Green Baron

Imaging a black hole - the EHT

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34 minutes ago, Cassel said:

If even the photons are moving away from us, how do we see them?

We don't.

It's not photons we're talking about all this stuff, it's the gas that emits them.  There's a ring of very, very hot gas, orbiting the black hole at very, very high speed.  Because it's very hot, it's very bright, and radiates photons in all directions.  Obviously, we only see the photons that are emitted in our direction, same as anything else.

For the gas that's moving towards us, the photons it emits in our direction are Doppler-shifted up and are therefore brighter.  For the gas that's moving away from us, the photons it emits in our direction are Doppler-shifted down and are therefore less bright.

34 minutes ago, Cassel said:

I hope you're right.

Well, there's also the fact that this black hole has been around for a pretty long time, so if it were gonna be a problem, we wouldn't be here in the first place.  ;)

34 minutes ago, Cassel said:

after all this ring is orbiting around the black hole

Yes, but,

34 minutes ago, Cassel said:

so the bottom is the closest to us, the top farthest, and the right and left sides move towards us or on the contrary, move away, depending on which direction the ring rotates. Either the picture is rotated 90 degrees or something does not fit.

I'm not totally sure that's the case.  I don't know anything about the specific orientation of the disk, nor is its appearance necessarily as simple as you'd think due to gravitational lensing distorting the heck out of things.

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10 minutes ago, Snark said:

We don't.

It's not photons we're talking about all this stuff, it's the gas that emits them.  There's a ring of very, very hot gas, orbiting the black hole at very, very high speed.  Because it's very hot, it's very bright, and radiates photons in all directions.  Obviously, we only see the photons that are emitted in our direction, same as anything else.

For the gas that's moving towards us, the photons it emits in our direction are Doppler-shifted up and are therefore brighter.  For the gas that's moving away from us, the photons it emits in our direction are Doppler-shifted down and are therefore less bright.
 

Oops, I've edited my previous post and added a bit about it.
 

10 minutes ago, Snark said:

Well, there's also the fact that this black hole has been around for a pretty long time, so if it were gonna be a problem, we wouldn't be here in the first place.  ;)

Apparently you are right, but the distance and angle, what if a small change of angle is enough for the wave to hit our solar system?

10 minutes ago, Snark said:

Yes, but,

I'm not totally sure that's the case.  I don't know anything about the specific orientation of the disk, nor is its appearance necessarily as simple as you'd think due to gravitational lensing distorting the heck out of things.

It still reminds me more of a synestia that will create the entire solar system all at once, once it cools down.

pjDncuC.png

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8 hours ago, Green Baron said:

Edit: I would interpret this as an evidence that the authors of these articles aren't cleverer than ourselves
:cool:

 

Overview on the EHT homepage:

https://eventhorizontelescope.org/

and special issue of the ApJ Letters, with summary:

https://iopscience.iop.org/journal/2041-8205/page/Focus_on_EHT

Scroll down for the links to the detail papers, which are pretty comprehensible.

--------------

I read that the 2018 observation campaign fell victim to adverse weather conditions, 2019 had technical problems. Hopes are on next year's campaign with added telescopes and probably refined methods of analysis.

 

You don't have to be super clever to work in the field. Competent and clever at best. Some people on these forums may well have more going on upstairs for sure, in my opinion of course. Not sure about you baron but my eyes are physically hurting reading round this, its been a marathon:wacko:

 I have a zillion questions from what i have seen and read so far. It is going to take time to comprehend and formulate intelligent questions from what data we have and even more time to answer those questions correctly.

Any step forward is progress, and this is definately progress. We have our first images of black holes. I never thought i would see one. Maybe only in mathematics as Einstein did. 

 

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30 minutes ago, Starstruck69 said:

 

You don't have to be super clever to work in the field....

Sorry for my being unclear. I was not referring to the authors of the EHT collaboration and the papers they produced, that is outstanding work. It was @p1t1o's remark about second hand sources, that on every site he read the description/explanation of what was presented was slightly different. With that, so i assumed, he meant pop science articles and social media sites commenting on the news. And, i may say, i have some experience with journalists :-) They can't know everything about everything, just like us, they read and try to understand, and sometimes they are good, sometimes we are better in that. And i wasn't 100% serious.

