[20k]

If anyone's interested in the accuracy, this is very 'visualisation grade' software. Its a bit of a pet peeve of mine that people present these sims as being very physically accurate, when they contain major inaccuracies, some of which are very obvious and/or deliberate. This one has some serious physical limitations

I wouldn't mind at all if it didn't say that this was a *physically accurate* black hole specifically, but this now falls under misleading science communication in a way that often gets hand waved away as if it doesn't matter, so we've got to clear some things up!

1. The accretion disk shouldn't be red, people just expect it because it looks cool. Black hole accretion disks are near universally hot enough to be blue. Interstellar did this too, and tried to handwave it away very unconvincingly

2. This is a non/low (?) spin black hole, which isn't super duper realistic

3. It ignores the position of the camera (which affects the lorentz shifting)

4. The doppler shifting isn't terribly accurate

5. It doesn't model the accretion disk temperature distribution or colour with any kind of accuracy. Usually you model accretion disks as a blackbody radiator, shift it by the doppler, and to display this convolve this against the human eye response (LMS), go to XYZ, then RGB, do a physical tonemapping step, before an sRGB conversion. This instead does none of that - no step of this is done with any physical accuracy. Its not even illustratively correct as we'll get into

6. The actual radiative transfer is very simplified compared to what you'd use for realsies, and isn't based on any real numbers, with very simplified equations. The opacity and emissivity of the disk is arbitrary, as is the size, and it does not correctly incorporate brightness or extinction, eg here https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca... is super simplified

7. The wrong equation is used for the doppler calculation. They use the I^3 variant, whereas the data you get out of a disk sample is *radiant flux* which is actually F_obs = F_emit / (z+1)^4. This is a very common mistake in image processing, which means that the doppler shift and observer brightness isn't correct. Surface brightness over here https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca... is *not* a spectral radiance but instead a radiant flux

Stuff like the brightness -> colouring conversion is particularly inaccurate. Eg if you check out the source:

https://github.com/aplavin/blackhole.plav.in/blob/2f004bfeca...

It maps the pseudo brightness completely arbitrarily to colour. The resulting colour/brightness here then doesn't correspond to anything remotely physical. It also performs a *linear* mapping of a linear quantity (brightness) to sRGB (which is a nonlinear process!!), which means that it doesn't even retain any of the underlying physical characteristics of the brightness simulation, which itself is quite inaccurate. Its vibes all the way down

This is all fine if you're doing visualisation, but this isn't an accurate simulation. I wish this was just called a visualisation of a black hole, but its being communicated as if this is super hard science with credentials and all

[KaiserPro]

I clicked on this because I worked on the infra that simulated the famous blackhole sim in interstella.

I thought "oooh this is interesting I wonder how they are going to do physically accurate on an end device" Recalling how the original particle sim was something like 100TB, took 2 weeks to generate and seemed to write in a way that killed disks. but that was >10 years ago, so what clever stuff has been done to model it locally.

Its been a long time since I've looked at black holes, but what I'm not understanding is why the stars surrounding the black hole are just points, and more over why the lines are straight to the centre of the hole. from memory the way light enters the hole appears non-linear and changes on view point.

[aplavin]

> why the stars surrounding the black hole are just points, and more over why the lines are straight to the centre of the hole

Sorry for confusion! Points + lines are just other users looking at the black hole right now, their camera locations and lines of sight. Nothing more! In the first hours of HN frontpage, there were a lot – and I can see how one can understand them as parts of actual scene :)

I decided not to change their style, not to make them more subtle – half a day later, there are already way fewer users online, and these points/lines don't look as crowded as they did.

