APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Comments and questions about the APOD on the main view screen.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Martin » Thu Apr 11, 2019 7:28 pm

Confused wrote: Thu Apr 11, 2019 4:19 pm
Nitpicker wrote: Thu Apr 11, 2019 7:34 am
Confused wrote: Thu Apr 11, 2019 7:30 am The thing I don't hear anyone talking about is why they had to get a black hole from more than 50 million light-years. Why can't they get an image of the (or a) black hole in our galaxy? If astronomers are unable to get an image of a black hole in our galaxy then how can they be sure that the image is what they think it is?
In absolute terms, the BH at centre of (comparatively featureless) M87 is much larger than the BH at the centre of the dusty Milky Way, and I might guess M87 is less obscured by the bits of the Milky Way in between. The BHs are comparable in terms of angular size from Earth.
Well let me put it another way. Is there any chance that this is fake news? I assume that among scientists it is understood that this is a theory that could be flawed in some way, but the TV news people are reporting is fact.
Confused, is it your assertion that everything in the observable universe is identical? Not to bust bubbles but 'fake news' is an exploitation of the lowest common denominator. Try harder to rise above it, my friend.
Last edited by Martin on Thu Apr 11, 2019 10:27 pm, edited 4 times in total.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Astronymus » Thu Apr 11, 2019 7:28 pm

Boomer12k wrote: Thu Apr 11, 2019 8:27 am Soo....um.... is the shadow made by gravity holding the light BACK then ???? or is it... illuminating gas on the other side...is projecting towards us...but the black hole is an object between and is blocking the light???

Thanks...

:---[===] *
I imagine this "shadow" more the a result of light bending than blocking.

Confused wrote: Thu Apr 11, 2019 4:19 pm
Nitpicker wrote: Thu Apr 11, 2019 7:34 am
Confused wrote: Thu Apr 11, 2019 7:30 am The thing I don't hear anyone talking about is why they had to get a black hole from more than 50 million light-years. Why can't they get an image of the (or a) black hole in our galaxy? If astronomers are unable to get an image of a black hole in our galaxy then how can they be sure that the image is what they think it is?
In absolute terms, the BH at centre of (comparatively featureless) M87 is much larger than the BH at the centre of the dusty Milky Way, and I might guess M87 is less obscured by the bits of the Milky Way in between. The BHs are comparable in terms of angular size from Earth.
Well let me put it another way. Is there any chance that this is fake news? I assume that among scientists it is understood that this is a theory that could be flawed in some way, but the TV news people are reporting is fact.
The center of our galaxy is obscured to us by dense gas clouds. It's actually easier to observe the more exposed core of another galaxy than or own.

Chris Peterson wrote: Thu Apr 11, 2019 7:13 pm
FLPhotoCatcher wrote: Thu Apr 11, 2019 7:07 pm What I don't understand (one of many, actually) is why do the radio observations need to be taken at practically the exact same time to be successfully combined? Doesn't the black hole look basically the same even a few hours later? And the radio waves detected at different radio dishes are not necessarily from the same sources.
In fact, the signals detected are from the same sources (that is, from the same spatial region). And they have to be at the same time because it's the correlation between them that creates the large effective aperture.
If I got that right, the telescopes were specially eqipped with atomic clocks to synchronize them.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by rstevenson » Thu Apr 11, 2019 7:32 pm

joe25 wrote: Thu Apr 11, 2019 1:35 pm This is actually a photo of angels dancing on the head of a pin. Can you count the number of them ?
42 -- obviously.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Martin » Thu Apr 11, 2019 7:38 pm

Chris Peterson wrote: Thu Apr 11, 2019 7:26 pm
Martin wrote: Thu Apr 11, 2019 7:19 pm
daddyo wrote: Thu Apr 11, 2019 5:42 am It’s claimed the telescope array has enough resolution to resolve writing on a coin at the distance between New York and Los Angeles. That’s crazy. I wonder how they collimated such a device. Awesome work. They will have a career in resolving other objects out there.
Wonder no more. The answer is algorithm, Computational science. And a overdue standing ovation to the woman who's effort made it all possible today: Katie Bouman.
This isn't really computational science, which centers around models and simulations. This is computational data analysis. (That doesn't detract from the algorithm development, but those are different things.)
So you're saying computational data analysis is not a computational science?

