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

[Bernie G]

Could accreting material on a neutron star’s poles impact with enough energy to initiate fusion reactions, some of which escapes the star as ultra-relativistic jets?

 

[Bernie G]

I think on a magnetized neutron star a plateau of accreted material would form and fusion reactions occur there. More than half the EM/light energy from the fusion reactions would exit the star. Half the ionized matter would exit out the magnetic pole and the other half would enter the star and cause more reactions there. Magnetic volcano is not such a good namefor this though it might look like some. Magnetic cannon describes it better. Squirt in a bunch of fuel and it shoots back at you.

 

[Bernie G]

A large amount of plasma fusion reactions might occur far above the plateau. Still its a situation where accreting matter at or near the pole undergoes fusion reactions so a lot of it will shoot back out. If this explains neutron star jets it still doesn't explain why neutron star mass seems to be limited to 2 SM.

 

[Jonathan Scott]

It is already assumed that X-ray bursts from neutron stars are caused by material falling onto the surface and immediately undergoing fusion because of the impact energy.
Jets are not yet fully understood, but quasars also have jets and are thought to involve black holes rather than neutron stars, so the same explanation could not work in that case.
I've previously heard that jets are probably caused by falling ionised plasma being accelerated out of the equatorial plane towards the polar directions by twisted magnetic fields (from relativistic spinning), but then being partially neutralised (perhaps combining with free electrons or even electrons derived from pair production) so that the resulting neutral material escapes the magnetic field. I'm not up to date with recent research on the subject.

 

[Bernie G]

Sorry to post so much, maybe the above thoughts explain little.

Do charged particles from fusion reactions even have sufficient energy to escape the surface of a 2 SM neutron star? My guess is no. If so, would whatever escapes a neutron star's surface have to have an ultra-relativistic source? If there is an ultra-relativistic source what choices are there for its location?: (1) above the star surface? (2) at the star surface? (3) on a plateau above the surface? (4) below the surface? (5) the core?

I think ultra-relativistic conditions could exist at the core. Not so sure about the other places.

 

[Hornbein]

Sorry to post so much, maybe the above thoughts explain little.

Do charged particles from fusion reactions even have sufficient energy to escape the surface of a 2 SM neutron star? My guess is no. If so, would whatever escapes a neutron star's surface have to have an ultra-relativistic source? If there is an ultra-relativistic source what choices are there for its location?: (1) above the star surface? (2) at the star surface? (3) on a plateau above the surface? (4) below the surface? (5) the core?

I think ultra-relativistic conditions could exist at the core. Not so sure about the other places.

Last I heard some thought that the jets were understood as an effect of general relativity, some disagreed.

The jets are similar to the jets from black holes, so (1) seems like the frontrunner.

 

[Bernie G]

It is already assumed that X-ray bursts from neutron stars are caused by material falling onto the surface and immediately undergoing fusion because of the impact energy.
Jets are not yet fully understood, but quasars also have jets and are thought to involve black holes rather than neutron stars, so the same explanation could not work in that case.
I've previously heard that jets are probably caused by falling ionised plasma being accelerated out of the equatorial plane towards the polar directions by twisted magnetic fields (from relativistic spinning), but then being partially neutralised (perhaps combining with free electrons or even electrons derived from pair production) so that the resulting neutral material escapes the magnetic field. I'm not up to date with recent research on the subject.

Sorry, I didn't read your post before posting above.

"It is already assumed that X-ray bursts from neutron stars are caused by material falling onto the surface and immediately undergoing fusion because of the impact energy."
Yes, but I wonder if charged particles from fusion reactions even have sufficient energy to escape the surface of a neutron star.

"Jets are not yet fully understood, but quasars also have jets and are thought to involve black holes rather than neutron stars, so the same explanation could not work in that case."
True, the above doesn't explain black hole jets. stars. We don't know what's in a black hole. But what happens on a neutron star?

"I've previously heard that jets are probably caused by falling ionised plasma being accelerated out of the equatorial plane towards the polar directions by twisted magnetic fields (from relativistic spinning), but then being partially neutralised (perhaps combining with free electrons or even electrons derived from pair production) so that the resulting neutral material escapes the magnetic field."
Why should this ionized plasma become partially neutralized and escape? Does it cool down? Neutral material would not follow magnetic field lines and it looks like the jets closely follow a magnetic pole.

 

[Bernie G]

Last I heard some thought that the jets were understood as an effect of general relativity, some disagreed. The jets are similar to the jets from black holes, so (1) seems like the frontrunner.

That makes sense. Gravity, magnetic field, and spin combine above the neutron star's magnetic pole to cause ultra-relativistic conditions to exist. Hmmm.