The direct outcome of all this is actually pretty simple: After more than 20 years of preparation the EHT has achieved an unprecedented angular resolution, with newest technology available since recently for data collection as well as computing power (it was the first time since years that i heard someone mentioning Moore's law :-)). The effort has strengthened and confirmed again the predictions of General Relativity.

More can be expected soon(tm).

Schwartzchild and Eensteen can be happy.

Edited by Green Baron

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5 minutes ago, Green Baron said:

Sorry for my being unclear. I was not referring to the authors of the EHT collaboration and the papers they produced, that is outstanding work. It was @p1t1o's remark about second hand sources, that on every site he read the description/explanation of what was presented was slightly different. With that, so i assumed, he meant pop science articles and social media sites commenting on the news. And, i may say, i have some experience with journalists :-) They can't know everything about everything, just like us, they read and try to understand, and sometimes they are good, sometimes we are better in that. And i wasn't 100% serious.

The direct outcome of all this is actually pretty simple: After more than 20 years of preparation the EHT has achieved an unprecedented angular resolution, with newest technology available since recently for data collection as well as computing power (it was the first time since years that i heard someone mentioning Moore's law :-)). The effort has strengthened and confirmed again the predictions of General Relativity.

More can be expected soon(tm).

Schwartzchild and Eensteen can be happy.

These are great times baron, i apologise if i misunderstood your intent i am well, very tired. 

In due course i am sure we will sort out the wheat from the chaff.

Hats off to everybody involved with EHT guys it is a fantastic achievement and i am sure there will be a lot more to come from them. 

And well Albert Einstein, genius a beautiful mind. Doubt him at your peril..

Baron this has been a great thread some great info/links here. Good job, have you slept yet? You seem to have been very busy:confused:

 

 

 

 

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1 hour ago, Cassel said:

edit:
Although I probably do not understand it correctly. If the magnetic waves of the black hole are directed towards us, then this picture does not make any sense at all. What we should see is the ring of exactly the same brightness like

There are two different things here:

The magnetic field lines do not directly create the image. Magnetic fields develop in the accretion disc of plasma (charged particles) from differential rotation speed being faster on the inner and slower on the outer part. They are twisted by the rotating black hole (through mechanisms i don't completely understand without diving deeper into it) in a form that they accelerate material from the disc towards the poles and from there out into space. The orientation of this jet, assuming that it is rectangular to the disc, enables them to calculate the disc's orientation.

The jet has been observed, and its orientation determined, long ago. The picture now obtained by the EHT correlates very well with that older observation, enabling them to give an estimate of an angle of the disk in respect to the line of sight from here to there (the 17° towards the north-northeast mentioned above).

 

The image, on the other hand, is obtained from material from the rotating disk, as explained above.

 

So, two separate things, magnetic fields - observation of radio waves.

 

11 minutes ago, Starstruck69 said:

Baron this has been a great thread some great info/links here. Good job, have you slept yet? You seem to have been very busy:confused:

 

Thanks for asking :-)

I am UTC (Canaries).

I spent some time (~3 hours) reading the articles and assimilating what was possible, but in principle and foremost i am at the pc right now because i am self teaching me graphics programming (and fighting against some problems), so i have been on the pc most of the time. OT ... sorry.

Edited by Green Baron
ENE NNE ne ?

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1 hour ago, Green Baron said:

There are two different things here:

The magnetic field lines do not directly create the image. Magnetic fields develop in the accretion disc of plasma (charged particles) from differential rotation speed being faster on the inner and slower on the outer part. They are twisted by the rotating black hole (through mechanisms i don't completely understand without diving deeper into it) in a form that they accelerate material from the disc towards the poles and from there out into space. The orientation of this jet, assuming that it is rectangular to the disc, enables them to calculate the disc's orientation.

The jet has been observed, and its orientation determined, long ago. The picture now obtained by the EHT correlates very well with that older observation, enabling them to give an estimate of an angle of the disk in respect to the line of sight from here to there (the 17° towards the north-northeast mentioned above).

 

The image, on the other hand, is obtained from material from the rotating disk, as explained above.

 

So, two separate things, magnetic fields - observation of radio waves.

 

Thanks for asking :-)

I am UTC (Canaries).