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 7:40 pm

Astronymus wrote: Thu Apr 11, 2019 7:28 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:13 pm
FLPhotoCatcher wrote: Thu Apr 11, 2019 7:07 pm What I don't understand (one of many, actually) is why do the radio observations need to be taken at practically the exact same time to be successfully combined? Doesn't the black hole look basically the same even a few hours later? And the radio waves detected at different radio dishes are not necessarily from the same sources.
In fact, the signals detected are from the same sources (that is, from the same spatial region). And they have to be at the same time because it's the correlation between them that creates the large effective aperture.
If I got that right, the telescopes were specially eqipped with atomic clocks to synchronize them.
Exactly. This accurate time stamping is possible because of the relatively long wavelength of radio waves compared with light. There are visible light interferometers, but they have to physically combine the light from different apertures (using fiber optics or mirrors) in order to combine the signals, because we lack the technology to timestamp light waves to a fraction of a wavelength. With better timers and phase sensitive detectors we could use this technique to make giant optical telescopes. Maybe someday.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by BDanielMayfield » Thu Apr 11, 2019 7:40 pm

Nitpicker wrote: Thu Apr 11, 2019 5:36 am And they still have aperture fever!
Of course. This is an incurable affliction. Now we need radio telescopes on the Moon, for really long baselines.

Then of course we'll need RF scopes on Mars, for inner solar system scale baselines ...

Then we'll want ...
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 7:42 pm

Martin wrote: Thu Apr 11, 2019 7:38 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:26 pm
Martin wrote: Thu Apr 11, 2019 7:19 pm

Wonder no more. The answer is algorithm, Computational science. And a overdue standing ovation to the woman who's effort made it all possible today: Katie Bouman.
This isn't really computational science, which centers around models and simulations. This is computational data analysis. (That doesn't detract from the algorithm development, but those are different things.)
So you're saying computational data analysis is not a computational science?
That's not how the term is generally used. Computational science usually refers to simulations. To replacing physical experiments with computational models. Not to using computers to analyze physical data.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Martin » Thu Apr 11, 2019 7:50 pm

Chris Peterson wrote: Thu Apr 11, 2019 7:42 pm
Martin wrote: Thu Apr 11, 2019 7:38 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:26 pm

This isn't really computational science, which centers around models and simulations. This is computational data analysis. (That doesn't detract from the algorithm development, but those are different things.)
So you're saying computational data analysis is not a computational science?
That's not how the term is generally used. Computational science usually refers to simulations. To replacing physical experiments with computational models. Not to using computers to analyze physical data.
LoL, do you also go by the name of Nitpicker? Generally speaking, my answer was sufficient as is. How about that round of applause...
Last edited by Martin on Thu Apr 11, 2019 8:02 pm, edited 1 time in total.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Kmcc29 » Thu Apr 11, 2019 7:55 pm

A schoolboy question, please: Since radio telescopes were used to "photograph" this black hole, how are radio waves rendered into visible light wave lengths?

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 7:58 pm

Kmcc29 wrote: Thu Apr 11, 2019 7:55 pm A schoolboy question, please: Since radio telescopes were used to "photograph" this black hole, how are radio waves rendered into visible light wave lengths?
The radio waves are recorded as numeric values representing intensity. Those numbers can be presented as intensities in an image, too. (In fact, there are thousands of APODs showing images where the data was collected at some wavelength invisible to the eyes, and that's the way such images are nearly always made.)
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 7:59 pm

Martin wrote: Thu Apr 11, 2019 7:50 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:42 pm
Martin wrote: Thu Apr 11, 2019 7:38 pm

So you're saying computational data analysis is not a computational science?
That's not how the term is generally used. Computational science usually refers to simulations. To replacing physical experiments with computational models. Not to using computers to analyze physical data.
LoL, do you also go by the name of Nitpicker? My answer was sufficient as is. How about that round of applause...
Personally, I find it useful to use terminology accurately. I know there are some people who don't worry much about that.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Kmcc29 » Thu Apr 11, 2019 8:09 pm

Chris Peterson wrote: Thu Apr 11, 2019 7:58 pm
Kmcc29 wrote: Thu Apr 11, 2019 7:55 pm A schoolboy question, please: Since radio telescopes were used to "photograph" this black hole, how are radio waves rendered into visible light wave lengths?
The radio waves are recorded as numeric values representing intensity. Those numbers can be presented as intensities in an image, too. (In fact, there are thousands of APODs showing images where the data was collected at some wavelength invisible to the eyes, and that's the way such images are nearly always made.)
I see! Thank you for your "illuminating" reply!