Question: Would the ultra-relativistic jet above the neutron star's pole go in both directions, and pierce the surface of the star?

 

[Hornbein]

That makes sense. Gravity, magnetic field, and spin combine above the neutron star's magnetic pole to cause ultra-relativistic conditions to exist. Hmmm.

Question: Would the ultra-relativistic jet above the neutron star's pole go in both directions, and pierce the surface of the star?

The crust of a neutron star is very likely the strongest, toughest stuff in the universe. I can't imagine it being pierced by anything. The outer surface is ultradense polymerized iron.

 

[Bernie G]

The crust of a neutron star is very likely the strongest, toughest stuff in the universe. I can't imagine it being pierced by anything. The outer surface is ultradense polymerized iron.

I think it would depend on the density of the jet but probably an ultra-relativistic jet would cut thru the crust like a hot knife thru butter. Not much can stand up to $$\frac{1}{3} \rho c^2$$

 

[Bernie G]

The crust of a neutron star is very likely the strongest, toughest stuff in the universe. I can't imagine it being pierced by anything. The outer surface is ultradense polymerized iron.

Consider a bubble of ultra-relativistic matter (from the core) propagating along the magnetic field lines that has reached the bottom of the iron crust of the star. Its density should be greater than the density of the iron crust, but even if its density was the same it would cut right thru the crust. The "hardness" effect of the crust shouldn't be able to generate a back pressure nearly equal to (rho)(c^2)/3. I think the gravity on the surface of a neutron star is so strong that the ions directly produced from fusion reactions would have inadequate energy to escape the star! But ultra-relativistic matter would. Ultra-relativistic matter is a different ball game.

 

[Jonathan Scott]

This idea of "ultra-relativistic matter" moving around within the core of a neutron star doesn't make sense to me. It's unbelievably dense solid material.
If it's something you invented, this is not the place to discuss it; this forum is for discussing subjects based on accepted scientific principles.

 

[Bernie G]

This idea of "ultra-relativistic matter" moving around within the core of a neutron star doesn't make sense to me. It's unbelievably dense solid material.
If it's something you invented, this is not the place to discuss it; this forum is for discussing subjects based on accepted scientific principles.

Yes, but what are the accepted scientific principles to describe the jets?

 

[Hornbein]

This idea of "ultra-relativistic matter" moving around within the core of a neutron star doesn't make sense to me. It's unbelievably dense solid material.
If it's something you invented, this is not the place to discuss it; this forum is for discussing subjects based on accepted scientific principles.

The core of a neutron star is superfluid. The electrons moving about are relativistic. The core is also a proton superconductor.

Superfluids seem to me to be the same as a superconductor except with neutral particles.

There was some interest in a quark plasma inner core, but with the discovery of a 1.97 stellar mass neutron star this view has gone out of style.

 

[Jonathan Scott]

The core of a neutron star is superfluid. The electrons moving about are relativistic. The core is also a proton superconductor.

Superfluids seem to me to be the same as a superconductor except with neutral particles.

There was some interest in a quark plasma inner core, but with the discovery of a 1.97 stellar mass neutron star this view has gone out of style.

I stand corrected on the word "solid", thanks. I guess it's a long time since I learned about neutron stars, when I think the core was described as probably being a "lattice" or "crystalline" structure of neutrons, although I think the structure is still somewhat poorly understood even now. I had certainly previously heard that energies were so high that particles would be moving relativistically, but I thought that this was only over tiny distances, and I do not recall having heard of any energy source which could result in a "bubble" or anything else moving at relativistic average speed over macroscopic distances through this material.

 

[Jonathan Scott]

Yes, but what are the accepted scientific principles to describe the jets?

As far as I know, the current assumption is that the jets are formed from infalling material which has been deflected towards the poles, possibly by relativistic twisting of magnetic fields. Certainly, strong jets appear to relate to large amounts of infalling material combined with strong magnetic fields. The exact details are not currently understood, but your alternative speculative suggestion that jets might originate on or inside neutron stars does not appear to fit with these current assumptions, and I think that's the best answer we can give to your original question (which however mutated a bit).

Although it is fun to discuss wildly speculative ideas, this forum is for discussions within the scope of accepted scientific principles, and although I find this frustrating myself, I have seen enough evidence to know the value of these rules. Although a limited amount of scientifically-based speculation may be tolerated, your suggestions seem too vague and speculative to me to be acceptable topics for further discussion. I'm not a mentor, so it's not my job to enforce the rules, but you'll get more help if you try to stay well within the guidelines.

