Astronomers reveal first image of the black hole at the heart of our galaxy
public.nrao.edu
public.nrao.edu
https://twitter.com/alex_parker/status/1116070667068170240?s...
JWST will have smaller “pixels” but is in the same ballpark.
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.
(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.)
[0] https://en.wikipedia.org/wiki/Chromosphere [1] https://en.wikipedia.org/wiki/Stellar_corona [2] https://sdo.gsfc.nasa.gov/data/
But I suppose you could be right for a single image from one angle, and I suppose that we don't get to see this particular object from many different angles.
See, e.g., https://www.stsci.edu/jwst/phase2-public/2235.pdf (although this was written when there was no image, certainly it would still be useful).
"Size comparison of the two EHT black holes": https://youtu.be/UOESt-G34vE
https://en.wikipedia.org/wiki/Astronomical_optical_interfero... https://en.wikipedia.org/wiki/Aperture_synthesis
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.
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.
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 full imaging stack has never been calibrated by looking at a known celestial body to compare images to validate their algorithms. They have calibrated their signals from results of other instruments, but their imaging algorithms change to fit their wanted results. This is my biggest problem with their approach. Anyone can modify algorithms of any arbitrary data to get an image of a glowing circle. A better method that shows a more true image would be to calibrate their imaging algorithms against a known celestial body to make sure their techniques produced comparable results from other instruments. Then they should have taken their calibrated imaging algorithms and gave it data from their target.
I'd have more confidence in the EHT if they would not change their imaging algorithms across images and give a side-by-side comparison of a known celestial body that other radio telescopes have imaged to verify their whole imaging stack.
To me this a just a big PR stunt and I'm very skeptical of their image.
Aren't they are peer reviewed?
What is your expertise in astrophysics?
https://ui.adsabs.harvard.edu/abs/2022arXiv220510267P/abstra...
Btw we released the 2017 calibrated data today, too.
I think people's priors here are out of whack -- perhaps the truth does lie somewhere in the middle, but if so, it will be much closer to ETH's version than the OP's.
"...We have seen, and taken a picture, of a Black Hole."
Now the you have published the data from 2017, If I publish my own "photo", and I chose blue with spots of white, using the same library you used and the same color maps:
https://github.com/liamedeiros/ehtplot/blob/docs/docs/COLORM...
Why yours will be more a picture than mine in blue? Maybe I will even splint a little bit of red in there...
I also would like to notice you did not explain why my blue "picture" would be less a "picture" than yours.
Taking a real picture of a black hole like with a cellphone camera would likely be just like a bright white star.
But I'm sure you're more of an expert than anybody serving in a peer review board.
Why should I trust you that you know more about astronomy than a team of astronomers and a peer review board?
I've asked you this three times so far and you've not given an answer.
No it doesn't. Most peer review doesn't even attempt to reproduce results, which is the real way to make sure the science is sound.
In the process of doing so, questions and clarifications may better reveal problems with the underlying science itself, which can result in the paper being withdrawn or declined. But peers don’t independently validate results.
At the same time it should be noted that published criticism has to meet the same bar. “You didn’t do the experiment the way I would have” is not really strong criticism. Experiments or observations can always be done better; this is a central ethos of science.
The strongest criticism is usually to conduct one’s own experiment the way one wants, and then show that it produced better results.
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 evidence, that would be evidence it is flawed.
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.
Then how can you say the criticism seems substantive? He brings nothing to the table to show that his criticism is valid, it's basically "I don't like, therefore wrong". The proper way criticize their paper would be conduct your own experiments using their parameters and methodologies and show that the results you obtain do not match theoretical results or results of other observations through other means.
>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.
We question their authority on this specific subject they seem to be criticizing. If you make a claim without having at least the background to support said claim, what value does it have? It's the same as a person without background in microbiology or virology claiming vaccines don't work when they don't even begin to understand the science behind it and the mountain of evidence that says otherwise.
