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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

#201

Post by queuebert »

fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

The point spread function of the detector is pretty well characterized, and from there the image is basically just a Fourier transform. It's not as magical as you might think.

Then it looks like they average a bunch of these images to get a maximum likelihood image. What is your issue with that?

Besides, to calibrate on a known celestial body, they'd have to have another micro-arcsecond resolution radio telescope to use. Do you have one they can borrow?

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

#202

Post by queuebert »

photochemsyn wrote: post #86
fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

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 an issue with this, wait 'til they find out about modern CT scans. Or hell even JPEGs.

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

#203

Post by adgjlsfhk1 »

jankovicsandras wrote: post #136
fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

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…

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.

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

#204

Post by guelo »

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.

There is so much post processing that the telescope resolution barely matters. Personally I'm skeptical of these images since the algorithms have a lot of data fitting to "what it should look like" built in to them.

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

#206

Post by brabel »

ISL wrote: post #94
zeven7 wrote: post #90

Earlier quoted context omitted.

It seems the common expectation is that GR is more likely to be the theory that needs to be modified the most - or more or less tossed out and replaced with a quantum theory of gravity. Is it possible that GR is just "right" and QM needs to be modified to fit into it?

Whenever we learn more about the connections between GR and the rest of physics, the early corrections are likely to appear as "GR+new stuff" or "QM+new stuff". Both theories have enough predictive power that we'll hang on to them as effective theories for the rest of humanity's existence. That said, the mathematical fundamentals of GR do not directly incorporate notions of the uncertainty principle. That fact alone,…

As I understand it, quantum physicis essentially predicts that the randomness of quantum fields effectively disappears at scales of just micrometers, let alone at the scale GR works on. How is the uncertainty principle supposed to affect bodies at the scale of light years?

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

#207

Post by adgjlsfhk1 »

whoopdedo wrote: post #145
KAMSPioneer wrote: post #126

Earlier quoted context omitted.

So I work at one of the participating institutes, and you're very much dead-on about transfer speeds/logistics limiting options here. I'm not an astronomer, so grain of salt, but the data is generated at a bit of an unwieldy pace: there are four collector nodes at each site, each of which generates ~16Gbps of raw data (though read speeds from disk after observation is more like 8Gbps). This, as you say, forces most l…

Where can I read more about how that volume of data is generated? I'm looking at the description of ALMA right now. So is each "node" a cluster of antennas? And each antenna is collecting a high-resolution snapshot across a wide frequency band. And each snapshot has to be timestamped. What's the sampling rate? It says the frequency range is 31GHz to 950GHz but how wide can a single snapshot be? Then to move it around…

much faster than infiniband. A suitcase full of hard drives.

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

#208

Post by raattgift »

dekhn wrote: post #166
raattgift wrote: post #64

Earlier quoted context omitted.

For a small-mass central black hole (CBH), the spin-spin coupling of the CBH and the bulk matter of a relatively small and sparse galaxy is so small that it the orientation of the spin axis is almost unconstrained. That from Earth we look down on the CBH's north pole (right-hand-rule: the bright features appear to circulate counter-clockwise, and there is decent evidence in them that the black hole's spin is in the s…

when you say spin-spin coupling, do you mean exchange of momentum between the spin of the black hole and the spin of the galaxy that contains it? I normally think of spin-spin in terms of atomic/subatomic particles ( https://en.wikipedia.org/wiki/J-coupling )

Yes, that's what I meant. Specifically the minimal-coupling of the galactic spin parameter \lambda (for galactic discs) and the Kerr(-Newman) spin angular momentum parameter J.

J reflects the entire history of the black hole, including mergers and infalling matter. The entire history of the galaxy includes outflows driven by jets from the central black hole, and one expects J (and available inflows) to determine whether the jets increase or quench star formation. So the pecularities of the history of a large well-fed central black hole's J can shape the distribution and composition of stars around it. A forthcoming paper goes into this in detail : https://par.nsf.gov/biblio/10322445-which-agn-jets-quench-st...

The inverse is relevant too: what's the angular momentum of things falling onto a central black hole? In a spinning galaxy with significant \lambda, visible matter is entrained (via gravitational minimal coupling, and possible weak-scale interactions with halo dark matter) in such a way that most of what falls onto the central black hole has a correlated spin, so if J for a well-fed black hole drifts a little from correspondence with \lambda, infalling matter will tend to correct that. (central dark matter might also contribute weakly).

The mechanisms for correlations between the spins are ripe for even more study. Chandrasekhar dynamical friction is a probable component. There may be other components. Jets are probably relevant, and jet strength depends on black hole mass and spin, and the environment surrounding the black hole, but the action of the jet itself on the matter distribution immediately around the black hole is through electromagnetic interactions (so we may introduce Pauli coupling, and thus our spins may not be precisely "minimal"ly-coupled). We need to see more central black holes in more galaxies to answer fun question like: can the size and spin of M87* over time and the consequent strong jets, if allowed to tumble, have randomized the orbits of star-forming clouds (and thus M87's abundant globular clusters) in nonspinning parent galaxy M87? Or is it much more likely that galactic mergers drove out M87's bulk spin? If the latter, why is M87* still strongly spinning?

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

#210

Post by JonShartwell »

snowwrestler wrote: post #197
JonShartwell wrote: post #161

Earlier quoted context omitted.

It’s absolutely in the spirit of science to question an experiment’s methods and results. If you disagree with the criticism then present some evidence. An appeal to authority is pretty unconvincing considering scientists have been confidently wrong about quite a lot in the past.

Criticism must bring substance as well. Sure, anyone can sit back and say “I don’t believe this, prove it better.” But without specific claims, such criticism can’t ever be answered and the conversation is not constructive or particularly scientific. One constructive approach to criticism here would be to take the documented imaging process and apply it to other data. If it produces results that don’t match existing…

I don’t know, the criticism in OP seems pretty substantive to me. I don’t know much about this subject so I can’t really weigh in on how much the post makes sense but regardless appeal to authority is essentially the opposite of modern science. That’s why nullius in verba has been a motto of science for 300+ years.

On that point, scientists don’t need you to chastise people for questioning their authority online. I think a lot of them would be offended at the idea that you think that is what they want.

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