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Comment by wumpus | Hacker News Reader

> The algorithms they use to make the image of the black hole were never tested against a known celestial body to calibrate the algorithms.

This is not true, as is much of the rest of your comment. Please read the papers, they say everything that the collaboration did.

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I've taken hours and read https://iopscience.iop.org/article/10.3847/2041-8213/ab0c57 . My take away was they did a good job calibrating their signals, but I've never seen anything about calibrating their imaging algorithms. They have not calibrated the whole imaging stack. My skepticism is in the algorithms, not the signals.

When you say the “whole imaging stack,” which one do you mean?

EHT imaged M87 with four teams working independently using different methods. Each of those teams used algorithms that were published and validated before the EHT results were published.

Did the 4 teams create their algorithms before getting the observation data and not modify them at all after seeing the results from the first run of their algorithms? Or was there data and algorithm tweaking to get the results that they wanted?

That famous photo of the scientist with the ring image on their laptop screen was exactly that: after all 4 teams had tuned their algorithms to make sure they could accurately image the simulated data (ring, crescent, disk, double point source)... then all 4 teams imaged the actual data. That was the first moment, Eureka!

Now that you've read the correct paper, you know that. You could have also learned it from the news releases, as it was an important part of the science.

You read the paper about calibrating the signals, that's a reasonable takeaway.

There's a different paper about how the 4 independent algorithms were tested to make sure they did the right thing with simulated data: ring, crescent, disk, double point source.

That's the process that you had an incorrect takeaway from the documentary about. The filmmaker is a member of the collaboration and was highly involved in the imaging.

First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/...

You'll have to follow the footnotes to find out the ages of these algorithms; CLEAN was invented well before I first used it in 1985, and I first ran into maximum likelihood in 1987 or so.

Thanks. I will read this paper.

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