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 prominence in one field to justify their opinions in an unrelated domain, e.g. putting credence in a software developer's pontifications on imaging black holes just because they're good at software. "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 this issue, so it's possible that when the op appealed to authority they were actually trying to appeal to the arguments presented in the paper by proxy, which is fine. But a bald appeal to authority is always flawed, and expert witnesses are just a concession the law has to make to get anywhere. In the words of Richard Feynman; "Science is the belief in the ignorance of experts".
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.
There was some hype about: FTL events, life based on cyanide not phosphorus…
Careful with “peer review” when the set of peers is invested in the same type of results.
How confident are we that our current simulations accurately reproduce the universe?
Given how many unpredicted and supposedly impossible exoplanet and star configurations that keep being found, I'd say the current model is not doing so well on the prediction front.
https://www.science.org/content/article/forbidden-planets-un...
In comparison, general relativity is one of the most well tested theories in physics, having been undergoing rigorous testing for over a century, and regardless, the point stands that the results were close to the model, thus providing evidence for the model's validity.
CPU performance and aerodynamics are two completely unrelated domains.
Newtonian gravity is good enough for that problem, and the problems have nothing to do with not understanding gravity well enough. The problems have to do with things like complex chemistry in stellar accretion disks, how grains in these disks stick to one another to eventually form rocks, and so on.
The fact that some models somewhere have problems has no bearing on whether the image reconstruction for Sgr A* is valid.
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 possibilities that can explain the measurements."
They seem to have gone to great lengths to address this issue, however. Multiple imaging approaches, synthetic data tests, etc.
https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/...
Why would looking at something that isn't a supermassive black hole at the center of a galaxy prove that this approach works or doesn't work? You'd have different constraints to apply. See for example VLBI measurements of quasars, which seem to employ the same kind of imaging approach. Theoretical models of quasars aren't the same as theoretical models of black holes. They seem to be using these theoretical models as constraints on data interpretation. Unless the theory is completely wrong, which seems unlikely, this looks like a valid approach.
If the original commenter has an issue with this, wait 'til they find out about modern CT scans. Or hell even JPEGs.
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
Rather than attempt to disentangle, large physics collaborations normally have a “You are on all papers we publish while here and X years after you leave”.
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.
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.
"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.
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?
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.
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.
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'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!"
I happen to live and work near JPL. The astronomers there have none of the qualms you do about this image, because it turns out the professionals working on this image actually took such things you're complaining about into consideration when refining the data. And if you had read the publication accompanying this image, you would have known that.
Also, they weren't just looking for a glowing circle...That's a shockingly ignorant way to characterize their work.
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?
How unexpected is that?
We only look down on its north pole approximately. Extending the spin axis of Sgr A* could miss our solar system by thousands of light years. A polar jet, moreover, can be slightly unaligned from the extended spin axis, and over a 27 kilolightyear distance, that can be even more significant. Finally, we don't know whether the spin axis of the black hole will keep pointing roughly towards us, or whether it sweeps through (up or down) or around the midplane of the galaxy (or on what time scale such "precession", if any, occurs: for all we know, in a few years we might have an image that evidences an Earth-based view almost perpendicular to the spin axis).
Active in the sense of (from <https://en.wikipedia.org/wiki/Active_galactic_nucleus>) "much higher than normal ... excess non-stellar emission" from the region very close to the central black hole. Our central parsec is simply dim in practically every wavelength compared to its enclosing central bulge. An active galactic nucleus in our galaxy would be very noticeable to the naked human eye: it would "light up" (with far ultraviolet to gamma radiation) lots of interstellar material that, having been heated, would glow very brightly in the reds and oranges.
The luminosity of AGNs and quasars (especially luminous AGNs) is mostly from matter-matter collisions between gas and dust on intersecting geodesics (a fancy sort of friction that becomes enormous in the material nearest the black hole), with a contribution from daughter products of those collisions.
There isn't much matter circulating close to Sgr A*. It's "starving". In the panel they tried to put it in terms of a human diet: if you were eating like Sgr A* is, scaled down to human size, you'd be eating a grain of rice every few million years. Good luck keeping your body heat up on that diet. :-)
In the past -- tens of thousands to many millions of years ago -- there might have been a lot of matter circulating around Sgr A*, being swept up into luminous jets, which generated the Fermi bubbles <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>. That's an area of current research: do central black holes eventually go radio-quiet in general? Is there a active-quiet-active-quiet cycle in central black holes in general? Or is this all an ultraviolet herring with the Fermi bubbles being produced by some mechanism that doesn't involve (or only very weakly depends upon) Sgr A*?
