Stargazing Event Horizon Telescope Results Released Yesterday (April 10, 2019)

[member659127]

@erbahar ,
Relativistic beaming results from the joint action of two phenomena: aberration, and Doppler. Both occur for radio waves just as readily as visible light. Aberration really has no valid derivation before SR - the one used by Bradley requires a corpuscular theory of light where speed of source affects speed of light, which is c only relative to its emission source. Doppler has a pre-SR derivation, but the predicted amount for a high speed jet would be way too small. Beaming is considered relativistic because it is this joint effect of a pure SR phenomenon and SR augmented Doppler.

Thank you for the insightfull answer. I am going to discuss the physics of the image with my modern physics class next week and want to demonstrate this. I am going to first discuss it in a classical picture. (That is something I always do to explain the phenomenology first not to intimidate them with SR directly which they have to replace their "common sense" with pure math.)

What you pointed out as the Bradley's explanation is just EXACTLY what I mean by Galilean addition of velocities by the way. I didn't know the name and history, thank you for that and also thank you for pointing out the Doppler shift has a secondary (or indirect I can say) effect on the intensity via the relationship of frequency with the energy. That was something I missed also.

I am not totally convinced though that all of these are "pure" SR effects. What I would say pure relativistic is stuff like time dilation, length contraction, redefinition of momentum, energy, etc... (One interesting aspect is that the relationship of frequency with energy is not SR but "pure" QM which is also non-classical anyway)

Thanks again!
Dogan

 

[mfb]

I have no idea how they put the data together for the image, I am more interested in what happens next.
Yeah it's amazing but it's blurred and does not have much detail
I am not being negative, the images are reminiscent of what the CMBR started out as
More telescope have been mentioned but that must have limitations? The size of the earth? Could any data from the JW Telescope be used? (when it is launched 2021)

James Webb is an infrared/visible telescope. You need a radio telescope, radio telescopes need to be big - problem one. You need to know the position of this radio telescope in space better than the wavelength (1 mm in this case) - problem two. And then you need to find a way to transfer hundreds of terabytes from this telescope to Earth - problem three.
Of course people are studying if this is possible, but it needs major R&D and will need at least many years before it can be launched.

 

[anorlunda]

What a great teaching event this news has become. Most questions and answers have been great. BH physics, GR physics, light, astronomy, observation methods, data reduction methods. I am hopeful that many people will be motivated to increase their understanding in all of those topics.

 

[PAllen]

(One interesting aspect is that the relationship of frequency with energy is not SR but "pure" QM which is also non-classical anyway)

Thanks again!
Dogan

That frequency determines energy per quanta is quantum. That energy of an EM emission shifts with relative motion exactly per the Doppler formula is pure SR, and was derived classically in Einstein's 1905 paper. In fact, the complete description of relativistic beaming is present in Einstein's 1905 paper, which is one of its distinguishing features from other work that anticipates almost all the rest of it.

 

[hmmm27]

On behalf of everybody not a scientist, but also not satisfied with popsci "artist's impressions" (beyond an appreciation of the wonderful artistry), this is just freakin' awesome.

 

[OmCheeto]

Great video. The interviewer sounds like the guy who did Tree 3 and Graham's number. The maths guy? I'll see if I can find him on YT

That would be Brady Haran [wiki entry]. He has at least 15 different Youtube channels. He's probably my favorite internet science communicator, in that, he asks real scientists the questions, and they try and answer them. Often times he asks that things be explained without using a lot of maths, which makes for some very funny sounds and facial expressions from the scientists.

 

[lpetrich]

Easiest-to-observe black holes. I've included a stellar one along with the galaxy-center supermassive ones. Source: Wikipedia

Galaxy	Distance	Mass	Sch Radius	Sch Rad Ang Xtnt	Shadow Ang Dia
Cygnus X-1	1.9 kpc	14.8 Msun	44 km	7.4*10^(-16) rad	0.80 nnas
Our Galaxy: Sgr A*	7.860 kpc	4.05 * 10^6 Msun	0.080 AU	4.9*10^(-11) rad	53 mcas
Andromeda Galaxy	778 kpc	1.7 * 10^8 Msun	3.3 AU	2.1*10^(-11) rad	22 mcas
Messier 87	16.4 Mpc	6.5 * 10^9 Msun	130 AU	3.8*10^(-11) rad	41 mcas

mcas = microarcseconds, nnas = nanoarcseconds. Notice how small Cygnus X-1's black hole is.

I think that the Event Horizon Telescope consortium may take on the Andromeda Galaxy after doing Sgr A*. However, its central BH's mass has big error bars on it.

