A Could gamma-ray bursts have an intragalactic origin?

[Line_112]

TL;DR Summary

This is indirectly evidenced by a map of the distribution of gamma-ray bursts in the night sky, made in the form of an elongated globe. And also the weakening of gamma radiation by the disk and the center of the Milky Way.

This is indirectly evidenced by a map of the distribution of gamma-ray bursts in the night sky, made in the form of an elongated globe. And also the weakening of gamma radiation by the disk and the center of the Milky Way, which leads to anisotropy in the possibilities of observing gamma-ray bursts. My line of reasoning is as follows:

1. Gamma radiation should be absorbed to some extent by dust and other components of the interstellar medium. As a result, with an extragalactic origin, fewer flares accessible for observation should come from the Milky Way, that is, anisotropy should appear on the map of their distribution, with a minimum in the plane and in the center of the Milky Way.

Since even the Earth's atmosphere absorbs gamma radiation (and much more effectively than visible radiation), being almost transparent to visible radiation, it is difficult to imagine that gas and dust clouds in the center and in the plane of the Milky Way, which are opaque to visible light, will be absolutely transparent to gamma radiation, especially since they essentially contain the same components as the atmosphere, only in a different ratio.

2. The sky map for gamma-ray bursts is given as a stretched globe, on which high latitudes are visible as if at an angle, although in fact everything in the sky is distributed equally. The size of the dots on the map is the same everywhere, and in theory it should be smaller at high latitudes due to the visual flattening of the dots, the plane of which is at an angle to us. This creates the illusion of greater density of dots at high latitudes. In addition, the equator is greatly stretched horizontally, which means that in the case of a uniform distribution of bursts in the sky, there should be a lower concentration of points in the equatorial zone on the map. Just as if we were to stretch a sheet of rubber to the right and left at the same time, the central part would stretch more strongly and the amount of rubber per unit area there would be less than closer to the edges. If we mentally compress the equatorial part of the map so that we get a round globe (as it should be on a spherical sky), then the concentration of points in the equatorial zone will increase. If this logic is correct, then this can also be an explanation for the apparent relative uniformity of the distribution of gamma-ray bursts, and in fact their concentration is towards in plane and in the center of the Milky Way.

In addition, even if we consider the distribution of bursts to be completely uniform, this will not yet be proof of the extragalactic origin of the sources. They can just as easily occur within a sphere in which the concentration of stars and matter is roughly the same (within a radius of half the thickness of the Milky Way's thin disk). As for cases of association with galaxies, I don't know how many there have been of gamma-ray bursts (perhaps few).

 

[phyzguy]

What's your point? It's well known that gamma ray bursts are extra-galactic. Look at the Wikipedia page, which says,

"In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic events occurring in distant galaxies which represent the brightest and most powerful class of explosion in the universe."

 

[Cerenkov]

Speaking as a rank amateur, it seems to me that if we posit the existence a sphere of stars within the Milky way galaxy, as described by Line_112, to observe the distribution of GRB's that we do, then the Earth must lie at or very near the centre of this sphere.

But why would there be such a sphere of stars centred on a point 25, 800 light years from the centre of the galaxy?

https://newatlas.com/space/earth-galactic-center-speed-vera/

To my limited knowledge there is a roughly spherical arrangement of stars centred on the core of the Milky Way. Which, I believe, is explained by them orbiting the galaxy's centre of mass.

https://en.wikipedia.org/wiki/Galactic_halo

But a sphere of stars displaced from that centre of mass by 25,800 light years runs counters to this.

And wouldn't the common motion of stars around the galactic centre quickly disperse this sphere?

And if such a sphere existed, why would we be at or very near to it's centre?

Surely these questions, if they are valid, need answering?


Thank you,

Cerenkov.

 

[Line_112]

But why would there be such a sphere of stars centred on a point 25, 800 light years from the centre of the galaxy?

