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April 10, 2019

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I get "Page not found."

wj: fixed it, I think. Sorry

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.

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)

hsh, I did to, go to News section of the NSF site and there's a link to the story there.

https://juanitajean.com/damn-i-love-science/

Linked fixed. Sorry about that, guys.

"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.

Are there non-rotating black holes? Of any significant size, that is.

It's hard to see how there could be.

"Not a very hospitable galaxy for life, I suspect."

The supermassive black hole at the center of the Milky Way Galaxy sez 'Hi!'.

The photon-capture radius of a non-rotating black hole is sqrt(27)/2 times its Schwarzschild radius.

Or (3*sqrt(3))/2.

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.

Snarki: Fermat quote? Or impressive truth (not obvious to us non-mathematicians)....

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

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.

Perl-written-in-the-style-of-FORTRAN

I've known programmers who wrote FORTRAN no matter what language they were using. :)

Notre Dame is burning down

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.

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