[HN Gopher] First image of a black hole: a CNRS researcher had s...
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First image of a black hole: a CNRS researcher had simulated it as
early as 1979
Author : melenaboija
Score : 81 points
Date : 2021-08-27 12:27 UTC (10 hours ago)
(HTM) web link (www.cnrs.fr)
(TXT) w3m dump (www.cnrs.fr)
| runjake wrote:
| I wish they covered more technical detail into how and with what
| tools the image was generated. Anyone know?
| ColinHayhurst wrote:
| See the paper mentioned by @grafelic
| raziel2701 wrote:
| Is the code freely available someplace? I found papers that talk
| about the math but I don't understand the math...
| peter303 wrote:
| Very Long Baseline radio astronomy has been around for decades.
| One of its early accomplishments was the realtime observation of
| plate tectonics motion between telescopes. These days that is
| observed routinely with high resolution GPS.
|
| One EHT speaker I asked said an important advance was scaling up
| the VBLI procedure a thousand times from hundreds of megahertz to
| hundreds of gigahertz to achieve resolutions needed to image the
| three largest super massive black holes. This involves huge
| improvements across the entire system from the antenna receiver,
| clock resolution and petabyte data handling.
| BitwiseFool wrote:
| I've never understood the whole "First picture of a black hole"
| media hype. Point a telescope at a known black hole and capture
| the image. Is that not a picture of a black hole?
|
| I know that light cannot escape a black hole and when you 'see'
| one you are either seeing the accretion disk around it, or the
| lensing it does to stars behind it. Regardless, the black hole
| itself is in the image, no?
|
| I'm not saying the effort behind producing the image _wasn 't_ an
| achievement, just that the whole presentation felt very staged
| and inauthentic.
|
| Edit: Isn't the picture in question _also_ just an image of the
| matter falling into the black hole? Per JPL: "to capture an
| image of the hot, glowing gas falling into a black hole"
|
| https://www.jpl.nasa.gov/edu/news/2019/4/19/how-scientists-c...
| SiempreViernes wrote:
| Have you ever wondered where your phone is, and some joker
| pulls out an image of Earth and says "here"?
|
| Well, you're that joker now buddy.
| wumpus wrote:
| That's a pretty funny analogy! And a nicely accurate one.
|
| This movie (https://www.youtube.com/watch?v=7nMUqy8Rfp0)
| shows what M87* looks at various resolutions.
| BitwiseFool wrote:
| Hey buddy, I had a genuine question. No need to be a jerk
| about it.
|
| How is this https://en.wikipedia.org/wiki/Astrophysical_jet#/
| media/File:... not _also_ an image of the black hole?
|
| This one too, https://en.wikipedia.org/wiki/File:V404Cyg_XRT_
| halo_fullsize...
|
| https://en.wikipedia.org/wiki/V404_Cygni
| skykooler wrote:
| It's an image that contains the black home, but does not
| resolve the hole itself. Just like you can't really say a
| satellite photo is of an ant, even though there are
| definitely some within its borders.
| SiempreViernes wrote:
| It is or it is not for the exact same reason why a picture
| of the moon is, or is not, a picture of the moon lander
| that's still there.
| NikolaeVarius wrote:
| I'm sure that nobody ever thought of trying to do this.
| mdasen wrote:
| There's a decent Netflix documentary on how difficult it was
| involving many teams across the world, software to interpret
| the data, etc.
|
| Black Holes: The Edge of All We Know
| vishho wrote:
| It was because she was a girl. That is all there is to it.
| Insta-famous. Not that it is a bad thing to promote women in
| science, but also let us not pretend that the hype fuel was
| based on anything else.
| lgl wrote:
| I can't downvote you but I'm sure you will very soon because
| this kind of idiotic and misogynistic comment is something
| that doesn't belong here, or anywhere really.
|
| If you think that an effort of hundreds of scientist and
| dozens of scientific institutions that took many years to
| bring us an unprecedented image of the universe was hyped or
| staged to make a single woman scientist insta-famous, you
| have largely misread the large majority of people that read
| hackernews.
|
| Nobody in their right mind will support this opinion, grow
| up.