I spent some time (~3 hours) reading the articles and assimilating what was possible, but in principle and foremost i am at the pc right now because i am self teaching me graphics programming (and fighting against some problems), so i have been on the pc most of the time. OT ... sorry.

Theres no need to apologise baron.

 Out of interest how did your assimilations come out so far?

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3 hours ago, Cassel said:

Oops, I've edited my previous post and added a bit about it.

Your edit to your previous post seems to imply that you're assuming that, 1. we're looking at the accretion disk along a direction that's perfectly parallel to the rotation axis, and 2. that the image is a "normal" one like we're used to looking at for things that don't bend space.

Do you have a basis for assuming #1?  If the accretion disk has any orientation at all other than perfectly facing us, then there would be a definite Doppler component.  Also, there is significant gravitational lensing since it's a black hole, and I'm not totally clear on the implications for how the various bits of the accretion disk would therefore appear in what we see.

I haven't read through all the papers and announcements in detail-- just, this video seemed to be by someone who had a pretty good idea what he was talking about, and he said it was due to Doppler effect, and that's entirely plausible to me.  Do you have some reason to think otherwise?  What are you basing your hypotheses on, here?  (i.e. citation?)

3 hours ago, Cassel said:

but the distance and angle, what if a small change of angle is enough for the wave to hit our solar system?

Again, I think the chance of any problem is so infinitesimal that it's effectively zero.

Either it's spraying stuff out in a wide cone, or else it's tightly focused.

If it's in a wide cone, then it'll be so attenuated by the time it gets to us that it'll be so faint as to be undetectable.

Even if you hypothesize that it is somehow a needle-sharp focus, like a laser beam across space... then that would mean the chances of hitting us would be practically zero.  Again:  this thing is far away from us.  The apparent angular size of that black disk in the picture is under 40 micro arc seconds of sky, i.e. smaller than the apparent size of a one-centimeter object 50,000 km away.  And it's big, much bigger than Earth's orbit around the sun.  Using that same image:

m87_black_hole_size_comparison.png

So the chance of something from that black hole hitting us-- even if evil aliens were deliberately trying to aim it at us-- would be like trying to hit a target smaller than a millimeter at a distance farther than the Moon is from Earth.  In short:  Not gonna happen at random.  ;)

Remember that the universe is full of hundreds of billions of galaxies, and an awful lot of them have big black holes at the center, and it's just a thing.  And we've been around a few billion years without that particular problem.  On the list of things we need to worry about, that's pretty far down the list.

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Obviously, the rotation axis is perpendicular to the line of sight and is almost perfectly horizontal on the released image. The bottom part is moving towards us, and the upper part is moving away - it can clearly be seen from the brightness distribution. The disc (which should look like a vertical line from our perspective) is warped into a circle by the black hole’s gravity.

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50 minutes ago, Snark said:

Your edit to your previous post seems to imply that you're assuming that, 1. we're looking at the accretion disk along a direction that's perfectly parallel to the rotation axis, and 2. that the image is a "normal" one like we're used to looking at for things that don't bend space.

1. Well I read about jets "are emitted as an extended beam along the axis of rotation"  https://en.wikipedia.org/wiki/Astrophysical_jet

50 minutes ago, Snark said:

Do you have a basis for assuming #1? 

Spoiler

OaPmhaM.jpg

50 minutes ago, Snark said:

If the accretion disk has any orientation at all other than perfectly facing us, then there would be a definite Doppler component.  Also, there is significant gravitational lensing since it's a black hole, and I'm not totally clear on the implications for how the various bits of the accretion disk would therefore appear in what we see.

If we're already playing a game of evidence, how was it proven? From what you see on picture, there is no event horizon in the picture, so it's not a black hole.
 

50 minutes ago, Snark said:

I haven't read through all the papers and announcements in detail-- just, this video seemed to be by someone who had a pretty good idea what he was talking about, and he said it was due to Doppler effect, and that's entirely plausible to me.  Do you have some reason to think otherwise?  What are you basing your hypotheses on, here?  (i.e. citation?)

Error in synchronizing telescopes that were at different heights, not the Doppler effect.
 

50 minutes ago, Snark said:

Again, I think the chance of any problem is so infinitesimal that it's effectively zero.

Either it's spraying stuff out in a wide code, or else it's tightly focused.

If it's in a wide code, then it'll be so attenuated by the time it gets to us that it'll be so faint as to be undetectable.

