
Raytracing a Black Hole - pablode
http://rantonels.github.io/starless/
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KaiserPro
I worked at dneg when this very shot was being rendered.

From what I remeber there were a few steps to this being rendered, the first
part was a massive particle sim. I was a systems engineer, so my job was to
keep the system running.

That particle sim ate at least 7, if not more hard disks. What ever it did, it
destroyed 8tb HDDs. The worst part was we couldn't take that file server
offline, as the render needed to finish. But, not only was the render
hammering and eating disks, the raid array was desperatly trying to rebuild
the groups at the same time.

As soon as the group was rebuilt, another disk would fail.

so much joy. As soon as we had some slack, we migrated away from that server
and gave something less stressful to do.

~~~
ghusbands
You're talking about a different black hole render. This is an original
project that runs on consumer hardware.

~~~
KaiserPro
....yes, yes I am.

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gattr
And in the coming years astronomers hope to image a black hole directly (in
radio wavelengths). The few closest supermassive black holes (in center of
galaxies) have their event horizon angular diameters just big enough to be
resolved by VLBI (very-long-baseline interferometry). See [3] for details and
a simulated image.

[1]
[https://en.wikipedia.org/wiki/Event_Horizon_Telescope](https://en.wikipedia.org/wiki/Event_Horizon_Telescope)

[2] [https://eventhorizontelescope.org/](https://eventhorizontelescope.org/)

[3] Seeing Black Holes: from the Computer to the Telescope
([https://arxiv.org/pdf/1804.03909.pdf](https://arxiv.org/pdf/1804.03909.pdf))

~~~
saboot
I believe this is supposed to happen this year, last I heard was this summer
but they haven't finished the analysis yet. The data was collected back in
April, petabytes of harddrives flown to a central processing location.

~~~
vanderZwan
That puts the other comment talking about 7x8TB harddrives being devoured in
rendering the Interstellar scene a bit into perspective

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jonas21
On a related note, there's a paper by the _Interstellar_ special effects team
and Nobel laureate Kip Thorne describing how they rendered the black hole in
the film and the tradeoffs they made:

[https://arxiv.org/abs/1502.03808](https://arxiv.org/abs/1502.03808)

~~~
gbrown
It's amazing that they put so much attention to detail in the same movie where
a botched docking maneuver causes an orbiting spacecraft to fall out of the
sky, and in which a black hole opens the way for programing mechanical watches
from the past.

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JohannesH
It is and I hate that movie for it. In theory I should love it, but the
disconnect between trying to be realistic and totally ignoring reality, killed
it for me. I usually love sci-fi movies, realistic or not. But I mean, if
you're going to put so much work into making a main element of the movie seem
physically correct and realistic, why wouldn't you put at least a little
effort into making the rest of the movie somewhat believable. The movie goes
between metaphysical, realistic and action-movie physics every other scene.

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codethief
For anyone interested, here are some videos of what it's like to fall into a
black hole together with some very good explanations:

\-
[https://jila.colorado.edu/~ajsh/insidebh/index.html](https://jila.colorado.edu/~ajsh/insidebh/index.html)

\- [https://physics.stackexchange.com/questions/26185/what-
will-...](https://physics.stackexchange.com/questions/26185/what-will-the-
universe-look-like-for-anyone-falling-into-a-black-hole/422817#422817)

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Sharlin
> Here we have an infinitely thin, flat, horizontal accretion disk extending
> from the photon sphere (this is very unrealistic, orbits below 3rS are
> unstable. More below) to 4 radii, coloured checkered white and blue on the
> top and white and green on the bottom. It is evident, with this colouring,
> that we've encountered another case of seeing 100% of something at the same
> time.

> For this image, I moved the observer up a bit, so he can take a better look
> at the disk. You can see two main images of the disk, one of the upper face,
> and one, inside, of the lower.

Wait, am I missing something? I don't see any green in the pictures.

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cousin_it
Cool, now I have an intuition for how a black hole distorts lines of sight.
Basically it's like a black ball hanging in space, with a "halo" that shows
you a distorted image of everything that's behind the ball. For example, if
there's a hula hoop around the ball, the near side of the hoop will look more
or less normal to you, but the far side will look like it's warped, like it's
refusing to go around the ball and instead shows up above or below it (or
both). And the innermost part of the halo shows infinitely many images of the
hoop (and everything else around the ball), stretched thinner and thinner.

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KenoFischer
I love this site, the method is very clever. I did a re-implementation of this
at one point for fun. One of my favorite things to do with this simulation is
to actually plot the path of the photons as they approach the black hole
(well, leave the black hole but you reverse time for ray tracing purposes).
Conveys the idea pretty well that there's something funky going on with
spacetime. E.g. here [https://imgur.com/OPHLMJL](https://imgur.com/OPHLMJL)
(just a screen shot from back then, it's much more fun with sliders that led
you move things around).

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p1mrx
I was rather confused by the section describing a "white and blue ... white
and green" image that doesn't actually contain any green.

Eventually...

> The lower surface is blue and not green because I'm lazy

Being lazy is fine (I've rendered zero black holes myself), but he could at
least be consistent.

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malandrew
This is pretty awesome to see since I did something related to this to
simulate gravitational lensing around black holes back in 2000 under the
guidance of Ronen Plesser at Duke University. Back then however, the computing
resources I had available were far more primitive and I can't even imagine how
long it would have taken me to render something like this back then. That
said, this is way more advanced than what I was doing as well.

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jayd16
I had never thought about it but in a sense black holes work as a mirror. Some
light will sling shot around the back of the hole and back in the opposite
direction.

~~~
monocasa
And some light will orbit for eons before either going in or escaping.

~~~
quickthrower2
Eons from whose point of view?

~~~
empath75
Not from the light. It’s always instantaneous

~~~
ZeikJT
Constant, not instant.

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kazinator
> _Also stereo pics are still cool_

Not so much when they're in the stare-into-the-distance configuration rather
than cross-your-eyes, and the images are uncomfortably far apart for your
inter-ocular distance.

FTFY: [https://i.imgur.com/jBhWrUY.png](https://i.imgur.com/jBhWrUY.png)

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zvrba
A fascinating topic. Another fascinating surface is a projective plane, that
I've never managed to grasp. Any suggestions on how to visualize a travel on
the surface of the projective plane?

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mr_toad
Greg Egan wrote a Java app to simulate the view near to and inside the event
horizon for his short story The Planck Dive. The view from inside, looking
back, at around 2M is particularly interesting

[http://www.gregegan.net/PLANCK/Tour/TourApplet.html](http://www.gregegan.net/PLANCK/Tour/TourApplet.html)

[http://www.gregegan.net/PLANCK/Planck.html](http://www.gregegan.net/PLANCK/Planck.html)

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ebvalaim
I did my own some time ago, and it can do Kerr black holes, too ;) No
accretion disks, though, but should be possible to implement.

[https://github.com/fizyk20/gr-raytracer](https://github.com/fizyk20/gr-
raytracer)

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m4r35n357
This software (and the site itself) is good fun, but you have to build it
yourself and feed it good parameters. Unfortunately it is not actively
developed (I've been in touch with the author in the past).

