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.
"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.
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.
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.
The EHT can resolve the two super massive black holes which are the largest on the sky. The Milky Way's SMBH is a relatively small one, but it's close enough to make up for that.
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?
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.
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
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.
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.
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.
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.
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.
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-....
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.
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
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.
From Luminets personal recollections on black hole imaging: https://arxiv.org/pdf/1902.11196.pdf