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Unveiling the first-ever image of a black hole [video] (youtube.com)
2164 points by doktorn on April 10, 2019 | hide | past | favorite | 488 comments

Good video that correctly predicted the image and describes why it looks the way it does [1].

TL; DR The dark area is the entire surface of the event horizon, including the side facing away from us, plus some more due to photons missing the event horizon "directly" being drawn in. One side is brighter due to its being Doppler boosted.

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

Smart move by Veritasium, making a video commenting the news just before the news actually happens. Time works in weird ways around black holes.

Anyways, it is a good one. So is that channel in general.

It is also a good video if you just watched Interstellar, because it also explains why the black hole looks the way it does in the movie. Note that the movie black hole rendering is slightly incorrect for artistic reasons, the video shows the more scientifically accurate version.

As far as I know, Veritasium and others occasionally join efforts and coordinate around soon to be published scientific discoveries in a goal to increase exposure. Don’t know if this was the case with the black hole image.

It probably wasn't coordinated, because he got the black hole that was being imaged wrong.

He said we would see a picture of Sagittarius A*, but we actually got the black hole at the center of M87.

They observed both, watch the follow-up: https://www.youtube.com/watch?v=S_GVbuddri8

"The Event Horizon Telescope Collaboration observed the supermassive black holes at the center of M87 and our Milky Way galaxy (SgrA*) finding the dark central shadow in accordance with General Relativity, further demonstrating the power of this 100 year-old theory."

But in the press conference they specifically said they weren’t releasing SgrA* yes because they hadn’t completed their analysis. They released pictures after that?

You're right, it looks like they are still observing Sagittarius A but what they released was only a simulation for that one.

I thought we got both, which is the best possible outcome: no one is wrong and there are more black hole photos.

We didn't get both, we only got M87. Sgr A is dimmer, so it needs more number crunching to get a good image

It's too bad we cannot see the accretion disk edge-on as in the video. That would have made it a perfect prediction. Maybe it's so thin that it's overwhelmed by the projections of the top and bottom of the back side of the disk.

May be we can see higher resolution if we build an additional telescope.

More distant (longer baseline), not merely additional sensors.

Resolving power is proportional to the (virtual) aperture size, not the total sensor area (that gives more signal strength).

Given the observation period has been multiple years, does that virtual size include the orbit of the Earth? Or is there something that limits it to still being Earth-sized?

So put some telescopes in orbit around the Moon and Mars.

A guy on Reddit actually asked this in the AMA. While that would increase the resolution, it would also be extremely difficult. The algorithms used to combine the data from the dishes relies on the exact position of the dish being known at the time of measuring, to a precision of fractions of millimeters. It's already hard to do on the earth's surface, but imagine doing it with a sattelite zipping around the earth at 20K km/s, or the moon at >1 km/s around the earth, or Mars at 24K km/s around the sun.

Not to mention getting the data back down here. For the analysis of M87, there were multiple petabytes generated: they had to use good old sneakernet and ship hard drives.

Wow, the video you posted is even more informative and clear than the actual press conference, and it was created by someone who hadn't even seen the image yet based purely on the mathematical predictions of what we would see.

Kind of sad that after all the amazing effort and resources that have gone into the creating the image that the international team couldn't have featured an explanation as clear as this in their actual press conference.

The video by Veritasium is by a guy who literally got a PHD on the subject of making physics more approachable through videos. He is exactly the person I would expect to provide a more clear and understandable explanation.


Why doesn't he work with the actual astronomers, then?

You don't have to watch his channel for very long to learn that he often does (see his video about the recent gravitational wave detection [1], plus a bunch more).

[1] https://youtu.be/iphcyNWFD10

Just by sharing the news he is working with them helping the global effort.

Because he’s busy making physics more approachable through videos.

Perhaps I should have phrased it as "why don't astronomers work with _him_?"

Different target audiences for a science YouTube channel and a scientific findings press conference.

It'd be extremely shocking if he hadn't been able to. The math has been known for a very long time the largest differences would be based on the orientation of disk relative to us but that has been mostly known since the original Hubble picture. If he'd been significantly wrong that'd mean our understanding of the physics was wrong or something unknown was happening at a pretty large scale.

Everyone knew what the image was going to look like, so it's not any harder to prepare in advance.

Here's the follow up video after the image was released: https://www.youtube.com/watch?v=S_GVbuddri8

So amazing that scientists were able to predict what something would look like that we have never seen before.

It's good science.

Been able to make testable predictions and then confirming them or disproving them is the entire (awesome) point.

After having said that, I did a bit more research into how the image was made. I am of course reserving judgement as I don't fully understand the underlying technology. But it sounds like they used an interpolation algorithm to come up with the image based on renderings of what we "think" a black hole should look like. This high level overview from a ted talk goes into how they 'unbias' the data. But it is obviously on a very basic overview: https://www.youtube.com/watch?v=P7n2rYt9wfU

Indeed. Whenever you go looking for something you think is already exists, as opposed to stumbling across an object, there is a danger that the parameters of your search will favor your preconceived notions. One will also tend to describe observed objects in terms that tends to fit your theory. I'm not saying that happened here just that it is a danger.

Astronomy/cosmology is one of those strange disciplines where rather than discover new objects in situ, one discovers their possibility in the mathematics and then goes out to find them. So I and many others were hoping that this image was radically different than the math, potentially opening the door to some new theories. Confirmation just isn't as much fun as raw discovery of the unknown. Example: the recent "cannonball star" observations. We are going to need some new science to explain how that is a thing.

Not sure why you're getting downvoted because (as a physicist) I'd say that especially in the face of a high-level discovery like today's, a healthy amount of scepticism is a good thing.

That being said, it seems your concerns are being addressed in the TED talk you linked to from 8:45 onward?

Moreover, in the NSF press conference today it was said that they had four different teams in four different locations across the globe last year, working on interpolating the data and generating the images and they basically asked the teams to lock themselves in, i.e. to not communicate with each other at all, and use (more or less) whatever interpolation algorithm they thought would fit the data best. And at the end, when the four teams met up last year, they had supposedly arrived at very similar-looking images.

I briefly(!) looked at the papers that were published today ("First M87 Event Horizon Telescope Results" I-VI) and while I'm anything but an expert when it comes to radioastronomy and imaging technology (I'm more a theoretical physics/mathematical general relativity kind of guy), I came across the following statements which, to me, all suggest that they've at least evaluated the data with due diligence (emphases all mine):

"IV. Imaging the Central Supermassive Black Hole" (https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85):

Section 5.2 confirms the statements from the press conference today:

> The imaging teams worked on the data independently, without communication, for seven weeks, after which teams submitted images to the image comparison website using LCP data (because the JCMT recorded LCP on April 11). After ensuring image consistency through a variety of blind metrics (including normalized cross-correlation, Equation (15)), we compared the independently reconstructed images from the four teams.

> Figure 4 shows these first four images of M87. All four images show an asymmetric ring structure. For both RML teams and both CLEAN teams, the ring has a diameter of approximately 40 μas, with brighter emission in the south. In contrast, the ring azimuthual profile, thickness, and brightness varies substantially among the images. Some of these differences are attributable to different assumptions about the total compact flux density and systematic uncertainties (see Table 2).