 

[lpetrich]

List of most massive black holes - Wikipedia -- I went through the entire list, and I followed the links to find out what the objects' distances were. From that, I calculated each BH's shadow diameter, 3*sqrt(3) times its Schwarzschild radius. It is in microarcseconds.

Where	Ang Dia
Milky Way Sgr A*	56
Messier 87	45
Andromeda Galaxy	30
NGC 1600	29
NGC 4889	23
IC 1101	22
NGC 6166	22
NGC 3115	21
NGC 1281	17
NGC 1270	16
Sombrero Galaxy	11
NGC 3842	10

The Andromeda Galaxy and NGC 1600 are next after Sgr A* and M87*, followed by several other galaxies.

 

[lpetrich]

I must note about my previous post that it has a rather optimistic estimate for the Andromeda Galaxy's central black hole's mass. I've seen lower estimates.

An obvious way to get more baseline for VLBI is to go into outer space, but not many radio-astronomy satellites have been launched, satellites like HALCA and Spektr-R.

 

[Zeke137]

davenn said:

Just in that 144MHz doesn't have a colour or one that is different from, say, 440 MHz

...and there speaks a radio ham, if I'm not much mistaken :)

 

[davenn]

An obvious way to get more baseline for VLBI is to go into outer space, but not many radio-astronomy satellites have been launched, satellites like HALCA and Spektr-R.

well there is a much easier way and it doesn't involve the massive cost of space based scopes and it also gives a massive VLBI
... namely observations 6 months apart on opposite sides of the Earth's orbit, an approx 300 million km baseline D

 

[websterling]

The observations have to be simultaneous for this to work.

 

[PAllen]

The observations have to be simultaneous for this to work.

I assumed the smiley meant @davenn was well aware of this.

 

[davenn]

The observations have to be simultaneous for this to work.

I assumed the smiley meant @davenn was well aware of this.

Actually, they don't, the data can be collected with good timing and then sync'ed once all data is collected
this is just the same for the Earth based radio telescopes that were involved in the M87 observations

NOT ALL of them could see M87 at the same time ... as we don't live on a flat earth, simultaneous obs's are impossibleDave

 

[mfb]

You cannot use that baseline for VLBI in the way the Event Horizon telescope did if you take the data 6 months apart. You need to record the same waveforms at multiple places to do interferometry.

NOT ALL of them could see M87 at the same time

But always more than one when they took data, otherwise recording data would have been pointless.

Independent of the physics: Think about it for a second. Would they have made an image with a <10,000 km baseline if there was a way to get a baseline 30,000 times longer with the same telescopes?

 

[davenn]

You cannot use that baseline for VLBI in the way the Event Horizon telescope did if you take the data 6 months apart. You need to record the same waveforms at multiple places to do interferometry.

But always more than one when they took data, otherwise recording data would have been pointless.

and there you just contradicted yourself
6 hours or 6 months, don't make any difference and there would still be more than one observing at the 6 months apartD

 

[mfb]

and there you just contradicted yourself

No I didn't. Maybe you misread my post?
You need simultaneous observations. 6 hours time difference between telescopes would ruin it in the same way 6 months do. The Event Horizon Telescope only used data where at least two telescopes could observe at the same time - more are better.

 

[Orodruin]

6 hours time difference between telescopes would ruin it in the same way 6 months do.

Depending on the distance between the telescopes ...
The point is that you need to observe the same wave front. That is how you do interferometry.

 

[websterling]

well there is a much easier way and it doesn't involve the massive cost of space based scopes and it also gives a massive VLBI
... namely observations 6 months apart on opposite sides of the Earth's orbit, an approx 300 million km baseline D

If it was this easy, it could have been done in the '70s, maybe even the '60s

 

[davenn]

If it was this easy, it could have been done in the '70s, maybe even the '60s

think about what you wrote
now think about the available technology at that time

so no, it couldn't have been done

 

[Zeke137]

The picture published by the EHT team is the result of months of observations of the black hole in M87, taken by several radio observatories, and then processed for several months afterwards by data-processing experts using supercomputers. The picture is not a photograph in the ordinary sense.

Note the use of radio observatories in collecting the data: no "glass" reflectors were used to collect visible light, but rather many radio telescopes with dishes made of metal to collect signals at millimeter radio wavelengths. Here's one of them, the ALMA array in the Atacama desert in Chile:

As @sysprog has mentioned, playing with brightness or contrast in the published picture will reveal no new data or information.

