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

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#### lpetrich

In the ESO's press conference, someone mentioned that it is hard to get a black hole's angular momentum from the shape of its shadow. So I tracked down how one calculates a BH's shadow's boundary, and I found [1801.00860] Shadows and strong gravitational lensing: a brief review. The math is a bit involved, but I implemented it in Mathematica, and I found that the shadow is approximately circular but offset toward the receding part of the limb. The radius is close to the radius in the nonrotating (Schwarzschild) limit: $3 \sqrt{3} M$, and the offset is $- (2a) ( n_{obs} \times n_{AM})$ with the observation and the angular-momentum directions. M = mass, a = (ang mom)/M, multiplied by G/c^2 to get lengths.

#### lpetrich

Messier 87 - Wikipedia -- someone updated that article very quickly. For the central black hole, M87*, the article quoted mass estimates like $(3.5 \pm 0.8) \times 10^9$ and $(6.6 \pm 0.4) \times 10^9$ solar masses, with a 2016 estimate of $7.22{}^{+0.34}_{-0.40} \times 10^9$ solar masses. The EHT consortium's estimate is $(6.5 \pm 0.2_{stat} \pm 0.7_{sys}) \times 10^9$ solar masses.

Those other mass estimates were made using the velocities of the stars and interstellar gas that surround the BH. They are well within the Newtonian limit, so the success of extrapolating toward the BH's event horizon is a success for GR, along with the approximately circular shape of the BH's shadow.

#### erbahar

All of us have seen the newly published beautiful image of the black hole. I was thinking about the feature in the photo regarding the luminosity differences between two sides (a clear result of rotation of accretion disk and relativistic beaming). I found myself thinking about the relativistic beaming phenomenon.

If you apply Galilean velocity addition you still get some beaming effect (classical aberration of light, etc...). Of course the effect gets much more enhanced if you use the Lorentzian addition of velocities and drammatically turns into a "headlight" sort of phenomenon if you approach speed of light. I agree with that...

But phenomenologically it is not something strictly "relativistic" right? I would argue "relativistic" in the context of "relative motion" and not necessarily special theory of relativity (SR). But people have obviously using it in the context of SR. Or am I missing something? The nomenclature seems somehow assertive of SR.

#### davenn

Gold Member
All of us have seen the newly published beautiful image of the black hole. I was thinking about the feature in the photo

Again as I and others have stated earlier in the thread ..... This is not a photo of the black hole ....
It is not an optical image

Dave

#### erbahar

Again as I and others have stated earlier in the thread ..... This is not a photo of the black hole ....
It is not an optical image

Dave
I am very well aware of this, thank you for reminding anyway. However, totally irrelevant to what I am saying I think... beaming occurs in every wavelength.

PS. I have posted this at general physics discussion under a totally different title to discuss the naming of the physical phenomenon, however it was moved here as a comment for some reason, it is loosely related to this topic. FYI

#### pinball1970

Gold Member
No, but I will watch it now, thanks!

#### DennisN

Hi, go to the post by OmCheeto (post #60 in this thread) and go down to the M87 video from Deep Sky Videos. If you click on it there you ought to be able to see it. Otherwise, try clicking on the video with the right mouse button and select "open in new tab" or "open in new window" or something, depending on what browser you are using. If it does not work, you can PM me.

#### pinball1970

Gold Member
Hi, go to the post by OmCheeto (post #60 in this thread) and go down to the M87 video from Deep Sky Videos. If you click on it there you ought to be able to see it. Otherwise, try clicking on the video with the right mouse button and select "open in new tab" or "open in new window" or something, depending on what browser you are using. If it does not work, you can PM me.
Thanks!

#### davenn

Gold Member
. However, totally irrelevant to what I am saying I think... beaming occurs in every wavelength.

have no idea what you mean by that

#### pinball1970

Gold Member
Hi, go to the post by OmCheeto (post #60 in this thread) and go down to the M87 video from Deep Sky Videos. If you click on it there you ought to be able to see it. Otherwise, try clicking on the video with the right mouse button and select "open in new tab" or "open in new window" or something, depending on what browser you are using. If it does not work, you can PM me.
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

#### sophiecentaur

Gold Member
Again as I and others have stated earlier in the thread ..... This is not a photo of the black hole ....
It is not an optical image

Dave
The problem has been in the use of the word "photo". If the word "Image' had been used for the pictures we have seen then we might not have seen so much confusion. Hubble is responsible for people assuming that we can 'see' anything out there.

#### davenn

Gold Member
The problem has been in the use of the word "photo". If the word "Image' had been used for the pictures we have seen then we might not have seen so much confusion.

Yup, Exactly

#### erbahar

have no idea what you mean by that
It means you will see the same intensity difference whether the signal you are receiving is light or radio waves or any other part of the spectrum.

The word "photo" was refering to what I am seeing on the screen with my "eyes". (Really meaningless discussion for me, will not comment further on the things which are outside of my main point.)

#### pinball1970

Gold Member
Again as I and others have stated earlier in the thread ..... This is not a photo of the black hole ....
It is not an optical image

Dave
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)

#### PAllen

@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.

#### erbahar

@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

Mentor
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

Mentor
Gold Member
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.

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#### OmCheeto

Gold Member
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
Cygnus X-11.9 kpc14.8 Msun44 km7.4*10^(-16) rad0.80 nnas
Our Galaxy: Sgr A*7.860 kpc4.05 * 10^6 Msun0.080 AU4.9*10^(-11) rad53 mcas
Andromeda Galaxy778 kpc1.7 * 10^8 Msun3.3 AU2.1*10^(-11) rad22 mcas
Messier 8716.4 Mpc6.5 * 10^9 Msun130 AU3.8*10^(-11) rad41 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

Gold Member
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 :)

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

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