Section 6, in turn, confirms the statements from the TED talk:

From the introduction to section 6:

> To explore the dependence of the reconstructed images on imaging assumptions and impartially determine a combination of fiducial imaging parameters, we introduced a second stage of image production and analysis: performing scripted parameter surveys for three imaging pipelines. To objectively evaluate the fidelity of the images reconstructed by our surveys—i.e., to select imaging parameters that were independent of expert judgment—we performed these surveys on synthetic data from a suite of model images as well as on the M87 data. The synthetic data sets were designed to have properties that are similar to the EHT M87 visibility amplitudes (e.g., prominent amplitude nulls). This suite of synthetic data allowed us to test the scripted reconstructions with knowledge of the corresponding ground truth images and, thereby, select fiducial imaging parameters for each method. These fiducial parameters were selected to perform well across a variety of source structures, including sources without the prominent ring observed in our images of M87.

From section 6.2:

> We then reconstructed images from all M87 and synthetic data sets using all possible parameter combinations on a coarse grid in the space of these parameters. We chose large ranges for each parameter, deliberately including values that we expected to produce poor reconstructions.

Finally, in the caption of figure 4 of "I. The Shadow of the Supermassive Black Hole" (https://iopscience.iop.org/article/10.3847/2041-8213/ab0ec7) they write:

> Note that although the fit to the observations is equally good in the three cases, they refer to radically different physical scenarios; this highlights that a single good fit does not imply that a model is preferred over others

…which, assuming that I'm understanding this correctly, means that the bias in the fits towards one model over another is low.


Again, I cannot stress enough that I've only skimmed the papers but from what I did read, I see no good reason not to trust their results.

This sort of reconstruction problem from VLBI measurements is under-determined so you need to insert priors/regularization to get anything at all. The priors in this case are pretty weak (from a quick read of the CHIRP paper). https://arxiv.org/pdf/1512.01413.pdf

ad Good science, I just randomly bumped into this video today that very nicely explains the differences between good science and bad science. https://www.youtube.com/watch?v=umo6pMCkcXs (safely skip the first 3 minutes)

Einstein predicted the existence of black hole back in early 1915. Pretty amazing.

Einstein first developed the theory and the equations that allowed for them to be discovered.

You can imagine that space-time equations have many solutions and properties that can't be contemplated all at once even having them right in front of you.

Schwarzschild took the equations and obsessed over them for countless hours and eventually discovered that one solution to them implied this phenomenon and therefore he discovered black holes by discovering a specific solution to Einstein's equations.

Of course no one knew at the time if the mathematical solution represented real physical objects that exist in the universe, because it doesn't always happen that way. Occasionally some obscure corner of the math predicts something that's a dead end or anomaly that doesn't have any meaning of value as far as it is known.

They had no way to know one possibility from the other.

I thought (relativistic) black holes were first predicted by Schwarzschild in 1916?

(As an aside, I have found a whole extra level to nominative determinism since starting to learn German — Schwarzschild = Black shield)

This is also called an aptronym.


It's a little of both, but yes Schwarzschild technically first predicted them.

> In 1915, Albert Einstein developed his theory of general relativity, having earlier shown that gravity does influence light's motion. Only a few months later, Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass.


Or was it the Revd. John Michell? https://en.wikipedia.org/wiki/John_Michell

Michell. And maybe Laplace.

Of course they "invented" Newtonian black holes, not relativistic black holes.

Even so - well ahead of the rest.

The Event Horizon Telescope site has had predicted images up for ages https://eventhorizontelescope.org/science

Side observation: This video, and the video you linked to got two million views in just a few hours. I didn't know black holes where this popular. (market opportunity here)

It's a very well made pop-sci video, which probably substantially increases the likelihood of it being reshared.

If one needs an intro, this video should be watched before watching the press release..

In the video he talks about the Schwarzchild radius but doesn't go into details. It is the distance from the center of the black hole to the event horizon.

Anything which is not in that radius or not already in a path towards it should be safe from not getting sucked by the black hole.

E.g. If our sun becomes a black hole, Schwarzchild radius would be 2.954Km i.e. anything outside ~3Km would be safe.

This was explained in the scishow video on that topic[1].


That’s an oversimplification. The Schwarzschild radius is where to find an uncharged & non-rotating black hole’s event horizon, and the event horizon is the surface at which newly generated photos (and all causal influences) can no longer escape.

The innermost stable circular orbit is further out than the event horizon, 3 times the Schwarzschild radius IIRC. Anything closer to that has an unstable orbit.

If the general theory of relatively was tested again and it proved to provide the next result, what does it say about actually is an black hole?

Thus far, from all the experiment and result observed, the theory has been proven to be correct.

Hence, it can be said with 99% certainty whatever it predicts must be correct. I hope it does mention about possibility of creating a worm hole.

No, that is not how science works. We can say with 100% certainty that the theory has not been falsified by any test to date.

A very good (technical) talk about the EHT project and the physics they try to do here: https://www.youtube.com/watch?v=JiS1OJNBrvk

It is a bit old (2012), but comprehensive and with both good audio and readable* slides.

*: In the sense that you can see the letters on them

Another link describing what a black hole is:

Part I: https://www.youtube.com/watch?v=VnJYo6LKzgA

Part II: https://www.youtube.com/watch?v=Nlry6LqWwJ0


I just stumbled upon Veritasium a week ago while learning about the double slit experiment in quantum theory and trying to see some actual evidence [1] of the experiment.

[1]: https://youtu.be/Iuv6hY6zsd0

Not sure if I missed it, but can we tell which way the accretion disk is from our view of it?

perpendicular - we see it almost exactly from the top. Mentioned during the Q&A (41:33 to be exact)

If we see it almost exactly from the top, then why is one half of the ring so much brighter than the other?

Relativistic beaming! https://youtu.be/zUyH3XhpLTo?t=490

So that would mean that the right side is tipped slightly away from us, right? Because the matter in the accretion disk starts approaching us at about halfway down the ring on the right side?

Yes, from paper 1:

"Third, adopting an inclination of 17° between the approaching jet and the line of sight (Walker et al. 2018), the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). "

Already watched the video, thanks. However in his example the disk is not perpendicular to the viewer so the beaming makes more sense there I think.

On the other hand, "almost exactly from the top" is not the same as "exactly from the top".

The video JumpCrisscross shared above says this is the black hole at the center of our galaxy, so why isn't its accretion disk oriented the same as the rest of the galaxy? Isn't that weird?

It's actually in a galaxy called Messier 87 which is 55 million lightyears away.

Oh, interesting! Wouldn't it be easier to photograph our own? :-)

Actually not. M87 is a 1000 times farther away than Sgr A* but also a 1000 heavier and thus a 1000 times bigger in diameter. (Diameter/radius scale proportionally with the black hole's mass.) Therefore, the actual angular size on our night sky is the same for both black holes and, from this point of view, both would be equally difficult to observe.

However, as they mention in the press conference, Sgr A* moves a lot faster relative to us than M87, so it's much harder to take a still image. (In the press conference they used the example of trying to take a photo of a toddler with an exposure time of 8 hours.)

During the press conference, they said photographing the M87 black hole was like shooting a hibernating bear, and photographing the Sag A* black hole of our galaxy like photographing a quickly moving toddler. Something about the speed making it much harder. It is also much smaller, but that's less of a problem because it's much closer. All in all apparently making it about the same angular size. But it sounds like they'll get to it, it's just harder.

That's a... weird analogy.

I think the actual analogy was lost in translation: the point is that, unlike its older brother, Sgr A* is not going to "pose" when you point your camera at it.

Ah, I thought it was about actually shooting bears and toddlers.

M87's black hole is currently eating something big, which makes it brighter. The black hole at the center of the milky way doesn't seem to have eaten anything lately, so it's accretion disk may be small or nonexistent.

> is currently eating something big

You mean: was eating something big 55 million years ago ;)

Nope, for the same reason we had photos of the Moon before we had photos of Earth.