 

[Itsnotablackhole]

The picture published by the EHT team is the result of months of observations of the black hole in M87, taken by several radio observatories, and then processed for several months afterwards by data-processing experts using supercomputers. The picture is not a photograph in the ordinary sense.

Note the use of radio observatories in collecting the data: no "glass" reflectors were used to collect visible light, but rather many radio telescopes with dishes made of metal to collect signals at millimeter radio wavelengths. Here's one of them, the ALMA array in the Atacama desert in Chile:

View attachment 245385

As @sysprog has mentioned, playing with brightness or contrast in the published picture will reveal no new data or information.

Hi, that's a great photo, by the way, thank you for your reply, and sorry i don't mean to seem contentious, you are clearly clever people, I just want to discuss this more slowly, point by point, so we may get to the truth of this, first black hole photo, as I am fascinated, thanks,,,,you said firstly if this was an asteroid it would have moved very quickly in front of the star! ... my answer is, yes if it were moving left or right! But it could be moving towards us, in which case it would not have moved quickly in front of the star. ... All solid objects with an edge, are capable of lensing , I.e. light bends around the objects edge. ... ...By asteroid I mean rock, and we don't know it's size because we don't know it's distance. ... Playing with the max brightness, and adjusting viewing angle will reveal new information on normal digital optical photo's, but the first black hole photo was based on an algorithm of what has been seen, not what hasn't been seen. So I fear ambiguity, I.e. how does the algorithm know what a black hole looks like, maybe from the human imagination, I.e. physics theory simulations, but Einstein said we would not be able to see a black hole ... in 2017 and 2018, dark objects rocks? Asteroids? can be seen heading across m87 near where the first black hole photo is taken. Should these not be considered and or at least ruled out or in? Depending on periphery observations and timelines ?

 

[sysprog]

Hi, that's a great photo, by the way, thank you for your reply, and sorry i don't mean to seem contentious, you are clearly clever people, I just want to discuss this more slowly, point by point, so we may get to the truth of this, first black hole photo, as I am fascinated, thanks,,,,you said firstly if this was an asteroid it would have moved very quickly in front of the star! ... my answer is, yes if it were moving left or right! But it could be moving towards us, in which case it would not have moved quickly in front of the star. ... All solid objects with an edge, are capable of lensing , I.e. light bends around the objects edge. ... ...By asteroid I mean rock, and we don't know it's size because we don't know it's distance. ... Playing with the max brightness, and adjusting viewing angle will reveal new information on normal digital optical photo's, but the first black hole photo was based on an algorithm of what has been seen, not what hasn't been seen. So I fear ambiguity, I.e. how does the algorithm know what a black hole looks like, maybe from the human imagination, I.e. physics theory simulations, but Einstein said we would not be able to see a black hole ... in 2017 and 2018, dark objects rocks? Asteroids? can be seen heading across m87 near where the first black hole photo is taken. Should these not be considered and or at least ruled out or in? Depending on periphery observations and timelines ?

Please re-read what @Zeke137 said. Your wild speculations are completely outside the realm of the possibilities consistent with the first-rate research and reporting associated with the image being discussed. And please also break your ideas into paragraphs and re-examine them before posting them.

 

[Zeke137]

yes if it were moving left or right! But it could be moving towards us, in which case it would not have moved quickly in front of the star

You are ignoring or discounting the dynamics of objects in the solar system. All objects within the solar system are under the influence of the gravitational fields of all the other objects in the system, with the Sun and planets being the major contributors to gravitational influence.

Asteroids follow orbits around the Sun, and the velocities at which they travel are determined by their distance from the Sun, which is different than the Sun-Earth distance. It is not possible dynamically for an asteroid to be "moving toward us", except momentarily. It's a little like walking along a road, and an automobile passes us: it's close by for a short while, and then the automobile continues on its' journey, getting further away from us. The dynamics of the walker and the automobile are different, and they come close to each other for a short while only. If you were to watch asteroids through a telescope, you would notice them moving quite quickly through the star-field. The likelihood of an asteroid occluding any chosen star is very small, and the period of occlusion is also very small.

All solid objects with an edge, are capable of lensing , I.e. light bends around the objects edge

The effect you mention is known as diffraction, not lensing - see e.g. https://en.wikipedia.org/wiki/Diffraction . The sharper the diffracting edge, in terms of the light's frequency, the greater the degree of diffraction. Conversely, a more rounded edge diffracts to a lesser degree. Asteroids, generally quite rounded objects, would not cause any discernible diffraction.