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by JohnD » Thu Apr 11, 2019 8:14 pm

Again, hang on! All this talk of light that is 1.5, 2 or 2.5 (various figures quoted) the radius of the Event Horizon, "will be sucked in!!!"
The Event Horizon is the Event Horizon - that is the distance from the BH itself at which, thanks to the gravity well, escape velocity equals light speed. Anything further out CAN get away, if it goes at light speed, in the right direction. Hawking himself said so, in theorising Hawking radiation. Stuff further out MAY go in, but it's not on that handcart to … whatever there is inside the EH!

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 8:19 pm

JohnD wrote: Thu Apr 11, 2019 8:14 pm Again, hang on! All this talk of light that is 1.5, 2 or 2.5 (various figures quoted) the radius of the Event Horizon, "will be sucked in!!!"
The Event Horizon is the Event Horizon - that is the distance from the BH itself at which, thanks to the gravity well, escape velocity equals light speed. Anything further out CAN get away, if it goes at light speed, in the right direction. Hawking himself said so, in theorising Hawking radiation. Stuff further out MAY go in, but it's not on that handcart to … whatever there is inside the EH!
That's true. But in this case, absent some kind of external influence that doesn't appear to exist, the light in that region is too close to escape (or at the least, so little escapes that the region appears black to our instruments). The important point is to explain why the actual event horizon is deep within the donut hole here.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by JohnD » Thu Apr 11, 2019 8:34 pm

OK. but how do we know that, please Chris? That the EH is so much smaller than the dark area, said to be the 'shadow' of the BH?
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by FLPhotoCatcher » Thu Apr 11, 2019 8:40 pm

Chris Peterson wrote: Thu Apr 11, 2019 8:19 pm
JohnD wrote: Thu Apr 11, 2019 8:14 pm Again, hang on! All this talk of light that is 1.5, 2 or 2.5 (various figures quoted) the radius of the Event Horizon, "will be sucked in!!!"
The Event Horizon is the Event Horizon - that is the distance from the BH itself at which, thanks to the gravity well, escape velocity equals light speed. Anything further out CAN get away, if it goes at light speed, in the right direction. Hawking himself said so, in theorising Hawking radiation. Stuff further out MAY go in, but it's not on that handcart to … whatever there is inside the EH!
That's true. But in this case, absent some kind of external influence that doesn't appear to exist, the light in that region is too close to escape (or at the least, so little escapes that the region appears black to our instruments). The important point is to explain why the actual event horizon is deep within the donut hole here.
As I understand it, the region appears black because the light is mostly all radiated from a disk spiraling in to the BH, so the black area is where no light comes from, either because there is no light-emitting matter behind it, and-or the light is bent, and a dark region appears. The dark region can be thought of as a gravitationally lensed image of the dark space beyond the BH. Also, the part of the disk moving away at a large fraction of light speed appears much darker.
And here is my applause for Katie Bouman :clap: I would love to talk to her about the project!

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by orin stepanek » Thu Apr 11, 2019 8:52 pm

[
M87bh_EHT_960.jpg
Reminds me of a doughnut! :mrgreen: A doughnut that eats instead of being eaten :lol2:
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 8:59 pm

JohnD wrote: Thu Apr 11, 2019 8:34 pm OK. but how do we know that, please Chris? That the EH is so much smaller than the dark area, said to be the 'shadow' of the BH?
I think that this image has been simulated based on GR, and the simulation and observation match closely.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Martin » Thu Apr 11, 2019 9:28 pm

Chris Peterson wrote: Thu Apr 11, 2019 7:59 pm
Martin wrote: Thu Apr 11, 2019 7:50 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:42 pm
That's not how the term is generally used. Computational science usually refers to simulations. To replacing physical experiments with computational models. Not to using computers to analyze physical data.
LoL, do you also go by the name of Nitpicker? My answer was sufficient as is. How about that round of applause...
Personally, I find it useful to use terminology accurately. I know there are some people who don't worry much about that.
Way to be an anchor, Chris. We both know computational science spans many disciplines. But such specifics were not really my original point, as you know. :shock:

