OT black hole pic.

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

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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.

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 Thanks, 
    - Win

The full set of papers which make up this report (there are six of them) go into a lot of detail about the processing that was done. If I recall correctly, there were no less than four independent teams, working with several different sets of data-processing "pipelines", working on the data, blinded to one anothers' results until the last. I'm only partway through the reading, and I don't pretend to understand all of the math (or even more than a fraction of it) but it's a worthy learning effort nevertheless!

Any form of image which is based on interferometry is necessarily somewhat synthetic - the image which results is a best-fit result generated from the data. There are, necessarily, interpolations made in the process (that is, the data is "under-constrained") because the interferometric relationship between any two of the radio telescopes "sweeps out" only a limited set of parts of the image field during any single recording pass.

The teams seem to have gone to a lot of effort to make sure their analysis process resulted in image data corresponding to "what was there" rather than "what we expected to see". They tested the analysis pipelines with synthetic image data first, artifically generating this based on various models of what the emission source might "look like", and confirming that the computed images actually matched up to the models that generated the test data.

Well it's all radio waves. 1.2 mm or something. I like the pic of the black hole in the center of our galaxy.

George H.

It's very cool. I read that there was so much data, they transported it on planes, by wire would have taken too long. We should put a dish on the moon. :^)

George H.

It's hard to beat the bandwidth of a jumbo jet full of disk drives.

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

110 million years ago, and bent right around the black hole and back to us. If we could increase the resolution a lot(*), we could get video of live dinosaurs!

(*) Quite a lot. In fact, a lot a lot alot!

Clifford Heath.

This has been used for decades in VLBI. Previously each radio telescope recorded the signal and clock sync on tape and the tapes were flown to the correlator site, The different tapes were synchronized and run through the correlator.So apparently they now use disks instead of tapes.

It is surprising that they still use disks, since for at least a decade there has been a protocol for transferring very high data rate interferometric data. Standard TCP/IP is useless, since the transmission window would be filled, before the acknowledge frame would be received from intercontinental distances. You might need hundreds or thousands parallel TCP/IP tubes to fully utilize the available bandwidth (up to 800 Gbit/s on a single DWDM fibre).

It is definitively a false color (black / red / yellow) image :-) The recording was done on a single 1.3 mm wavelength.

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

I meant the other animations of the black hole that are mixed up with the actual, very fuzzy radio telescope image. But more generally, the silly artists' conceptions that are not always identified.

I've seen versions of that actual image that are zoomed or otherwise manipulated to look like movies.

It sure was a ton of extended hype over that one fuzzy image.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Clifford Heath wrote in news:ypTrE.86002$ snipped-for-privacy@fx20.iad:

Quite doubtful.

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

John Larkin wrote in news: snipped-for-privacy@4ax.com:

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 wrote in news:906fe972-18db-432e- snipped-for-privacy@googlegroups.com:

Absolutely.

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

snipped-for-privacy@downunder.com wrote in news: snipped-for-privacy@4ax.com:

Colorization, yes. Imagery, no.

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.

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:

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

VLBI allows you to zoom in on a tiny patch of sky at very high resolution provided that the source if bright enough.

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

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:

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.

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Regards, 
Martin Brown

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.

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Regards - Rodney Pont 
The from address exists but is mostly dumped, 
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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