[HN Gopher] Astronomers reveal first image of the black hole at ...
___________________________________________________________________
Astronomers reveal first image of the black hole at the heart of
our galaxy
Author : sohkamyung
Score : 600 points
Date : 2022-05-12 13:16 UTC (9 hours ago)
(HTM) web link (public.nrao.edu)
(TXT) w3m dump (public.nrao.edu)
| muxneo wrote:
| Size of rings prove Einstein's Theory of relativity. This is an
| amazing work
| storedsun wrote:
| 22SAS wrote:
| This is some great work, kudos to the researchers working in the
| Event Horizon Telescope team.
| jackallis wrote:
| ithought this was old news from couple of years ago, did i miss
| something?
| pdabbadabba wrote:
| The previous image was of M87.[1] The new one is of Sagittarius
| A*, which is the black hole at the center of our own galaxy.
|
| [1] https://www.nasa.gov/mission_pages/chandra/news/black-
| hole-i...
| Aardwolf wrote:
| I also remember this were photos of the milky ways black hole
| several years ago, am mixing two memories or did news
| articles then also talk about Sagittarius A*?
| [deleted]
| m-watson wrote:
| That was a different black hole that is further away. This
| black hole is much closer in the center of our galaxy. So now
| we have pictures of 2 black holes to compare!
| daniel-thompson wrote:
| Very interesting. The previously-released M87 image had just a
| single "shadow", but this one (of Sag A*) has multiple bright
| "lumps". Maybe it's in the linked papers which I haven't gotten
| to yet, but why the difference? Is it due to the observation
| method or does it reflect a real difference? Or both?
| misja111 wrote:
| Yeah I was wondering the same. From the M87's images I
| understood that the bright part of the ring was moving towards
| us, that's why it was brighter. But with this explanation, how
| can there be 3 bright lumps then on Sag A's ring ..
| adgjlsfhk1 wrote:
| I think it is just that this is an extremely noisy image.
| [deleted]
| fesoliveira wrote:
| From the announcement presentation, this happened due to this
| image being an average of many, many different images. Due to
| it's size, the motion of the accreting material around SgtA*
| moves much, much faster relative it than the material around
| M87. While the accreting material around both BHs move at
| similar speeds, M87 is about 2000x more massive than SgtA _.
| Due to that, the material around M87 takes weeks to orbit it,
| while the material around SgtA_ takes hours. Since each data
| point can be minutes or hours apart, the final image for a
| single data point can vary greatly between other measurements,
| and thus the need to average everything. To put things in
| perspective, we just confirmed through this image that SgtA* 's
| shadow is about the size of the orbit of Mercury around the
| Sun. M87's shadow, on the other hand, has a radius larger than
| the distance of the Voyager probe to the Sun.
| mabbo wrote:
| > "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.
| mhandley wrote:
| Any evidence supporting general relativity at these scales is
| presumably also evidence in favour of dark matter actually
| being matter, as opposed to gravitational theory needing
| modification. Seems like we can still learn quite a bit from
| ruling out alternatives, even if it's not the quick answer we
| might like.
| monocasa wrote:
| The Schwarzschild radius of a 4M solar mass black hole like
| Sagittarius A* is only (lol) about 7M km. Most of the MOND
| theories I've seen are about fall off curves at very large
| distances (ie. galatic scales) being more complex than GR
| suggests, so I'm not sure this is really proof either way.
| (And I say this as not a MOND adherent).
| nerdponx wrote:
| Why is that the case?
| cozzyd wrote:
| Well maybe it's more evidence against MOND-like theories
| explaining dark matter, but those already have little buy-
| in nowadays.
| ISL wrote:
| 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 watching a beautiful
| sunrise on a summer's morning. You've seen it before, but
| _darn_ if it isn 't pretty.
| f1codz wrote:
| How long does it take to train to fully appreciate this like
| you do, if that is even possible for someone in a full time
| job in an unrelated field.
| system16 wrote:
| How long is a piece of string? It depends...
| bldk wrote:
| can't GR be a micro macro scale solution where perhaps that's
| why the theories do not work out?
| xcambar wrote:
| > 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'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).
| zeven7 wrote:
| 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?
| sillysaurusx wrote:
| The most likely explanation is that we have no clue, just
| like every other point in history. Science is always new.
|
| 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.
| [deleted]
| KineticLensman wrote:
| > 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.
| babypuncher wrote:
| Back when Trump was making a big stink about TikTok I
| didn't understand it, because my feed was almost
| exclusively high quality short form educational content
| from physicists, doctors, linguists, etc. It's a great
| format for people who want to share their knowledge with
| the public in a way that is easy to digest, but do not
| have time to script and edit 15+ minute videos.
| dahdum wrote:
| > 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.
|
| 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.
| ISL wrote:
| 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, I believe, means that GR is an incomplete
| description of space/time/physics.
| raattgift wrote:
| Just to cause trouble, since we're straying far far from
| today's presentations (except arguably UCL's Z. Younsi in
| the ongoing ESO Q&A panel). :-) Can we write down the
| uncertainty principle in covariant form? Maybe! There is
| active theoretical work ongoing (e.g.)