Can you expand on this?

What they're saying is that we had to send a camera away from the Earth (in a rocket) in order to photograph it properly, and similarly you'd need to send a camera away from our galaxy (in a biiiig rocket) in order to be able to photograph it properly.

Nope. The view of our own galaxy's supermassive black hole is completely obstructed by matter within our own galaxy. You can't see to the core of our galaxy; it's too dense. You'd have to send a rocket quite some distance outside of the galactic plane to get a good view of it.

The images are made with radio telescopes, which cuts through the dust quite easily. We have many other radio observations of Sagittarius A* [1], albeit at much lower resolutions. There are also numerous observations of Sagittarius A* in X-ray wavelengths, which is also fine because they are so energetic they simply punch through. All the dust and gas in the galaxy is transparent at most wavelengths except the visible one.

The Event Horizon Telescope is interesting because it is, in essence, a radio telescope that uses a "sensor" that is the size of the entire Earth. As such, it is able to make much higher resolution observations.

[1] https://en.wikipedia.org/wiki/Sagittarius_A*#/media/File:Clo...

[2] https://en.wikipedia.org/wiki/Sagittarius_A*#/media/File:X-R...

The observed both supermassive black holes at the center of M87 and our Milky Way galaxy Sagittarius A

Not according to Veritasium's comment on his own video as well as the RelAstro group who produced the material[1]: "As there seems to be some general confusion, please note that the image shown here is a simulated one and not an actual image. So far we only have an image of M87. Kind regards, the RelAstro group. "

[1] https://www.youtube.com/watch?v=VnsZj9RvhFU

Ah you're right. Looks like they all should've skipped Sagittarius A instead of adding confusion.

apparently from the top. i hope we get to find another one sideways because they look cool ;)

That was a great video, never grasped why interstellar and such showed black holes with the rings on top and bottom.

So is that hazy diagonal line in the image the accretion disc, viewed edge-on from the Earth?

It doesn't seem to be that accurate, as expectation was for it to have smoother photo sphere, but it has irregular bulges (5 of them). I think they discussed it briefly in the press conference as well. It would be interesting to see if this would change understanding of general relativity and may be give a hint for a theory of quantum gravity.

I'm not sure how much we can truly draw from small irregularities in the image. This isn't actually a low resolution image. It is an algorithmically interpolated image created by comparing possible interpretations of the spotty and noisy data gathered from multiple points at different times processed against images of what we think a black hole should look like.

Look at the expectation examples in the scientific paper from 2013 that is, from ca. 6 years ago:


It matches quite good, I'd say. Page 4.

What bothered me more about the video is that of you watch the whole thing, he ends up talking about some theory which leads to another type of image prediction. He never actually explains why he chose to go with the former prediction rather than the latter.

The whole video was him explaining why the image would look the way it ended up looking. darkpuma was overly patient when explaining this to you.

You were a user acting in bad faith that very literally jumped in at the end just to write a troll bait comment in that thread. Your comment had nothing substantive to even do with any discussion, or even any relation to anything I said.

There is nothing complex about my original statement there. The EHT website itself has a gallery of simulated images and I'd like to know why he chose that one specifically.

In the video he says "just trust me."

This is a perfectly reasonable criticism, I don't care how many downvotes or personal attacks I get.

It has nothing to do with anyone "being patient." That thread was 90% bullying, which you are taking part of.

Can you link to the comment of yours that I replied to? I can't see it for some reason.

> Good video that correctly predicted the image and describes why it looks the way it does

This is of course a bummer, since this means that the acquired image does not give us any new clues of where our understanding of physics is wrong.

I think this is unhelpful parroting of comments on actual cutting edge physics experiments like the LHC. The degree matters substantially - there, we have good guesses of what we might see, but there's uncertainty and new data is immensely valuable for narrowing hypotheses. It's the research frontier.

Reasoning about an image of a black hole is very much within the realm of standard science. Veritasium was able to explain the prediction using essentially ideas that are so basic they're at the high school level. If our basic understanding of physics down to the high school level was wrong (e.g., very far from the research frontier), there would be very very serious issues.

It's probably a bit too early to say because e.g the magnetic field data that was also collected hasn't even been scrutinized yet. This will also almost for sure lend a better understanding of the relativistic jets, in order to hopefully one day tell why they are this way or another depending on the particular black hole rather than just "they are somehow often there".

It's still very early and like the detection of gravitational waves, I think it feels like more of a symbolic step into a new era of space science. It's easy to forget that yesterday, black holes were a result of mathematics and only indirectly shown that they "ought to exist".

So first, I think we need to cut them some slack! Second, I think that if we at all WANT to shatter the Standard Model, I think we first need to be able to do science at the extremes of it! The LHC is one way, probing into the details of black hole mechanics might end up being another

We've furthered our understanding of the truth of the universe. That's not a bummer.

I expect that at the resolution that this picture is taken it would be surprising if new radically physics was found, since it would require our current models to be very different from reality to see significantly different results

Ok, wait a second. I liked a lot of this video, but there are some aspects which are kind of ridiculous. He says his reason for his confidence in this prediction is "I think it's going to look like a fuzzy coffee mug stain." He doesn't give an actual reason.

He does talk a lot about theory, a lot of it interesting and novel to me, but by the end of the video, most of this theory suggests a different-looking image!

How about forgetting that video for a moment and trying to consider the following picture:


Taken from here: https://eventhorizontelescope.org/science (the official site of the project).

On the left is how it would look like if we weren't so far -- we are 55 million light years far from that. You know the distance from us to our Sun, which you see on the sky but can cover with your own thumb? That object is 3,500,000,000,000 times farther than the Sun is far from us.

On the right is what we can reconstruct from the signals measured because we are so far and we have "only" the telescope the size of the Earth. More details would be visible (the picture would look more like the one on the left) either if we had even much bigger telescope than the Earth, or if the black hole of the same size were much closer to us, which it is not.

The entire video is his description of the reasons for why it'll look like a fuzzy coffee mug stain. It's "fuzzy" because of the low resolution, not because the black hole itself is fuzzy. Undoubtedly there will be work to improve the best quality photograph of a black hole, now that we have one at all.

That's not correct. Around 25% of the video is discussion around the concept of the radius of photon sphere to the event horizon, and what constitutes the light surrounding the photon sphere (one explanation he gives is that there are infinite reflections). Then he spends the last 30% of the video talking about reflections of the acretion disk. This is the theory that he never included in his original prediction, but doesn't explain why he made that call.

Uh.. It's the reason that the "shadow" is larger than the Schwarzschild radius. He's describing the ratio of the "rim" to the "hole". So while the picture may be fuzzy, there's information in it anyway about what the pictures means relative to how large/spin we think the black hole is. In fact I wish he'd said more about the Doppler effect.


I think what you're hoping for is a more exhaustive survey of what black holes are theorized to look like, with different possibilities. Is that right?

The problem here is your expectation does not match the product. It's like you went to a car dealer and are upset they didn't sell you an airplane.

It isn't surprising to me that Derek focuses on one form, since Veritassium is providing content for the armchair consumer, that he chooses what he believes to be the best model and presents that. This isn't a PhD defense, after all, it's just a timely video so that folks can appreciate the image that the EHT group has released (is going to release, at the time of Veritassium's video.)

Did you have some other models in mind?

Interesting to me is that Veritassium's presented model doesn't explain the corona-like features, nor any attempt at explaining the "blobs" although he does say that blobs would be exiting to see. And there they are! What fun.

