Gamma ray burst associated with LIGO GW event

[looking4sophia]

Thanks for the clarifications above.
I also saw that an "accretion disc' acts like a 'traffic jam' or 'firewall' as some have described it ;
Before any gas or dust can even reach the EH.

Apparently 'spaggetification' also happens outside the EH due to the tremendous G gradient ??

 

[Nugatory]

Apparently 'spaggetification' also happens outside the EH due to the tremendous G gradient ??

You can strike the word "also" - spaghettification is the result of tidal forces (caused by the gradient) which increase without bound as you approach the event horizon - so any body, no matter how rigid, will spaghettify somewhere above the horizon on the way through. Conversely, a sufficiently non-rigid body can be spaghettified by even the weaker forces around an gravitating object that is not a black hole.

 

[Ken G]

Not quite-- the tidal forces increase without bound (theoretically) as you approach the singularity, not the event horizon. The EH has no local significance. Indeed, for very large black holes, like supermassive black holes in galaxy centers, there is no significant spaghettification at the EH. The significance of the EH is only a matter of global geometry, all forward timelike paths inside the EH connect globally to the singularity. But the local spacetime there is mundane, on scales small enough compared to the EH.

 

[Mantuano]

That FGrB may be the energy and info expelled by the reduction of apparent "surface" of both black holes when merging into one of less total "surface" than the sum of both individually considered. But we have no means to re-translate it into a significant info. Sure, g-waves do travel at light speed, but, once again, we do not know how is that the g-mediator, call it graviton or whatever, does exit the black hole. This is a problem that will laast a while to be solved.

 

[Mantuano]

Do a fast acceleration of any celestial bodies( black holes) produce gravitational waves?

Any periodic moving mass produces a g-wave. because the deformation of s-t is locally related to its mass. Only, the intensity of that wave is correspondingly infinitesimal as compared with a black hole or a neutron star or for that, a normal star. MO.

 

[Jonathan Scott]

That FGrB may be the energy and info expelled by the reduction of apparent "surface" of both black holes when merging into one of less total "surface" than the sum of both individually considered. But we have no means to re-translate it into a significant info. Sure, g-waves do travel at light speed, but, once again, we do not know how is that the g-mediator, call it graviton or whatever, does exit the black hole. This is a problem that will laast a while to be solved.

Firstly, what do you mean by the reduction of apparent "surface"? Black holes (rather counter-intuitively) scale linearly in size with mass, so any "surface" scales with the square of the mass, so the "surface" of a merged combination in that sense is greater than the surface of the separate black holes.

And secondly, nothing has to exit the black hole; the gravitational field of the black hole forms during its formation. Only changes need to propagate anywhere, and there are no changes occurring inside the event horizon.

 

[Jonathan Scott]

That FGrB may be the energy and info expelled by the reduction of apparent "surface" of both black holes when merging into one of less total "surface" than the sum of both individually considered...

And thirdly, although the apparent gamma ray burst was small compared with the total energy of the black holes, it would still require a very substantial amount of energy having to escape. This suggested mechanism doesn't seem to be anywhere near on the right scale.

 

[Mantuano]

I did use quoted "surface" to mean the equivalent of the event horizon surface. which is less than linearly summed,.after they merge The final surface of the event horizon is the surface corresponding to the quadratic sum of the masses, which is different than the square of the final mass, as clearly may be seen. Tthat difference has to be explained somwhow in terms of info and energy being expelled or annihilated otherwise. And this has to occur just at merging time

 

[Mantuano]

Firstly, what do you mean by the reduction of apparent "surface"? Black holes (rather counter-intuitively) scale linearly in size with mass, so any "surface" scales with the square of the mass, so the "surface" of a merged combination in that sense is greater than the surface of the separate black holes.

And secondly, nothing has to exit the black hole; the gravitational field of the black hole forms during its formation. Only changes need to propagate anywhere, and there are no changes occurring inside the event horizon.

 

[Mantuano]

With respect to g-field / s-t shrinkage occurring at the time of black hole collapsing from a mass suitable to it, the field / s-t shrinking already were around the body, so it looks as being a sudden discontinuity in value of that g-field / deformation, unless a different unknown effect is in operation.