| <https://arxiv.org/abs/2110.15951v2> ("... a geometric
| formalism for the generalised uncertainty principle which
| is covariant and connects features of the underlying
| geometry with the deformation of canonical commutator
| relations ... [and] an elegant interpretation for the
| standard dispersion relation p^2=-m^2: it describes flat
| spacetime in the Milne coordinates, with rest mass m
| giving the measure of geodesic length from origin").
| brabel wrote:
| 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?
| kloch wrote:
| We can't even measure the gravitational constant to more
| than about 4.5 significant digits. Most other natural
| constants are in the 7-12 digit range and improving along
| with our technology. Measurement of big G hasn't
| convincingly progressed since the vacuum tube era.
|
| We have a lot more to learn about gravity, especially at
| laboratory scale and smaller.
| ISL wrote:
| As a laboratory-scale experimentalist, I heartily agree,
| but must also point out the existence of compelling
| precision equivalence principle tests.
|
| 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.
| asdfman123 wrote:
| I majored in physics, and at least half of the enjoyment is
| seeing how pure and beautiful the theory is, how it all works
| out somehow, while wiping tears away from your eyes at the
| library.
|
| (That's counterbalanced with the tears shed over your midterm
| grades.)
| markus_zhang wrote:
| Just curious but why?
| onceiwasthere wrote:
| They want an exciting disruption to current theory.
| GuB-42 wrote:
| Side note: Einstein didn't believe in black holes, at least
| initially.
|
| 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.
| BurningFrog wrote:
| Basically they're bored/want mysteries to solve.
| zeven7 wrote:
| tbf, there is already a mystery to solve. This just means
| we have no new information to help us solve it.
| ohgodplsno wrote:
| We're kind of at a dead end between both leading
| theories. A counterexample to either of them would mean
| that we got it wrong somewhere, and might help us figure
| out where, potentially unlocking more later.
|
| 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.
| _joel wrote:
| Many papers/authors postulating something different to what
| Einstein did?
| adgjlsfhk1 wrote:
| GR and quantum field theory don't work together, so at least
| one of them is wrong, and it would be good to figure out
| which and how.
| markus_zhang wrote:
| Thanks. Can you please point me to some popular science
| article that explains why the two do not agree with each
| other?
| tzs wrote:
| Here are a few that might help:
|
| 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.youtube.com/c/pbsspacetime
| rootbear wrote:
| Brian Greene's "The Elegant Universe" does a very good,
| completely non-technical, job of explaining the conflict
| between the two theories. It then goes on to explain why
| String Theory is one possible solution to the problem.
| zeven7 wrote:
| There's also a Nova documentary version if parent would
| prefer to watch something:
| https://www.pbs.org/wgbh/nova/series/the-elegant-
| universe/
|
| I'll add an additional recommendation: Stephen Hawking -
| The Theory Of Everything
| markus_zhang wrote:
| Perfect! Thank you.
| GoblinSlayer wrote:
| tl;dr they don't conflict with each other, they conflict
| with a third assumption that particles have zero size. GR
| suggests they would be black holes, and those have
| mathematical difficulties. String theory is an attempt to
| model particles of finite size and thus eliminate black
| holes.
| boschnix wrote:
| I liked Sean Carroll's take on this with Steven Strogatz
| in the recent episode of Joy of Why.
|
| https://www.quantamagazine.org/where-do-space-time-and-
| gravi...
| perardi wrote:
| _so at least one of them is wrong_
|
| 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.
| jeremyjh wrote:
| Why would that matter at this scale ?
| dotnet00 wrote:
| Black holes are extreme enough to be one of the places
| where both can matter.
| jeremyjh wrote:
| Scale was not the right word - maybe I meant distance or
| resolution. Does QM make a prediction that could be
| falsified at this resolution?
| ckosidows wrote:
| You're saying this team has proven neither of them wrong in
| that their findings agree with GR, is that correct?
| Essentially, nothing new has been learned about these two
| theories?
| colechristensen wrote:
| GR and QFT essentially have to meet at black holes and
| this is where you'd expect to find an anomaly with ought
| to help open doors to new physics, but what we see here
| is that this observation seems to still obey GR just fine
| and a a closer look will be necessary to find any
| anomaly.
|
| 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.
| kuekacang wrote:
| Sometimes physicists like the theories--especially the
| battle-tested ones--proven wrong so that those theories needs
| to be refined or reevaluated. Something related to the joy of
| problem solving.
| mabbo wrote:
| Quantum Physics and General Relativity make different
| predictions in specific circumstances which are beyond our
| ability to test to figure out which one is wrong. They can't
| both be perfectly correct. But in every test we can make,
| both seem to model reality really well.
|
| 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".
| zeven7 wrote:
| Relatedly, before general relativity, people already knew
| something was wrong with Newton's theory of gravity from
| observing the orbit of Mercury, which didn't follow the
| theory accurately. At that time Mercury, being so close to
| the Sun, was an extreme condition that showed the flaws in
| the theory.