I didn't mean a special sphere. It's just that in the thin disk of the Milky Way the concentration of stars is approximately the same, with some increase in the spiral arms and decrease between them. And the Sun is located almost in the middle of the thickness of this layer. Therefore, if we mentally outline a sphere around the Sun with a radius of half the disk thickness, then the concentration of stars in it will be approximately the same everywhere, and therefore the number of gamma-ray bursts coming from all sides can also be approximately the same, without concentrating in any one direction. That is, there will be an effect similar to cosmological.

 

[Cerenkov]

That's fine Line_112, but that doesn't really answer my questions.


How does such a sphere remain intact and keep it's spherical shape when it is subject to the sideways motion of galactic rotation? Because it is displaced from the galaxy's centre of mass by 25,800 light years?

I cited the Halo stars as one example of a roughly spherical structure centred on the galaxy's centre of mass. More or less the same happens with globular clusters. They generally orbit the Milky Way's centre of mass, which is located at the core. What you are positing flies in the face of these examples, making your sphere very special indeed.

It would be special because your sphere could not hold together for very long in the face of the shearing forces of galactic rotation. Which implies that if we do find ourselves at the centre of such a sphere, then we would do so at at very special moment in galactic history. The moment when the Earth temporarily occupies the centre of a temporary sphere of gamma ray emitting stars before that sphere is disrupted by the tidal forces of galactic rotation.

You only have to look at Vera Rubin's ground-breaking work on the rotation rates of other galaxies to understand that structures like this gamma-ray emitting sphere of yours couldn't form (due to rotational forces) and couldn't persist for the very same reason.

You invoke this sphere to explain the distribution of gamma ray sources in the celestial sphere, but in doing so you generate the problem of explaining it's origin and continued existence.

So, can you please explain how, in defiance of galactic rotation, this sphere could first form?

Can you further explain, how it could persist and resist the rotational forces acting upon it?

Lastly, can you explain why it is we find ourselves at the centre of such a structure?

Without adequate explanations for these things your sphere seems to be no more than an ad hoc explanation of the distribution of gamma ray sources in the celestial sphere.


Thank you,


Cerenkov.

 

[Ibix]

I think his idea is simply that all GRBs that we detect come from inside this spherical region. GRBs may occur outside it but are not detected due to something or other.

 

[Cerenkov]

Then isn't it incumbent upon Line_112 to give a reason for the non-detection of GRB's from outside this spherical region?

 

[Ibix]

Then isn't it incumbent upon Line_112 to give a reason for the non-detection of GRB's from outside this spherical region?

I think it's supposed to be something to do with absorption by the interstellar medium. No numbers provided, though.

 

[Cerenkov]

Ok then.


But since you've taken an interest in this thread Ibix, could I please ask you to check the logic of what I'm about to say? It's about Line-112's map of the distribution of gamma ray sources and what that distribution implies about the position of the Earth relative to the centre of the Milky Way.

I believe that back in the 1920's Harlow Shapley plotted the positions of globular clusters on the celestial sphere and found that a majority were clustered in one part of the sky. From that finding he deduced that their distribution could not be centred upon the Earth. If it were then they would be spread more evenly across the sky.

From this deduction Shapley was able to demonstrate that the globular clusters were orbiting the centre of the Milky Way's mass, which is located at it's core. He was further able to show, from their distribution, that the Earth could not be located at the centre of the galaxy, at or near it's centre of mass. He was also able to calculate that the Earth was displaced tens of thousands of light years from the galactic centre.

If all of that holds together, then applying that logic in reverse, if intragalactic GRB's were spread evenly throughout the disk of the Milky Way, we would observe a greater concentration of them in the plane of the galaxy. We would also see more of them clustered towards the galactic centre and fewer of them in the anti-centre direction. There would be more in Sagittarius and fewer in Perseus.

But since Line-112's GRB map shows no concentration along the galactic plane and no clustering in Sagittarius and diminishment in Perseus, only two possible conclusions remain.

