OT black hole pic.

Clifford Heath <no.spam@please.net> wrote in
news:ypTrE.86002$dN3.67291@fx20.iad: 

> Some of the radiation used to make that picture came from the
> Earth...





  Quite doubtful.

> 110 million years ago, and bent right around the black
> hole and back to us.

  Maybe you need to rethink/relearn what a black hole is.

John Larkin <jjlarkin@highland_snip_technology.com> wrote in 
news:q1fvae5ufdalg0hqak26qrpm8pgf886n0v@4ax.com:

> It's always hard to tell real pictures from animations and "artists
> conceptions." There should be a convention to identify unreal images.
> 
> 

  It is hard to tell for an idiot like you.

  And that convention you mention...  is typically referred to as the 
description.  They're usually included, especially if you are at the 
picture source, not just some lame jerk like you reposting it devoid of 
info.

George Herold <gherold@teachspin.com> wrote in news:906fe972-18db-432e-
a573-02630c0b8d61@googlegroups.com:

> We should put a dish on the moon. :^)
> 

 Absolutely.

  One here, one on the moon, and maybe even one on Mars.

upsidedown@downunder.com wrote in 
news:jb20bepoa94mbln2hhc3fo793148ooi0or@4ax.com:

> Anyway, even optical astronomical raw pictures are heavily processed
> to make published pictures more beautiful.
> 

  Colorization, yes.  Imagery, no.

On 11/04/2019 18:42, George Herold wrote:
> My son shared this video by Vertasium on the black hole pic,
> https://www.youtube.com/watch?v=zUyH3XhpLTo
>
> I thought it was nice.
>
> and this,
> https://www.youtube.com/watch?v=S_GVbuddri8
>
> Amazing stuff.
>
> George H.
>

A very scrappy pic for 4 petabytes (4 million gigabytes) of data

On 12/4/19 5:31 pm, N_Cook wrote:
> On 11/04/2019 18:42, George Herold wrote:
>> My son shared this video by Vertasium on the black hole pic,
>> https://www.youtube.com/watch?v=zUyH3XhpLTo
>>
>> I thought it was nice.
>>
>> and this,
>> https://www.youtube.com/watch?v=S_GVbuddri8
>>
>> Amazing stuff.
>>
>> George H.
>>
> 
> A very scrappy pic for 4 petabytes (4 million gigabytes) of data

A feature of the exceptionally low signal-to-noise ratio.
Possibly the weakest signal that has ever been recovered, but they 
actually did recover it.

On 12/04/2019 02:03, Winfield Hill wrote:
> John Larkin wrote...
>>
>> On Thu, 11 Apr 2019, George Herold wrote:
>>
>>> My son shared this video by Vertasium on the black hole pic,
>>> https://www.youtube.com/watch?v=zUyH3XhpLTo
>>>
>>> https://www.youtube.com/watch?v=S_GVbuddri8
>>
>> It's always hard to tell real pictures from animations
>> and "artists conceptions." There should be a convention
>> to identify unreal images.

This one is by any reasonable definition an (indirect) image - although 
it is an image made from the coherence function measured at the Earth.

This is a contour map view made by VLBI of the jet much further out:

https://www.researchgate.net/figure/Wide-field-EVN-image-of-the-jet-in-M87-Contours-are-traced-at-1-1-2-4_fig1_241343018

Or as false colour images from the VLA at 43GHz and as a movie:

https://www.aoc.nrao.edu/~cwalker/M87/

VLBI allows you to zoom in on a tiny patch of sky at very high 
resolution provided that the source if bright enough.
> 
>   These images have been called pictures, i.e., photographs,
>   and I think that's a fair name.  They're created from a
>   200GHz, "telescope" with a diameter of the whole earth.
>   Made from data from multiple simultaneous radio telescope
>   images, in perfect phase synchronization.  The more you
>   read about it, the more you'll agree this is a real image.

