Comment by aplavin
15 hours ago
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.
>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
It's AI garbage - OP asked the LLM for "physically accurate", Claude gave them this, and they didn't know any better.
>and they didn't know any better.
i think an "astrophysicist at Harvard's Black Hole Initiative studying quasars and black hole environments" who "work[s] with raytracing/radiative transfer simulations professionally"probably has a decent understanding of what's going on...
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> 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.
>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
“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.
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Always funny when people claim that scientific term apply to their software and then disregard any founded criticism in a non scientific way.
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>I don't see "simplified" as being opposite to "accurate".
Is it accurate to model a cow as a sphere?
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.
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.
> 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?
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.
>> 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 me try to 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, 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?
it's common to use a colormap, but not using a perceptually uniform colormap in the year 2026 is quite a blunder
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