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Astronomers reveal first image of the black hole at the heart of our galaxy

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Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#291

Post by codethief »

ISL wrote: post #188
hammock wrote: post #155

Earlier quoted context omitted.

Should have clarified. Does a black hole have fuzzy edges or sharp edges?

The edge should be quite sharp. Any deformation or movement in the edge will be smoothed extremely quickly, on timescales comparable to the light-crossing time of the object -- in this case ten seconds or so. If you're a photon and you're in, you stay in. If you're out and heading out, you get out. (if you skim the surface, you might make an orbit and then leave :) ). It is that fact that makes the edge quite sharp.

An observer at infinity won't see anything cross the horizon, though, by the very definition of what a horizon is.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#292

Post by codethief »

sandworm101 wrote: post #233
ISL wrote: post #188

Earlier quoted context omitted.

The edge should be quite sharp. Any deformation or movement in the edge will be smoothed extremely quickly, on timescales comparable to the light-crossing time of the object -- in this case ten seconds or so. If you're a photon and you're in, you stay in. If you're out and heading out, you get out. (if you skim the surface, you might make an orbit and then leave :) ). It is that fact that makes the edge quite sharp.

I disagree. The edge of a BH is essentially an asymptote. While there is a mathematical bright line, when looking at it you should see light in all manner of red/blue-shifted colors near the event horizon. Since that light is coming in from a variety of directions it leaves in a variety of directions too. Everything would look soft and fuzzy around the edges. Out of focus.

Out of focus? I don't know about you but I find the black hole "edge" in the simulated images in Interstellar quite sharp.

(Or are you talking about resolving matter/light near the event horizon? In that case I agree – one won't really resolve any structures anymore due to light getting bent and redshifted in a myriad of ways.)

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#293

Post by codethief »

wthomp wrote: post #91

For those wondering if we could get sharper images with JWST, here’s the previously imaged black hole (same angular size as our own) compared to a single pixel from Hubble’s wide field camera 3: https://twitter.com/alex_parker/status/1116070667068170240?s... JWST will have smaller “pixels” but is in the same ballpark.

No wonder one of the questions in the Q&A session at yesterday's NSF press conference went like this:

Journalist: Why is the image so blurry?

Answer by one of the panelists: It's actually one of the sharpest images I've ever taken.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#294

Post by codethief »

rcxdude wrote: post #290
pyinstallwoes wrote: post #279

Earlier quoted context omitted.

How is that even possible? Anyone involved in the research in anyway is an author even without contributing to writing the paper with words? Perhaps that’s why.

Yes, that's basically how it works (kind of like movie credits). On papers with fewer authors, there's a kind of ranking system in the order of the authors: the first author is generally the one who did the experimental work and the actual write-up, the next few may have helped with the write-up and run some of the experiments, the next may have just helped build some of the experimental setup, or otherwise had some…

> On papers with fewer authors, there's a kind of ranking system in the order of the authors

It depends very much on the field of research and the paper in question. In some fields, it's very common to list the names of the authors alphabetically, no matter the size of their contribution.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#296

Post by oldgradstudent »

queuebert wrote: post #202
photochemsyn wrote: post #86

Earlier quoted context omitted.

You mean, this? https://iopscience.iop.org/article/10.3847/2041-8213/ac6615 >"Since the interferometric measurements are often incomplete in the Fourier domain, the inverse problem of reconstructing an image from the observed data set is usually underdetermined. Consequently, the image reconstruction requires prior information, assumptions, or constraints to derive a reasonable image from the infinite number of possi…

>"Since the interferometric measurements are often incomplete in the Fourier domain, the inverse problem of reconstructing an image from the observed data set is usually underdetermined. Consequently, the image reconstruction requires prior information, assumptions, or constraints to derive a reasonable image from the infinite number of possibilities that can explain the measurements." If the original commenter has a…

Funny that you mention CT scans.

To quote from a paper[1] on the history of CT scanning:

"Initial images were of inert objects, then specimens from an abattoir, including bullocks brains and pigs bodies"

or

"The prototype was installed at Atkinson Morley’s Hospital in South London where the first patient, a middle aged lady with a suspected frontal lobe tumour, was scanned on 1st October 1971. The surgeon who operated on her shortly afterwards reported that ‘‘it looks exactly like the picture’’"

The default scientific approach to a new imaging algorithm, and especially a new implementation, it to try it on a simple well understood examples first.

[1] Beckmann, E. C. (2006). CT scanning the early days. https://www.birpublications.org/doi/10.1259/bjr/29444122

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#297

Post by SiempreViernes »

codethief wrote: post #291
ISL wrote: post #188

Earlier quoted context omitted.

The edge should be quite sharp. Any deformation or movement in the edge will be smoothed extremely quickly, on timescales comparable to the light-crossing time of the object -- in this case ten seconds or so. If you're a photon and you're in, you stay in. If you're out and heading out, you get out. (if you skim the surface, you might make an orbit and then leave :) ). It is that fact that makes the edge quite sharp.

An observer at infinity won't see anything cross the horizon, though, by the very definition of what a horizon is.

The light crossing time refers to the time needed to traverse a diameter of distance.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#298

Post by wolfram74 »

kristopolous wrote: post #285
dillondoyle wrote: post #281

Earlier quoted context omitted.

That's incredible science and engineering. The Reddit ask science thread said it would be akin to taking a photo of a donut on the moon. So impressive even if off by a lot.

That's in the article actually

When a research group comes up with a useful/good enough metaphor/analogy they will use it over and over again.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#299

Post by wolfram74 »

gilbetron wrote: post #225
hammock wrote: post #155

Earlier quoted context omitted.

Should have clarified. Does a black hole have fuzzy edges or sharp edges?

Does the sun have fuzzy or sharp edges?

In case you weren't being rhetorical, the sun's edge would either be the chromosphere[0] or the corona[1], the corona being famously fuzzy and also quite bafflingly hot. The chromosphere is "smoother", but still very interesting on any given day [2].

[0] https://en.wikipedia.org/wiki/Chromosphere [1] https://en.wikipedia.org/wiki/Stellar_corona [2] https://sdo.gsfc.nasa.gov/data/

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#300

Post by panda-giddiness »

thaway321 wrote: post #289
panda-giddiness wrote: post #282

Earlier quoted context omitted.

> I don’t know, the criticism in OP seems pretty substantive to me. That's because it's a straw man argument. As has been stated elsewhere in this thread, the OP's concerns are addressed in the actual papers, which the OP conveniently ignores. > appeal to authority is essentially the opposite of modern science. Well, it's a good thing they're not doing that then. An appeal to authority is when you rely on an expert's…

>"Appeal to authority" doesn't apply to actual authorities in their domain – otherwise you would never be able to call expert witness at a trial, for example. Not OP but I disagree, an appeal to authority can be any authority, even those that are experts in the field. Even the most knowledgeable experts make mistakes, so appealing only to authority is not enough, granted I haven't read the paper nor have any stake in…

> expert witnesses are just a concession the law has to make to get anywhere.

I'm not sure why you don't think that applies here? Only a slim fraction of the population is knowledgeable enough to grok the methodology of EHT.

I mean, if an appeal to authority were as you defined it, then engineers would be making an appeal to authority when they invoke Newton's laws (after all, they haven't derived them), biologists would be making an appeal to authority when they write python code (after all, they didn't write the python compiler), and so forth. Trusting that specialists can do their jobs isn't a logical fallacy – it's a type of inductive reasoning and, critically, a type of reasoning essential for the modern world to function.

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