| zalequin wrote:
| You're either immature or brainwashed by the propaganda,
| because in the last decade the forceful advancement of
| diversity, social "justice" and cancel culture (to mention
| only a few things that are part of the same, larger, thing)
| have been more than clear - it's become nauseating and
| tiresome.
|
| To pretend that we don't promote women for the sake of
| promoting women is like saying we don't hire asians,
| blacks, and jews because they're asians, blacks, and jews.
| Of course we do.
| vishho wrote:
| All the downvoters were male. You are a male. And I am a
| girl BTW.
|
| You got so riled up, because deep down you know it is true.
| Even she knows the majority of the attention had to do with
| her gender.
|
| I am not sexist. I usually, like the question poser, don't
| see gender or race. But then it is pushed by activists (see
| Grace Hopper replacing lena.jpg) who want to have their
| cake and eat it too: they judge by gender and race, but you
| should judge without. I am done doing that.
|
| If you see Neil deGrass Teison added to the speaker list,
| you just know somewhere someone went: this panel lacks
| diversity. So Teison is de diversity pick, not the merrit
| pick. Just like Katie was highlighted, while using software
| written by men, who got lots of flack online, because
| clearly they were non-inclusive to women when building
| Scipy and Numpy for free.
| atombender wrote:
| What's new is that scientists were able to capture an image of
| its silhouette. Black holes, as you say, don't emit any light,
| so we can only see surrounding objects -- the accretion disk
| and jets of hot gas. For comparison, the kinds of images we've
| been able to capture with Hubble look like this:
| https://fineartamerica.com/featured/core-and-optical-jet-
| of-....
| BitwiseFool wrote:
| But even in the image they generated, it is just the matter
| surrounding the black hole we see, right?
| atombender wrote:
| Well, we can observe the absence of light, which (semantics
| aside) is also something you can see.
| wumpus wrote:
| This is usually called the "shadow" of the black hole.
|
| The press release we're discussing calls it that.
| [deleted]
| terramex wrote:
| You can image many stars and black holes as point sources
| without issues. For M87 you can even capture its huge particle
| jet using telephoto lens, digital camera and small star
| tracker.
|
| This gives you their magnitudes, spectral lines, ability to
| detect planets passing in front of them etc. But if you want to
| resolve their image beyond point light it becomes very hard -
| there are hard physical limits on what size of aperture you
| need to resolve any detail. There are tricks to increase
| effective aperture by measuring phase of electromagnetic waves
| reaching antennas across the globe. It is called
| interferometry:
| https://en.wikipedia.org/wiki/Astronomical_interferometer
|
| Here is a list of the stars we have imaged beyond point source
| so far:
| https://en.wikipedia.org/wiki/List_of_stars_with_resolved_im...
|
| M87 is the first black hole imaged beyond point source.
| ISL wrote:
| The big challenge is that black holes are quite small. In order
| to say that you have "seen a black hole", it is necessary to
| rule out that you have seen something similar to a black hole
| but larger than what general-relativity would predict.
|
| The black hole at the center of M87 is large (about the size of
| our solar-system), but it is 55 million light-years away. If I
| computed things correctly, it subtends about 70 picoradians on
| the sky. That is about the same angular size as Alan Shepard's
| lunar golf ball as seen from Earth.
|
| So yes, if a black hole is at the center of a galaxy, its
| (non-)image will be in any image of a that galaxy. But, proving
| that you've seen a black hole means ruling out that it is some
| other kind of compact object that might be somewhat larger than
| a black hole. The only imaging-based way to do so is to image
| its event horizon, which requires resolving the angular size of
| the black hole itself.
| grafelic wrote:
| _I used the IBM 7040 mainframe of Paris-Meudon Observatory, an
| early transistor computer with punch card inputs. The machine
| generated isolines that were directly translatable as smooth
| curves using the drawing software available at the time._
|
| From Luminets personal recollections on black hole imaging:
| https://arxiv.org/pdf/1902.11196.pdf
| ColinHayhurst wrote:
| Great read, thank you. It goes on ...
|
| "The first step was to integrate the equations of light ray
| trajectories in Schwarzschild space-time and draw the isoradial
| curves (i.e. at constant radial distance from the black hole)
| of a thin disk around the black hole, as they would be seen by
| an observer above the disk's plane" ....
