRON STARS: INJECTION OF HOT BUBBLES INTO A MAGNETIC TOWER", at http://iopscience.iop.org/article/10.1086/379752/pdf

 

[Bernie G]

Why do you have this fascination with the term "ultra-relativistic"? Surely merely "relativistic" is enough in this context. I don't know how long accreting material can stay in orbit, but I wouldn't be surprised if some material could remain around for an extended period before its orbit became unstable for some reason. Another problem I think I previously forgot to mention with your alternative idea about material being emitted from the magnetic poles is that the jets are along the spin axis, not from the magnetic pole.

Ultra-relativistic velocities are much rarer and harder to achieve than relativistic velocities. If something is moving at >0.9c an explanation of how it could move at 0.1c is not satisfactory. If some material could remain around for an extended period, how would it be supported? If the magnetic field supported it, it should be radiating. Thanks for the interesting source ... I think it says the jets follow the spin axis of the disk ... isn't this the magnetic axis of the star?

 

[Jonathan Scott]

Neutron stars are generally identified by being pulsars, and the whole reason why pulsars pulse is that their magnetic poles are not on the spin axis (and indeed are not even necessarily directly opposite one another).
Material in an accretion disk is in a semi-stable orbit, initially driven by the angular momentum of the accreting material, but effects such as friction, pressure and interactions with magnetic fields eventually cause material to fall into unstable orbits and either fall to the surface or get ejected, especially as jets. Note that material in a lower orbit needs to move more rapidly to stay in orbit, so if there is any interaction with slower material in a higher orbit, that tends to cause the lower material to fall inwards.
I strongly recommend that you study some of the relevant physics, including introductory information on neutron stars, accretion disks and jets. As I said at the start, the jet creation processes are not fully understood, but I think you need to catch up with current understanding before you try to extend it.