Even if you hypothesize that it is somehow a needle-sharp focus, like a laser beam across space... then that would mean the chances of hitting us would be practically zero.  Again:  this thing is far away from us.  The apparent angular size of that black disk in the picture is under 40 micro arc seconds of sky, i.e. smaller than the apparent size of a one-centimeter object 50,000 km away.  And it's big, much bigger than Earth's orbit around the sun.  Using that same image:

 

So the chance of something from that black hole hitting us-- even if evil aliens were deliberately trying to aim it at us-- would be like trying to hit a target smaller than a millimeter at a distance farther than the Moon is from Earth.  In short:  Not gonna happen at random.  ;)

Randomly maybe not, but ... unfortunately, I am not allowed to write about it.
 

50 minutes ago, Snark said:

Remember that the universe is full of hundreds of billions of galaxies, and an awful lot of them have big black holes at the center, and it's just a thing.  And we've been around a few billion years without that particular problem.  On the list of things we need to worry about, that's pretty far down the list.

If you think that we are in some respect exceptional to such an extent that we can not be threatened by a sudden and new threat to our planet, that's cool. I do not think so, that is, we are exceptional, but that does not mean that there are no new and sudden threats waiting for us.

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16 minutes ago, sh1pman said:

... the rotation axis is perpendicular to the line of sight ....

At these speeds, combining pure euclidian geometry and spacetime effects, even a slight angle causes magnitudes of difference in signal strength. The whole thing is actually rotating almost face-on, with a deviation of 17°. There is an image showing the orientation of the arm of the jet aiming towards us. The opposite is invisible.

M87_jet.jpg

(turn it to the left ~90° to align with the EHT image)

The bright point is the galaxy M87.

Space is mindbogglingly huge.

Edited by Green Baron

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15 minutes ago, sh1pman said:

Obviously, the rotation axis is perpendicular to the line of sight and is almost perfectly horizontal on the released image. The bottom part is moving towards us, and the upper part is moving away - it can clearly be seen from the brightness distribution. The disc (which should look like a vertical line from our perspective) is warped into a circle by the black hole’s gravity.

In that case, the brightness of the ring should be the same, because the ring is circling around the black hole and in no point moves away from us or does not moves towards us.

Edited by Cassel

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54 minutes ago, Cassel said:

Well I read about jets "are emitted as an extended beam along the axis of rotation"

Okay, yes, I get that.  But that's a general description of a general phenomenon.  I was just curious where you were getting the information upon which you were basing the assertion about this particular black hole's orientation.

54 minutes ago, Cassel said:

If we're already playing a game of evidence, how was it proven?

Dunno.  I'd suggest going and reading the various papers and what-not involved with the observation, which I haven't done.  I'm not particularly asserting things one way or the other-- merely echoing what I've heard, from folks who sound like they know what they're talking about.  I only brought it up because it sounded as though you were asserting otherwise, so I was kinda curious where you were getting that from (e.g. perhaps you're reading or listening to folks different from what I've heard).

54 minutes ago, Cassel said:

If you think that we are in some respect exceptional to such an extent that we can not be threatened by a sudden and new threat to our planet, that's cool.

No, nothing exceptional.  It's just that I think that a blindfolded guy shooting bullets at random is unlikely to get lucky and hit a one-millimeter target hundreds of thousands of km away, is all.  ;)

52 minutes ago, Cassel said:

In that case, the brightness of the ring should be the same, because the ring is circling around the black hole and in no point moves away from us or does not moves towards us.

Actually, that's the exact opposite of what @sh1pman just said-- go back and read what he wrote again.  ;)   Not that I'm making any assertions about whether his statement of orientation is correct-- just that if it were, it would explain the observation.

The statement I've seen here that seems most credible to me-- since it cites specific numbers-- is this one,

54 minutes ago, Green Baron said:

The whole thing is actually rotating almost face-on, with a deviation of 17°.

...I assume Baron didn't just make up the number "17 degrees" ;) , so this makes sense to me, and would also explain the presence of Doppler shift.  Apologies if I've missed it, Baron, but where did you get that number from? A fair number of citations flying around these days, and I've only been kinda skimming here.  :)

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The 17° is mentioned in paper number V. I put it in a spoiler in a post of mine on the previous page. It was first derived from the jet by VLBI in 2018. It is not an invention of mine ;-)

A direct link to the cited work:

https://iopscience.iop.org/article/10.3847/1538-4357/aaafcc/meta

The paper mentions as well a "counterjet", which is shown in many images, but not as clearly accentuated as the one pointing towards us.