 

[Jonathan Scott]

I did use quoted "surface" to mean the equivalent of the event horizon surface. which is less than linearly summed,.after they merge The final surface of the event horizon is the surface corresponding to the quadratic sum of the masses, which is different than the square of the final mass, as clearly may be seen. Tthat difference has to be explained somwhow in terms of info and energy being expelled or annihilated otherwise. And this has to occur just at merging time

I'm still puzzled as to what you mean here by "less than linearly summed". (a + b)^2 = a^2 + b^2 + 2ab which is always greater than a^2 + b^2. OK, there are complications relating to spinning and angular momentum, but the general rule is that the event horizon radius scale for the black hole is proportional to mass.

 

[Jonathan Scott]

With respect to g-field / s-t shrinkage occurring at the time of black hole collapsing from a mass suitable to it, the field / s-t shrinking already were around the body, so it looks as being a sudden discontinuity in value of that g-field / deformation, unless a different unknown effect is in operation.

Sorry, I don't understand what you're saying here. Gravitational waves are the most sudden thing that can happen to the field, and those propagate at c. Apart from those, the distant field is unaffected by collapse to a black hole.

 

[jhart]

I'm essentially a layman so I fully expect the answer to this to be "no", but since the energy that is supposed to have gone into the production of the GW in GW150914 has been estimated by LIGO as 3 solar masses is there no known mechanism for some of that energy to be converted back into mass locally and thus produce this GRB?

I'm thinking of the massive local distortions in space. Could vast Gravitational Waves separate virtual particles into pairs? Something similar to the "Schwinger effect"?

If something like that was a big enough effect to produce a GRB that we could detect then the energy lost to the GWB would presumably have to be taken into account in the model for the event itself?

 

[Jonathan Scott]

I'm essentially a layman so I fully expect the answer to this to be "no", but since the energy that is supposed to have gone into the production of the GW in GW150914 has been estimated by LIGO as 3 solar masses is there no known mechanism for some of that energy to be converted back into mass locally and thus produce this GRB?

The fact that the apparent GRB was only about half a second after the GW event places some strong constraints on possible mechanisms. Unless there are further unlikely coincidences involved, this suggests that the source of the GRB was only at most a fraction of a light second away from the merger event (noting for comparison that the radius of the sun is about 2.3 light seconds).

 

[jhart]

The fact that the apparent GRB was only about half a second after the GW event places some strong constraints on possible mechanisms. Unless there are further unlikely coincidences involved, this suggests that the source of the GRB was only at most a fraction of a light second away from the merger event (noting for comparison that the radius of the sun is about 2.3 light seconds).

Yes, that's why I was thinking of some interaction with virtual particles. As I understand it the problem people have with both these events being connected is that there should not be enough normal matter within 0.4 light seconds of the merger (I got this from Nature Vol 531 page 431 "But most observers now consider it to be a coincidence...our astrophysical expectation has been that the gas from stars that formed the binary black hole has long dispersed".)

But what I am thinking is that 3 Solar Masses is a very large amount of energy, if there is any mechanism to convert some of it back into matter, or directly into photons, within the first 0.4 seconds that could account for the GRB.

Then I thought: There are ways to exchange energy with "the vacuum",could that be it?

If spacetime in the region of the merger is being stretched and compressed at 250 Hz and presumably the local wave strain is very high, would that be enough for pair production by the separation of virtual particles?

I then had a quick, and probably naive look at virtual particles on wikipedia and found this: "Another example is pair production in very strong electric fields, sometimes called vacuum decay. If, for example, a pair of atomic nuclei are merged to very briefly form a nucleus with a charge greater than about 140, (that is, larger than about the inverse of the fine structure constant, which is a dimensionless quantity), the strength of the electric field will be such that it will be energetically favorable to create positron-electron pairs out of the vacuum or Dirac sea, with the electron attracted to the nucleus to annihilate the positive charge. This pair-creation amplitude was first calculated by Julian Schwinger in 1951." (https://en.wikipedia.org/wiki/Virtual_particle#Pair_production).

Which is why I added the Schwinger effect to my original post, if a strong electric field can produce that effect then presumably it's possible for a large GW strain to do the same thing? I.e. create conditions where pair production is energetically favorable.

If this happened then I would expect the GW to lose energy separating the virtual particles into pairs. That energy would then be converted into photons when then particles annihilated with whatever partner they could find.

That might not be the mechanism, it's just a wild guess on my part. But maybe there is some other mechanism that could take energy back out of the GWs and dump it into the local space.