Yea sort of. I mean I said I liked the episode, I just think this part is bad form (I'm paraphrasing):

>why can you expect it to look like this? well because it's just going to look like this.

Now, I'm not trying to say his prediction was unwise. I just think it's first of all bad form to say something like "the reason is just trust me," in scientific discussions (even if you are correct)... but second I actually do want to know at least some explanation to that question. Granted, I'm not saying the video does not explain anything about the image. I wanted to know: why can we be sure it will look like this, and not other simulated images?

That's all.

You can see on the EHT's own website a gallery of other simulated models of what could be expected from a radio image.

And the second part of my criticism, was that by the end of the video, he was using images inspired by other models, and particularly of one where the accretion disk dominated the image.

I dont care how many downvotes I get, I know the difference between right and wrong and this is a perfectly reasonable criticism.

Anyways, since my posts lost 60 karma in 1 hour somehow (almost uniformly coming from posts in other threads, wtf?) some other opportunistic types see it as a chance for bullying. Even writing stuff like 'you've obviously got your jimmies rustled mate!' or other extremely bad faith assumptions like 'if you cant understand why it's fuzzy, it's far away!' The best is the troll bait comment, 'do you really think one person is downvoting you?' Groupthink, bullying, and authority define right and wrong for some people--they can't even write something that even addresses an actual comment or argument. People are crazy. Eventually they just start addressing the negativity itself, abandoning any substantive argument, and focusing on the negativity itself. The next step is using the negativity as its own justification (you deserve negativity because otherwise you wouldnt be receiving negativity kind of assumptions implicig in the above troll bait comment).

But still all that I dont think explains why comments in unrelated posts (even ones that were being complimented) got the same time-unform mass-downvotes?? I think I haven't experienced anything like this before on this site until recently. I lost 60 karma in the a few hours.

Well, for the record, it wasn't me. I did however read through your comments just now, and it seems there is a pattern of not really engaging in dialogue but just blasting your opinion over and over. Looking at your comments on Julian Assange, for example, it seems clear that you do not think there is any difference between what a NYTimes reporter does and what Assange did. I can't speak to everyone else but to me the difference is quite obvious, and probably that has something to do with why you're being downvoted. You're repeatedly stating that they're the same, without describing why you believe this, and then kind of insulting other people for their belief that in fact they are different. So anyway, I've spent way, way too much time responding to you. Good luck to you sir.

Hmm there is some groupthink, lack of reason, or bullying going on here.

Look at this image for yourself. The article is titled: "Here is what scientists think a black hole. Looks like:" https://www.sciencemag.org/news/2019/04/here-s-what-scientis...

There are not massive differences in the images, but the Vetiasium prediction was (and this is very plain) much more accurate.

This isn't controversial at all.

I also thought the particular statement, "why is it like this, because it is just going to look like this" was bad form.

This is very plainly reasonable.

I think the fact that you and a few other users turned this into an opportunity to go through the effort of writing belittling comments and even put downs and troll bait over something as plain and ordinary as this is indicative of some bad qualities of humanity expressing themselves here.

Of course, your only response will be further negativity as bad people dont possess the ability to admit when they were wrong.

And the statement about Assange is very widely expressed. See here(1). There are articles all over the media, just like that one, echoing the same exact view. They are literally everywhere.

Finally, I noticed over the last 30 minutes all my recent comments went down by -1 each. That really makes it look like I'm engaging with some quite petty and insecure people.

Edit: see, right after I wrote this comment, all my recent comments each, in perfect synchronization, down by -1 again haha.

The reason for the fuzziness should be obvious. It's really far away and it's really hard to see. Expecting a jump from "never seen before" to "seen in amazing visual clarity" is unrealistic.


He isn't explaining why the blackhole would look like a fuzzy coffee mug stain. He's explaining why the _picture_ of the blackhole will look like a fuzzy coffee mug stain.

To your point, it's like taking a picture of Uranus with film and waiting for it to develop. People familiar with the matter can guess what the _image_ will look like not what Uranus actually looks like.

This is all very clear in the first 25 seconds of the video if you actually listen to what he's saying.

The first 25 seconds of this video actually does not have sound. The 25 seconds after he begins talking is him talking about Einstein and history.

Unless I'm misunderstanding your intentions and you just meant that as a condescending insult?



> "What? You obviously didn't read what I wrote. Are you ok?"

You're ranting about Saturn and Jupiter for some reason. Why don't you calm down and look at page eight of the paper that Veritasium video was based on: https://ve42.co/luminet "Image of a spherical black hole with thin accretion disk Astronomy and Astrophysics, vol. 75, no. 1-2, May 1979, p. 228-235"

Look at that last image, and squint at it until it gets fuzzy. Lo and behold, a fuzzy coffee mug stain!

Perhaps it was a mistake for him to make the focus of the video on the physics of black holes, rather than the limitations of state of the art radio interferometry... but I don't think so.

Really awesome link, thanks for that! It's always interesting to see theory that is decades out in front of experimental confirmation, and then proves to be dead right.

Yeah, I did a double-take when I saw that was published in 1979. I think that's really cool.


You truly believe that all of the downvotes on all of your comments are the work of one account?

Mate, you insulted me first, and have just repeated that insult again. I've tried to be charitable with you.

How did you come to the conclusion that I "insulted you first?"

>He says his reason for his confidence in this prediction is "I think it's going to look like a fuzzy coffee mug stain." He doesn't give an actual reason.

He doesn't need to give a reason. The reasons why it would look like a "fuzzy coffee mug stain" are well known since Hawkings...

Did you see the movie Interstellar? He included it in his video. That's what the black hole looks like, except with the relativistic beaming make one side brighter than the other.

Here's the image from the movie: https://www.wired.com/wp-content/uploads/2014/10/ut_interste...

Now imagine that image being taken far away by several ground-based telescopes put together at the edge of their capabilities and using math to error correct and stitch together the final result. What you get is what we saw.

Ah, sure. Also, if you go to the EHT's own website, they have a gallery of predicted, simulated images.

Here is another prediction: https://www.sciencemag.org/news/2019/04/here-s-what-scientis...

I just wanted to know why he went with that one because his prediction was really accurate. And I thought him saying 'just trust me' was bad form.

He did talk some about this, but he didn't really say anything about why he thought his illustration would be so accurate compared to a lot of other stuff seen in the press.

I dont care (or have any idea why) how many downvotes or insults I get. It is a perfectly reasonable question and criticism.

I don't see the difference, the predictions are the same.

The only changes in the image depend on what angle the black hole is being viewed at which would influence whether we see a band across the middle and the slimmer inner ring.

Lol the image I linked is obviously very different.

There is some groupthink going on here affecting people like you and others. The above is obviously plain.

There are 4 images on that page, 1 of which is the Interstellar movie rendition that I already linked to. They are also all the same model only in better detail as graphics technology has improved.

Perhaps you should post exactly what image you're talking about and what you think is different.

In the images I linked to, the black hole images don't have any "blobbiness," and seem to have these perfect gradiants.

In the veritasium video the "coffee stain" was not really as blobby as the real image, but it seemed a lot closer than the smooth-gradiant, no blobbiness and no irregularities predictions.

I dont just mean the fuzziness from low resolution.

This isn't really a big deal, but it's also obvious that I am just stating plain facts about what is in these images.

At the time I saw this video when he said "you can be confident, because... (no reason given)" was really the thing that I thought was annoying.

I think you can see the differences in the images. They're not huge but the smooth gradiants vs irregularities/coffee stain/blobbiness is plain to see I think.