|
| The fact that general relativity continues to hold up to
| every observation we can make is remarkable.
| albrewer wrote:
| I'd be willing to bet that the discrepancy is something
| that we generally consider invariant but in reality
| should be a ratio between two things that are very large,
| but get bigger or smaller at _slightly_ different rates
| depending on the scale or distances you're working with.
|
| 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.
| lordnacho wrote:
| Could it happen that the universe simply never provides
| us with the required evidence? Eg if there's an anomaly
| but only when something that never happens happens. Like
| a large enough mass/charge/etc or some flavor of unlikely
| coincidental occurrence, like an eclipse is a bit of a
| coincidence.
| drewrv wrote:
| I've heard it said as "The universe is under no
| obligation to make sense to us". It's possible that the
| events where the two theories diverge will always be out
| of reach for us to observe.
| [deleted]
| [deleted]
| _joel wrote:
| Anton Petrov is doing a good rundown on youtube now
| api wrote:
| I'm looking forward to JWST shots of stuff like this.
| zekica wrote:
| JWST is not large enough to have that kind of resolution. EHT
| collaboration has effective lens size comparable to the
| diameter of the earth.
| imglorp wrote:
| Yes, IR better penetrates the dust cloud hiding Sgr A*, so
| here's hoping.
| nuccy wrote:
| The EHT reveals the black hole shadow of about 50 micro-
| arcseconds [1], while JWST has resolution of about 0.1 arcsec
| [2], thus resolution of JWST is more than 2000 worse.
|
| 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...
|
| 2. https://webb.nasa.gov/content/about/faqs/facts.html
| imglorp wrote:
| Interesting, thank you.
| wthomp wrote:
| Unfortunately JWST won't come close to being able to resolve
| Sgr A*. They measured its diameter in micro-arcseconds, whereas
| JWST's limiting resolution will be measured in 10s-100s of
| milli-arcseconds.
| Cthulhu_ wrote:
| And would it even be able to see past the dust clouds and
| stars and stuff in front of it?
|
| I mean if they could, they could do another longer term
| observation like from that clip where you can see stars
| swishing around it.
| dotnet00 wrote:
| JWST is an infrared scope pretty much specifically so it
| can see through dust clouds.
| anothernewdude wrote:
| Yeah, we know. We've already seen this image.
| evanb wrote:
| You might be thinking of the image of M87 from a few years ago.
| M87 is in a different galaxy. This image is of Sag A*, the
| black hole at the center of the Milky Way.
| murat124 wrote:
| This image apparently has not captured as much attention as the
| image of M87, but anyway, I have a question, maybe someone with
| the knowledge can answer:
|
| 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?
| ehsankia wrote:
| > This image apparently has not captured as much attention as
| the image of M87
|
| To be fair, to most non-scientific people the two photos look
| basically the same, and "orange halo" kinda loses it's appeal
| quickly
| nuccy wrote:
| Likely it is not about the mass, but about the arrangement of
| clumps of matter circling around the super massive black holes
| in the accretion disk. During the presentation they speak about
| much shorter time-scales for Sgr A* in comparison with M87,
| saying that for Sgr A* they were "making the image while it was
| changing" [1]. Also see other variations of the image (many
| teams analyzed data independently) here [2].
|
| 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
| aaroninsf wrote:
| Q: why are galaxies like ours so good at golf? A: there's usually
| a splendid hole in one.
| awsrocks wrote:
| dredmorbius wrote:
| There seem to be numerous submissions of this topic.
|
| 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)
|
| https://news.ycombinator.com/item?id=31353221
| wthomp wrote:
| 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.
| MeteorMarc wrote:
| And here you see the new picture compared with the 2019 picture
| of Messier 87:
|
| https://blackholecam.org/
| belter wrote:
| Similar comparison in size.
|
| "Size comparison of the two EHT black holes":
| https://youtu.be/UOESt-G34vE
| wnevets wrote:
| That really puts the significance of this new image into
| perspective.
| guelo wrote:
| 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.
| boringg wrote:
| How much post processing is happening? This isn't raw co-
| ordinated but rather fit data?
| SkyMarshal wrote:
| So you're saying no, JWST won't provide significantly sharper
| images of black holes than the Event Horizon Telescope?
| sandworm101 wrote:
| 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.
| chrsw wrote:
| 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?
| terramex wrote:
| It is possible in principle, but gets harder as
| wavelength of captured light gets smaller and so far it
| is done only for long radio waves on planet scale.
|
| https://en.wikipedia.org/wiki/Astronomical_optical_interf
| ero... https://en.wikipedia.org/wiki/Aperture_synthesis
| hbrav wrote:
| JWST would be unable to resolve the black hole at all.
| holoduke wrote:
| Aren't these black hole images based on ultra sensitive radio
| telescopes?
| JBorrow wrote:
| Yes, basically a bunch of huge telescopes across the planet
| have their images combined to give an effective mirror size
| of the entire earth, so one satellite is not going to cut
| it (even including the fact that IR has a shorter
| wavelength).