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Chris Peterson » Thu Apr 11, 2019 9:33 pm

Martin wrote: Thu Apr 11, 2019 9:28 pm
Chris Peterson wrote: Thu Apr 11, 2019 7:59 pm
Martin wrote: Thu Apr 11, 2019 7:50 pm

LoL, do you also go by the name of Nitpicker? My answer was sufficient as is. How about that round of applause...
Personally, I find it useful to use terminology accurately. I know there are some people who don't worry much about that.
Way to be an anchor, Chris. We both know computational science spans many disciplines. But such specifics were not really my original point, as you know. :shock:
Well, I don't know the details of your original point. Mine is simply that this is no more computational science than somebody using his calculator to figure out a reaction rate in a chem lab.
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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Nitpicker » Thu Apr 11, 2019 10:16 pm

Martin wrote: Thu Apr 11, 2019 7:28 pm
Nitpicker, not to bust bubbles but 'fake news' is an exploitation of the lowest common denominator. Try harder to rise above it, my friend.
Martin, you have incorrectly attributed the words of "Confused" to me, by mangling the quote tags.

It might be best to ease off on the condescension, too.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Nitpicker » Thu Apr 11, 2019 10:27 pm

Confused wrote: Thu Apr 11, 2019 4:19 pm
Nitpicker wrote: Thu Apr 11, 2019 7:34 am
Confused wrote: Thu Apr 11, 2019 7:30 am The thing I don't hear anyone talking about is why they had to get a black hole from more than 50 million light-years. Why can't they get an image of the (or a) black hole in our galaxy? If astronomers are unable to get an image of a black hole in our galaxy then how can they be sure that the image is what they think it is?
In absolute terms, the BH at centre of (comparatively featureless) M87 is much larger than the BH at the centre of the dusty Milky Way, and I might guess M87 is less obscured by the bits of the Milky Way in between. The BHs are comparable in terms of angular size from Earth.
Well let me put it another way. Is there any chance that this is fake news? I assume that among scientists it is understood that this is a theory that could be flawed in some way, but the TV news people are reporting is fact.
No chance. All theories can be flawed. But the image provides more evidence to match the theory. I would be less likely to worry about the interpretations of most TV news reporters on a topic such as this.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Nitpicker » Thu Apr 11, 2019 10:48 pm

With M87 being 12 degrees north of the celestial equator, I am not sure how the South Pole Telescope might have helped in this image. Certainly useful for Sgr A*, however, the data from which, I assume, is currently being analysed. I am now wondering how a resolution of 20 micro arc seconds was achieved on M87 without the SPT.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Nitpicker » Thu Apr 11, 2019 11:12 pm

Nitpicker wrote: Thu Apr 11, 2019 10:48 pm With M87 being 12 degrees north of the celestial equator, I am not sure how the South Pole Telescope might have helped in this image. Certainly useful for Sgr A*, however, the data from which, I assume, is currently being analysed. I am now wondering how a resolution of 20 micro arc seconds was achieved on M87 without the SPT.
To answer my own question, the west-east span from Hawaii to Spain also gives a baseline distance pretty close to the diameter of Earth.

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Re: APOD: First Horizon-Scale Image of a Black... (2019 Apr 11)

Post by Nitpicker » Thu Apr 11, 2019 11:15 pm

neufer wrote: Thu Apr 11, 2019 1:38 pm
Nitpicker wrote: Thu Apr 11, 2019 11:43 am
Light that approaches a radius of about 2.5 or 2.6 times the radius of the event horizon, spirals inward and crosses the event horizon, never to be seen again. That's the explanation for the size of the shadow, as I understand it.
Light that approaches a radius of about 1.5 times the radius of the event horizon does, indeed, spiral inward and cross the event horizon, never to be seen again.

Light that approaches a radius of 1.5 to ~2.5 times the radius of the event horizon escapes... but on such a bent trajectory that it still misses us.
Thanks neufer, I am sure you are right. I will work harder to understand this point.