 

[Bernie G]

There was some interest in a quark plasma inner core, but with the discovery of a 1.97 stellar mass neutron star this view has gone out of style.

.

I'm look for explanations of possible causes of neutron star ultra-relativistic jets and/or what could cause the apparent mass limitation of a neutron star to 2 SM. They don't have to be caused by the same thing.

Lets consider that outside above the star a magnetic pinch or some other relativistic effect caused a huge concentration of mass-energy. This outside of the star model says this concentration can eject as ultra-relativistic matter. Does the accreting matter never reach the surface of the star but instead blows up above the star or is directed away from the star by fields? Does a magnetic pinch prevent the ultra-relativistic jet from touching the star? This model doesn't explain the apparent mass limitation of 2 SM. To me magnetic jets seem a more sensible way to vent excess mass-energy out of a neutron star. I'd like above the star model of jet formation explained better.

 

[Bernie G]

... I think that's the best answer we can give to your original question (which however mutated a bit). ... Although it is fun to discuss wildly speculative ideas, this forum is for discussions within the scope of accepted scientific principles.

Forget the original question, we're way past that. Fusion reactions are puny compared to ultra-relativistic matter. Yes, this forum is for discussions within the scope of accepted scientific principles, so I'd like the above the star model of jet formation explained better.

 

[Jonathan Scott]

How is your "ultra-relativistic matter" getting its energy?
I thought the core matter got its additional energy from gravity, in which case lifting it up from the core to the surface will take that energy away again.

 

[Bernie G]

How is your "ultra-relativistic matter" getting its energy?
I thought the core matter got its additional energy from gravity, in which case lifting it up from the core to the surface will take that energy away again.

Ultra-relativistic matter travels at a high percentage of c and has enough kinetic energy to escape a neutron star from the core or the surface.

How can ultra-relativistic matter be formed above a neutron star which has a radius of at least 1.7X the Schwarzschild radius? There isn't enough gravitational energy to make ultra-relativistic matter there. The most energy the accreting matter can get from gravity there is how much ... maybe 0.3M(c^2) ? Thats less than the energy of some neutron star ultra-relativistic jets.

 

[Bernie G]

I do not recall having heard of any energy source which could result in a "bubble" or anything else moving at relativistic average speed over macroscopic distances through this material.

A neutron might collapse under extreme conditions. Maybe a neutron would collapse if it was required to produce a pressure greater than (rho)(c^2)/3. if a neutron collapsed shouldn't it become ultra-relativistic quark matter and radiation?

 

[Bernie G]

How is your "ultra-relativistic matter" getting its energy?

Collider experiments show that when a nuclei disintegrates it results in roughly 10% quark type matter and 90% energy. If neutron collapse happens something like this should be expected. A bubble of this stuff would displace neutrons.

 

[Jonathan Scott]

Collider experiments show that when a nuclei disintegrates it results in roughly 10% quark type matter and 90% energy. If neutron collapse happens something like this should be expected. A bubble of this stuff would displace neutrons.

Regardless of what you do to a neutron, baryon number conservation means that the bits must have at least enough rest mass to create a proton (and an electron), which is barely less than the original neutron rest mass. So the amount of additional kinetic energy is negligible. For a collider, the incoming particles already had the energy.

 

[Bernie G]

Regardless of what you do to a neutron, baryon number conservation means that the bits must have at least enough rest mass to create a proton (and an electron), which is barely less than the original neutron rest mass. So the amount of additional kinetic energy is negligible. For a collider, the incoming particles already had the energy.

Instead of a collider the energy source to generate ultra-relativistic matter at the core of a neutron star would be the enormous gravitational energy used to compress the neutrons there. The pressure at the core is pretty close to (rho)(c^2)/3. Can that be a coincidence? Where else can these extreme ultra-relativistic conditions exist …. outside the star? Not even fusion explosions can produce an ultra-relativistic situation. So IMHO the extreme situation in a neutron star’s core is the most logical candidate for the production of ultra-relativistic matter. I think outside the neutron star there’s insufficient gravitational energy to produce ultra-relativistic matter. It doesn’t make sense to me that the gravity from a 2 SM object could create ultra-relativistic matter at a distance of 1.7 SR, without even getting into the issue of it all being deflected away. I’m open to any explanation how ultra-relativistic matter might be generated outside a neutron star.