ETA: I forgot to re-read my own (grandparent) comment. The "luminous structures nearby" are not just an accretion disc. Jets count, too. Also anything that they strike (molecular gas clouds, for instance) will tend to become luminous in some part of the spectrum (sometimes this results in "frustrated lobes", sometimes "light echoes" or ionization echoes from flares).
The beams come from the accretion disk. There are two opposing beams because the disk has two opposing faces. The profile of the disk is narrow, so it stands to reason that very little radiation would leak out around the edge. On the other hand, there is a black hole in the middle of the disk and that should be smearing the beam out quite a lot. Somehow the magnetic fields and currents within the disk must conspire to keep the beam fairly narrow.
M87 and its CBH M87* are much more massive than the Milky Way and its respective CBH Sgr A*, but it M87 a giant elliptical galaxy that is almost circular (as far as we can tell from the highly random orbital motions of constituent parts like hydrogen and molecular gas clouds, resolvable globular and other star clusters, and so forth). So there is essentially no (bulk) galactic spin for M87* to couple to. M87*, the black hole, has significant spin however.
For a galaxy with strong axisymmetry to the point of a thin disc, there are still open questions about spin-spin coupling with a sufficiently massive CBH, under the assumption that the CBH spin and the galactic spin were identical in the early universe and that the CBH spin has not become perturbed (e.g. by black hole mergers, which may change the spin parameter, which translates to a CBH spin axis unaligned with the galactic spin axis, or a counter-rotating CBH, or some combination), and that the galactic spin has not become perturbed (by close-encounters or mergers with other galaxies). There are additional reasons why a jet and counter-jet may not trace out the extended spin axis of a CBH.
Finally, the spin-spin coupling is probably driven by the galactic spin imposing its "will" upon the CBH, rather than the other way around, because of the large mass-ratio and the distribution of mass at significant spatial remove from the CBH. However, there is a chicken/egg conundrum for very large CBHs, since we don't know if they become so huge (principally) primordially or by hierarchical mergers or by some other mechanism. The biggest CBHs may drive the initial angular momentum in the early protogalaxy, and then both the CBH and the later-time bulk galaxy will influence each others' spins. That is, the spin-spin can be correlated without any significant direct linking (in terms of forcing a drifting spin to realign), because the coupling can be arbitrarily weak.
So, we should not be surprised by central black holes spinning differently from their enclosing galaxies. But, we have a lot to learn about your question from further observations of CBHs!
Indeed today's event <https://www.eso.org/public/news/eso2208-eht-mw/> involved many of the techniques mentioned on the pages above, with paper III (freshly un-embargoed, so I have not perused it) appears to be a good starting point if you feel technically inclined.
I'm not exactly sure what you mean by "non-quantum" -- in general making sense of extragalactic central black hole observables (and even obtaining them in the face of e.g. astronomical and atmospheric extinction) depends very sensitively on understanding various types of scattering (especially Compton and its inverse) and atomic electron transitions / (quantum-mechanical) spin-orbit interactions. This has to enter into matching the results of a simulation from data obtained by observatories.
I believe you are asking about how to solve the trajectories of electromagnetic radiation generated just outside these central black holes, since essentially that's what determines the images released to the public today.
I'm going to restrict this to the "lens" of the production of hard X-Rays and gammas around a black hole by inverse Compton scattering. <https://svs.gsfc.nasa.gov/vis/a010000/a011200/a011206/index....> has a pretty couple of visualizations. (It is not a coincidence that the swirls vaguely resemble some of the images that were revealed in today's ESO presentations.)
