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A Ring of Controversy Around a Black Hole Photo (profmattstrassler.com)
107 points by lelf 17 days ago | hide | past | web | favorite | 18 comments

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".

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.

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.

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


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

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.

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.

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

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

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.

So, at 6:38 he says that we would mostly see just a disk, if viewing strictly from the jet vector, yet PaulHoule’s comment fades below and the original empath75’s is intact. For now I assume there is some relativistic effect in action which makes me see them this way.

Remember the black hole from interstellar? Some gravitational simulations were used for the imagery. It was changed for artistic purposes, but you can see the back side of the accretion disc from the front.

They explain how they did it in this video: https://www.youtube.com/watch?v=MfGfZwQ_qaY

Their advisor, who provided them the relativistic equations they use for the computer graphics simulation is Kip Thorne: https://en.wikipedia.org/wiki/Kip_Thorne

He wrote a (good) book about the whole endeavor: The Science of Interstellar

It might look a bit different if you are looking right down the jet that comes from the pole.

Does the accretion disk emit light, or is the light source coming from somewhere else? (i.e. if the accretion disk is just cosmic dust why would one expect to see the disk?)

Yes, the accretion disk emits light because the matter in the accretion disk is very hot. This is a combination of friction as well as the compression of the material by gravity.

Parts of the accretion disk get hot enough to emit light.

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