 

[Jonathan Scott]

The local energy density in a gravitational wave, even close to the source, is many orders of magnitude smaller than the energy density typically involved in gamma ray production.

I personally find it very implausible that there could be any mechanism by which gravitational wave energy could be converted to gamma rays. My own conclusion would have to be that if the GRB is real, then whatever events were involved in creating the GW also separately resulted in creating the GRB.

 

[jhart]

The local energy density in a gravitational wave, even close to the source, is many orders of magnitude smaller than the energy density typically involved in gamma ray production.

Isn't that energy density in this case 3 x the mass of the Sun x c² / ((4/3) x π x (0.4xc)³)?

Which is approx 5.4 x 10⁴⁷ J / 7.2 x 10²⁴ m³

I.e. about 7.4 x 10²² J/m³ right?

Is that really smaller than the energy density typically involved in gamma ray production?

Am I missing something?

 

[Jonathan Scott]

Isn't that energy density in this case 3 x the mass of the Sun x c² / ((4/3) x π x (0.4xc)³)?

Which is approx 5.4 x 10⁴⁷ J / 7.2 x 10²⁴ m³

I.e. about 7.4 x 10²² J/m³ right?

Is that really smaller than the energy density typically involved in gamma ray production?

Am I missing something?

I haven't checked your figures, but that seems plausible. Although that's an extremely high energy density compared with everyday experience, the key point is that for a gravitational wave the energy is evenly distributed with a density of something like that order of magnitude. To produce gamma rays, you have to have interactions involving particles with energies in MeV (or temperatures of bulk matter with corresponding kinetic energy), but I don't believe that gravitational waves could impart local energies anywhere near on that scale.

A well-known process which generates gamma ray flashes is when an accumulation of material on the surface of a neutron star undergoes chain reaction fusion, and in general the temperature of a neutron star where there is a lot of infalling material can reach gamma-ray levels, although the luminosity of such events wouldn't be enough to explain the visibility at such a distance.

As far as I know, the apparent GRB would be be similar to that expected from a neutron star collision at that distance, but of course that is not consistent with the theoretical model which expects objects of the observed masses to be black holes.

 

[jhart]

... but I don't believe that gravitational waves could impart local energies anywhere near on that scale.

Fair enough! Thanks for your answers!

 

[newjerseyrunner]

I have a sort of out there hypothesis: What if one of the two objects that collided wasn't a black hole, there are other theoretical objects out there with the mass way beyond neutron stars. Cosmic strings are theoretically capable of producing both a gravitational wave and gamma ray bursts: http://news.nationalgeographic.com/...erse-cosmic-strings-gamma-ray-bursts-physics/

 

[Jonathan Scott]

The wave profile from the GW observation showed two compact objects. Even if cosmic strings exist (which I doubt), I don't think they would behave as compact objects, and their gravitational effect is not at all like that of a conventional object.

 

[newjerseyrunner]

I have another set of questions, is there any data on how old the two objects that collided were? And how would a massive, double lobed star like Eta Carinae die? I could imagine an instability in a star like that causing one lobe to collapse or explode, which would catastrophically destabilize the other lobe. I could easily imagine a star that big with a shape such as that quickly turning into a double-black hole pair that would very quickly merge. The black holes would exist for only a short period of time, but still produce a gravitational wave. During this time, there would still be a massive amount of material that has not fallen into the hole yet, that could easily produce a gamma ray burst, which would come after the gravity event due to having to get through all of that material.

EDIT: Bah! I thought about it for a bit, the events I described would explain the gravity wave and gamma ray, but would also require a burst of neutrinos a little before the gravity wave event during the actual collapse. Was there any detection of neutrino blasts?

 

[Jonathan Scott]

From the shape of the GW, we can determine the masses of the objects (basically by simulating various theoretical models and seeing which ones fit best). From the point at which the "ring down" phase started (where the objects started to merge), we can place limits on their sizes. From the amplitude of the wave, we can determine the approximate distance of the event. From the time difference between the two detectors and other phase information we can identify areas of the sky from which the signal probably originated. Everything up to that point was beautifully consistent with two black holes spiralling together and merging.

I don't think we have any other information about the GW event itself.

We then have the unexpected apparent GRB.

As mentioned at the start of this thread, one of the speculative theories to explain the GRB is that the pair of black holes merged inside a star, so you might find that paper interesting.

