Some (Interested Layman's) "What if?"-Questions Regarding Neutron Stars

[Godot]

Hi @ all!

I'm an interested layman with some background - mostly popular science books and TV shows, and Phil Plait's Bad Astronomy blog. Reading about the just-published gravitational wave observation results made me revisit some old thoughts about neutron stars, and what would happen if and when...

(1) two of pass each other closely on hyperbolic trajectories?

  (1a) have a less close pass? Would there be a - kind of - critical distance they'd have to keep?

  (1b) could / does the acceleration on the inbound branch make one collapse further and form a black hole (due to relativistic mass dilation)

 (2) one neutron star does such a pass on another massive collapsed object ??? (black hole or white dwarf, either would be OK)

 

 

Why do I wonder? Wellll...   ...during their periastron, their gravities should cancel each other out, which might or might not bring the gravity below the "degeneracy threshold".

Would that lead to a "de-degeneration" of the collapsed matter? Loss of matter? (as gravitational waves or classical photons?) What about tidal forces, spaghettification? Angular momentum?

Also, assuming that one or both of the neutron stars were on the light side, just north of chandrasekar's limit, would such a mass loss cause a "de-degeneration??? And if so, a fast one (BOOOM!!!!) or a slow evaporation???

 

... I could go on, but I won't. Well, not now.

 

I'd be happy with links to any sites, lectures or even arXiv papers - as long as they contain enough text to understand them. I'm a molecular / microbiologist and did physics as a major during my school finals, worked with radioisotopes, yadda yadda -  and have a reasonable grasp of stuff that goes on on the small end. But my math knowledge is pretty ... meh: At some point after the third or so integral sign, the little cogwheels unlink and it all goes "whirrrrr...."

 

Thanks in advance and I'm hoping for some enlightening answers!

[beecee]

2 hours ago, Godot said:

Hi @ all!

I'm an interested layman with some background - mostly popular science books and TV shows, and Phil Plait's Bad Astronomy blog. Reading about the just-published gravitational wave observation results made me revisit some old thoughts about neutron stars, and what would happen if and when...

(1) two of pass each other closely on hyperbolic trajectories?

  (1a) have a less close pass? Would there be a - kind of - critical distance they'd have to keep?

  (1b) could / does the acceleration on the inbound branch make one collapse further and form a black hole (due to relativistic mass dilation)

 (2) one neutron star does such a pass on another massive collapsed object ??? (black hole or white dwarf, either would be OK)

 

 

Why do I wonder? Wellll...   ...during their periastron, their gravities should cancel each other out, which might or might not bring the gravity below the "degeneracy threshold".

Would that lead to a "de-degeneration" of the collapsed matter? Loss of matter? (as gravitational waves or classical photons?) What about tidal forces, spaghettification? Angular momentum?

Also, assuming that one or both of the neutron stars were on the light side, just north of chandrasekar's limit, would such a mass loss cause a "de-degeneration??? And if so, a fast one (BOOOM!!!!) or a slow evaporation???

 

... I could go on, but I won't. Well, not now.

 

I'd be happy with links to any sites, lectures or even arXiv papers - as long as they contain enough text to understand them. I'm a molecular / microbiologist and did physics as a major during my school finals, worked with radioisotopes, yadda yadda -  and have a reasonable grasp of stuff that goes on on the small end. But my math knowledge is pretty ... meh: At some point after the third or so integral sign, the little cogwheels unlink and it all goes "whirrrrr...."

 

Thanks in advance and I'm hoping for some enlightening answers!

My non professional answer is that with (1) ) (1a) and (1b) a merging would be the final result and a combined collapse to a BH. I think we also have gravitational radiation from merging Neutron stars?

With (2) the same final formation of a BH from remnants of both.

I am puzzled by whatever you mean by the gravity's cancelling each other out. That essentially happens at Lagrange points where the fields balance.

2 hours ago, Godot said:

Also, assuming that one or both of the neutron stars were on the light side, just north of chandrasekar's limit, would such a mass loss cause a "de-degeneration??? And if so, a fast one (BOOOM!!!!) or a slow evaporation???

From my own view Neutron stars like any degenerated matter are balanced just near the EDP, and NDP and not much tipping is needed. Even a White Dwarf can be tipped above the EDP to form a Neutron star or BH.

Just my thoughts, some based on what I have read in Thorne's book, but don't despair, one of our bright professionals is sure to be along to answer your questions and/or tidy up or modify my answers.

[beecee]

Anyone else like to tidy up, modifiy, add?

[MigL]

Neutron stars don't have an extended radius around them  from which gravitational escape is impossible, like Black Holes do.

Unless by 'close' you mean close enough to exert some 'drag' on each other, and lose some energy ( such as via gravitational waves ), there will be no capture or merging.

Not sure what you mean by gravity cancelling, but where two neutron stars are close enough for mass to spiral from one to the other, neither will de-collapse to white dwarf. Rather they will lose energy fairly quickly, due to gravitational wave emission, spiral in to each other and, depending on mass, either form a larger neutron star, or a Black Hole.

[beecee]

8 minutes ago, MigL said:

Neutron stars don't have an extended radius around them  from which gravitational escape is impossible, like Black Holes do.

Unless by 'close' you mean close enough to exert some 'drag' on each other, and lose some energy ( such as via gravitational waves ), there will be no capture or merging.

The first sentence is correct and as I see it...The second, I'm of the opinion that if they were in any orbit around one another, that "gravitational drag" would be likely a given and compulsory, and as such, merging a certainty over time, and as such a BH would form. 

