Suppose it to be spinnng around a horizontal axis. Then photons coming towards us should have a blue shift, those going away from us a red shift, their speed being the same. Could this explain the change in luminosity?
Tullio

Perhaps, but the real reason is some of the photons are coming at us directly, the others via gravitational lensing from the far side of the hole. As the lens is spherical there is aberration and of course not all the photons get pointed at earth.
IIRC there was an article about a scientific calculation on what such a picture should look like published a few days ago, a rehash of journal articles from a couple decades ago. It matches.

As to red/blue shifts I don't know if they have looked for spectral lines in their data.
Also I don't know the angle of the accretion disk, if we are polar, equatorial, or at some random angle (most likely)

Perhaps at some point LIGO will be able to measure a spin rate and angle.

From an article by Remo Ruffini which I published in 1973, a Kerr-Newman black hole should have three parameters, mass, charge and angular momentum, while a Schwarzschild black hole has only mass.
Tullio
Ruffini says also that photons suffer a gravitational red shift.

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As to red/blue shifts I don't know if they have looked for spectral lines in their data.

There are no spectral lines to look for since the photons are not emitted from atoms. There are no atoms in a black hole. They are gone and lost forever and what we can see/observe are only photons with wavelengths all from the spectrum radio waves to gamma waves. Then of course there are a lot of other elementary particles that the black hole spew out but we cannot see them.

Ruffini says also that photons suffer a gravitational red shift.

Hmm. Photons can have many energy levels that manifest as a spectrum all from radio waves to gamma rays .
E=h*c/λ, E is photon energy, h is the Planck constant, c is the speed of light in vacuum and λ is the photon's wavelength.
How can one tell one photon from another if it is redshifted or not when there are a lot of photons with different energy levels coming from a black hole regardless of the gravity?
For instance there are red, green, blue, UV, IR photons emitted from a black hole all together.
OK. The gravity make them slow down but that would only make perhaps the UV turn blue, blue turn green, green turn red and red turn IR.

I just saw this and since there are misconceptions about black holes.
How Do You Observe a Black Hole?
https://www.youtube.com/watch?v=C-OyMPAq2PU
Brian Greene start to explain escape velocity and the nature of black holes.
Sigh...
First he, as a thought experiment, he uses a cannon to illustrate escape velocity and pointing the cannon upwards. Then shooting balls that of course will fall down if the balls are not fast enough.
But that test will require a lot of testing, gun powder and thinking to find the escape velocity.
Why didn't he point the cannon horizontally instead? I think Karl Schwarzschild did that.
First shot maybe reach one kilometer, more gun powder and it reach 10 kilometer and with some more gun powder perhaps 1000 km. If you shoot more balls with higher velocity then the ball eventually will not land on earth and instead it will make a turn around the globe and hit you in your neck.
Everyone realise that there is no need to go further then the first three step and use math knowing the circumference of our earth to calculate it.

Then Brian seems to have a problem with the words mass and matter!
Doesn't he know the difference and that matter is an object and mass is a property of matter and not an object?
First of all a black hole is nothing but a region in space, nothing else. Then matter with the property mass can fall in to it.
But the matter doesn't get compressed to a very small point as Brian says.
No, it convert to energy according to E=m*c*c that still have the same mass.
Energy doesn't need space but matter does.

The "Nature Briefings" of April 10 supports my interpretation. Light is blueshifted and redshifted according to the spinning of the black hole.
Tullio
"One side appears brighter because more of the radiation is shifted towards the observing wavelengths".

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Hmm.. I think I have to catch up some reading:)
Nature published this yesterday.
Black hole pictured for first time — in spectacular detail

https://www.nature.com/articles/d41586-019-01155-0
The findings were also published and explained in detail in a suite of 5 papers in Astrophysical Journal Letters on 10 April.
https://www.nature.com/articles/d41586-019-01155-0#ref-CR1

btw. The collaboration is now looking for funding to establish a foothold in Africa, which would fill in a major gap in the network. The plan is to relocate a 15-metre dish — a decommissioned Swedish telescope:) — from Chile to the Gamsberg Table Mountain in Namibia. For now, the network has already secured two major additions: a dish in Greenland and an array in the French Alps

And redefining what Servers down really means ?:)

Make Your Own Gravitational Waves with 'BlackHoles@Home 2019-04-19T11:00:03Z
https://www.space.com/black-holes-at-home-gravitational-wave-simulations.html
https://blackholesathome.net

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Apr 3, 1999 - May 3, 2020

Here's one more explanation to what we see when looking at a black hole like the M87.
It describes how gravitational lensing works and why one side of the accretion disc is brighter than the other.
https://www.youtube.com/watch?v=zUyH3XhpLTo
That the light is redshifted, as far I understand it, is because M87 is "moving" from us due to the universe expansion.
And that light is of course redshifted for all photons that we can see regardless if they spin faster or slower in the ring.

