Continued Controversy on the Ring of Light

For general readers: A week or so ago, I wrote about my skepticism concerning the claim of a “detection” of the photon ring that’s widely expected to lie hidden within the image of a black hole. A nice article in Science News appeared today outlining the current controversy, with some quotes from scientists with differing … Read more

Has the Light From Behind a Black Hole Been Seen? Does the Claim Ring True?

Back in 2019, the Event Horizon Telescope (EHT) made history as its scientists used it to create an image of a huge black hole — or rather, of the “accretion disk” of material surrounding a black hole — at the center of the galaxy M87. The dark central gap reveals where the disk’s material vanishes from view, as it presumably flows toward and disappears into the black hole.  

EHT’s image of the M87 galaxy’s black hole’s accretion disk, created from radio-wave measurements. [How do we know there’s a black hole there? I left an answer in the comments.]

What the image actually shows is a bit complicated, because there is not only “light” (actually, radio waves, an invisible form of light, which is what EHT measures) from the disk that travels directly to us but also (see the Figure below) light that travels around the back of the black hole.  That light ends up focused into a sharp ring, an indirect image of the accretion disk.  (This is an oversimplication, as there are additional rings, dimmer and close together, from light that goes round the black hole multiple times. But it will be a decade before we can hope to image anything other than the first ring.)

BHDisk2.png
Left: A glowing accretion disk (note it does not touch the black hole). Light from the right side of the disk forms a direct, broad image (orange) heading toward us, and also a focused, narrow, indirect image (green) heading toward us from the left side, having gone round the back of the black hole. (Right) From the entire accretion disk, the direct image forms a broad disk, while the indirect image would be seen, with a perfect telescope, as a narrow circle of bright light: the photon ring. Unfortunately, the EHT blurs this picture to the point that the photon ring and the disk’s direct image cannot be distinguished from one another. [Long and careful explanation given here.]

Regrettably, that striking bright and narrow “photon ring” can’t be seen in the EHT image, because EHT, despite its extraordinary capabilities, doesn’t yet have good enough focus for that purpose.  Instead, the narrow ring is completely blurred out, and drowned in the direct image of the light from the wider but overall brighter accretion disk. (I should note that EHT originally seemed to claim the image did show the photon ring, but backed off after a controversy.) All that can be observed in the EHT image at the top of this post is a broad, uneven disk with a hole in it.

The news this week is that a group within EHT is claiming that they can actually detect the photon ring, using new and fancy statistical techniques developed over a year ago.  This has gotten a lot of press, and if it’s true, it’s quite remarkable. 

However, having looked at the paper, I’m skeptical of this claim, at least so far.  Here’s why.

  1. Normally, if you claim to have detected something for the first time, you make it clear to what extent you’ve ruled out the possibility it actually isn’t there… i.e., if there’s only a 0.01% chance that it’s absent, that’s a strong argument that it’s present. I don’t see this level of clarity in the paper.
  2. Almost everyone is pretty darn sure that in reality the photon ring is actually present. That introduces a potential bias when you search for it; at least unconsciously, you’re not weighing the present vs. absent options equally. For this reason, it’s important to demonstrate that you’ve eliminated that bias. I don’t see that the authors have done this.
  3. Simulations of black hole surroundings and theoretical estimates both suggest that the photon ring should have significantly less overall brightness than the broad accretion disk. However, the ring measured in this paper has the majority of the total light (60%). The authors explain this by saying this is typical of their method: it combines some of the disk light near the photon ring (i.e., background) with the actual photon ring (i.e. signal). But normally one doesn’t claim to have detected a signal until one has measured and effectively subtracted the background. Without doing so, how can we be sure that the ring that the authors claim to have measured isn’t entirely background, or estimate how statistically significant is their claim of detection?

I’ve included more details on the following section, but the bottom line is that I’d like a lot more information before I’d believe the photon ring’s really been detected.

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Could CERN open a portal to… somewhere? (anywhere?)

For general readers:

Is it possible that the particle physicists hard at work near Geneva, Switzerland, at the laboratory known as CERN that hosts the Large Hadron Collider, have opened a doorway or a tunnel, to, say, another dimension? Could they be accessing a far-off planet orbiting two stars in a distant galaxy populated by Jedi knights?  Perhaps they have opened the doors of Europe to a fiery domain full of demons, or worse still, to central Texas in summer?

Mortals and Portals

Well, now.  If we’re talking about a kind of tunnel that human beings and the like could move through, then there’s a big obstacle in the way.  That obstacle is the rigidity of space itself.

The notion of a “wormhole”, a sort of tunnel in space and time that might allow you to travel from one part of the universe to another without taking the most obvious route to get there, or perhaps to places for which there is no other route at all, isn’t itself entirely crazy. It’s allowed by the math of Einstein’s theory of space and time and gravity.  However, the concept comes with immensely daunting conceptual and practical challenges.  At the heart of all of them, there’s a basic and fundamental problem: bending and manipulating space isn’t easy.  

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