1. The GRB's are evenly spread across the sky because they are located far outside the Milky Way.

2. The GRB's are evenly spread across the sky because they are located in a sphere centred upon us.

But as I have already pointed out, any spherical arrangement of GRB's centred upon us would be quickly disrupted by the tidal forces of galactic rotation. Which leaves the first possibility as the most likely answer.

Furthermore, Line_112 has yet to offer any viable explanation as to how such a spherical structure of stars could evolve in a rotating galaxy, how such a structure could persist over time and why we happen to find ourselves at or very near the centre of it right now.



If you could check my facts and my logic I would appreciate it, Ibix.


Thank you,


Cerenkov.

 

[Line_112]

What's your point? It's well known that gamma ray bursts are extra-galactic.

Quote from: https://www.astronet.ru/db/msg/1191481
This is one of the most serious sites on astronomy.

"Based on the type of angular distribution of gamma-ray sources on the celestial sphere and the nature of the statistical dependence that describes the growth in the number of burst observations during the transition from strong (near) bursts to weaker (distant) ones, it was established that gamma-ray sources are galactic objects. Their distribution in space is limited by the height above the galactic plane by the average distance z ~1 kpc and apparently resembles the distribution of the intermediate spherical subsystem of the Galaxy. The total number of gamma-rays occurring in the Galaxy per year can reach ~104."

 

[Cerenkov]

Does the Astronet source say anything about...


A.
How such a spherical subsystem could have originated?

B.
How it could have persisted?

C.
Why we seem to find ourselves at it's centre?


Thank you,


Cerenkov.

 

[Line_112]

I think it's supposed to be something to do with absorption by the interstellar medium. No numbers provided, though.

This was just one hypothesis, based on the fact that they emit little energy, and therefore cannot be detected from afar. But it is no less likely that they are recorded from the entire galaxy, so there is a concentration towards the plane of the Milky Way, despite the fact that there is stronger absorption there.

 

[Line_112]

Does the Astronet source say anything about...

No, it simply indicates the distances at which we can observe them.

 

[Cerenkov]

This was just one hypothesis, based on the fact that they emit little energy, and therefore cannot be detected from afar. But it is no less likely that they are recorded from the entire galaxy, so there is a concentration towards the plane of the Milky Way, despite the fact that there is stronger absorption there.

I see no concentration of GRB sources along the plane of the galaxy in your map, Line_112.

Could you please show me where this concentration is?

 

[Cerenkov]

No, it simply indicates the distances at which we can observe them.

Then if your source says nothing that can answer my questions Line_112, could you please answer them?

Here they are again.


A.
How could such a spherical subsystem have originated?

B.
How it could have persisted?

C.
Why we seem to find ourselves at it's centre?


Thank you,


Cerenkov.

 

[Line_112]

I see no concentration of GRB sources along the plane of the galaxy in your map, Line_112.

So I wrote in the thread that this is an illusion of uniformity, citing two arguments in favor of this: the obvious significant absorption of radiation in the area of the Milky Way plane (without which the concentration of points at the galactic equator should have been much higher) and the stretched map in the area of the galactic equator, while we are talking about the distribution of flares over the celestial sphere. On the map, there are 180 pixels between the poles, and 360 along the equator. But the celestial sphere will have 360 everywhere. It turns out that with a uniform distribution of points of the same size (and it is the same there), the number of gamma-ray flares along the equator was 2 times greater than between the poles, namely, the plane of the Milky Way passes along the equator and the center of the galaxy is located.

 

[Cerenkov]

Then I don't understand the point of you attaching your map in support of your claim. It shows us nothing of what you claim is there because what you claim we are seeing is an illusion.


As Ibix has also pointed out, you have cited no values about absorption by the interstellar medium. Therefore your claims about it and what you claim it does to our observations of GRBs cannot be checked or tested by us.


Also, could you please apply yourself to answering my three questions.

I stand by my contention that, for the reasons I gave, this spherical subsystem could not have formed and could not have persisted.