And redefining what Servers down really means ?:)

Make Your Own Gravitational Waves with 'BlackHoles@Home 2019-04-19T11:00:03Z
https://www.space.com/black-holes-at-home-gravitational-wave-simulations.html
https://blackholesathome.net

I downloaded their software from their website and was able to get it running on a Raspberry Pi.

Who would have thought you could simulate black hole collisions on a Pi, amazing.

This is the mp4 generated when running the code, I will play around with it and see if I can generate longer ones with them orbiting each other until they collide.

https://www.youtube.com/watch?v=jNL4MkzGwOU

Virgo and one of the LIGO detectors have seen for the first time a black hole-neutron star merging. The other LIGO detector was temporarily out of commission. The event must still be confirmed by data analysis.
Tullio

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https://phys.org/news/2019-04-black-hole-light-speed-plasma-clouds.html

Spinning black hole sprays light-speed plasma clouds into space

Just saving the thread before it closes.

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

https://www.space.com/black-hole-disk-should-not-exist.html

Steve

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Warning, addicted to SETI crunching!
Crunching as a member of GPU Users Group.
GPUUG Website

https://www.space.com/black-hole-disk-should-not-exist.html

Steve

An interesting case. An exception that becomes the rule.

Could it be partly the "Information" that doesn't get destroyed when matter goes in? I mean is it some sort of effect of that "Information?"

I remember Stephan Hawkings and Leonard Susskind had a tiff on this subject

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ᴡᴇ ᴅᴀʀᴇsᴀʏ ᴀʙᴏᴜᴛ ᴛʜᴇ ᴘᴀsᴛ ᴛʜᴀᴛ ɪᴛ ɪs ғɪɴɪᴛᴇ ʏᴇᴛ ᴡᴇ ᴅᴀʀᴇ ɴᴏᴛ ʙᴇʟɪᴇᴠᴇ ᴛʜᴇ ғᴜᴛᴜʀᴇ ɪs.

Are you thinking of the black hole information paradox?
https://en.wikipedia.org/wiki/Black_hole_information_paradox
Physical information is information, a particular fact about a thing's identity or properties, of a physical system that determine its value at any other time.
If you change thing's identity or properties it will change this information.
But physical information cannot change thing's identity or properties and has no effect whatsoever to any physical objects or processes. That would be very weird and like being able to erase history.

Team plans colour film of black hole at galaxy's centre
https://www.bbc.com/news/science-environment-49571917

The team that took the first ever image of a black hole has announced plans to capture "razor sharp" full colour video of the one at the centre of our galaxy.

Satellites would be launched to supplement the existing network of eight telescopes to make this movie.

The researchers say the upgraded network will be able to see the supermassive black hole consuming the material around it.

The team has been awarded the Breakthrough Award for Physics.

WOW!

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For the first time, NASA’s planet-hunting Transiting Exoplanet Survey Satellite (TESS) watched a black hole tear apart a star from start to finish, a cataclysmic phenomenon called a tidal disruption event.
https://www.youtube.com/watch?v=85tdoDt1Qh0

Star Ejected from Milky Way's 'Heart of Darkness' Reaches Mind-Blowing Speed
https://www.livescience.com/star-ejected-milky-way.html

As humankind's ancestors were learning to walk upright, a star was launched out of the supermassive black hole at the center of our galaxy at a staggering 3.7 million mph (6 million km/h).

Five million years after this dramatic ejection, a group of researchers, led by Sergey Koposov of Carnegie Mellon University's McWilliams Center for Cosmology, has spotted the star, known as S5-HVS1, in the Crane-shaped constellation Grus. The star was spotted traveling relatively close to Earth (29,000 light-years away) at unprecedented, searing speeds — about 10 times faster than most stars in our galaxy.

Nothing is suppose to escape from a black hole???

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Nothing is suppose to escape from a black hole???

From inside the event horizon. Star didn't make it inside.