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

[DennisN]

Did you watch the video on M87 they recommended at the end?

No, but I will watch it now, thanks!

 

[DennisN]

"The Earth goes round the Sun
The Sun goes round the Milky Way
The Milky Way goes round the center of the Local Group
And the Local Group goes round the center of the Virgo Supercluster
The center of the Virgo Supercluster is M87
Technically, the Earth is going round M87"

An very fascinating video! Worthy for posting in "Our Beautiful Universe" thread, so I'll post it there too.

 

[DaveC426913]

This is a very good explanation of what the black hole image shows.

Indeed. An excellent explanatory video.

So, based on what we are seeing, can we deduce at what angle the accretion disc is to us?

 

[BillTre]

xkcd has an interesting take on the M87 black hole:

 

[robphy]

Here is Katie Bouman's TED talk "How to take a picture of a black hole"


while she was finishing her PhD at MIT in 2017.

She's been a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics
and will be an Assistant Professor at Caltech in Fall 2019.
https://people.csail.mit.edu/klbouman/

And this article on the Comp Sci grad student who helped construct the image from the noisy data:

https://www.sciencealert.com/this-2...lped-bring-us-the-first-image-of-a-black-hole

 

[CookieSalesman]

What does the picture of the black hole actually imply?

I had some begruding idea that this may be sensationaism. Maybe the picture is just too cool for everyone. Is this the reason that it's just blown up everywhere?

 

[Orodruin]

Here is Katie Bouman's TED talk "How to take a picture of a black hole"


while she was finishing her PhD at MIT in 2017.

She's been a postdoctoral researcher at the Harvard-Smithsonian Center for Astrophysics
and will be an Assistant Professor at Caltech in Fall 2019.
https://people.csail.mit.edu/klbouman/

I remember watching that TED talk a couple of years back!

 

[anorlunda]

And this article on the Comp Sci grad student who helped construct the image from the noisy data:

I agree. I've seen her speak. She is a very impressive young woman.

 

[sophiecentaur]

There are no 'warning' messages in the press about the fact that the Radio telescope images are not optical images. For interferometry, they have to use phase sensitive detection, which is hard to achieve for optical frequencies over a big area telescope. However, resolution is potentially higher for short wavelengths and there is a factor of about 10⁶ between optical and microwave wavelengths. So it is not beyond the realms of possibility to use a smaller optical telescope array with the same resolution. The actual area of microwave dishes is not in proportion to the aperture width so the signal level would not scale as badly as it might seem.
All we need is optical amplifiers with sufficiently low noise performance (and a few other improvements) and then we could actually 'see' the black holes.

 

[davenn]

There are no 'warning' messages in the press about the fact that the Radio telescope images are not optical images.

Yes, True, and this has annoyed me a lot because (as I commented much earlier in this thread) it is making people think that are looking at an optical image of a black hole ... and this misunderstanding is widespread across the net

 

[sophiecentaur]

Yes, True,

However - and I felt a bit bad about my comment. I forgot to mention it was a fantastic bit of radiophotography. The other signs of the presence of a black hole (orbiting stars and lensing) are not really as 'obvious' as a real shadow.
10/10 for the project, I say. The quantity of data involved in the processing was pretty stunning.

 

[Janus]

Indeed. An excellent explanatory video.

So, based on what we are seeing, can we deduce at what angle the accretion disc is to us?

It's been estimated that the polar axis of the BH is ~17 degrees to the line of sight.

 

[JLowe]

Yes, True, and this has annoyed me a lot because (as I commented much earlier in this thread) it is making people think that are looking at an optical image of a black hole ... and this misunderstanding is widespread across the net

A lot of people, probably most people, think most images they see from space are actually what their eyes would see.

 

[DaveC426913]

It's been estimated that the polar axis of the BH is ~17 degrees to the line of sight.

Ah. So we're looking down/up its pole.

That is so damned cool.

 

[davenn]

A lot of people, probably most people, think most images they see from space are actually what their eyes would see.

Yes, even with optical images, that is true. I spend a lot of time talking to people about buying a telescope and explaining that what they see in the nice pic's is not what they will see through the eyepiece.
The come to understand that with a good home scope and camera, they can produce images like the ones they see online etc but it takes some serious effort with gear, exposures and processingDave

 

[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.

 

[member659127]

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]

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 imageDave

 

[member659127]

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 imageDave

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]

No, but I will watch it now, thanks!

Can you send the link please?

 

[DennisN]

Can you send the link please?

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]

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]

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

have no idea what you mean by that

 

[pinball1970]

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]

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 imageDave

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]

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

 

[member659127]

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 referring 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]

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 imageDave

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.