[vee-kay]

Someone refers to a sci-fi-esque (more imaginative than scientifically accurate) virtual rendition of an interesting scientific phenomenon (black hole) in a fanous sci-fi movie (Interstellar), in their scientific analysis/critique comment on a HN thread about the virtual sci-fi-esque rentition of such a sci-fi object (black hole)(yes, a simplified easy-on-eyes pseudo-accurate rendition of a black hole, for VR/AR immersion at home, counts as sci-fi-esque, IMHO), and someone else who worked on such famous object (black hole) depicted in that exact sci-fi movie, responds to the comment.

Peak HN, right here!

[reactordev]

You have reached the end of the internet. We hope you enjoyed your stay. /s

[gattr]

On a related note, there's an annoying mistake in one of the Fatalities in "Mortal Kombat 1": Liu Kang teleports with his opponent into outer space, summons a black hole with a snap of his fingers, and throws the poor sod in. But the accretion disc is red where it rotates towards camera, and blue where it rotates away!

[JadeNB]

Boy, I really hope somebody got fired for that blunder.

[aplavin]

Some are fair – of course this is a simplified visualization! Observationally, we don't really know how fast a given black hole is rotating, and here I indeed assumed a non-rotating one. It's not an inaccuracy per se, more like a missing feature. The camera mode has a (half-hidden) toggle to enable Kerr metric and set spin, but even there it's not a default.

I consider the colormap choice to be completely arbitrary though, without affecting accuracy. Basically, it represents intensity at a given frequency, the image like one would get from a telescope. It wasn't intended as a faithful optical color representation! And really, in my (admittedly biased) view of a radio astronomer, I tend to assume frequencies invisible to the human eye anyway.

[20k]

>of course this is a simplified visualization

Its titled a "physically accurate black hole"! Please don't do this, if its intentionally not physically accurate and heavily simplified! The general public on here don't know better, and it takes someone else with years of experience simulating black holes to dig through your code to show what you've simplified. There's like a few hundred people who have the right experience worldwide to know that you've got some of your equations incorrect

The issue is when you're communicating doppler, if you want to correctly show the change in doppler, you can't make the intensity or colour mapping arbitrary

There's two ways to communicate accurately an example linear change in emissive power:

1. Use a perceptual brightness system, so that a linear change in power represents a linear perceptual change in perceived brightness. This accurately communicates to a viewer the underlying shift in power emission, if you want to show off how a radio telescope perceives a black hole for example

2. Use an emitted power <-> sRGB mapping (with tonemapping), so that a linear change in power is perceived as if it were a physical light getting brighter. This is more "what would this look like to a person?"

At the moment the change in your image brightness doesn't correspond to anything, which means that its not really communicating any science, and it doesn't correspond to doppler. Which is fine if its just illustrative and that's clear, but again vanishingly few people will know this is a visualisation not a physically accurate render

[aplavin]

> Its titled a "physically accurate black hole"! Please don't do this, if its intentionally not physically accurate and heavily simplified!

It also doesn't exert the gravity an actually accurate black hole should :) And also, even on a phone with two cameras, they only cover a part of sphere – while a real black hole would bend light coming from all 4pi directions. Some simplification is generally required ("the map is not the territory") and I don't see "simplified" as being opposite to "accurate".

Colormap choice: it can be a useful mode to show proper linear power -> linear perceived brightness mapping – true! But that's only one of many possible choices, and scales like logarithmic are very common in scientific images.

[20k]

>I don't see "simplified" as being opposite to "accurate".

Are black hole accretion disks generally red in real astrophysical cases?

They're most accurately represented as being blue. Red is fine for visualisations because it looks cool (which is fine!), but blue is the physically accurate colour. Visualisations claiming to be accurate like this presenting red black holes is becoming an increasingly large science communication problem

The way that the colour and brightness are mapped together is also not correlated correctly, and some of the equations just aren't right. The doppler isn't correct at all here, partly because its simulated incorrectly (with the camera problems), and partly because the mapping done at the end doesn't correlate to any reasonable brightness

Stuff like this: Its not accurate at all. It isn't simplified, its just wrong - which is totally fine for a visualisation, if that's the intent. But:

>scales like logarithmic are very common in scientific images.