They have a very hard time of it. Every individual scope measures the 
signal it sees with an H-maser timestamp. Then they combine every base 
station with every other in pairs and aim to find the white light fringe 
(the scopes use a finite bandwidth). Doing it at these frequencies 
requires knowing all the baselines to a fraction of a wavelength.

Then by combining loops of three baselines for phase and four baselines 
for amplitude you can get pure observables that depend only on the shape 
of the sky brightness distribution. This is the core of VLBI technique.

They have one other constraint that allows them to push the envelope 
which is that the sky brightness function must be everywhere positive.

SgrA* has given them a bit of headache though. It is the right size to 
be able to resolve (nearer but also smaller) - but the bad news it that 
it violates the assumption made in VLBI that the object doesn't change 
its appearance in the time it takes to do the observations.

There are six papers describing the detailed processing used.

There are also simulations of the appearance of an accretion disk around 
  a black hole which when convolved with the psf of the Event Horizon 
Scope would look very close to what has been observed.

-- 
Regards,
Martin Brown

On 12/04/2019 08:31, N_Cook wrote:
> On 11/04/2019 18:42, George Herold wrote:
>> My son shared this video by Vertasium on the black hole pic,
>> https://www.youtube.com/watch?v=zUyH3XhpLTo
>>
>> I thought it was nice.
>>
>> and this,
>> https://www.youtube.com/watch?v=S_GVbuddri8
>>
>> Amazing stuff.
>>
>> George H.
>>
> 
> A very scrappy pic for 4 petabytes (4 million gigabytes) of data

That is the problem with trying to synthesise the effect of a telescope 
the size of our planet to zoom in that far. They hope to add a satellite 
antenna in orbit. This would allow a few other targets to be imaged.

I'd like to see Cygnus-A core imaged this way - its accretion disk is 
edge on to us with the jets in the plane of the sky:

http://www.aoc.nrao.edu/~ccarilli/cyga.shtml

Trouble is it is too far away for the present instrument to resolve:(

I'm sure they are looking for other that are worth the effort of trying 
to image.

-- 
Regards,
Martin Brown

On Fri, 12 Apr 2019 09:44:45 +0100, Martin Brown wrote:

>They have a very hard time of it. Every individual scope measures the 
>signal it sees with an H-maser timestamp. Then they combine every base 
>station with every other in pairs and aim to find the white light fringe 
>(the scopes use a finite bandwidth). Doing it at these frequencies 
>requires knowing all the baselines to a fraction of a wavelength.

Do they only get one pixel at a time with radio telescopes and build up
the image by putting them together after the session. I know visible
and a bit either side can be done with sensors similar to those in my
camera but I've not heard of a camera that can go down to radio
frequencies.

-- 
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail	rpont (at) gmail (dot) com

On 12/04/2019 10:35, Rodney Pont wrote:
> On Fri, 12 Apr 2019 09:44:45 +0100, Martin Brown wrote:
> 
>> They have a very hard time of it. Every individual scope measures the
>> signal it sees with an H-maser timestamp. Then they combine every base
>> station with every other in pairs and aim to find the white light fringe
>> (the scopes use a finite bandwidth). Doing it at these frequencies
>> requires knowing all the baselines to a fraction of a wavelength.
> 
> Do they only get one pixel at a time with radio telescopes and build up
> the image by putting them together after the session. I know visible
> and a bit either side can be done with sensors similar to those in my
> camera but I've not heard of a camera that can go down to radio
> frequencies.

It is all interferometry so basically using Young's slits in reverse to 
measure what you would see by placing a sine & cosine mask on the sky 
and measuring total intensity passing through that shadow mask.

You literally compute painstakingly the coherence function of every pair 
of dishes along the track that each of the baselines sweep out as the 
Earth rotates and then compute a model brightness distribution that is 
consistent with those hard observational constraints.

Everything gets measured and computed in the u-v plane of Fourier space 
and is only converted into an x-y image plane at the very final step.

There are a heck of a lot of tricky technical issues to make it work!

-- 
Regards,
Martin Brown