| pfortuny wrote:
| Networks of such. And a lot of very complicated
| interpolation.
| [deleted]
| hammock wrote:
| How sharp do we expect an infinite-res picture to be?
| fsh wrote:
| The resolution of these telescopes is limited by diffraction,
| not by the number of pixels on the sensors. The achievable
| angular resolution is roughly the wavelength divided by the
| aperture diameter [1]. JWST works in the few um wavelength
| range and has a 6.5 m aperture, such that the angular
| resolution is ~0.1 arcsec. The EHT works with 1.3 mm
| wavelength and has an effective aperture of roughly the earth
| diameter (~13000 km). This leads to an angular resolution of
| a few ten uarcsec which is more than 1000 times higher than
| that of JWST.
|
| [1] https://en.wikipedia.org/wiki/Angular_resolution
| marricks wrote:
| Then why did we build the JWST! /s
| amelius wrote:
| Can we invert the diffraction process numerically?
| fsh wrote:
| No, this is fundamentally impossible. There are
| infinitely many possible objects that would produce the
| same blurry image.
| amelius wrote:
| I think you just sort of rephrased the question :) Also,
| if you have a photo of a tree, then there are infinitely
| many objects that will produce that photo; however, that
| doesn't make it a bad or worthless photo.
|
| 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.
| [deleted]
| adgjlsfhk1 wrote:
| no
| hammock wrote:
| Should have clarified. Does a black hole have fuzzy edges
| or sharp edges?
| dekhn wrote:
| this is sort of getting into the definition of black
| holes and event horizons. I don't think they really have
| solid surfaces, I would expect all imaging here to show
| fuzzy samples.
| hammock wrote:
| Like, would it be a gradient from dense-to-fuzzy as you
| move outward from the center, until you reach the event
| horizon outside of which is nothing?
| dekhn wrote:
| I couldn't really say for sure but I think
| macroscopically (viewed from a low-resolution telescope)
| it would look fuzzy, but close up, it would look very
| spiky and dynamic with all sorts of stochastic events
| happening.
| gilbetron wrote:
| Does the sun have fuzzy or sharp edges?
| ISL wrote:
| 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.
| sandworm101 wrote:
| 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.
| sam-2727 wrote:
| While it won't be able to image more sharply on its own, JWST
| can still help to constrain certain factors in their modeling,
| thus obtaining better images.
|
| 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).
| NelsonMinar wrote:
| I love this quote, it's great popular science communication. "the
| brightness and pattern of the gas around Sgr A* was changing
| rapidly as the EHT Collaboration was observing it -- a bit like
| trying to take a clear picture of a puppy quickly chasing its
| tail."
| fasteddie31003 wrote:
| 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 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.
| photochemsyn wrote:
| 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 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.
|
| https://arxiv.org/pdf/1701.04760.pdf
| queuebert wrote:
| >"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.
| heyitsguay wrote:
| It's the usual HN physics thread stuff - for some reason
| physics really brings out the confidently incorrect crowd.
| jankovicsandras wrote:
| 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.
| hbrav wrote:
| 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.
| jankovicsandras wrote:
| 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.
| ClumsyPilot wrote:
| 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.
| Koshkin wrote:
| 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.
| Voloskaya wrote:
| 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.
| adgjlsfhk1 wrote:
| 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.
| gnulinux wrote:
| > 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?
| quasarj wrote:
| Thank you! I read over their process from the first one and it
| sounded like they were just using ML to make up most of the
| image! I need to read a lot more of the details but I am quite
| skeptical of these images...
| fsh wrote:
| The papers do not mention any machine learning.
| queuebert wrote:
| 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?
| fasteddie31003 wrote:
| 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?
| jasonwatkinspdx wrote:
| They absolutely could, but doing so would be a pointless
| waste of nontrivial resources.
| dotnet00 wrote:
| Checking against callibration measurements isn't the only way
| to do things. With M87's SMBH for instance, they had a
| simulated image of what they ought to see given general
| relativity and what they knew about M87. The extracted data
| matches that fairly closely, thus lending credibility to the
| result for obtaining parity with physics without actually
| applying those physics to the data.
| JacobThreeThree wrote:
| >With M87's SMBH for instance, they had a simulated image of
| what they ought to see given general relativity and what they
| knew about M87.
|
| 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...
| dotnet00 wrote:
| Those configurations aren't "impossible" due to fundamental
| well tested physics like general relativity. They're
| "impossible" from the perspective of our understanding of
| the formation of planetary systems, which is understandably
| less well developed given how much more difficult it is to
| study since as a science, exoplanet detection is just 30
| years old, with the majority of detections being less than
| 15 years old.
|
| 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.
| JacobThreeThree wrote:
| If general relativity based models have struggled to help
| predict or explain planetary system formation and
| exoplanet observations, I think we should have the same
| level of expectation about how helpful a general
| relativity based black hole model will be.
| DiogenesKynikos wrote:
| General Relativity has pretty much nothing to do with
| planet formation.
