Comment by jankovicsandras | Hacker News Reader

Comment by jankovicsandras | Hacker News Reader

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jankovicsandras

I share your skepticism. To others: Before voting me down, please consider these arguments.

As I understand, this image is not from visible light, not a photo, more like plotting radio measurements. "black holes" are the brightest objects in the universe. It's a bit like an alien scientist showing an X-ray picture of a skeleton:"This is a human!" Some quotes from https://en.m.wikipedia.org/wiki/Black_hole :

"Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly."

The same article is full of words like "implies", " inferred", "indirect" etc. It's not directly proven black holes even exist, see Alternatives paragraph. I'm not sure it's physically possible to take a visible light picture of a "naked" event horizon - then black hole images are pure phantasy.

While the skepticism of the comment you are replying to is understandable, yours is not.

"Visible light" is not a better or truer electromagnetic spectrum than x-ray or radio. It's a human construct only defined by what our human eyes have evolved to capture, based on what is most useful for us here on earth, nothing more.

There is nothing wrong with getting measurement of an object in any random frequency that happens to be the most interesting/practical. Rendering those results as an image in visible light is also simply the best way to visualize the results for us humans. It is certainly more understandable than hundreds of plots.

> It's a bit like an alien scientist showing an X-ray picture of a skeleton

If that alien organism has evolved to see x-rays, as it might be the most useful spectrum for their particular environment, they would find your comment quite puzzling as that would be exactly what they would see should they meet us.

I think there's some confusion on your part about what the image purports to show.

I shall put aside the parent comments concern about the signal analysis techniques. Those may be valid concerns, and I don't know enough to assess them.

> I'm not sure it's physically possible to take a visible light picture of a "naked" event horizon The event horizon telescope isn't purporting the image emission from the event horizon itself. While the theory of those emissions (Hawking radiation) is very persuasive, they would be incredibly weak for a black hole of even stellar mass, and even weaker for a supermassive black hole. What is being imaged here is hot around the black hole, which is heated due fluid dynamic effect (compression or viscosity, I'm not sure which dominates) as it spiral in to the black hole. The 'image' of the event horizon is the 'shadow' where the black hole blocks our view of the hot gas on the far side.

The fact that this shadow is compatible with the expected size given the mass of this black hole is a scientifically interesting result.

Thanks for your reply!

I also think it's scientifically interesting and appreciate the work.

But it should be called a model or illustration, because a human could never see this with bare eyes.

But our “bare eyes” are, too, merely instruments that the brain receives signals from; these signals have an electro-chemical nature, and in the brain they have to pass through a number of layers of interpretation before they reach the consciousness.

A picture is not reserved for something we can see with bare eyes - an infrared camera produces a photo, we don't call that an illustration - such cameras are used in military, geology, earth mapping and agriculture, etc. Most images in industry and astronomy could never be seen with bare eyes, because our eyes can see only 1% of what our instruments can.

Ofcourse each wavelength of light works a bit differently, like with the X-ray example, you need to understand how X-ray works to understand what you are looking at.

A model or illustration is something that would be product of our calculation or imagination, that was given visual form.

I agree that in science, as we extend our perception with instruments, it's difficult draw the line between an image and an illustration or diagram.

I'm maybe grumpy because this relatively featureless image of relatively massaged data is presented by mainstream news as "FANTASTIC new photo of a Black Hole! WOW! It looks just like in Interstellar!"

It's proof that there's a ton of mass in the dark part of the picture (cause stuff is orbiting it). It's also proof that the thing at the center isn't outputting a significant amount of radio waves. If you know the mass, and the volume, that's enough to say it has to be of black hole density.

> It's a bit like an alien scientist showing an X-ray picture of a skeleton:"This is a human!"

What is the problem here? Surely skeleton (or other things detectable via X-rays) is an integral part of a human. If you have no way of seeing an alien, but have an x-ray of them, wouldn't you say we have a significantly better understanding of this alien species, than having nothing at all?

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