 

[Jonathan Scott]

Gravitational energy gives the particles in the core so much kinetic energy that their speeds are relativistic, corresponding to incredible temperatures. If you move any of that matter back up to the surface, it will simply lose the corresponding amount of energy so that it will match the kinetic energy of the surface material (which is still pretty incredible). Fusion reactions allow you to convert a bit of rest mass into kinetic energy, and so does neutron decay to a proton, but the relative amounts of energy in both cases are still small compared with the gravitational energy lost through falling onto a neutron star.
What's this about "ultra-relativistic matter" being generated anyway? If material falling towards a neutron star is caught up in an accretion disk, being sped up by angular momentum conservation, then deflected away towards the poles and given a little extra energy, for example by rotating twisted magnetic fields (which cause an induced electric field effect), then it will have more than enough energy to escape at a relativistic speed. In contrast, I can not think of anything that could happen at the surface which could propel any massive particle back into space.

 

[Bernie G]

Gravitational energy gives the particles in the core so much kinetic energy that their speeds are relativistic, corresponding to incredible temperatures. If you move any of that matter back up to the surface, it will simply lose the corresponding amount of energy so that it will match the kinetic energy of the surface material (which is still pretty incredible). Fusion reactions allow you to convert a bit of rest mass into kinetic energy, and so does neutron decay to a proton, but the relative amounts of energy in both cases are still small compared with the gravitational energy lost through falling onto a neutron star.
What's this about "ultra-relativistic matter" being generated anyway? If material falling towards a neutron star is caught up in an accretion disk, being sped up by angular momentum conservation, then deflected away towards the poles and given a little extra energy, for example by rotating twisted magnetic fields (which cause an induced electric field effect), then it will have more than enough energy to escape at a relativistic speed. In contrast, I can not think of anything that could happen at the surface which could propel any massive particle back into space.

For an infalling particle the maximum gravitational potential energy that it could gain outside a black hole is 0.5mc^2 (I think). The gravitational potential energy outside a neutron star is even less. Gravity outside a neutron star and even a black hole just isn't strong enough to directly accelerate a particle to ultra-relativistic velocities. Electrons in an accreting disk should be at least relativistic but the ions which are the vast bulk of the disk not nearly so much. In your model of accretion disk material exiting the magnetic poles, why does it all head away from the star instead of heading towards the star?

 

[Jonathan Scott]

For an infalling particle the maximum gravitational potential energy that it could gain outside a black hole is 0.5mc^2 (I think). The gravitational potential energy outside a neutron star is even less. Gravity outside a neutron star and even a black hole just isn't strong enough to directly accelerate a particle to ultra-relativistic velocities. Electrons in an accreting disk should be at least relativistic but the ions which are the vast bulk of the disk not nearly so much. In your model of accretion disk material exiting the magnetic poles, why does it all head away from the star instead of heading towards the star?

That gravitational energy is much more energy per particle than could be released by fusion. Rather than anything arising from the surface, it is energetically far more likely that the material heading away from the poles is a fraction of the infalling gas, which already has acquired the kinetic energy from falling, and would only need relatively minor electromagnetic acceleration to escape again. As I've mentioned before, the exact mechanism of that acceleration is not understood, but it is thought to be related to the electromagnetic field of the neutron star being twisted by relativistic delay effects.
Here's a recent news article which illustrates the current view: http://astronomynow.com/2015/08/05/neutron-star-takes-on-black-holes-in-jet-contest/

 

[Bernie G]

As I've mentioned before, the exact mechanism of that acceleration is not understood, but it is thought to be related to the electromagnetic field of the neutron star being twisted by relativistic delay effects.

Thank you for the good responses. The original question was answered and I've learned a lot but still have great reservations about the formations of jets outside a neutron star. Jets outside the star are a poor candidate to explain the apparent mass limiting of a neutron star to about 2 SM. And there's something else: I've read that large scale neutron star accretion and jet activity does not always happen simultaneously. If the jets were caused by the electromagnetic field outside the star, shouldn't the jets occur simultaneously with the accretion? If the jets originated from the core there could be considerable delay.

 

[Jonathan Scott]

As far as I know, the upper limit on a neutron star mass occurs because it is expected that beyond some limit it would collapse into something else which would look different (either a black hole or perhaps some kind of quark star). See the Wikipedia entry for Tolman-Oppenheimer Volkov limit.
I've not seen the suggestion that accretion and jet activity do not occur at the same time. Can you provide a reference? Of course, material may be first captured in an accretion disk, then it gradually falls inwards, and I would expect jet activity to be more correlated with material falling in than with the initial capture.

 

[Bernie G]

I've not seen the suggestion that accretion and jet activity do not occur at the same time.

http://www.astronomy.com/news/2015/08/neutron-stars-strike-back-at-black-holes-in-jet-contest
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? Would it regulate its radius to 1.00 SR?

 

[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).