271–280 of 329 posts
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.
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.
Is the EHT "only" planet scale, or is it taking a second measurement 180 days later to increase the effective diameter of the virtual antennae to the width of the earth's orbit?
Earlier quoted context omitted.
JWST is nowhere near the caliber of telescopes necessary to resolve black holes. Very literally, we would need an optical telescope bigger than new york city to even make an attempt.
What about an array of space telescopes creating a kind of "virtual lens"? Putting aside the engineering scale and cost of such a project, would something like that even be possible? Or would that be pure science fiction?
However, there’s no free lunch. By using arrays of telescopes instead of a single filled dish/mirror, they are missing a lot of information. Imagine a telescope the size of the earth, but you only use light from a few dozen spots on the surface and let the rest fall through. This is why they had to do all that complicated image reconstruction processing to create the image shown in the papers.
I am impressed. I have a few ignorant questions: 1. There are three bright blobs on the image; I assume they are the same object, behind the BH. What are they/is it? They said the image was averaged; so presumably whatever the blobs are wasn't moving? 2. Is it correct that the rest of the ring, ignoring the three blobs, is the far side of the accretion disk? Why can't I see this side of the accretion disk? 3. Accordi…
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…
> “We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity," And ten thousand physicists sighed disappointingly.
Gravitational physicist here. Every time we look in a new place and see that GR still works, it is pretty amazing. Part of this is the fact that everyone in the field works very hard to find a crack in GR's armor, and so far it has resisted everyone. The other part is that GR has a romantic beauty to it, both in structure and in predictions. Each time GR matches reality in a new context, the feeling is akin to watchi…
I have been thinking about this off and on since reading your comment. Is it really the structure that is beautiful, or is it that we can convert a large wall of symbols[3] into about eight easily memorized ones? That is, is it the notation that is beautiful, rather than the calculations it describes?
Relatedly:
> ... and in predictions. Each time GR matches reality in a new context, the feeling is akin to watching a beautiful sunrise on a summer's morning.
But how does one get predictions?
If you use white chalk on a blackboard to write down the constraints, boundary conditions, a realistic stress-energy (like, oh, anything satisfying Klein-Gordon or the way Weinberg writes down Belinfante), and so forth, to actually capture a realistic physical system in our universe (with actual broken global symmetries), the chalkboard's albedo sure gets higher. I'm certain you know this, and within an hour or two would go reaching for Etk/Cactus or even NRPy+/SENR. :-) And I haven't even gotten into things like Israel Junction conditions and other approaches to more-than-one-source problems.
I agree that conceptually GR is (or really, the EFEs are) amazing, and that it's a nice sandbox (oh the fun you can have in a (-,+) or (+,+,+,+,+,+,+,+,+,+,+,+,...,+) spacetime! Or Misner's mixmaster! Or lots of the entries in https://www.cambridge.org/core/books/exact-solutions-of-eins...>), but when it comes to doing (and especially intuiting[1]) actual physics maybe familiarity breeds frustration or something. It is wonderful that the "sandbox" can, with effort and additional details (NS EoS, say), grind out astrophysical, cosmological, and even laboratory observables.
> darn if it isn't pretty
Darn if it isn't impressive how much work (including observation/experiment) went into the matching. :-)
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[1] Is it sharp enough to cut paper? Your answer to the question about the "sharpness" (in a different sense) of the event horizon got me wondering about extended objects, like what happens to a tissue-paper space capsule on a hyperbolic orbit grazing the point of no return, if a tiny corner of the space capsule is allowed to dip below it? Does it tear? Does it drag the rest of the capsule in, even though a good sneeze could rip its structure apart? Is the answer https://en.wikipedia.org/wiki/Mu_(negative)> because of the nature of the horizon?
I started scribbling on this, then decided I really wanted to pretend the Weyl curvature tensor away so started thinking of really really massive BH -> Rindler approach (hoping Egan [2] had done the work already), abandoned that (because I don't think it works in general -- binding energy even in tissue paper might raise a "bump" (and thus tidal forces) on the BH horizon but I don't see how that works for the Rindler horizon, and I don't really trust intuitions built on staticity), and so on.
So, maybe I'm being a bit dumb at the moment, but a simple "what if?" turned into an "I have no idea" in spite of reasonable working knowledge of GR and some ideas about how to get the idea (with a sinking feeling that anything I arrive at is going to annoy me even more than not knowing at all, especially when trying to make sense of "no drama").
I dunno: something so hard to work with doesn't (to me) evoke romance. It's more like the feeling of summoning a cat who really doesn't want to come until your pspspspsing arrives at an acceptable-to-the-cat approximation of cat food being dispensed.
[2] http://www.gregegan.net/SCIENCE/Rindler/RindlerHorizon.html ("a constantly accelerating observer in flat spacetime trailing an object behind them")
[3] For anyone who has stumbled upon this rant and who has never seen anything like the full horror, check the tip of the iceberg at https://profoundphysics.com/einstein-field-equations-fully-w...> (eyeballing just that page, things look reasonably OK; I have not really looked at anything else on that site).
[4] Oh, "Contritutions" (sic). http://einsteintoolkit.org/guidelines.html> I'm starting to feel better now.
Earlier quoted context omitted.
Could they not zoom out and take a picture of the stars around Sagittarius A* to compare that to the knowns locations of these stars?
They absolutely could, but doing so would be a pointless waste of nontrivial resources.
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…
I cannot get over how many authors that article has.
Earlier quoted context omitted.
Didn’t I already reply to you weeks ago about a similar comment? Now you can read the actual papers which explain in detail why your comment is incorrect.
Thanks for calling them out (again). Honestly people in this forum are too eager to upvote contrarian opinions. I hold a PhD in physics, and I wouldn't feel qualified to challenge ETH's work.