I believe that it now falls to you to address this issue and to also explain why we on Earth happen to find ourselves at or very near the centre of such a structure.



Thank you,

Cerenkov.

 

[Bandersnatch]

1. Gamma radiation should be absorbed to some extent by dust and other components of the interstellar medium.

But to what extent? Attenuation by 10 or even 90% doesn't preclude detection. It's not all or nothing. You can't just hand-wave it and call it a day.
Rather than coming up with fanciful arguments of dubious value (no, the ISM is very much not like the atmosphere in composition or attenuation properties) check the literature. Read up on methodology of gamma ray observations, maybe try and find extinction maps for high energy astronomy. You want numbers and understanding, not pictures and guesses.

2. The sky map for gamma-ray bursts is given as a stretched globe,

This is your main argument, and it's based on not understanding how sky map projections work.
The map is an equal-area projection. Probably Hammer. Equal-area projections are chosen specifically because they don't distort relative areas. They only distorts angles and orientations (shapes). That's why they're good for density maps. The density of signals is >not< distorted.
The argument about how you think you can stretch the map to fit a sphere is neither here nor there. If in doubt, take it up with the maths.
And the dots in the attachment are not distorted at all, because they are markers of point-like sources, and not any sort of representation of the areal extent of the signal. Their shape and size is not a part of the map. If they were, they'd still have the same sizes, because it's an equal-area projection.

On the map, there are 180 pixels between the poles, and 360 along the equator. But the celestial sphere will have 360 everywhere

No! The N-S is half the length of E-W, because a meridian on a sphere is half the length of its equator! Figuratively, the sphere is split along a meridian and unwrapped. When you go 'east' beyond the edge of the map, you end up on the 'western' edge. But when you go 'north' past the edge, you come back from the north.
These projections are also used for the globe of the Earth, where you can see this clearly. You can't circumnavigate the globe by going from one pole to the other, once.

As a general rule, if a source provides you with a statement - like the one that the data is isotropic - and illustrates it with a figure you're unsure you understand, then the first instinct should be to verify your understanding - not to doubt the underlying claim.


The debate over the origin of the GRBs is now some three decades old. There's plenty of peer-reviewed publications to refer to.
References to random websites are not acceptable on this forum. If you find an argument on a website that you want to bring up, track down its source publication.

 

[Cerenkov]

Line_112,

I have two things to say to you, which I will do across two separate posts.

Below is a contour map of weak gravitational lensing, taken from the Wiki page on that subject.

https://en.wikipedia.org/wiki/Weak_gravitational_lensing

If I claimed that there was a spherical structure in this image, caused by a gravitational lensing phenomena that I have cited no values for, would you be persuaded by my claim?

And would you be further persuaded if I also claimed that this map is actually an illusion, with the spherical structure there, but unable to be seen by us?

?

 

[Cerenkov]

Have you heard of Occam's Razor, Line_112?

https://en.wikipedia.org/wiki/Occam's_razor

I would suggest that your argument is disfavoured by the use of the Razor.


Thank you,

Cerenkov.

 

[Line_112]

This is your main argument, and it's based on not understanding how sky map projections work.

But I still don't understand how you can unfold the globe without distorting the proportions. Usually they show two hemispheres separately, then both have a rounded shape. And the map of gamma-ray burst distribution doesn't remind me of a geographic map at all. In order to lay out the entire surface of the sphere in the form of a map, you need to tear it apart, turning it into a piece of canvas. Then the proportions will be more or less maintained. But here we see a contraction towards the poles. Once I tore ball apart and got a two-headed torn structure in the form of a canvas. There is +-, but the proportions more or less corresponded to what was on the surface of the sphere.
Plus, high latitudes "look" not at us, and the dots, as you right wrote, are simply superimposed on this matrix and have the same sizes everywhere. This means that near the poles, in the case of a uniform distribution of gamma-ray bursts on the celestial sphere, in theory, there should be a higher visual concentration of points than near the equator, but we do not see this, which logically should mean anisotropy (I will not confirm this, but this is how it seems to me).