 

Edited by Green Baron

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So, I've seen three assertions here:

  • @Cassel:  "The rotation axis points directly at us"
  • @sh1pman:  "The rotation axis is perpendicular to pointing at us"
  • @Green Baron:  "The rotation axis points mostly at us, but is off by 17 degrees"

I'm guessing Baron's is the correct one, just because he must have gotten that number from somewhere, but I'm curious.  For each of the three of you, where did you get your information?

[EDIT]  Whoops, ninja'd by Baron.  Thanks, man.  :)

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Yeah, looks like the rotation axis is pointed away from us, but at an angle (17 deg to the right?) that results in a difference in brightness.

Quote

Combined with previous observations of M87’s jet, which show it’s inclined at an angle of 17° relative to our line of sight, this tells us that M87’s black hole likely spins clockwise from our point of view, with its spin axis pointed away from us at an angle.

 

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Ok, to make that clear. When looking from above on an object that is turning clockwise, its rotational axis vector (here the z-axis) points away from the observer. That is a left handed coordinate system for the ones like me who fight with 3D stuff and the like (and are about to loose).

M87's black hole rotational axis points away from us, in reference to the image we all stare at since yesterday, to the lower left, by 17° from the observational eyesight (the camera's front vector). So, seeing positive z as the normal of the rotational plane that is spanned up by the accretion disc, it's anti normal points towards us, to the upper right, by 17°. The jet pointing towards us marks that vector, which is, in terms of KSP, the anti-normal, in terms of 3D graphics it is simply a unary- on the normal (be it normalized or not).

Were we to implement an algorithm to cull the jet from our viewport, we would have to define near and far plane, camera front, x-axis deviation and y-axis deviation and compare them to our selection of objects we want to draw.

That's where i got stuck.

*crack zosh*

good night everybody :-)

 

 

Edited by Green Baron

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LOL I see that even the newscaster cretins on ABC have an interest in space! 

At this point, I'd point this out as "a scientific discovery to rival most everything discovered in the 1900s."

 

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7 hours ago, sh1pman said:

No way. With such rotation, the poles would be invisible to us.

Well, what about the event horizon? If it's a black hole, where is it? It should be visible in the form of a light, thin ring.

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3 hours ago, Cassel said:

Well, what about the event horizon? If it's a black hole, where is it? It should be visible in the form of a light, thin ring.

It The event horizon is inside the dark area, having a little less than half its diameter. It itself is invisible.

There is no ring because this is not an optical image. Measured were the radio waves from the disc alone, in a very narrow band around ~1.3mm lambda and such a subtle structure is below the resolution power of the Interferometer. Resolution power is demonstrated in some of the images with a small white circle.

They will try in the future to observe at shorter wavelengths, but for this the dishes must be extremely smooth in order not to introduce errors from unevenness. Shorter wavelengths (higher frequency) would mean better resolution with given diameter (resolution ~= lambda/diameter).

Edited by Green Baron
Clarification clarification

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25 minutes ago, Green Baron said:

Are you sure ? We don't have nothing about Sag A* yet ?

Ahh, my mistake, everyone's talking about M87. I'll go clear out that comment.

Anyway, that makes it even sillier to talk about it being dangerous to us. The thing in the image is 53.49 million light years away.

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I believe this image comes from the paper where they are showing what the image would look like for various axes of rotation for the black hole and the accretion disk.

For reasons I don't quite understand but are something to do with relativity it is the direction of rotation of the hole (the black arrows)rather than the direction of rotation of the accretion disk (the blue arrows) that has determined where the bright spots are.

 HyyVY.jpg

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Yes, the black hole's rotation and spacetime distortion plays the bigger part. But, in this case, both, the disc and the hole co-rotate.

Didn't want to overcomplicate above ...

Edit: and, overall, from paper number I's abstract: "The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole."

"Relativistic beaming" being the signal amplification for the approaching part as well as the dampening for the retreating part. So, the Doppler argument is untouched.

Edited by Green Baron

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