However, I think the answer to your specific question about double-lobed stars is outside the scope of this thread, and quite possibly too speculative for discussion within these forums unless you can find any suitable references.

 

[Jonathan Scott]

Was there any detection of neutrino blasts?

There was no detection of any neutrino emissions above normal background levels.

For general information about the event, try the Wikipedia page: https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves

 

[jhart]

I have another set of questions, is there any data on how old the two objects that collided were? And how would a massive, double lobed star like Eta Carinae die? I could imagine an instability in a star like that causing one lobe to collapse or explode, which would catastrophically destabilize the other lobe. I could easily imagine a star that big with a shape such as that quickly turning into a double-black hole pair that would very quickly merge. The black holes would exist for only a short period of time, but still produce a gravitational wave. During this time, there would still be a massive amount of material that has not fallen into the hole yet, that could easily produce a gamma ray burst, which would come after the gravity event due to having to get through all of that material.

EDIT: Bah! I thought about it for a bit, the events I described would explain the gravity wave and gamma ray, but would also require a burst of neutrinos a little before the gravity wave event during the actual collapse. Was there any detection of neutrino blasts?

The Eta Carinae system has a semi-major axis of 15.4 AU, why would they "very quickly merge"? Black Hole pairs will orbit teach other just like any other pair of objects with the same mass. There are factors, such as the Gravitational Waves themselves, that mean the time to merger will be different from that of two stars orbiting each other, but from what I have read there is no reason to suppose these two Black Holes could not have existed for 100s of millions of years before the merger.

The issue with the GRB comes from the proposal that a Black Hole pair of this size would normally be expected to form either as the result of a binary system of very large, low-metallicity stars which, independently, underwent supernova, or from two independently formed black holes which migrated together in a dense star cluster. See my earlier reference to Nature vol 531, according to that feature it is expected that, in the dense star cluster scenario, the Black Hole binary would be ejected from the cluster at high speed. Later in the same feature it says that any gas around at the formation of the Black Holes should have dispersed before they merge.

More data should help and hopefully we won't have to wait long. Once a 3rd observatory is up and running the area of the sky they need to search for GRBs will be reduced and if they see Black Hole mergers are normally not accompanied by GRBs then this one can presumably be put down to coincidence or some freak accident of formation like the merger inside a star concept.

On the other hand if every Black Hole merger is accompanied by a GRB then presumably they have to come up with new hypotheses.

 

[nikkkom]

Isn't that energy density in this case 3 x the mass of the Sun x c² / ((4/3) x π x (0.4xc)³)?

Which is approx 5.4 x 10⁴⁷ J / 7.2 x 10²⁴ m³

I.e. about 7.4 x 10²² J/m³ right?

Is that really smaller than the energy density typically involved in gamma ray production?

That's equivalent to almost a thousand tons of mass/energy equivalent crammed into that poor, tortured cubic meter of space. I find it not at all implausible there is an "insignificant" effect we miss or underestimate today which turns "small fraction" of that energy to EM radiation.

 

[jhart]

That's equivalent to almost a thousand tons of mass/energy equivalent crammed into that poor, tortured cubic meter of space. I find it not at all implausible there is an "insignificant" effect we miss or underestimate today which turns "small fraction" of that energy to EM radiation.

If it turns out that there is I'm going to say "called it" :) Especially if the mechanism is some kind of interaction with virtual particles.

 

[Jonathan Scott]

That's equivalent to almost a thousand tons of mass/energy equivalent crammed into that poor, tortured cubic meter of space. I find it not at all implausible there is an "insignificant" effect we miss or underestimate today which turns "small fraction" of that energy to EM radiation.

For comparison, I think that's something like 10^11 times smaller than the mass of the corresponding volume of neutron star material, which is definitely able to emit gamma rays.

 

[nikkkom]

Gamma rays in magnetar flares are emitted by "empty" space filled by magnetic fields, when those fields shift into a slightly less energetic configuration. However, those fields are 10-100 times denser than this too.

 

[jhart]

Gamma rays in magnetar flares are emitted by "empty" space filled by magnetic fields, when those fields shift into a slightly less energetic configuration. However, those fields are 10-100 times denser than this too.