|
| 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.
| dotnet00 wrote:
| You might as well be saying that if fluid dynamics models
| have struggled to help predict or explain CPU performance
| increases, we should have the same level of expectation
| about how helpful a fluid dynamics based model of
| aerodynamics will be, i.e. complete nonsense
| gamblor956 wrote:
| One can always rely on some commenter on HN assuming that
| professionals in another industry don't know how to do their
| job properly and just need some random programmer to tell them
| how they should actually be doing things.
|
| 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.
| h2odragon wrote:
| I loved to pick on my astrophysicain buddies about their over-
| reliance on interpolation. It's not invalid in itself but they
| do seem fond of making sweeping generalizations that fit neatly
| into the smooth spots in their spectrums.
| wumpus wrote:
| 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.
| fasteddie31003 wrote:
| I did read them and I'm not satisfied with their methods.
| wumpus wrote:
| You read the 10 just published papers? Impressive.
| Mehringotio wrote:
| Either you are an expert in this field than it should be
| you who writes a clear argument and present it or you are
| not an expert.
|
| Aren't they are peer reviewed?
|
| What is your expertise in astrophysics?
| gilbetron wrote:
| He has a theoretical degree in astrophysics.
| Saint_Genet wrote:
| He still didn't read and understand 10 papers this fast
| panda-giddiness wrote:
| 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.
| belter wrote:
| I think you are talking about the conversation we had here.
| So in this case you replied to a different person.
|
| https://news.ycombinator.com/item?id=31281773
| wumpus wrote:
| No, this one, same user, same skepticism, 19 days ago:
| https://news.ycombinator.com/item?id=31134691
|
| Btw we released the 2017 calibrated data today, too.
| belter wrote:
| Thanks! You anticipated my question:-)
| malfist wrote:
| Why do you think you know more about astronomy than a team of
| scientists publishing peer reviewed information?
| fasteddie31003 wrote:
| Peer reviewed has nothing to do with the scientific method.
| It is just a layer of scientific bureaucracy. Just give me a
| calibration image of another celestial body and I'll be
| happy.
| malfist wrote:
| You realize peer review isn't just something you do and
| they automatically publish you, right? Peer review makes
| sure your science is sound.
|
| But I'm sure you're more of an expert than anybody serving
| in a peer review board.
| snowwrestler wrote:
| Peers review the _paper_. The purpose of peer review is
| to ensure that the paper clearly communicates the work of
| the authors.
|
| 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.
| OrderlyTiamat wrote:
| I'd just like to disentangle criticisms of the practice
| of peer review from whether this commenter is an expert
| or not. The former is valid or invalid irrespective of
| the latter.
| fasteddie31003 wrote:
| Peer review has let plenty of bad science through. Don't
| burn me at the stake because I speak heresy against the
| holy theologians of astronomy.
| malfist wrote:
| All you're saying is: They're wrong, not gonna say how,
| but trust me.
|
| 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.
| oldgradstudent wrote:
| You might try publishing that comment as a dialog, but
| try not to ridicule the Pope's position too harshly,
| though. It didn't end up well for Galileo.
| DiogenesKynikos wrote:
| Bad papers do get through, but anything as high-profile
| as the first image of the supermassive black hole at the
| center of the Milky Way will get intense scrutiny.
| JacobThreeThree wrote:
| >Peer review makes sure your science is sound
|
| 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.
| pfortuny wrote:
| You're being downvoted for saying exactly what happens in
| the biological, economical and social sciences...
| Unbelievable.
| zenmaster10665 wrote:
| this guy astronomies.
| pfortuny wrote:
| Sorry but as this is a press conI doubt the thing has really
| passed "peer review" properly speaking.
|
| 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.
| wumpus wrote:
| We published 10 papers today.
| [deleted]
| JonShartwell wrote:
| 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.
| snowwrestler wrote:
| 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
| evidence, that would be evidence it is flawed.
| JonShartwell wrote:
| 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.
| fesoliveira wrote:
| >I don't know much about this subject so I can't really
| weigh in on how much the post makes sense but [...]
|
| 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.
| denton-scratch wrote:
| 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. 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"
|
| The only "light" I can see is a ring with blobs in it; that's why
| I suppose the ring in the image is not the accretion disk, at
| least, not as viewed from the pole. Most other commenters here
| assume (or know) that it _is_ the accretion disk, and we _are_
| looking at a pole.
|
| 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.
| kryptn wrote:
| > 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?
|
| 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-...
| denton-scratch wrote:
| OK, that explains that; thanks.
| mc4ndr3 wrote:
| potato quality, get an iphone
| NHQ wrote:
| This image came out several years ago or I have seen the future.
| josu wrote:
| Yeah, this image is quite old, around 27k years or so.
| bowsamic wrote:
| What? This is totally new
| Voloskaya wrote:
| third, slightly more plausible, option: What you have seen a
| few years ago was the image released of the blackhole at the
| center of the galaxy M87 [1].
|
| Today's announcement is about the blackhole at the center of
| our own galaxy.