Lensing, in the astrophysical sense of gravitational lensing, is caused by the "warping" of space-time around VERY massive objects, like stars, galaxies, or clusters of galaxies. An asteroid is just not massive enough, by a factor of many billions.

in 2017 and 2018, dark objects rocks? Asteroids? can be seen heading across m87 near where the first black hole photo is taken. Should these not be considered and or at least ruled out or in?

Again, the picture is not a photo! It has not been taken with a camera. It is the product of long-term data acquisition, analysis and processing, and has been produced by a computer. It is not a photo.

And again, the data were acquired by radio observatories, not by optical telescopes. A radio observatory simply does not, and cannot, "see" or observe asteroids, since asteroids do not emit EM radiation or light at radio frequencies. If an asteroid passed by the field of view of a radio observatory, it would be completely invisible to that observatory.

So your idea of asteroids or rocks causing features in the picture published by the EHT team are, frankly, completely without merit, and not tenable physically.

 

[sophiecentaur]

Should these not be considered and or at least ruled out or in?

Do you seriously think that stuff like that is not considered? More or less every observation in Astronomy is examined again and again before any conclusions are reached about its cause. Your suggested explanation is so 'alternative' (most polite word I can think of) that it would get considered for no more than a second. The Physics just does not fit.

It has already been pointed out that the motion of all celestial objects is such that no three objects can lie on a straight line (i.e. the same as a beam of light) for longer than an instant.

 

[Drakkith]

All solid objects with an edge, are capable of lensing , I.e. light bends around the objects edge.

No, that is entirely false. Solid, opaque objects do not bend light around themselves. The effect of diffraction isn't even a bending of the wavefront, it's an interference effect.

Playing with the max brightness, and adjusting viewing angle will reveal new information on normal digital optical photo's, but the first black hole photo was based on an algorithm of what has been seen, not what hasn't been seen.

I have no idea what this is supposed to mean.

So I fear ambiguity, I.e. how does the algorithm know what a black hole looks like, maybe from the human imagination, I.e. physics theory simulations,

It 'knows' because we know how radio waves behave and how to generate a real image using them. There is no ambiguity here. And note that a simulation based on physics theories is about as far from 'imagination', i.e. 'made up', as you can get.

but Einstein said we would not be able to see a black hole

We can't see the black hole. But we can see the accretion disk, which is what the image is showing. And it is distorted in just such a way as we would expect the black hole's gravity to do.

 

[sysprog]

... the motion of all celestial objects is such that no three objects can lie on a straight line (i.e. the same as a beam of light) for longer than an instant.

Could that statement be moderated a little? It seems to me to be an overstatement of something that as stated is almost, but not quite, true. I think that in principle it's possible that three emitted particles could lie along the same line for longer than an instant, a microsecond, or a second.

 

[Drakkith]

Could that statement be moderated a little? It seems to me to be an overstatement of something that as stated is almost, but not quite, true. I think that in principle it's possible that three emitted particles could lie along the same line for longer than an instant, a microsecond, or a second.

It's techically true since a line has no width, so three moving objects moving in different directions cannot stay along the same line for more than an instant. But in reality the movement between them could be slow enough for an object to block out a star for more than a second or two. It's just really, really unlikely since the orbits of the vast majority of objects in the solar system don't allow them to line up with Earth in this way. I.E. when the tangent line of Earth's orbit intersects an object, that object will almost certainly have some significant component of its velocity perpendicular to the line.

 

[sysprog]

It's techically true since a line has no width, so three moving objects moving in different directions cannot stay along the same line for more than an instant.

That would still be not only for an instant, but would instead be for as long as the size and speed and paths of concurrent line traversal of the objects allowed for them to remain co-aligned; however, the statement that I was suggesting might be more accurate if modified didn't include any provision that the objects had to be moving in different directions, and no-one has examined all celestial objects to ensure that no 3 objects ever move along the same line for longer than an instant, and even given that a line has only 1 dimension, three moving 3-dimensional objects could as far we know remain aligned along some line forever, or at least for a lot longer than an instant, however long that might be.

 

[pinball1970]

So does this count as the first direct detection of black holes?

I don't think anyone answered this so it is worth replying now the thread has sprang back to life.
I think this is the first direct observation although 'direct' and 'observation' have to be defined.
One can never directly observe a black hole only what comes out of it and how it affects it's neighbours orbits, stars.
The difference with these images (again definitions matter) the region around the event horizon has been illustrated adding colour to the radiation so one can see what is there.
I think that is the first you are referring to.

Edit. The guys can correct this where necessary. There is a great little video of stars moving in weird orbits due to a black hole but I cannot find it.
Edit 2. Found it.
https://www.eso.org/public/videos/eso1825e/First indirect? Conclusive?