Sure. What scale are you using for the doppler brightness here? Because as far as I can tell, its a piecewise mapping of the form ~pow(x, 2.2), after being run through a non smooth function `afmhot` - a function which doesn't have a linear brightness response. So the brightness in this image doesn't really correspond to anything related to doppler or brightness, and the colour also doesn't correspond to anything involving colour (or the doppler). The entire image's look is basically accidental

Here's a specific comment from the event horizon telescope talking about exactly this problem with specifically the afmhot transform being used, because its important for visualisation:

https://github.com/achael/eht-imaging/issues/85

Which shows some of the problems here

[EugeneOZ]

“Physically accurate” indeed raises the bar significantly.

You’ve already done great work here. That said, the feedback seems to come from someone who spent considerable time analyzing your work. Even if only a few of the suggestions are ultimately valuable, that’s still a meaningful contribution and worth considering.

[aplavin]

Sure, most of the raised questions are reasonable potential feature additions to be made – things like rotating black holes, or linear brightness-to-screen-pixel mapping. They just aren't "inaccuracies", in my opinion.

[7bit]

Always funny when people claim that scientific term apply to their software and then disregard any founded criticism in a non scientific way.

[20k]

Its frustrating because these issues are all fixable, and some of them are just bugs, but there's a mentality in this kind of science communication that ehh it doesn't matter because its just for the public. This does a real disservice to what people are trying to actually achieve in educating the public. Its also, unsurprisingly, a lot of hard work and validation to get from visualisation-grade, to physically accurate, and its a lot easier to not do that

[aplavin]

Note that most of the points you raised are clearly not bugs – most notably, things like non-rotating black hole or colormap choice. At the very most, these can be considered missing features, but they don't affect correctness in any way.

[7bit]

I don't understand what you are saying.

The only criticism is to call that accurate, when it's simplified. OP ist defending the use of accurate with dumb arguments. The fix would simply be to not claim "accurate" and continue to provide a probably great visualisation (idk, haven't looked at it)

[radicality]

Now after reading the OPs responses and how defensive they are of some high quality constructive criticism, I don’t even want to go back and play more with the visualization.

[stackghost]

>I don't see "simplified" as being opposite to "accurate".

Is it accurate to model a cow as a sphere?

[aplavin]

To describe cow's gravity? Pretty much so. Then, for visualization and even for many biological purposes, it's accurate enough to mode the cow as a bunch of organs with known processes happening in them. But that's still far from atoms and quarks that constitute the cow.

[stackghost]

For an object with the mass of a cow, the gravitational effects are minute, and thus if we study small gravitational interactions we would surely want to model the distribution of mass of the cow.

Either way, no layperson (to whom this black hole sim is targeted) would consider a simplified spherical cow to be accurate. That's why the spherical cow is a meme.

Perhaps you're getting the pushback you're getting, because you have a different idea of what accuracy in physical simulations means.

[yoaviram]

Great job. Please consider turning on rotation by default (for those who missed it, it's in the parameters). The overwhelming majority of astrophysical black holes are expected to be spinning (Ker) black holes.

[aplavin]

That option for rotating (Kerr) black holes generally works, but not on all devices in my experiences. Debugging on someone's phone is not that straightword, so I went with the most accessible experience by default.

Also note that the visual difference for the camera warp is really marginal between rotating vs non-rotating black holes.

[gilrain]

> completely arbitrary

You agree that it isn’t “physically accurate”, then… but seem to argue that you shouldn’t be called out for the false title?

It’s fair enough to be called clickbait when you really did score extra clicks with a slick falsehood, surely?

[aplavin]

Arguing about colormap choice seems very strange to be – this is such a common practice in astronomy (and other fields!). The vast majority of images you see in published papers apply some arbitrarily-chosen colormap and color scheme. No matter if you look at observational or theory papers, it's very rare to find a real true-color image. And for a bunch of good reasons!