|
| "The final black and white "photographic" image was obtained
| from this pattern. Lacking of an appropriate drawing software,
| I had to create it by hand. Using numerical data from the
| computer, I drew directly on negative paper with pen and Indian
| ink,placing dots more densely where the simulation showed more
| light (a few thousands dots for the full plate). Next, I took
| the negative of my negative to get the positive, the black
| points becoming white and the white background becoming black.
| The result converged into the pleasantly organic, asymmetrical
| form reproduced in Figure 8, both visually engaging and
| scientifically revealing."
|
| I am feeling grateful to have started by scientific/engineering
| computing career one year later than the authors paper in 1980,
| and as it happens the first year without punched cards at my
| Univ.
| actually_a_dog wrote:
| Amazing. Kip Thorne's simulation for the movie _Interstellar_
| took "a year of work by 30 people and thousands of computers."
| Of course, that was also an _animated_ simulation with a high
| level of visual detail.
|
| https://www.wired.com/2014/10/astrophysics-interstellar-blac...
| sydthrowaway wrote:
| This needs to be reimplemented in JavaScript
| colordrops wrote:
| Ugh it must have been so satisfying to take all that science and
| data and generate an image like that in _1979_.
| sydthrowaway wrote:
| This would be an amazing album cover.
| ffhhj wrote:
| In the comparison image M87's blackhole has an almost perfectly
| circular black spot, while in the simulated image the center is
| half a circle due to the disk. Is this caused by some missing
| effect in the calculations, the angle of the disk, or something
| else?
| wumpus wrote:
| We're looking down on M87* from one of its poles. The image
| from the paper is viewed close to the equator.
| yawaworht1978 wrote:
| I never understood this, do black holes have poles from any
| distance?
|
| I know if you're too close, everything gets distorted, but I
| would have thought they look the same from any direction or
| angle, never managed to grasp the concept.
|
| Maybe there is some 3d sim to explain this?
| ludwigschubert wrote:
| I'm only an enthusiast, but my understanding is that it's
| the black hole's rotation that causes poles in 3D. The
| visible accretion disc, I believe lies in the plane in
| which the black hole rotates.
| gus_massa wrote:
| If the black hole is not spinning, it should look the same
| from every angle. A spinning black hole is deformed (like
| the spinning Earth.)
|
| Anyway, we are not seeing the black hole (because it looks
| just like a black circle in front of a black background).
| The interesting part of the image is a disk of material
| spinning around it. There is a nice 3d cardboard simulation
| and clear explanation in a video by Veritasium
| https://www.youtube.com/watch?v=zUyH3XhpLTo
| wumpus wrote:
| The stuff falling onto the black hole has an orientation --
| it forms an accretion disk at the "equator".
|
| If the black hole is spinning, it has poles. We expect all
| black holes to be spinning. This is a subtle change in the
| shadow itself, but...
|
| And if the accretion disk and black hole have misaligned
| poles, there should be a huge warp in the disk close to the
| black hole as the black hole frame-drags the accretion
| disk.
| ludwigschubert wrote:
| Is the misalignment _necessary_? I always thought the
| hole got its rotation from the infalling matter.
| wumpus wrote:
| Over billions of years, the angular momentum of the stuff
| falling in changes.
| yawaworht1978 wrote:
| But if it's infinitely small(not the event horizon, the
| black holes singularity), then a rotation or poles are
| hard to imagine. Is the singularity rotating or the whole
| event horizon area? It's hard to put this in descriptive
| words, i hope my point gets across.
| drewrv wrote:
| Yeah I thought about this and looked into it a little
| bit. A "point" has zero dimensions so my intuition
| thought that there's nothing TO spin.
|
| What happens at the singularity in a rotating black hole
| depends on your quantum theory of gravity. Some theories
| have the singularity as a "ring" instead of a point. I
| believe loop quantum gravity has a "planck star" in the
| center of a black hole.
|
| Macroscopically, rotating black holes can be thought of
| as rotating the space around the event horizon. So the
| spacetime curvature doesn't just pull you directly to the
| center, there's an angular aspect as well.
|
| https://en.wikipedia.org/wiki/Planck_star
|
| https://www.youtube.com/watch?v=UjgGdGzDFiM
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(page generated 2021-08-27 23:02 UTC)