Pretty much nobody is using exact analytical solutions to the Einstein Field Equations of General Relativity to predict central black hole observables. Instead one uses a combination of numerical methods <https://en.wikipedia.org/wiki/Numerical_relativity> and approximations to the full Einstein Field Equations including linearized gravity, the effective one body formalism, and post-Newtonian expansions (the wikipedia article for which has a handy chart of the domain of applicability for these <https://en.wikipedia.org/wiki/Post-Newtonian_expansion>). One can do standard model physics set against any of these formalisms (or against several as things plunge inwards and/or climb outwards from the near-horizon) and get useful results.
If one sat down (as a theorist) and were to grind out an exact analytical solution (this would have to be for a very tiny sample of light-producing events to be tractable cf. [1]), one would find there is no need to make quantum corrections to the gravitational side of the Einstein Field Equations. The reason for this is that General Relativity guarantees a small patch of flat spacetime around every point everywhere. As long as the "small patch" is big enough to enclose an electron-gamma scattering event, there is no need for quantum corrections. This translates in practice to not having to introduce higher-order terms "correcting" the formalisms above for strong gravity, and in fact partially justifies each of those.
Where we worry theoretically is when spacetime curvature nearby is so strong that the "small patch" starts being smaller than a gamma ray. Smaller can be read as a combination of spatial extent vs wavelength or longer than the half-period of the frequency. When that happens, we have to mathematically stabilize the spacetime around the electron-gamma interaction in order to use the Standard Model's description of the scattering, and then we have to figure out how to undo the stabilization so the emitted photon has the right energy.
We would want to do this by adding in quantum corrections to whatever gravitational formalism we are using. These are easiest to see as additional higher-order terms added on to the Taylor-series-like post-Newtonian expansion.
It turns out that the strength of the local spacetime curvature (and thus the inverse of the extent of the "small patch" of flat spacetime: stronger curvature, smaller patch of flat space) outside even stellar-mass black holes is much larger than we need for pretty much any Standard Model physics to be feasible without -- or with only very gentle -- quantum corrections. For supermassive black holes, local spacetime curvature just outside the horizon is smaller than for stellar black holes, so the local patch of flat space everywhere near the black hole is much larger than that in any particle physics laboratory here on Earth. Since the tidal effects of Earth and the sun don't make much difference to physical experiments done at e.g. CERN, the even gentler tidal effects of Sgr A* and the weaker still tidal effects around M87* can basically be ignored.
Where do we start needing significant corrections, and start having to think about not using some of these formalisms instead of harder and harder work designing numerical methods based on the full theory of General Relativity? (For example, we might end up having to add many many many higher-order terms to our Taylor-series-like post-Newtonian expansion, each adjusting by something like a tiiiiiny 1/c^{ever larger number}). The answer: it's tractable until we are deeeeeep inside the event horizon, where we can't see the results of what's going on from outside. Very near the singularity the expansion approach starts requiring millions, billions, billions-to-the-power-of-billions of additional small correcting terms to retain accuracy, and it's a losing battle, even with mathematical tricks to shrink the number of terms and/or sizes of exponents ("renormalization", which is out of scope for this answer). At the singularity, this approach can only fail. Far from the singularity, but within the horizon of a large black hole, it works just fine. And in any event we only really care about what's outside the horizon, because we can't interact with anything inside: it just leaves no imprint for our telescopes to detect.
General Relativity and its approximations work perfectly well outside Sgr A* for known particle physics (and even some higher-energy extensions to the Standard Model).
Today's results fail to support several alternatives to General Relativity that correspond to a need for quantum gravity corrections just outside the horizon of Sgr A*. Among them are theories which predict "bouncing" or "reflecting" surfaces, and radiating compact stars (e.g. quark stars, boson stars -- things that are even more compact than neutron stars, but held up from collapse by an as yet undiscovered degeneracy pressure as in <https://www.einstein-online.info/en/explandict/degeneracy-pr...> for electrons).
So, in other words, there is no need for a theory of quantum gravity for the findings made public today. (The findings do cause possibly fatal trouble for alternative theories of gravity that expect quantum effects just at the horizon of Sgr A*.)
- --
[1] a discussion of how this works, and a neat simulator, for one photon around a Kerr black hole: <https://duetosymmetry.com/tool/kerr-circular-photon-orbits/>
The links are really helpful btw. Where do you get your daily news feed? If you have something like 'hacker news for astronomers', or some very active blog, do let know please.