|
| [1]: https://www.nationalgeographic.com/science/article/first-
| pic...
| slimginz wrote:
| That was the M87 black hole image that came out back in 2019
| https://solarsystem.nasa.gov/resources/2319/first-image-of-a...
| coryfklein wrote:
| I'm sorry, I am really confused. Didn't we get "the first picture
| of the black hole at the center of our galaxy" like 2-3 years
| ago? I definitely remember seeing a nearly identical photo, and
| lots of press coverage about a particularly young woman who was
| closely involved in the project. What that something different?
| synu wrote:
| That was M87, a different galaxy. Same group of scientists,
| though.
| black_puppydog wrote:
| as crazy as it sounds: that black hole was actually in a
| different galaxy :)
| infogulch wrote:
| Funnily enough, M87* is bigger than Sgr A* by about the same
| factor than it is farther away (~2000x ?), and these effects
| mostly cancel out so the effective resolution of each is
| about the same. They chose to image M87* first because there
| is less dust/gas obstructing the view through intergalactic
| space to M87 than through the bulk of the milky way disk.
| sgregnt wrote:
| The image from a few years ago, was taken of a blackhole in a
| different galaxy.
| ritwikgupta wrote:
| That image was also captured by the EHT of the supermassive
| black hole (M87*) at the center of the M87 galaxy. The woman
| you're thinking of is Dr. Katie Bouman, now faculty at Caltech.
| She is also listed as an author on this work of imaging Sgr A*.
| dseGH3FETWJJy wrote:
| Nope, that was a black hole in another galaxy- Messier 87
| [deleted]
| jrgd wrote:
| I find the whole thing amazing and captivating - yet the image is
| ... huh ... slightly underwhelming. It looks like some gaussian
| blurred random image. I wish it could be the kind of crisp image
| JWST 'sent'.
|
| It's difficult to force oneself to not romanticise these un-
| visible things based on artists visualisation we got accustomed
| to.
| BitwiseFool wrote:
| It reminds me of all the hype and exuberance around the "first
| ever picture of a black hole". An achievement worthy of being
| lauded, for sure, but something just felt so artificial about
| the coverage. And truth be told, the photo itself was
| underwhelming in light of how incredible it was made out to be.
| Mehringotio wrote:
| Speak for yourself :-)
|
| 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
| ashes-of-sol wrote:
| JacobThreeThree wrote:
| Not to mention, as the article points out, this isn't even an
| image of a black hole. It's an image of clumps of gas, near
| the center of the galaxy.
|
| >Although we cannot see the black hole itself, because it is
| completely dark
| kloch wrote:
| It's actually one of the sharpest images ever made - in terms
| of angular resolution. The Sag.A* ring is about 51
| microarcseconds in diameter. The EHT has a theoretical
| resolution of ~25 micro arcseconds. For comparison NirCam on
| Webb has a pixel resolution of 70 miliarcseconds (about 2800
| times worse resolution than EHT).
|
| 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.
| exhilaration wrote:
| I also want to point out that the mass around Sagittarius A*
| is rapidly shifting which makes getting a sharp image still
| harder. From the NYT:
|
| 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....
| JohnBooty wrote:
| Wow, that's incredible. Is that because of all the material
| the black hole is "devouring?"
| [deleted]
| bjelkeman-again wrote:
| M87, according to the original link is 1000x the mass of
| Sag A, which has a diameter 17x that of our sun. It is mind
| (and space) bending.
| brandmeyer wrote:
| > all while compiling an unprecedented library of simulated
| black holes to compare with the observations
|
| 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.
| [deleted]
| [deleted]
| mabbo wrote:
| > 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)?
| kloch wrote:
| For Interferometry to work the data from different
| baselines has to be collected at the same time so waiting 6
| months does not help. Spacecraft could theoretically be
| used to extend the baselines but the volume of data to be
| transferred is prohibitive with current spacecraft comm
| tech.
|
| 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.
| KAMSPioneer wrote:
| 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 locations to ship physical
| drives, and also makes centrally planning these
| observations rather tricky, as there's very little
| visibility into each station's observations until some
| time afterwards.
|
| 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.
| kloch wrote:
| How many seconds of observation data are required for one
| of these images?
| KAMSPioneer wrote:
| For the entire image? I'm not sure, but a lot. Usually an
| EHT observing session is days in length, and the
| responsible astronomer(s) will reside at the telescope
| for a week or so...but I don't believe that 100% of that
| time is spent feeding data into the collectors. I can ask
| my coworker tomorrow for clarification on the actual
| observing time and post an update.
| whoopdedo wrote:
| 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 are you using
| InfiniBand or something even faster?
| KAMSPioneer wrote:
| So ALMA, being an array, is a bit of a different beast
| than single-dish telescopes like the one where I'm
| employed; they do indeed have an array of antennae and
| correlate all the collected data at a central correlator
| (at least, for normal observations). My institute has a
| single, much larger primary reflector (30 meter diameter)
| and does not require such a process during normal
| observation. However, during VLBI observations, which EHT
| is, the receiver is dumping data to four collector
| computers, which is what I was referring to as "nodes"
| generating ~16Gbps of data apiece.