Edit: from the horses mouth himself, one of the lead researchers says he didn't expect the image to look like it did: https://youtu.be/ZrDhHDBHkQY

Some of the people here in other parts of this thread have been really offensive for this. It's honestly pretty ridiculous.

The general model of what a black hole looks like is well understood. The highest definition rendering is that in Interstellar, except for one side being brighter than the other due to the relativistic beaming. They kept that part out of the movie to just make it look nicer.

All the models are the same, and the real picture is "blobby" only because of the process in how it was taken. I think you are refusing to accept that but there's nothing else to say about it. It wasn't a direct photo, it was a complex assembly of several different radio telescopes around the world stitching data together. If we were actually next to it, it would very much look like the one from interstellar.

The video you linked isn't about the prediction being wrong, more that he just didn't expect to really see a black hole at all. Even though black holes are generally understood for decades, there's a certain shock and awe to seeing it real for the first time.

Lol ok then we can agree to disagree. Even the YT video I just linked to opens with an intro containintlf a simulation, which once again, has subtle but pretty obvious and appreciable differences.

Also, my complaint was in fact that I didnt know why Veritasium was confident in their prediction. This complaint is for a matter of fact completely consistent with one of the lead researchers outright saying they didn't know what to expect. I never said I was exclusively complaining about there being simulated models which have some differences. You and others criticized me after I said he should have substantiated why he was confident in his prediction. I gave what I believed was my the foremost reasoning for saying that.

I had little idea what the picture would look like...

I have no idea why you're so intent in disagreeing with me. I'm substantiating my ideas with facts. And saying 'just bbelieve me' I think is also bad form.

At this point I feek like your disagreement has to do with psychological or social biases unless you are able to address the factual content of my comment.

But the one thing you said that was interesting was about the blobbiness. I think what you are trying to saya is that it is fully expected by the researchers to be error. Do you have a good interview or other source on this?

Higher resolution official release seems to be: https://www.nsf.gov/news/special_reports/blackholes/download...

Does that image have a weird pulsing optical illusion for anyone else?

It's the color scheme. I think in matplotlib it's called "hot". I do a lot of 2D kernel density plots that by having a black zero level and dozens of contour levels produce a smooth look with aesthetics similarities to this. I used to use that scheme because "heatmaps" but stopped because of the pulsing illusion.

I'm not sure if this image is real color or just lightness value and they used a color scheme for drama.

Grrr, why aren't scientists all using perceptually uniforms color schemes! This would still look awesome in `plasma`. Is there any where I can get the data and do it myself?

One of my favorite talks ever is on this subject: https://www.youtube.com/watch?v=xAoljeRJ3lU

'Inferno' would be nice for this, also perceptually uniform, and has the benefit that space is still black.

Can you run it through the colormap in reverse to (approximately) recover the data?

Based on my analysis the published image is too processed to be able to invert the colormap to get to the brightness temperature data. I had better luck with Paper IV Fig. 15. See: https://physics.stackexchange.com/questions/472641/what-woul...

Technically yes -- colormaps are 1-dimensional non-self intersecting curves in RGBA space. You just grab them by the... I mean just straighten them.

I don't know if an explicit formula for the colormap is given, but you can always do "xs = np.linspace(0,1,100); ys = { cm.hot(x):x for x in xs}" and recover an approximate inverse. Then apply this function to each pixel of the image.

You can easily remap it between different colour maps if you assume that is is a standard hot map.

It's the latter. This is an image in radio-frequency brightness of the object, so not visible frequencies of light. But yeah, it also looks like the 'hot' colormap to me.

I think my eye is trying to bring it into focus. It is like when the camera on your phone can't quite figure out what it is looking it and keeps adjusting.

I suspect this is because it's extremely blurry, if you watch it on a large screen it might trick your eye into trying to refocus, obviously without success.

Interesting that so many people see this but for me it's absolutely static.

If you are focused and calm, or have bad sight, you won't see it naturally. To force it, move your focus from 1cm to the left, then right, again and again, quickly.

Yes, reminds me of the Eye of Sauron.

Funnily, it reminds me of Soundgarden's album, Superunknown, which had the famous song 'Black Hole Sun.'


The supreme astronomical example of the Eye of Sauron is this Hubble shot of the star Fomalhaut and its debris disk: https://en.wikipedia.org/wiki/Fomalhaut#/media/File:Fomalhau...

Yes, fascinating! If you shift the focus of your eyes from the outside to the inside of the hole, it seems to "pulsate"

looks like the image data was cleaned up with bicubic interpolation, or something of the like.


I don't even have to move my eyes, I stare at it and it's constantly moving away from me. I had to check that it's not actually a movie. Strangest thing.

Yes, and I also see a spot in the shape of it after looking away, though that may just mean my monitor is too bright

Some time ago I've seen a picture over the Internet where the description said the more you see it "moving" the more likely you're stressed.

As for the black hole, looking it at full screen I see it pulsating a little.

Yes if you dance your focus around the image, it appears to pulsate. Probably your pupils constricting and dilating due to the high contrast in the image.

It does look like it pulsates to me! That's an interesting illusion :)

Stare at it till there are two, then have fun snapping them in and out.

Relieved it isn't just me

I get it if I move a bit when on an angle, I assume it's just my crappy monitor's viewing angles causing it.

moving the picture on my screen caused some eye bug

You mean to tell me this is not a gif?!

I literally did double-check the file extension

And a really great explanation of why it looks the way it does:


editing that image reveals all kinds of details: https://imgur.com/a/TvQsgbA (and I don't even know what I'm doing)

Mind you, that's a JPG you are editing, so in the 8 bit sRGB color space. That means manipulations can lead to errors and illusions due to the color space being non-linear and clipped[0].

The original data was likely linear and at a much higher precision. If the source was a 16 bit linear grayscale PNG for example you could be much more assured you're not seeing the effects of JPG compression and things that were actually measured.

EDIT: Found better sources:

16-bit sRGB PNG: https://eventhorizontelescope.org/files/eht/files/20190410-7...

180 MiB original TIFF: https://www.eso.org/public/images/eso1907a/

[0] https://www.youtube.com/watch?v=LKnqECcg6Gw

Thanks a lot for the explanation and the better sources, the TIFF image should probably be a torrent because it's not downloading very fast, the PNG image does give much nicer renders: https://i.imgur.com/zZcD5Na.jpg

Those 'details' aren't real. The image is the result of a complex interpolation algorithm that takes very noisy and incomplete data as its input. The resolution is quite limited.

I do (I think...) the bands are atifacts:


The article linking to that image: https://nsf.gov/news/news_summ.jsp?cntn_id=298276

Thanks for the source article! I had heard about this but not seen any material on it until now.

The additional pixel density probably doesn't add any details though. The original image looks like a smoothed-out version of a low-res image anyway...

Is this link down for anyone else?

Probably because of HN effect again. Yes it is down.

Can someone stick it on IFPS?

Slashdot effect

So how much this picture cost ?


So basically nothing in the grand scheme of anything.

I've taken to measuring moderately large amounts of money in "juiceros". Forty million dollars is one third of a juicero.

That's half the cost of a single F-35 fighter plane. Just US alone will pay for around 2500 of them (2010 estimate), and plans to pay around 4 times more than that to maintain them. So just F-35 total costs for US are equivalent to 25000 scientific projects like this one. To compare, it would be one new project like this every day for 70 years!

This specific project is more European or even a world project than just US, if I understood correctly.

It makes sense to compare the costs to a single plane but to the whole fleet is just stupid. You can't defend a country with scientific projects.

