
A Ring of Controversy Around a Black Hole Photo - lelf
https://profmattstrassler.com/2019/06/14/a-ring-of-controversy-around-a-black-hole-photo/
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SiempreViernes
As far as I can tell from an slightly extended skim of this text, this is a
case of people from an adjacent field (theoretical GR) writing a paper that
finishes with a remark about their abstract model that does not easily
translate to the one used by the EHT.

In fact, I find this rather nice summary towards the end of the article:

"In particular, EHT’s simulations show all of the effects mentioned above;
there’s none of this of which they are unaware. [...] Thus it’s not enough to
argue the photo itself is ambiguous; one has to argue that EHT’s more subtle
analysis methods are flawed. No one has argued that yet, as far as I am
aware."

To me this reads very much like "I probably shouldn't have used 'controversy'
in the title".

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PaulHoule
The unit of resolution of that photo is just a little bit smaller than the
size of the hole in the middle. Thus you are looking at the inverse
convolution function that generates all the in-between pixels as much as you
are looking at the black hole.

Eyeballing it you can't judge much at all, maybe the central hole is really
smaller, maybe the ring is a little thinner, maybe not. It is a Rorschach test
as much as anything else.

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jankotek
Image was made by comparing polarization of photons on each pixel. BH gravity
bends space and that changes photon plane. It is all in authors papers.

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jonah
This video by Derek Muller (Veritasium) helped me understand this phenomenon.

[https://www.youtube.com/watch?v=zUyH3XhpLTo](https://www.youtube.com/watch?v=zUyH3XhpLTo)

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woogiewonka
The article states that the photon sphere does not exist, therefore his
explanation is incorrect.

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Causality1
When I first saw the photo with very little explanation attached, I took the
ring of light around it to be the accretion disc and found it suspicious that
it would be so perfectly perpendicular to earth.

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empath75
Even if it was the accretion disk, it would look that way no matter how it was
facing earth because gravity would bend the light from the far side around.

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michaelcampbell
To all viewers from any viewpoint relative to it? That's the bit I don't
understand.

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kaslai
Derek explains the physics in a reasonably understandable manner in this video
on his Youtube channel:
[https://www.youtube.com/watch?v=zUyH3XhpLTo](https://www.youtube.com/watch?v=zUyH3XhpLTo)

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michaelcampbell
I've watched it, but his explanation (which is the best I've seen; don't
misread me), basically goes into why it looks "thus" when viewed edge-on of
the accretion disk. But there are as few like that as there are viewed from
the poles; so why do they _ALL_ look like this?

If that's just the way it is I'll accept it, but I haven't heard or seen a
good explanation yet.