|
| 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!).
| adgjlsfhk1 wrote:
| much faster than infiniband. A suitcase full of hard
| drives.
| whoopdedo wrote:
| That's for moving between sites. I'm talking about the
| link between the antennas to each observatory's main
| computer.
| Valgrim wrote:
| Why not ship cases of hard drives then? With the
| plummeting cost of space launches, it seems reasonable to
| include enough DV(1) for a return mission.
|
| (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.
| bell-cot wrote:
| I wonder what sort of range/throughput you could get with
| "Heavy" versions of the inter-satellite communications
| lasers which SpaceX is putting on their Starlink
| satellites...
| privong wrote:
| > Spacecraft could theoretically be used to extend the
| baselines but the volume of data to be transferred is
| prohibitive with current spacecraft comm tech.
|
| 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.
|
| [0] http://www.asc.rssi.ru/radioastron/
|
| [1] https://arxiv.org/abs/2204.09144
| VikingCoder wrote:
| Can someone do the math for me?
|
| 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?
| Dave_Rosenthal wrote:
| https://www.wolframalpha.com/input?i=50+microarcseconds+*+%
| 2...
|
| 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.
| devoutsalsa wrote:
| Hydrogen isn't smaller than helium? Or hydrogen isn't an
| atom?
| VikingCoder wrote:
| Thank you! That's freaking bonkers.
| nuccy wrote:
| Well, given that JWST has at least 2000 worse resolution that
| EHT (see my comment below on that topic with some links). Thus
| the blurriness of this observed object is just a result of
| enormously small size versus distance to it. Any star observed
| by JWST is much-much bigger (i.e. has bigger angular size).
| During the live event [1] they make a lot of size/distance
| comparisons, like resolving individual bubbles in a beer glass
| in New York from Munich Biergarten, or a donut on the surface
| of the Moon resolved from the Earth.
|
| 1. https://www.youtube.com/watch?v=rIQLA6lo6R0&t=1930s
| jeffbee wrote:
| Yeah, the thing about "supermassive" black hole is that it
| sounds terrifying in extent but it actually is not. The sun
| contains almost all of the mass of our solar system but the
| SMBHATCOTG contains essentially none of the mass of the
| galaxy.
| bell-cot wrote:
| True.
|
| OTOH, consider the potential downsides to living in a galaxy
| where the central black hole was far bigger, brighter, and
| cooler-looking...
| yellow_postit wrote:
| There's a good Video from Kip Thorne showing why the "real"
| images differ from the idealized one that made much fanfare in
| Interstellar
|
| (Edit) to add that it's about 22minutes in.
|
| https://youtu.be/GlmMxmWHEfg
| jrgd wrote:
| Hey that's amazing; thanks.
|
| 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.
| Maursault wrote:
| Didn't we see this image last April? What is new here? tia
| jack-bodine wrote:
| This announcement was released simultaneously with 6 papers that
| use the newly released data. They are linked in the bottom of the
| press release and are definitely worth checking out.
| wumpus wrote:
| 10 papers total in this batch.
| kloch wrote:
| One of the findings they announced at the press conference is
| that the spin of the black hole is not aligned with the galactic
| plane but is tilted "towards us" so that it is viewed face on.
|
| How unexpected is that?
| raattgift wrote:
| 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 same
| direction (i.e., the accretion structure is prograde rather
| than retrograde)) is probably just a funny coincidence.
|
| 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!
| dekhn wrote:
| 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)
| raattgift wrote:
| 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?
| foobarian wrote:
| With all the copious computing power today and given this
| problem seems mostly non-quantum, do simulations bring any
| significant insight at all?
| raattgift wrote:
| Yes, simulations are in heavy use in galaxy dynamics. Two
| (example) research groups:
| <https://www.nao.ac.jp/en/research/project/cfca.html>
| <https://pweb.cfa.harvard.edu/research/science-
| field/computat...> and the most relevant wikipedia page
| <https://en.wikipedia.org/wiki/Computational_astrophysics>.
|
| 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.
| foobarian wrote:
| Thank you for the pointers! By non-quantum I meant that
| to simulate the motions at that scale (including
| rotation) it seemed like you could go quite far just by
| using relativistic physics. But I guess there is not much
| ordinary about black holes so my mental model is likely
| quite a ways off.
| raattgift wrote:
| Ok, I think there are a couple ways of digging out a
| question to answer from your comment as I understand it.
|
| 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/>
| [deleted]
| zeven7 wrote:
| For quasars, don't the beams shoot out of the poles? Let's hope
| our nearby buddy doesn't become that active.
| Mehringotio wrote:
| The distance should be that far away that a potential spread
| would be relatively wide I would argue.
| willis936 wrote:
| The "us" in "let us" are humans that are alive 30,000 years
| after a hypothetical quasar starts at SgrA*. The image would
| look realtime to us. Just weird relativity things.