The thing is every time someone proposes the idea to slash the military budget to fund something else there are at least a hundred other people with a different idea on what to use the funds on. If the funds were spread over so many different projects you end up with an insignificant sum in each of them. Spending the money on military might be actually be advantageous because of large investments in new military technology end up benefiting the civilian sector. (Isn't that the point of the F-35?)

It’s the opposite: most of the military money goes to the stuff which, if actually used, ends the human civilisation as we know it.

The same goals that US has could be achieved with orders of magnitude less military spending, while also reducing the risks for the whole humanity.

So every alternative to the current practices is infinitely better.

Whenever this type of question comes up, how much science cost, think about the following:

It costs more to do a sciency Hollywood movie about than it costs to actually do the science. Sending an actual probe to the orbit of Mars is in general cheaper than making a sci-fi movie.


the original tiff is 7416x4320

it's still too many pixel, it can be a fifth of that while conveying the same amount of information.

I'm puzzled by this, if each of those pixel is actually captured by the lenses, why is it all this much uniform? was it smoothed or does this suggest that it's actually a gigantic uniform cloud of gas?

haven't seen the whole video of the release, I'll have to catch up later in the evening, but this really seems to have captured way too much compared to the actual lens resolution and I wonder what would be the "confidence interval" or astrophysical equivalent on each of those pixels.

There is no lens. This was done using eight radio telescopes (or arrays) around the globe to create a "virtual" radio telescope which is effectively the size of the earth. After that the data of the individual telescopes was processed to produce an image.

There is some more info in the wikipedia article for the Event Horizon Telescope (EHT): https://en.wikipedia.org/wiki/Event_Horizon_Telescope

Thanks for the link. More reading reveals the amount of data produced goes into Petabytes. You can't just upload it to drop box or push it via FTP; hence correct icon of an airplane because those drives with data are indeed delivered by regular means of transportation.


The picture is not captured by lenses, or an optical telescope at all. It is created by inverting the data received at eight radio telescopes (or eighty individual dishes) around the world. And the smoothing is just due to the inherent limit in the resolving power of the telescope array. The impressive bit is that we see more than a single bright dot.

From the press conference, they said that the raw captured data took up 6 cubic meters of hard drives

> cubic meters of hard drives

Astronomy and high energy physics are pretty much the only science I know where this is an applicable unit of measurement

Related video, made by Veritasium yesterday, is one of my favorite videos in a long time. He explained how the prediction of this image was made (before the image got released) and the video is great and fun to watch.


Note that the prediction of the light being brighter on one side did come out.

What are you basing that on? (Edit:) From one of the papers released today:

> The ring is brighter in the south than the north. This can be explained by a combination of motion in the source and Doppler beaming. As a simple example we consider a luminous, optically thin ring... Then the approaching side of the ring is Doppler boosted, and the receding side is Doppler dimmed...This sense of rotation is consistent with the sense of rotation in ionized gas at arcsecond scales ..Notice that the asymmetry of the ring is consistent with the asymmetry inferred from 43 GHz observations of the brightness ratio between the north and south sides of the jet and counter-jet


(Edit 2:) Ahh, I see your comment now says "did come out". I initially read it as "did not come out", which was either a misreading on my part (likely) or an earlier edit by you.

It's confirmed in the press conference by the scientists. They said its the Doppler beam effect

Are north and south in astronomy defined relative to Earth’s poles? What about “lateral” directions, since east and west are relative (no poles, ie. no east of earth)?

Using the right-hand rule: knowing the direction of spinning, if you point your thumb up and wrap the other four fingers in the direction of rotation, the thumb will be pointing North. Oposite of that is South. East can then be defined along the direction of spinning (eastward or counterclockwise looked from North, the way Earth is spinning) and West - opposite to that, clockwise looked from North, opposite the direction of rotation.

I don't know for sure how that's defined (I ctrl-f'd and it's not explained in the paper), but this says the "North" is to the right of the image, and from context it sounds like it's the north pole of the accretion disk, i.e., the direction of the rotation axis with the right-hand rule.

> The approaching side of the large-scale jet in M87 is oriented west–northwest (position angle $\mathrm{PA}\approx 288^\circ ;$ in Paper VI this is called ${\mathrm{PA}}_{\mathrm{FJ}}$), or to the right and slightly up in the image.

In paper I, Figure 3, it says North is to the top of the image and East is to the left.

Whoop. You're right. I misread again.

Previous work on this was done for the movie Interstellar. The resolution of the rendering software was so high that team members were able to examine the black hole very closely - Because Gargantua was spinning at almost the speed of light, the rendering showed that spacetime warped into shapes never seen before. This led to the publication of —> https://arxiv.org/abs/1502.03808

Kip Thorne describes his work not this in a book called the science of interstellar.

Kip’s description of black holes here is also fascinating: https://youtu.be/oj1AfkPQa6M — first time I learnt what “warped” space-time means :)

Sean Caroll has a great podcast, mindscape [0]. One of the recent episode featured Kip Thorne as a guest and had some great discussions about Gravitational Waves, Time Travel, and Interstellar [1]. It's a very informative and entertaining podcast, I recommend it.

[0] https://www.preposterousuniverse.com/podcast/

[1] https://www.preposterousuniverse.com/podcast/2018/11/26/epis...

Agree with the recommendation.

Kip has studied black holes all his life — this podcast goes into the work on LIGO that finally got Kip (and collaborators) the Nobel Prize. I found it amusing that there is some “Nobel guilt” for scientists that comes with the prize, because the size of them teams that usually collaborate and make a large project like LIGO happen (over 20 years) is incredibly large.

I also find it inspiring that Kip speaks with so much... love ... about warped space time :)

There is a video that I cannot find where Christopher Nolan describes the process of rendering the black hole for his movie - they used Kip’s equations to render Gargantua and when the first images were seen, he realized that Kip has never actually seen a black hole before - even though he has spent his entire life studying it.

Wow, that brings me back. I studied GR under Robert Brandenberger, and we used Caroll's book. What a wonderful text.

Definitely going to listen to his podcast!

> Kip’s description of black holes here is also fascinating: https://youtu.be/oj1AfkPQa6M — first time I learnt what “warped” space-time means :)

In this video he makes a comment which I struggle to fully understand:

He says that ALL of the matter which belonged to the cooled-off star is DESTROYED in the process of creating a black hole.

That concept of complete destruction eludes me. I assume what he means is, the matter was converted entirely to energy. Right?

But if that's true - where is all of that energy? Is it stored (somehow?) in the Black Hole? Is it dispersed throughout the galaxy? What HAPPENED to the mass (energy)?

It's all squished into the black hole and from the perspective of everyone outside, converted into... more mass of the black hole. The mass of the black hole comes from the mass that created it. As you feed it more stuff, it gets more massive.

As to what physically happens to the stuff once it's inside, I don't know if we know for certain. It gets dragged towards the center. From the point of view of the rest of the universe, it might never actually reach the singularity: GR would make it look like it's going slower and slower and slower.

Speculation about what is actually inside the event horizon is at most mathematical extrapolation, since we can't actually crack one open and look.

International collaboration on scientific projects (International space station, CERN) always fills me with hope and optimism for humanity.

It's a nice contrast to opening the papers and reading the regular news, dominated by politics, with all the pessimism that creates.

Hooray for science.

If I understand it, this class of “telescope” is made up of arrays of telescopes spread as widely over the hemisphere as possible. We can only get data like this by collaborating with as many different sites as possible. It literally can’t exist without broad support from many countries.

As one of the scientists said in the interview, the next step is a telescope bigger than the earth. Hopefully we can collaborate on those too but if that involves a lot of satellites in a heliocentric orbit that may limit contributions considerably.