14 minutes ago, MigL said:

Not sure what you mean by gravity cancelling, but where two neutron stars are close enough for mass to spiral from one to the other, neither will de-collapse to white dwarf. Rather they will lose energy fairly quickly, due to gravitational wave emission, spiral in to each other and, depending on mass, either form a larger neutron star, or a Black Hole.

Agreed with the highlighted part, although the opposite is possible I believe with White Dwarfs accreting mass, from a companion and becoming a Neutron star or even a BH.

The last part has me thinking somewhat...I would have thought a BH forming from  two Neutron stars merging would be a cert....but hey, it's been a while since I was into this stuff. Still lovely to be discussing science rather then politics, religion and such! 

[MigL]

If in a long orbit about each other, any energy loss would be small, as it would be via gravitational waves.
On long enough time scales they would eventually merge.

IIRC, the limit for electron degeneracy, after which collapse to a neutron star is mandatory, is approx. 2.3 solar masses.
While BHs have various collapse points ranging from 4 to 10 solar masses.
Depending on which one eventually turns out to be correct, if the lower, then a resulting BH is assured.
However, if the limit for BH formation is the upper, 10 solar masses, then two small neutron stars will not necessarily result in a BH.

[beecee]

18 minutes ago, MigL said:

If in a long orbit about each other, any energy loss would be small, as it would be via gravitational waves.
On long enough time scales they would eventually merge.

IIRC, the limit for electron degeneracy, after which collapse to a neutron star is mandatory, is approx. 2.3 solar masses.
While BHs have various collapse points ranging from 4 to 10 solar masses.
Depending on which one eventually turns out to be correct, if the lower, then a resulting BH is assured.
However, if the limit for BH formation is the upper, 10 solar masses, then two small neutron stars will not necessarily result in a BH.

On the highlighted part that is most likely correct, as I am now recalling (before I read your post) an article as to the variability of Neutron star collapse points. Thanks for that. 

Edited November 10, 2021 by beecee

[joigus]

I would say these are problems for so-called numerical relativity; that is, numerical simulations with Einstein's equations, and parametrizing the collision data. I'd think impact parameter and velocities of approach, masses, and so on.

I've found a reports-like paper that could be what you're looking for.

https://arxiv.org/pdf/1909.06085.pdf

I hope it lives up to your expectations. Haven't had time but to skim through it a little bit.

[Godot]

Many thanks to all the contributors for the answers!

Especially the arXiv-link to that paper has been useful (though IMHO it looks like a Master thesis - even better, as there's more explanatory text, which is stuff that I do understand). What I've read so far is still south of my "comprehension threshold". Well, at least as long as I don't really delve into the included math...  ...I'm just way better with a more, er ... verbal concepts.

 

Still...  

...almost all that info / thoughts have been about what happens and how when neutron stars DO collide / go into their death spiral. 

But what I was asking has rather been about what happens when they just don't catch each other into an orbit...

 

We do know that they can get quite the kick during their creation, eventually leaving their planetary nebula's remnants. So my assumption was that two neutron stars with such a history - let's say a speed of a thousand km/sec - fly towards each other, with just enough offset to leave each other's gravity wells. If their periastron distance were e.g. a thousand AU, I'd guesstimate that they'd just bend their flight paths a bit, giving that hyperbolic pass I'd been pondering. But what would that safe pass distance be, order-of-magnitude-wise? 100AU? Ten? 1AU, or even a fraction of an AU???

How would that affect them? Would they shed energy from mass? Magnetic due to interaction of their magnetic fields? Angular momentum? Thermal energy?

Would mass loss possibly cause one to decompress (maybe only partially)? (Like, if and when the gravity reduction on the side towards the other neutron star - L1-wards - would lower the gravity below the electron degeneracy pressure limit?) Would mass loss cause a neutron star just north of Chandrasekar to erm ... discombombulate? Would the summing up of gravities on the outward side maybe cause a collapse of a neutron star just south of Tolman-Oppenheimer-Volkoff to go snap! and become a black hole???

What about tidal forces? Shouldn't the "kneading" affect them, increasing their thermal energy? Does relativistic mass dilation play any role when they pull each other towards each other?

 

Yeah, I know...   ....questions, questions, questions - and I wonder about even more of those. And based on a quite whacky base scenario. But it's something that surely will happen every now and then, so...

Also:  ...isn't asking weird questions one of the driving forces of theoretical physics?

 

Cheers + thanks again for all the input, which already is quite a bit helpful !!!

[Phi for All]

14 minutes ago, Godot said:

Yeah, I know...   ....questions, questions, questions - and I wonder about even more of those. And based on a quite whacky base scenario. But it's something that surely will happen every now and then, so...

Also:  ...isn't asking weird questions one of the driving forces of theoretical physics?

Asking questions in a science discussion forum is SO much better than making wild guesses to fill the gaps in our knowledge. Asking questions has a far better chance of yielding a trustworthy explanation. We get far too many folks who want to promote a wild guess but only support it with wavy hands and stompy feet. Thanks for the questions, they're so much easier to deal with!

[beecee]

4 hours ago, Phi for All said:

Asking questions in a science discussion forum is SO much better than making wild guesses to fill the gaps in our knowledge. Asking questions has a far better chance of yielding a trustworthy explanation. We get far too many folks who want to promote a wild guess but only support it with wavy hands and stompy feet. Thanks for the questions, they're so much easier to deal with!

Well said!