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?
Is it at all possible that the glow is more of a spherical cloud and the black spot would be visible from any angle you look at it?
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. According to the article, at least one submillimeter telescope was important. But submillimeter is infrared, isn't it? I thought infrared was blocked by dust, and if there's one thing there's a lot of at the centre of the galaxy, it's dust?
[Edit] Questions 1 and two were prompted by this remark in the article:
"The new view captures light bent by the powerful gravity of the black hole"
But if that is indeed the accretion disk, then that isn't light that's been bent by the gravity of the black hole.
Perhaps the explanation is that many other commenters haven't actually read the article, possibly because they already know the story.
It's the opposite actually! Infrared light is able to go through dust.
> Another reason [to look at the universe in the infrared] is because stars and planets form in clouds of gas and dust, and this dust obscures our view. Infrared light penetrates these clouds and allows us to see inside.
https://www.nasa.gov/content/goddard/webb-conversations-its-...
If "doppler boost" is regions that are moving towards us, then they presumably aren't swirling around the BH at near-light speed?
Is the ring of light the accretion disk or not? If it is the accretion disk, why is some of it moving towards us?
And why does it seem that the ring of light is oriented perpendicular to our line-of-sight? Is that really coincidence? Don't most accretion disks rotate on roughly the axis of the host galaxy's rotation? If we're looking directly at one of the poles of the BH, shouldn't we see some sort of beam pointing right at us?
Between the images of M87 and Sgr A, one noticeable difference is that the image of M87 appears to have a single cluster of light "below" the blackhole whereas the image of Sgr A has three surrounding the blackhole. Is this because of the mass and spin differences between the two blackholes?
1. https://www.youtube.com/watch?v=rIQLA6lo6R0&t=1930s
2. https://physicsworld.com/wp-content/uploads/2022/05/First-SG... from https://iopscience.iop.org/article/10.3847/2041-8213/ac6429
To be fair, to most non-scientific people the two photos look basically the same, and "orange halo" kinda loses it's appeal quickly
This is truly amazing!
https://www.wolframalpha.com/input?i=diameter+of+moon+%2F+0....
~= 9 cm object on the moon
Google says donuts are 12-14 cm in length on average…
Search for black hole ends with a bagel hole?!
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And ten thousand physicists sighed disappointingly.
You wouldn't be surprised if your door opened just as usual when you put your key in the lock. The day it starts jamming however, you get very interested.
Black holes are a solution to the general relativity equations, but Einstein thought they were just a mathematical quirk, and that in real life, they wouldn't have been able to form.
So ever time someone says "Einstein was right" when talking about black holes, then no. He was right about general relativity, but he was wrong about the existence of black holes.
I'll add an additional recommendation: Stephen Hawking - The Theory Of Everything
https://gizmodo.com/why-cant-einstein-and-quantum-mechanics-...
https://www.theguardian.com/news/2015/nov/04/relativity-quan...
https://en.wikipedia.org/wiki/Problem_of_time
https://physics.stackexchange.com/questions/387/a-list-of-in...
For a good general source if you want to learn a lot more from a good popular science point of view (but one that takes great care to not accidentally mislead by oversimplification as often happens with popular science) about general relativity and quantum mechanics, try PBS Space Time, especially after Dr. Matt O'Dowd took over as host and main writer.
https://www.quantamagazine.org/where-do-space-time-and-gravi...
It might just not be possible to see anything odd without having a black hole right there to study, but there’s always hope that the next new observation will provide a clue as the previous ones repeatedly have not.
This is a semantic nitpick, but I don’t think it’s useful to think of these theories as “wrong”. They are both models that make predictions about physical phenomena that, when tested, are extremely accurate. They provide incomplete and inconsistent predictions of what happens at the very edges of physical reality, and they need reconciled.
The best place to look for new data where we might find reality disagreeing with either model is in the extreme parts of the universe, like black holes. If there was even a hint in this photo that General Relativity wasn't perfectly accurate, we might be able to take the discrepancy and build a new model that solves the disagreement.
Whoever does that gets a Nobel Prize and has their name as immortalized as "Einstein".