Constructing a telescope on Mars would be a valuable investment when a permanent presence is based there.

Mars is smaller than Earth, so planet-wide radio interferometry would be a smaller "aperture" than possible on Earth. If you're talking about extending the telescope to include both Earth and Mars, I imagine that doing the interferometry over changing speeds and distances would be challenging to say the least.

The speeds and distances of the planets are well known at this point and easily predicted. By the time of establishing a permanent presence on Mars the requirements of communications would already put in place the information needed if the DSN isn't already capable of it now. The compute needed would be greater, but so would the availability of it in the future too.

I hope one day we'll construct a telescope that uses the Sun for gravitational lensing. I've seen this paper once that claimed you could use it to image surface of exoplanets directly with pretty high (for our current astronomy standards) resolution. I think it talked about this: https://en.wikipedia.org/wiki/FOCAL_(spacecraft).

I know this comment will sound a bit unrelated to the main topic but reading this made this thought pop up in my mind and I thought it would make sense to share it. This comment is, however, related to the sub topic of the quoted sentence:

> It literally can’t exist without broad support from many countries.

This is the same constraint for the, let's call it, "peace on Earth" problem, or just "peace".

If only more of us could realize this is what it takes to solve that problem... which itself is part of the puzzle, i.e. how to increase awareness about the need to solve this.

While there are a number of people and organizations trying to do this, I see that there seems to be more possible fronts that could be used to tackle this and accelerating the reach for stability and sustainability of the state of peace.

One example of a possible front (and I honestly don't know if those already exist) is: through marketing it would be possible to influence people enough to be interested in the outcome of "peace on Earth" and pay some money for that, in a way that it doesn't feel like a donation, and more like an investment or maybe acquiring a service that would be hopefully realized in the coming years (hence the importance of the marketing capacity of that entity, as this mindset needs to be set in the consumers in order to make them buy the good).

Of course, the reporting to the consumers on the use of the invested money toward that effort has to be as transparent and honest as possible, as those approaches are arguably required for a sustainable state of peace. And hopefully it would make enough sense for an entity to operate in the way of the outcome it is seeking. Even though we are moving from a state of no-peace, which is hopefully unsustainable. In other words the effort could be be defined as "safely and confidently accelerating the maximum point of unsustainability of the no-peace state such that it inevitably transitions to a sustainable state of peace".

That's then possibly a private endeavor (not that it could not be a public one as well, but you need to raise enough money to pay for the possibly expensive marketing and then pay all of its employees), because there is now an identifiable market willing to pay some amount in exchange for obtaining the "product" of peace, which in other words just mean the modulation of humanity and its mindset in order for it to operate in such a way that it is always aligned to its own common good, or maximum known state of well-being, sustainably.

We already know that groups and individuals are not great at doing that, on average. So if an individual is not always able to operate towards its own good, or maybe some are but don't have access to the resources that would allow them to do so, how could then a group of individuals be able to do so? Unlikely.

And yes, exploring the universe and finding more about its mysteries and teaching humanity about them is a valid and great approach and a subset of all the possible approaches.

It is a subset because in order for an individual to be interested in knowing more about the mysteries of the universe, or consciousness and other topics, they have to have this mindset, well, set in the mind.

Therefore there are many more fronts that could be, and to many extents currently are, covered. So all I'm arguing here is we are not doing enough to reach the tipping point before possible big catastrophes happen, therefore we should do a lot more than what we're currently doing. There are many entity/company/organization models to explore that could benefit us in a spectrum of possibilities ranging from private to public.

So true, I was also recently thinking I should read more science/engineering news because that's actually positive stuff happening.

The papers with the scientific details are here (open access):


Article in physics world with comparisons to simulations:


"AskScience" AMA on Reddit about the breakthrough:


From reddit:

>"Hi, regarding the image itself: What I don't understand is why does it look like a donut and not a bright sphere? Assuming the black hole is actually spherical and not disc shaped, I would expect the Halo to be spherical and surrounding the black hole? so all we would see would be the ball of bright gas, even though there is a black hole in the middle?"

This is also what I would have expected.

Material can come in towards the black hole from any angle. However, because matter can't just pass through other matter, matter travelling in the wrong directions will collide more frequently than matter travelling in the right direction. Because of the conservation of angular momentum, the "right" direction will depend on the average angular momentum of everything in the cloud that is collapsing into the disk.

You might be interested to know that this is the same reason all the planets in our solar system orbit in the same disk: all the matter that is now in our solar system was originally a very thin cloud of gas with a small amount of overall angular momentum. As gravity drew it together it flattended out into a disk and eventually the clumps became planets (and the sun in the middle.)

The same reason planetary rings, solar systems, and (spiral) galaxies are flat: friction and conservation of angular momentum. Internal drag forces will eventually cancel out velocity components perpendicular to the plane of rotation, turning a cloud into a flat plane.

Things don't simply form a halo around a black hole. Instead you get a relatively flat accretion disk of things that orbit around the black hole.

This was a great explanation:


I am not trying to throw cold water on this, but I have some questions.

This ted talk has a very basic explanation of how they constructed this image. I was curious if anyone with image interpolation experience could weigh in on the method. https://www.youtube.com/watch?v=P7n2rYt9wfU

When she first starts explaining their method around 8:00m in, I was initially very skeptical of this result because she said that they feed images of what we "think" a black hole should look like and use algorithms to compare the captured data with those images.

She then goes into explaining the measure they take to keep the resulting image from being biased by passing environmental images and images of other astronomical anomaly to make sure that those images return similar results.

But I can't for the life of me figure out how passing non-stellar imagery could return something similar. And if it does, why do we need to feed it an example of what we think it should look like at all?

(I haven't watched the video, but I do have professional expertise on this topic.)

With interferometry, you're getting an incomplete sampling of the Fourier transform of the sky image, and if you just invert the samples, you get what we call a "dirty" image.

But you know your sampling of the Fourier plane exactly, since that's just a function of the projected baselines between every pair of telescopes during the observation, so you can create a "dirty beam" - now all you have to do is remove the effects of the dirty beam from the dirty image. Of course, that's a deconvolution problem, and given that you don't have all the information - you sampled it - it can never be exact.

But it can be very good! There are very sophisticated radio synthesis image deconvolution algorithms, including CLEAN and Maximum Entropy. For Maximum Entropy methods, you can apply a Bayesian prior on your images - most of the time, the prior we apply is a blank sky (seriously!) but if we have other constraints that we can use (e.g., the approximate size of the region with extended emission), Bayes tells us that we would be remiss not to use it.

If you look at this image [1] from Paper IV [2], we show the image results from different techniques on different observing days. Those are the inputs to what is the "consensus image" - you can check how close they all are to each other.

Does that make sense...?

[1] https://iopscience-event-horizon.s3.amazonaws.com/2041-8205/... [2] https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85

Yes, at ~6:53 in the video she shows how they are selecting images to include that look like a black hole. If you plug in enough noisy images you will eventually get a few that look like a bright donut.

Was just wondering this myself. How opinionated is this photo?

Probably very opinionated. I can't help but take this with a grain of salt. relevant example .How long did it take for people to evolve our view of dinosaurs as information was reevaluated.

This 9 min video [0] does an excellent job explaining what we are looking at.

[0] - https://www.youtube.com/watch?v=zUyH3XhpLTo&feature=youtu.be

The US unveiling is WAY better than the EU unveiling that is linked to above. They have images, animations and graphs that's easily understandable by the layperson, and it's scientists instead of politicians speaking.


They talk about how the image was produced, and how they made such a small image out of the 5 PetaByte of data they gathered from stations all over the world.