In any case, such puzzles are very entertaining, especially when it comes to things of an astronomical scale. Moreover, gamma-ray bursts are among the main astronomical threats, but if it turns out that they have an intragalactic nature, then the danger will be greatly exaggerated.

 

[phyzguy]

Here is an equal area projection map of the Earth, similar to the GRB map. Areas are not distorted, but of course shapes are. It's not possible to map a spherical globe on to a flat sheet of paper without distorting something. But these equal area projections have the advantage that area is preserved. That's why the GRB map shows a uniform density.

 

[Line_112]

Here is an equal area projection map of the Earth, similar to the GRB map. Areas are not distorted, but of course shapes are.

Okay, so I was wrong with that argument. But remain two more - the highly probable absorption of gamma radiation in the plane of the disk and the fact that the dots on the gamma-ray burst map are not inserted correctly. Since these dots (spots) do not geometrically belong to the map itself (unlike the continents on the sample of the world map you presented) and are the same size everywhere, a false sense of their density increasing in the direction of the poles is created, as well as to the right and left in the temperate latitudes, where the surface of the globe is also located at a strong angle relative to us.

 

[Cerenkov]

Okay, so I was wrong with that argument. But remain two more - the highly probable absorption of gamma radiation in the plane of the disk and the fact that the dots on the gamma-ray burst map are not inserted correctly. Since these dots (spots) do not geometrically belong to the map itself (unlike the continents on the sample of the world map you presented) and are the same size everywhere, a false sense of their density increasing in the direction of the poles is created, as well as to the right and left in the temperate latitudes, where the surface of the globe is also located at a strong angle relative to us.

There are two problems with your reply, Line_112.

The first is that you still haven't cited any values for gamma ray absorption by the interstellar medium. Until you do so or link to a reputable source which does, we have no way of testing and checking the validity of your claim that GRB's are of intragalactic origin. "Highly probable" is not sufficient.

The second problem is that if you now admit that the map does show a uniform density of GRB sources, then there are only two options available to you. Either this uniformity is due to the GRBs lying far outside our galaxy or it is due to there being a spherical subsystem of GRBs within the Milky Way, with the Earth lying at or very near it's centre.

If you opt for the second then it still falls to you to answer my three questions about this spherical subsystem. It is all very well to claim something in this forum, but you should also be prepared to defend what you claim when questioned about it. That is how this forum works. I therefore politely ask you once again to defend your claim about this intragalactic sphere of GRBs by answering my questions.


Thank you,

Cerenkov.

 

[Line_112]

The first is that you still haven't cited any values for gamma ray absorption by the interstellar medium.

As for absorption, I searched a lot and found nothing. However, it is possible to roughly compare the amount of gas (excluding hydrogen) and dust in the path of gamma rays in the plane of the Milky Way with those in the Earth's atmosphere. The Earth's atmosphere is transparent to solar rays, but absorbs short-wavelength ones well. The disk of the Milky Way is opaque, which means that it contains more light-absorbing matter. Even if hydrogen is transparent, it means that the radiation is absorbed by other components, since nothing is visible through the disk of the Milky Way to the other side. Scientists have all the information necessary to clarify this issue. For example, if much less gamma radiation comes from galaxies located beyond the plane of the Milky Way than from those located in another part of the celestial sphere (as is observed for visible light), then the absorption is significant.

The second problem is that if you now admit that the map does show a uniform density of GRB sources, then there are only two options available to you.

I have admitted the fallacy of only one of my two arguments concerning the map. The other is that a dot of the same size on this map at the equator will cover a smaller area of the sphere's surface than in other parts of this globe. Another way of thinking (but with approximately the same meaning) is that the number of dots per unit area of the projection of this map visible to us, given their equal size and uniform distribution of gamma-ray bursts across the celestial sphere, will be greater near the poles and in the temperate latitudes to the right and left of the map, compared to the equator. This argument is good because even if the map (more precisely, the map matrix) is mathematically correct, it still remains valid.