The fact that general relativity continues to hold up to every observation we can make is remarkable.
Granted, I only ever got as far as E&M physics in college so I could be way off here but that scenario has turned up so many times in history.
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 watching a beautiful sunrise on a summer's morning. You've seen it before, but darn if it isn't pretty.
That said, the mathematical fundamentals of GR do not directly incorporate notions of the uncertainty principle. That fact alone, I believe, means that GR is an incomplete description of space/time/physics.
Everyone is different, but most scientists seek areas where experiment doesn’t match the predictions. It’s the only way we learn.
One such instance is the W Boson Anomaly: https://vm.tiktok.com/ZTdpwrmoj/?k=1
If the equations were right, the experimental error would be zero (modulo uncertainty bars). Instead, we’re quite confident the standard model is wrong (or “incomplete” to phrase it diplomatically).
As an aside, this is also a great example of TikTok turning a corner. I now have 184 educational videos saved, along with dozens of science videos. I learn more on TikTok than any other source now, which I didn’t expect. There’s an avid physicist community, and I made friends with someone who works at CERN. https://twitter.com/simoneragoni?s=21&t=xIkxhA--TzKDWA5XN3ve... Get ready for TikTok to become the new Wikipedia within a decade.
I've also learned a lot from TikTok, where short form content has led to 30 second tutorials that leave 30 minute YouTube equivalents in their dust. My learning topics include smartphone photography, wood working, and knots. I was also surprised at how informative it can be.
It'll be interesting to see how TikTok's content moderation compares against Wikipedia. We won't have notability wars, but there is massive scope for disinformation and banal wrongness.
I too have been surprised with the amount of genuinely educational and interesting material on TikTok. It won't replace Wikipedia but it's a great companion to it.
We have a lot more to learn about gravity, especially at laboratory scale and smaller.
While we can only measure G to ~10 ppm, the equivalence principle has been tested at the 10^{-14} level (and ~10^{-9} at meter-scales). The EP is the property that makes gravity really special and simultaneously the thing that makes gravity hard to test.
The core assertion that all things fall the same way is axiomatic to GR and has been very well tested. We have everything left to learn about gravity, but at the same time, GR has held up far better than it "should" have against a battery of really great experiments.
That's beautifully worded. It brings up the respect scientists can have for one another's work (in the best case scenarii, let's skip the bad seeds for a moment).
(That's counterbalanced with the tears shed over your midterm grades.)
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. :-)
- --
[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.
It’s difficult to force oneself to not romanticise these un-visible things based on artists visualisation we got accustomed to.
The reason it looks blurry is that the black hole features are close to the resolution of EHT so it's only a dozen or so pixels worth of information enlarged to typical image size.
EHT is essentially a radio telescope with a dish the size of the Earth. The only way to get higher angular resolution is to use higher frequencies (which they are working on) or use radio telescopes in space to get longer baselines than the diameter of the Earth.
Would it be possible to use the same trick in space? IE: get a baseline the diameter of Earth's orbit (roughly)?
Even on Earth they resort to shipping cases of hard drives instead of transferring over the Internet.
One technique where simply waiting 6 months works very well is in measuring parallax. The Gaia spacecraft takes advantage of this.
Space-based very long baseline interferometry (VLBI) has been done at lower frequencies, most recently with the RadioAstron satellite[0]. There hasn't yet been a VLBI satellite observing at the same frequencies that the EHT uses, but there are mission concepts being discussed. [1] discusses some of the technical challenges.
(1) https://www.smbc-comics.com/comic/delta-v
edit: We could also send the (super)computer that will process these images in LEO, so we don't even have to worry about atmospheric re-entry.
But I'm optimistic that some institutions (hopefully including mine!) will be able to transfer these data over the network after the next run of EHT observations. Exciting stuff for sure.
I wish I could shed some more light on the ins-and-outs of exactly how these observations work, but I just run the computers, man. :) What I can tell you is that in order to move data off of the collector machines, they typically use m5copy, which is a part of the JIVE project (they have a Github repo: https://github.com/jive-vlbi/jive5ab). All communication between the control computer and the collectors happens within a private, physically-distinct network, but it's just standard commodity networking equipment between the control computer and the collectors. The folks in charge of the node's design are in the process of removing some of the bottlenecks to make electronic transfers more viable (the current spec doesn't even include a 10Gbps uplink!).