| raattgift wrote:
| There is vanishingly small likelihood of Sgr A* becoming
| active (in the sense of developing highly luminous structures
| nearby it). There is little in the central parsec to feed it,
| and it is low in mass for a central black hole. There is a
| lot of astronomical hunting to be done to find the weak polar
| jet from Sgr A*.
|
| 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).
| quasarj wrote:
| So I have a question about that.. I thought it would only
| have an accretion disk if it was active. So what gives? I
| guess I'm wrong? What constitutes "active" if not "stuff is
| falling in"?
| raattgift wrote:
| Unexpected question from someone whose nickname starts
| with "quasar"! :-)
|
| 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).
| px43 wrote:
| Kind of makes me nervous that both black holes we've imaged are
| pointing right at us. I'm imagining some super advanced
| civilization somehow using black holes as powerful telescopes
| that are for some reason intent on mapping out our region of
| space. I know M87 is 55 million light years away, so that makes
| no sense, but I'd really like to see some black holes that are
| looking in some other direction.
|
| 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?
| queuebert wrote:
| It may also precess, so that the axis of rotation is changing
| with time. Previous galactic collisions may also have caused
| two holes to merge into this one, with a net spin not
| orthogonal to the Galactic plane.
| smm11 wrote:
| So earth will be sucked down this black hole and shredded how
| many days from now?
| mescaline wrote:
| > Because the black hole is about 27,000 light-years away from
| Earth, it appears to us to have about the same size in the sky as
| a donut on the Moon.
|
| I'm still sad we can't post donut emojis here. This place sucks.
| [deleted]
| yawz wrote:
| > EHT team members talk about a sharpness of vision akin to being
| able to see a bagel on the surface of the Moon.
|
| This is truly amazing!
| nojonestownpls wrote:
| _Scientists discover a bagel on the surface of the Moon!_
|
| _Search for black hole ends with a bagel hole?!_
|
| [Become a paid subscriber to read the full story.]
| emerged wrote:
| solarist wrote:
| Math actually checks out:
|
| 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...
| Sporktacular wrote:
| I recall the EHT imaging 2 objects back in 2019 - M87 and another
| black hole. Does anyone remember what that was, or am I mistaken?
|
| I thought it was Sagittarius A* back then.
| kloch wrote:
| They collected data on both back in 2017. It took until now to
| develop the image processing techniques to account for the
| rapid changes in the accretion disk around Sag.A*.
| Sporktacular wrote:
| Ah, so they didn't release an image of it back then? Or was
| it just a less precise image? Thought I saw one but can't
| find it now among all these newly release images. Thanks BTW
| DiogenesKynikos wrote:
| They only released the image of M87 back then.
| belter wrote:
| Announcement press conference:
|
| "Press conference on Milky Way galaxy discovery from the Event
| Horizon Telescope collaboration"
|
| https://youtu.be/KgvPA9RmEnk
| bholevid34 wrote:
| Extremely cool video, "Meet Sgr A*: Zooming into the black hole
| at the centre of our galaxy":
|
| https://www.youtube.com/watch?v=Zml0dZCjaFw
| nyc111 wrote:
| Matt Strassler: <<The details of the reconstructed image depend
| on exactly what assumptions are made.>>
| https://profmattstrassler.com/2022/05/12/in-our-galaxys-cent...
|
| What does this mean? If they assembled an image to fit their
| assumptions, that would be circular reasoning. I don't
| understand.
| uwagar wrote:
| tbh the image isnt inspiring. kinda like a low res computer
| simulation.
| tjpnz wrote:
| It's an object 26k light years from Earth and emits no light.
| That they were able to capture an image at all is both a
| scientific and technological triumph.
| Apocryphon wrote:
| Funnily enough, Arcade Fire released a new album this week, which
| just happens to have a song entitled Sagittarius A*
|
| https://www.youtube.com/watch?v=rAUpD4FchZI
|
| https://genius.com/25770411
| ramigb wrote:
| Can the smart people in here confirm if we are getting sucked
| into this someday or not?
| hathym wrote:
| don't worry, we will destroy the planet before that.
| ashes-of-sol wrote:
| kloch wrote:
| Some perspective that may help:
|
| 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.
| ComputerGuru wrote:
| > 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).
| drewrv wrote:
| Reading between the lines of this page:
| https://en.wikipedia.org/wiki/Timeline_of_the_far_future
|
| 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.
| jepler wrote:
| On the timescale from now until the sun goes nova, confident
| "no".
|
| 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...
| perardi wrote:
| [pushes up glasses]
|
| 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.
| jepler wrote:
| Thanks for the correction. You're right, current scientific
| thinking is that the sun is not capable of going
| "supernova".
| neals wrote:
| So, what kept us from pointing a camera in that direction and
| snapping this picture up until now?
| the8472 wrote:
| We have done so many times over the years. But their resolution
| is only good enough to show the stars in the vicinity, not the
| details of the accretion disc.
|
| https://en.wikipedia.org/wiki/Sagittarius_A*#/media/File:Sgr...
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