The only difference here is that I don't show a colorbar with explicit color-number mapping, for simplicity sake.

[agos]

it's common to use a colormap, but not using a perceptually uniform colormap in the year 2026 is quite a blunder

[aplavin]

> not using a perceptually uniform colormap in the year 2026 is quite a blunder

Then you are up for a big surprise if you browse through modern published papers :)

[mncharity]

>> I consider the colormap choice to be completely arbitrary though

> Arguing about colormap choice seems very strange to be – this is such a common practice in astronomy (and other fields!).

Let's see if I can give a feel for why "physically accurate" and "arbitrary color", when applied to a physical object, seems a problematic juxtaposition. Especially in outreach. Even in astronomy, whose relation with color is... notably flexible. Especially when the colors "arbitrarily" chosen, seem instead optimized for breeding misconceptions. Consider the Sun.

A solar observatory outreach center had a big Sun ball a few meters across. They painted it yellow. When asked why yellow, they explained "It's what people expect".

For years I'd ask first-tier astronomy graduate students (something like): "A five-year old comes up to you says 'I'm told the Sun is a big hot ball! Awesome, I love balls. What color is the ball?' How do you answer the five-year old?". Most said yellow. Of the few who got it right, about half had learned it in a class covering common misconceptions in astronomy education. A follow-up question of "What color is sunlight?" gets most to a "Wait, that doesn't make sense, does it?" moment. Two incompatible memorized factoids, that have managed to remain unintegrated since kindergarten or so.

All fields face challenges of information representation, especially in outreach. But astronomy... is special. Imagine zoology presenting elephants as green, from kindergarten through undergraduate, in education and outreach. PBS and zoos colorize their elephants green, with DaVinci and spray paint respectively, because it's what people expect. A kindergarten student thus misled, only years later might hear "gray", if they become a zoology graduate student, and take a "we suck at teaching" elective seminar, offered at their first-tier center for zoology research, because it just happens to also be a first-tier center for zoology education research.

The closest similar case I can think of in other fields, is video representations of molecular biology. Where a tormented kinesin mouse, desperately clinging to a microtubule wire in a hellish hurricane, with a flailing blur of a vacuole balloon tied to it's tail... somehow gets represented as a lumbering donkey, dragging a massive canal barge, on a quiet summer day. Later revised by making the donkey and barge jiggle in place, for an extra slathering of misleading bogosity. With authors explicitly saying they prioritized "pretty" over fueling misconceptions.

Other highlights include the 2002 "Universe is green" front-page news - outreach outside of their focus, using open-source color software with a bug, and not managing an integrated understanding's "wait, that's not plausible".

Perhaps the app's black background might be changed to green? Given that it's an arbitrarily-chosen colormap, but physically accurate visualization, of a physical object. Or perhaps a nice Scottish tartan, or pink pokadots, for the accretion disk? Both would mitigate the educationally problematic juxtaposition of "accurate" and arbitrary color, by emphasizing the aphysicality of that arbitrary. Actually not kidding (much). When an aphysical representation choice is needed, one can do worse than to optimize for fewer misconceptions, no? Better a tartan Sun than a yellow one?

[biorach]

I think you're being very harsh. I read it as a side project of a scientist meant to entertain as much as educate. Holding it to the same standards as the Event Horizon project seems pedantic and excessive.