 

[Cerenkov]

As for absorption, I searched a lot and found nothing. However, it is possible to roughly compare the amount of gas (excluding hydrogen) and dust in the path of gamma rays in the plane of the Milky Way with those in the Earth's atmosphere. The Earth's atmosphere is transparent to solar rays, but absorbs short-wavelength ones well. The disk of the Milky Way is opaque, which means that it contains more light-absorbing matter. Even if hydrogen is transparent, it means that the radiation is absorbed by other components, since nothing is visible through the disk of the Milky Way to the other side. Scientists have all the information necessary to clarify this issue. For example, if much less gamma radiation comes from galaxies located beyond the plane of the Milky Way than from those located in another part of the celestial sphere (as is observed for visible light), then the absorption is significant.

Then, if you found nothing to support your claim and if you rely on others to clarify the issue, your claim (that absorption is sufficient) remains unsupported by you personally.

I therefore find myself unpersuaded by your argument and the lack of evidence to support it.

Your say so and your personal belief in the absorbing powers of ISM do not make a convincing argument.

I have admitted the fallacy of only one of my two arguments concerning the map. The other is that a dot of the same size on this map at the equator will cover a smaller area of the sphere's surface than in other parts of this globe. Another way of thinking (but with approximately the same meaning) is that the number of dots per unit area of the projection of this map visible to us, given their equal size and uniform distribution of gamma-ray bursts across the celestial sphere, will be greater near the poles and in the temperate latitudes to the right and left of the map, compared to the equator. This argument is good because even if the map (more precisely, the map matrix) is mathematically correct, it still remains valid.

Does this mean that you reject the first of the two possible options? That the uniform distribution of the GRBs across the map points to their extragalactic origin?

If so, then do you still hold to the second option? That they are intragalactic and there is a spherical subsystem of stars within the disk of the Milky Way, with the Earth at or near it's centre?

If so, then it falls to you to answer my three questions about the improbability of the existence of such a sphere. This will be my last time of asking Line_112.

Please answer them or at least inform me that you will not answer them.



Thank you,


Cerenkov.

 

[Line_112]

Does this mean that you reject the first of the two possible options? That the uniform distribution of the GRBs across the map points to their extragalactic origin?

I haven't studied this issue enough to have a clear opinion. It seems to me that both the extra- and intra-galactic variants are possible. But scientists should in any case check the absorption capacity of the Milky Way disk (if it hasn't been checked yet) to give preference to one of these variants.

 

[Cerenkov]

I haven't studied this issue enough to have a clear opinion. It seems to me that both the extra- and intra-galactic variants are possible. But scientists should in any case check the absorption capacity of the Milky Way disk (if it hasn't been checked yet) to give preference to one of these variants.

I see.


The map you posted does give preference to the extragalactic origin of GRBs because there is no clustering of them on the plane of the galaxy, which would have been the case if they were intragalactic.

But you clearly cannot bring yourself to admit or accept that.

My three questions (which are based upon the science of galactic rotation) also give preference because they rule out the possibility of there being a spherical subsystem of intragalactic GRBs.

But you clearly cannot bring yourself to address them.

I therefore wonder, if, when the absorption capacity of the Milky Way disk is found to rule out the possibility of intragalactic GRBs, you would dismiss that finding and continue in your beliefs?

Beliefs for which you have presented no real evidence, which are not supported by the available evidence and which do not stand up under questioning.


Goodbye, Line_112.

 

[phyzguy]

The other is that a dot of the same size on this map at the equator will cover a smaller area of the sphere's surface than in other parts of this globe.

Why do you think this? It is an equal area projection. So dots of the same area will cover the same area of the sphere.

 

[phyzguy]

So, @Line_112 , are you just going to ignore the many redshift measurements of GRBs that have been made? These measurements firmly place them at cosmological distances.

https://www.frontiersin.org/journal...nces/articles/10.3389/fspas.2023.1124317/full