Yeah, no kidding. The presentation in the American conference is much more insightful and gives a stronger perspective. And the EU conference didn't even show the image until 8 minutes in.

I really really liked this press conference, I highly recommend it, well worth the watch. It's fairly short (~30m for the main part) and they explain the process step by step: how it was captured -> how it was processed -> what it means.

It's very well communicated in a way most can understand, it's concise and it has great accompanying graphics.

One of the cool things about this was that the data was too large to ship over the internet (in a reasonable amount of time). They actually shipped physical disks full of data.

Even today, never underestimate the bandwidth of a station wagon full of disks...

"This is more realistic of the uncertainties involved in this high-end image reconstruction. Still amazing though! Fig. 4 in https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85 "


Yeah, apparently radio interferometry is still very manual and so involves many relatively subjective decisions to produce an image.

That's probably why they had several analysers that they then combined into progressively larger teams until they could produce this Consensus-A picture.

There is non-manual ways to do it (called self-calibrating), but those need many more antennas. (What you really need is good coverage of the (u,v) plane AND many more different baselines between pairs of telescopes than the number of individual antennas.) If you do not have that self-calibration fails and leads to horrible image artifact or does not converge at all. They limited the influence of the manual calibration by observing a Quasar which is basically a point source between subsequent observations of M87* to get an independent amplitude calibration.

Some quasar other than M87 I suppose :P

(It is a quasar, simbad says so and that's good enough for this setting!)

Yes. They used 3C 279 which is more than 100 times further away than M87.

For those wondering how the image was constructed: https://www.youtube.com/watch?v=hMsNd1W_lmE

Basically, the image has been constructed by calculations on massive measurement data-sets from multiple synchronized telescopes around the world.

So this isn't a "photo" in the normal sense. It's a reconstruction of many, many radio waves.

It doesn't sound like they just snapped a picture. The one guy says they used "supercomputers" for 6 months to get the image.

Sunspots look black relative to the rest of the sun but are actually very bright. Could this be the same thing? How did they set the black level? Is there a description of the procedure somewhere?


Found the paper describing the data processing: https://iopscience.iop.org/article/10.3847/2041-8213/ab0c57

As far as I know K. Bouman [0] was the scientist leading the charge on the image processing/reconstruction. A few of her later papers probably have hints [1, 2] about how this is done, but I haven't seen the official release.

[0] http://people.csail.mit.edu/klbouman/

[1] https://arxiv.org/pdf/1903.08832.pdf

[2] https://arxiv.org/pdf/1702.07361.pdf

Thanks, I think I added the link to the paper while you were writing this. From skimming it I can't tell the answer to my question though.

How do they know what appears "black" in the image is really black vs. relatively black?

If you observe a very wide band of light (e.g., EM radiation) and there is nothing received from those spots, then, for all intents and purposes, the region of that image is black.

Now, if you're asking if, perhaps, the region isn't really black, but rather it's emitting some sort of small radiation relative to the bright region, it would be essentially impossible to know without much higher resolving powers (since it might even be indistinguishable from the background noise generated by the surrounding region). There is no way to really know if it's "perfectly black" vs. "orders of magnitude darker than the surrounding regions."

Makes sense. So I guess they could probably tell us an upper bound on how bright it is.

Indeed! That’s for sure: it’s probably not hard to extract a bound on the magnitude of a part of the spectrum from this analysis.

Any idea how bright it might be? Eg, could it be as bright as the sun? The moon?

The project's director was Shep Doeleman


Indeed, from what I gather from this thread and external links this “image” seems to be more of a plot than an image. In fact, are we looking at a matplotlib plot of the data with a “hot” colormap? The iopscience paper even references matplotlib. I’m just making some educated guesses here, but it’s still fun to think about. BTW: Python for the win! iopscience paper makes several references to Python tools (e.g., numpy, Jupyter etc.)

Every image is a plot... This one just has had a bit more processing gone into it than your average demosaiced and noise reduced vacation photo.

Another interesting thing about that iopscience paper is that you can turn MathJax on/off with a link at the top. Mathjax is off by default, but when you turn it on, you get a nicely rendered equation instead of a gif image.

Summary of their summary:

“arising from the rapid atmospheric phase fluctuations, wide recording bandwidth, and highly heterogeneous array”

(Filtering out bad data)

I don't get the whole "oh it's too blurry and nothing is visible" comments. It's a black hole, what did you expect to see? Interstellar CGI?

Yes, we're using a telescope the size of the Earth to look at an object the size of our solar system in a galaxy about 55 million light years away. It's an infinitesimally small patch of sky.

On the other hand, the jet from the M87 black hole is quite large and we have good images of it. It's even resolvable by amateurs, I hope to take a picture of it over Easter with a small telescope.


> 55 million light years

didn't he correct himself and said kilometers

55 million light years is about correct. Wikipedia still has 53.5 ± 1.63 Mly from older observations, but appendix I in paper https://iopscience.iop.org/article/10.3847/2041-8213/ab1141 has a bit more on the distance measurements they used. They arrive at 16.76 ± 0.75 Mpc, which translates into 54.7 ± 2.4 Mly.

He corrected himself to say 500 billion billion kilometers after mistakingly saying light years.

I haven't done the math, but I believe that roughly equates to 55 million light years.

Yup, My bad.

It is a letdown. Although I wasn't expecting Jupiter level detail this pic doesn't blow me away because it's just a blurry ring. Jupiter level detail will blow me away.

The significance of the image is not in its quality, but in its mere existence.

It's enough to confirm various predictions, and should give a new baseline for truth about black holes.

Consider yourself lucky that a black hole isn't Jupiter level distance from us.

At a jupiter level distance we'd be well within the event horizon. At that distance I expect to see four dimensional book cases and my daughter.

Jupiter level quality would mean that we are so close that we would be instantly torn apart.

Jupiter level quality is what I want. Not jupiter level distance.

It's just a stupid collection of small pixels but somehow it feels very overwhelming looking at it for the first time.

What a time to be alive

Because that collection of pixels is really out there

I mean, in the end, everything that you're looking at is just a collection of cones and rods in your retina. It's the information that it conveys that really matters.

Excellent example of successful international collaboration, with distributed team. Great results and promising future work: they say Sagitarius-A* is their next target!

The telescope's announcement is up, too: https://eventhorizontelescope.org/

The EU is finally learning from the US when it comes making a lot of fanfare for discoveries and other inventions.

Too bad they don't present it well. I just see self congratulating politicians and officials on some youtube stream.

Telling that it's a US organization that hosts the actual picture.

esa.int and eso.org seem to be down actually.

The European broadcast presentation is not great.

The speakers are referencing images and diagrams that are not visible on screen.

The accomplishment speaks for itself. The delivery can be improved.

Both ESO and the NFS hosts the images, don't know what gave you any other impression.

And while the EC stream was pretty bad, at least they let you skip back in the stream and left it up after the presentation ended. The NFS stream wouldn't allow you to go back (useful if you joined late) while it was up.

Personally I liked the ALMA stream best, but it's down now :(

https://eventhorizontelescope.org/ is hosted in the US and the linked image links to a Harvard.edu web server.

Why is the European Commission doing this? When I recognized Carlos Moedas I immediately skipped to what mattered. The reason why he was ever appointed as Commissioner for Research, Science and Innovation is, to me, more remote than the black hole about which he knows absolutely nothing.

because it's one Commissioner per member state, and apparently nationality is the most important criteria for appointing ministers

Well this was mostly a US-run effort. It's headed by Harvard University and the key South Pole Telescope is North American.

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