Of course I'm estimating the "density" based on the 0.4 second time difference between the GW event and the GRB, so I'm thinking that this is a minimum energy density. To heap further unjustifiable speculation on: it could be that there was a delay between the GW energy being converted into mass and the mass being converted into photons which would make the volume in which that happened smaller.

 

[Jonathan Scott]

As far as I know, there is no known mechanism by which gravitational waves could give rise to electromagnetic waves in empty space. There is of course no definitive theory which covers both gravity and quantum effects, but one would not expect to get anywhere near quantum effects in this situation, as the energy density is many orders of magnitude lower than that involved for example in neutron stars.

It would be difficult to extract much energy from a gravitational wave into a solid object. As I said before, if the GRB is real, it seems it must have been created separately as part of some aspect of the merger event, not driven by the gravitational wave.

Black holes are not supposed to be able to maintain any significant magnetic fields (unlike neutron stars in general, and certainly unlike magnetars), so magnetic field effects are not expected to be relevant.

 

[newjerseyrunner]

I wonder if there is some way to pin down which event actually happened first. The gravity wave getting to us before the GRB doesn't necessarily mean that that's the order it happened in.

Black holes are not supposed to be able to maintain any significant magnetic fields (unlike neutron stars in general, and certainly unlike magnetars), so magnetic field effects are not expected to be relevant.

Don't spinning black holes produce some of the very powerful magnetic fields?

A large amount of plasma being held by a magnetic field of one of them, suddenly being released by the reconfiguration of the fields by the merger?

 

[Jonathan Scott]

I wonder if there is some way to pin down which event actually happened first. The gravity wave getting to us before the GRB doesn't necessarily mean that that's the order it happened in.

I don't know what you have in mind, but I can't think of any plausible scenario which could be associated with any other order, although as I've already said, it is more likely that both had a common cause rather than the GW in some way giving rise to the GRB.

Don't spinning black holes produce some of the very powerful magnetic fields?

No, that's neutron stars (especially magnetars).

There are ideas that a black hole could somehow retain a "frozen" magnetic field from a precursor body, but I don't think that's considered mainstream at present.

 

[newjerseyrunner]

I don't know what you have in mind, but I can't think of any plausible scenario which could be associated with any other order, although as I've already said, it is more likely that both had a common cause rather than the GW in some way giving rise to the GRB.

I was suggesting that they actually happen at or near the same time, but the light took longer to reach us that the gravity wave. Light is slowed by matter and gravity waves are not. A black hole forming would actually produce a gravity wave, then a very short time later, a neutrino blast, then several hours later a gamma ray blast, even though all three events happened at the same time. Obviously not the case here, just explaining why I don't think we should take the time delta to mean much right now.

No, that's neutron stars (especially magnetars).

There are ideas that a black hole could somehow retain a "frozen" magnetic field from a precursor body, but I don't think that's considered mainstream at present.

Interesting.

 

[jhart]

I was suggesting that they actually happen at or near the same time, but the light took longer to reach us that the gravity wave. Light is slowed by matter and gravity waves are not. A black hole forming would actually produce a gravity wave, then a very short time later, a neutrino blast, then several hours later a gamma ray blast, even though all three events happened at the same time. Obviously not the case here, just explaining why I don't think we should take the time delta to mean much right now.

Intergalactic space is so nearly devoid of matter that the gamma rays would probably arrive before the neutrinos. Neutrinos have mass (see https://en.wikipedia.org/wiki/Neutrino#Mass) current estimate is 0.32 eV. Photons are expected to be massless and the current upper bound set by experiments is 10^-18eV.

Over 750 million light years a Neutrino with a kinetic energy of 7 MeV should, if the 0.32 eV figure is correct, be slowed down by about 40 minutes.

In 1987 there was a famous supernova, SN 1987A, in the LMC about 168,000 Light Years away. A burst of neutrinos was observed, but they arrived essentially at the same time as the photons. It did allow physicists to set an upper limit to the neutrinos mass of 16eV.

I can't find anything useful on the refractive index of inter galactic space, but based on the number density of Hydrogen atoms, which is less than 1 per cubic meter, a photon could travel about 10,000 light years before interacting with a single Hydrogen Atom even assuming it interacts with every Hydrogen Atom it passes. Let's say that slows it down by an average of a millisecond, that works out at 75 seconds over 750 million light years. I think that is probably way too high, but it's enough for me to think that the photons should arrive before the neutrinos.