[20k]

All they need to do is not put the label physically accurate on it then. If you call something physically accurate and decorate it with your credentials as a harvard phd in astrophysics building radiative transfer sims, people expect it to have a degree of accuracy. This sim, from a physical perspective, is wrong

That's 100% fine if you present it as a visualisation with limitations and I absolutely love people making fun side projects like this and presenting them. I built a whole tutorial series on doing this, because I think people getting stuck into the field is absolutely great, and more power to everyone who wants to write anything no matter how accurate it is

Its the fact that this is being presented and stated as if its a physically accurate sim made by someone with experience in the field so it must be spot on, when in reality its little better than an artists impression of a black hole, that bothers me. Its science miscommunication. Coming away from this, you might think:

1. Black hole accretion disks are red

2. Black holes do not warp the background around them, only the accretion disk

3. You might get notions about the intensity distribution of the doppler shift, or the way that cameras work near black holes etc

None of which is particularly correct, and there's a lot more wrong with it too

[gilrain]

The person you’re replying to did not hold it to that standard — they only pointed out that the standard it claimed to hold itself to was not actual.

If correcting misinformation is “harsh”, reality is fucked.

[wanda]

You know, I am interested in the accuracy.

I like what OP has created, but out of curiosity, where might I find the most physically-accurate, browser-based black hole simulation?

[reactordev]

I agree. I was able to position the camera so that the entire black hole effect was negated and we were back to having a star. All I needed to do was turn the camera just right.

[KinetiNode]

but why was the picture taken of black hole have accretion disk yellow?

[20k]

They used a greyscale -> colour mapping, it wasn't really red/yellow. It was just for vibes. Its one of my minor pet peeves about the EHT visualisations, but given that its visualisations for effect its relatively fine. I'd have preferred blue given that its such a common misconception, but if you're a paper author trying to get your work publicly recognised then rule of cool is a good enough excuse

[imp0cat]

https://www.youtube.com/watch?v=eQZ3LAexNxE

Love, Death & Robots: Black hole used red for the disc, too.

[mazurnification]

at 1 - is it red due to red shifting due to gravity?

[20k]

They're blue, in general black hole accretion disks are very hot, and anything past a certain temperature looks pale blue as follows:

https://20k.github.io/assets/kerraccrete.PNG

This is a colour and relative brightness accurate example of a hot accretion disk. The size, emissivity and absorption are set to arbitrary parameters, but this is human-eye-colour accurate with correct doppler and radiative transfer for a spinning black hole. Its as correct as I can make a specific model, for what a human would see standing next to a black hole taking into account the limitations of the human visual system

You can get a red accretion disk like this:

https://i.postimg.cc/pV8VWKhw/verycold.png

But it requires the disk to be extremely cold, which is physically pretty suspect

One interesting feature is that the temperature and brightness scale differently, so that its actually hard to observe the colour shift, as the brightness changes much faster than the colour. So its not something you ever really see to the human eye

That said these don't do accretion disk within the ISCO, which is a major limitation

[aplavin]

It's purely my color map choice – the underlying simulated image is simply a number at each pixel. Transforming that number to the actual displayed color is generally an arbitrary choice, as common for the vast majority of images in astronomy/astrophysics papers. The only difference is that I don't show a numeric colorbar here, for the sake of simplicity.

[FrustratedMonky]

"an astrophysicist at Harvard's Black Hole Initiative"

He probably knows. It's in a browser, there are probably some trade-offs. Calm down.

[gilrain]

Keep your need for simplified representations of reality (which claim to be complete) out of our information-based community.

[folkrav]

From an information theory perspective, isn’t a representation by definition a simplification?

[FrustratedMonky]

Running a simulation in a browser is not going to be a complete representation of reality. To think that is possible is really weird. So really, what is happening, we are arguing over the 'Title'?

[20k]

I've done this as have many other people, its absolutely possible and there are good sims floating around. The OPs simulation is just presenting itself as more than what it is

[FrustratedMonky]

From your other answers, you know what you are talking about. So wont argue the point.

Because I think we would really be arguing about, what level of reality can be calculated in a browser. Sure, a simulation can be done in a browser. But that could be anything from a thermostat with a single simple equation, to modeling all of the air flow thermo-fluid dynamics in a house down to millimeters volumes. There are limits. And I guess if using WASM browsers have gotten a lot more capable. It would come down to what fidelity we are saying is 'reality'.