by wj
There's something to be said for us not losing track that there are great things happening in the world beyond politics. Like this one:
Image of a Black Hole
I admit that my first thought was :How can they take a picture of something that absorbs all light and reflects nothing?!?!?" But, of course, what they actually imaged was the shadow it causes in the glowing gas around it. Still, way cool.
I get "Page not found."
wj: fixed it, I think. Sorry
Posted by: hairshirthedonist | April 10, 2019 at 03:05 PM
Not exactly a shadow, as the photons we’re detecting have orbited the black hole at a sufficient distance not to fall into it - the ones which have gone all the way around and escaped orbit in just the right direction to head towards us.
So what we’re seeing is the photon disc (about 2.6 times the diameter of the event horizon, apparently).
Not a very hospitable galaxy for life, I suspect.
Posted by: Nigel | April 10, 2019 at 03:05 PM
So what we’re seeing is the photon disc (about 2.6 times the diameter of the event horizon, apparently).
"2.6" might be the golden ratio squared though I can't find it characterized as such.
How to Understand the Image of a Black Hole (YouTube)
Posted by: CharlesWT | April 10, 2019 at 04:42 PM
hsh, I did to, go to News section of the NSF site and there's a link to the story there.
Posted by: Priest | April 10, 2019 at 04:56 PM
https://juanitajean.com/damn-i-love-science/
Posted by: John D. Thullen | April 10, 2019 at 05:39 PM
Linked fixed. Sorry about that, guys.
Posted by: wj | April 10, 2019 at 06:22 PM
"2.6" might be the golden ratio squared though I can't find it characterized as such.
Not quite. The photon-capture radius of a non-rotating black hole is sqrt(27)/2 times its Schwarzschild radius. (paper)
For rotating black holes it's more complicated.
Posted by: Pro Bono | April 10, 2019 at 08:18 PM
Are there non-rotating black holes? Of any significant size, that is.
Posted by: wj | April 10, 2019 at 08:26 PM
It's hard to see how there could be.
Posted by: Pro Bono | April 10, 2019 at 08:54 PM
"Not a very hospitable galaxy for life, I suspect."
The supermassive black hole at the center of the Milky Way Galaxy sez 'Hi!'.
Posted by: Snarki, child of Loki | April 11, 2019 at 08:24 AM
The photon-capture radius of a non-rotating black hole is sqrt(27)/2 times its Schwarzschild radius.
Or (3*sqrt(3))/2.
Posted by: CharlesWT | April 11, 2019 at 12:34 PM
For the orbits of photons, Misner, Thorne & Wheeler equation 25.71 is the differential equation to solve.
I have a rather simple Perl script that produces accurate numerical solutions, which alas, the comment box is too small to contain.
Posted by: Snarki, child of Loki | April 11, 2019 at 01:12 PM
Snarki: Fermat quote? Or impressive truth (not obvious to us non-mathematicians)....
Posted by: Girl from the North Country | April 12, 2019 at 02:13 PM
The supermassive black hole at the center of the Milky Way Galaxy sez 'Hi!'.
Although fairly quietly.
It’s about a thousandth of the size of the M87 monster, and “exceptionally dim” for its size:
https://www.nature.com/articles/nature10767
Posted by: Nigel | April 12, 2019 at 05:36 PM
The program is a 1-2 hundred lines of Perl-written-in-the-style-of-FORTRAN, so not very useful to read. Accurate, yes. Validated against published calculations. Surprisingly simple individual calculations in each iteration. Fast. Write-only. Coyote ugly.
Did the program for 'light echos' around a black hole; each echo has one more trip around the hole before escaping.
Posted by: Snarki, child of Loki | April 13, 2019 at 04:23 PM
Perl-written-in-the-style-of-FORTRAN
I've known programmers who wrote FORTRAN no matter what language they were using. :)
Posted by: CharlesWT | April 13, 2019 at 05:30 PM
Notre Dame is burning down
Posted by: cleek | April 15, 2019 at 03:54 PM
Yup. Let's hope it's an accident. They're saying it may be connected to the renovation - on C4 News they've just reported that la fleche (the spire) has just collapsed.
Posted by: Girl from the North Country | April 15, 2019 at 04:06 PM