Sagittarius A*, the black hole in the Milky Way galaxy, is a harder target. It is less than one-thousandth the mass and size of the M87 hole and, therefore, evolves a thousand times faster. The M87 black hole barely budges during a weeklong observing run, but Sagittarius A* changes its appearance as often as every five minutes.
https://www.nytimes.com/2022/05/12/science/black-hole-photo....
It also sounds like this is the combination of an image-generating model hypothesis as well as the raw data itself. Ie, this is the image that the model produces which best-fits the sparse interferometry data.
Let's say I'm 6 feet tall... what object would I have to hold out at arm's length, to have the same angular width as the entirety of this image?
A bacteria? A virus?
The answer is ~200 picometers.
Wolfram lists some helpful comparisons:
1/2 the distance between base pairs in DNA
3x the atomic diameter of helium (the smallest atom)
Suffice to say you'd have a hard time seeing it as it would be 3,000x smaller than the wavelength of visible light.
>Although we cannot see the black hole itself, because it is completely dark
No one ever before was able to see this.
It feels very similar to when I hold an expensive CPU in my hand or a very expensive (because handmade) watch which is 'more' than just a CPU or watch.
It's the marvel of our time. Craftsmanship
OTOH, consider the potential downsides to living in a galaxy where the central black hole was far bigger, brighter, and cooler-looking...
(Edit) to add that it’s about 22minutes in.
My comments was more about the culturally idealised images we have in mind rather than criticising the work and the tech (far from it actually, but given the downvotes I might have not expressed myself really clearly -> apologies to anyone who felt bad/sad about what i wrote).
I really appreciate the small animation you pointed at 22min.
What does this mean? If they assembled an image to fit their assumptions, that would be circular reasoning. I don't understand.
"Press conference on Milky Way galaxy discovery from the Event Horizon Telescope collaboration"
I thought it was Sagittarius A* back then.
[1] https://www.nasa.gov/mission_pages/chandra/news/black-hole-i...
This thread seems to be the leading one:
Astronomers Reveal First Image of the Black Hole at the Heart of Our Galaxy
https://public.nrao.edu/news/astronomers-reveal-first-image-... (https://news.ycombinator.com/item?id=31353677)
Others, as of submitting this comment:
https://www.eso.org/public/news/eso2208-eht-mw/ (https://news.ycombinator.com/item?id=31353692)
https://public.nrao.edu/news/astronomers-reveal-first-image-... (https://news.ycombinator.com/item?id=31353677)
https://www.youtube.com/watch?v=rIQLA6lo6R0 (https://news.ycombinator.com/item?id=31353643)
https://www.youtube.com/watch?v=4Ws0iPDSqI4 (https://news.ycombinator.com/item?id=31353587)
https://www.nsf.gov/news/news_summ.jsp?cntn_id=305028&org=NS... (https://news.ycombinator.com/item?id=31353583)
https://nitter.kavin.rocks/ehtelescope/status/15247172729037... (https://news.ycombinator.com/item?id=31353547)
https://www.cnet.com/science/space/watch-live-astronomers-re... (https://news.ycombinator.com/item?id=31353480)
https://beta.nsf.gov/blackholes (https://news.ycombinator.com/item?id=31353474)
https://www.youtube.com/watch?v=rIQLA6lo6R0 (https://news.ycombinator.com/item?id=31353463)
https://www.nsf.gov/news/news_summ.jsp?cntn_id=305148 (https://news.ycombinator.com/item?id=31353757)
https://eventhorizontelescope.org/blog/astronomers-reveal-fi... (https://news.ycombinator.com/item?id=31353786)
https://www.nytimes.com/2022/05/12/science/black-hole-photo.... (https://news.ycombinator.com/item?id=31353823)
https://www.quantamagazine.org/black-hole-image-reveals-sagi... (https://news.ycombinator.com/item?id=31353874)
https://www.bbc.co.uk/news/science-environment-61412463 (https://news.ycombinator.com/item?id=31353939)
Today's announcement is about the blackhole at the center of our own galaxy.
[1]: https://www.nationalgeographic.com/science/article/first-pic...
It is physically impossible (regardless of the exposure time) for JWST to resolve Sgr A*.
1. https://physicsworld.com/wp-content/uploads/2022/05/First-SG...
I mean if they could, they could do another longer term observation like from that clip where you can see stars swishing around it.
https://en.wikipedia.org/wiki/Sagittarius_A*#/media/File:Sgr...
Roughly speaking, the sun orbits the galactic center at a velocity of 220km/s. To fall into, or to be sucked into, the central black hole would require the loss of all this velocity, which means applying acceleration to the sun opposite the direction of its orbit. Lots of acceleration. That has to come from somewhere.
I suppose there's some extremely tiny amount of drag that occurs due to the sun moving in the interstellar medium, but aside from that there's not a lot that applies acceleration to the sun opposite the direction of its orbit. Really the only other thing that comes to mind are the gravitational waves that are radiated by co-rotating objects. This is the effect that causes close by black holes to eventually come close enough that they merge. But in objects traveling at slower speeds in larger orbits, this effect is also negligible on the scale of billions of years. (These are the gravitational waves observed by LIGO). https://en.wikipedia.org/wiki/Two-body_problem_in_general_re...
The Sun is nowhere near massive enough to become supernova.
https://en.wikipedia.org/wiki/Sun#After_core_hydrogen_exhaus...
It will become a red giant, and then eventually end up a white dwarf.
It seems like the assignment of "nova" to a common stage of solitary low-mass stellar development is outmoded, so a change in nomenclature could help explain my confusion. For instance, this 1986 book https://archive.org/details/privatelivesofst00gall/page/68/m... states "Stars called novae explode and grow much brighter over a period of days or weeks, then return to normal again, usually over several years. Although we have ideas about nova stars, we have a lot more to learn about them. [...] When a red giant collapses and is well on its way to white dwarfhood, it may go through one or more periods of being unstable. At such times the star may erupt as a nova. This may be especially so of the more massive stars."
The sun itself may get ejected into intergalactic space when the Milky Way merges with Andromeda. (< 5 billion years from now)
Earth will probably be totally engulfed by the sun when it goes red giant, or it might not in which case presumably it will continue orbiting. (7.59 billion years from now)
By 100 billion–1 trillion years from now all galaxies in the local group are expected to have merged, so there will probably be other opportunities for the sun to get yeeted into intergalactic space.
By 10–100 quintillion it's expected that 90-99% of all stellar remnants will be ejected.
Finally, at 10^30 (1 nonillion) years from now, we get this gem: Estimated time until most or all of the remaining 1–10% of stellar remnants not ejected from galaxies fall into their galaxies' central supermassive black holes. By this point, with binary stars having fallen into each other, and planets into their stars, via emission of gravitational radiation, only solitary objects (stellar remnants, brown dwarfs, ejected planetary-mass objects, black holes) will remain in the universe.
One thing to keep in mind though is that by the time our sun gets sucked into a black hole, the galaxy will have merged so it may very well be a different black hole, or this paticular black hole may have merged with multiple other ones.
If the Sun were replaced by black hole with the same mass as the Sun at the center of the Solar System we wouldn't automatically get sucked into it. A very cold Earth would continue to orbit the black hole exactly as it does the Sun today. Only if the Earth's orbit were perturbed by some other body would it have a chance of joining the black hole.
Not any more meaningfully than the chance of current-Earth being put on a trajectory to crash into the sun if its orbit were perturbed. A black hole doesn't magically have a stronger (instantaneous) gravitational pull than that of any other body; the same formula for gravitational force at distance D given object masses Mi is preserved. Now the typical means of formation for a black hole generally result in masses much greater than that of our sun, which is why they are generally heavier and, accordingly, stronger (and they gain mass as they suck up things around them, hence the "instantaneous" disclaimer above).
I'm still sad we can't post donut emojis here. This place sucks.