Why isn't the black hole white? The 2019 Stack Overflow Developer Survey Results Are InDoes matter accumulate just outside the event horizon of a black hole?Ramifications of black hole stellar systemHow does an accreting black hole acquire magnetic fields?Could we verify the structure of a black hole by observing an orbiting object?Black hole without singularity?Black Hole growthShouldn't we not be able to see some black holes?M87 Black hole. Why can we see the blackness?What part of the EM spectrum was used in the black hole image?Why don't we see the gas behind the black hole?

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Why isn't the black hole white?



The 2019 Stack Overflow Developer Survey Results Are InDoes matter accumulate just outside the event horizon of a black hole?Ramifications of black hole stellar systemHow does an accreting black hole acquire magnetic fields?Could we verify the structure of a black hole by observing an orbiting object?Black hole without singularity?Black Hole growthShouldn't we not be able to see some black holes?M87 Black hole. Why can we see the blackness?What part of the EM spectrum was used in the black hole image?Why don't we see the gas behind the black hole?










5












$begingroup$


I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the matter surrounding the black hole? Or is the matter around the black hole disposed in a disk shape and the astronomers got lucky that the disk was not oriented towards Earth?










share|improve this question







New contributor




Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$
















    5












    $begingroup$


    I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the matter surrounding the black hole? Or is the matter around the black hole disposed in a disk shape and the astronomers got lucky that the disk was not oriented towards Earth?










    share|improve this question







    New contributor




    Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.







    $endgroup$














      5












      5








      5





      $begingroup$


      I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the matter surrounding the black hole? Or is the matter around the black hole disposed in a disk shape and the astronomers got lucky that the disk was not oriented towards Earth?










      share|improve this question







      New contributor




      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      I recently saw the first image of a black hole. As I understood, it is covered with bright, hot matter. In this case, how can we see the black disk (event horizon), instead of a bright disk due to the matter surrounding the black hole? Or is the matter around the black hole disposed in a disk shape and the astronomers got lucky that the disk was not oriented towards Earth?







      black-hole matter disk






      share|improve this question







      New contributor




      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      share|improve this question







      New contributor




      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      share|improve this question




      share|improve this question






      New contributor




      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.









      asked 7 hours ago









      Cristian MCristian M

      261




      261




      New contributor




      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.





      New contributor





      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.






      Cristian M is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.




















          3 Answers
          3






          active

          oldest

          votes


















          2












          $begingroup$

          The black hole image that you saw is not a photograph in the traditional sense. A traditional photograph is created when visible light strikes a digital sensor or film in a camera.



          The image of M87 that you saw was created by an elaborate, complex, globe-spanning and labor-intensive operation.



          To start with, the telescopes used were radio telescopes. These radio telescopes "see" radio waves with a 1.3mm wavelength like we see visible light, which has a wavelength from violet (380 nanometers) to red (700 nanometers). Think of it like infrared vision or night vision.



          Eight radio telescopes all over the globe were pointed toward the same black hole at the same time over the course of four days. Each radio telescope collected an enormous amount of data by observing the black hole in the radio spectrum, not the visible light spectrum. According to the Event Horizons Telescope website, each of the eight radio telescopes produced about 350 terabytes of data per day. This radio spectrum observation data was timestamped using an extremely accurate atomic clock at each location.



          The data was then shipped to supercomputing centers to be processed by an algorithm. The computer algorithms work by lining up the data from the different telescopes using the accurate timestamps and by aligning the observed data spatially. This process is called very-long-baseline interferometry (VLBI). The basic idea is that if you take two distinct observations of the same object from different locations and synchronize them. This helps to eliminate atmospheric noise by seeing what both different images have in common. While it may seem like a highly artificial process, it is very effective at eliminating noise.



          The image you see is therefore the result of a computer algorithm processing radio observations of the black hole from 8 different locations on earth. The choice of color was likely a choice made by the computer scientists who wrote the algorithm, but it appears to bear some relation to the intensity of the radio energies observed: more energy shows as brighter, while darker spots with less energy are deeper red or black. This choice of color might make sense because the strong gravity of a black hole will tend to redshift any light emanating from nearby or passing close to the black hole. On the other hand, black holes are said to be enormously energetic in a broad spectrum of electromagnetic energy. First-hand accounts of nuclear explosions, which unleash X Rays and Gamma Rays and other far-ultraviolet energy have been described as having all kinds of exotic color.



          While this may seem a bit disappointing, it's worth noting that visible light does not propagate through space as well as radio. Radio penetrates dust and gas and all the intervening detritus in space much better. Visible light tends to be blocked and re-absorbed. Think of Wifi signals (radio) versus visible light. The Wifi penetrates walls, while the visible light gets blocked by walls, curtains, etc. The EHT website has some helpful infographics on VLBI.






          share|improve this answer











          $endgroup$












          • $begingroup$
            So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
            $endgroup$
            – Cristian M
            6 hours ago










          • $begingroup$
            The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
            $endgroup$
            – S. Imp
            6 hours ago










          • $begingroup$
            Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
            $endgroup$
            – S. Imp
            6 hours ago










          • $begingroup$
            Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
            $endgroup$
            – S. Imp
            6 hours ago










          • $begingroup$
            There is no answer here to the question asked.
            $endgroup$
            – Rob Jeffries
            2 hours ago



















          2












          $begingroup$

          What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly.



          The disk is referred to as geometrically thick, but optically thin (see sections 1 and 2 of paper V issued by the Event Horizon Telescope collaboration on 10 April 2019). This is actually the opposite of the disk visualised in the film "Interstellar".



          Because the disk is geometrically thick, it covers the whole picture. Because it is optically thin, we can see through it to the black hole. That is the basic answer to your question.



          In an optically thin plasma, the brightness you will see is proportional to the optical path length (physical length multiplied by an absorption coefficient) along that sightline. The photon ring marks radiation travelling towards us that has been bent around the black hole, or has even orbited it several times. Hence those sight lines have larger optical path lengths and that is why we see it as a bright ring.



          Radiation travelling towards us from plasma in front of the black hole, has a small optical path length and is not very bright. In addition, the sight lines to plasma behind the black hole cannot travel through the black hole or even close to the event horizon. Hence the circular "shadow" inside the photon ring.






          share|improve this answer











          $endgroup$




















            1












            $begingroup$

            The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower than the intensity in the bright ring around it. So in that sense it really is a dark spot.



            It is described in the papers as the "shadow" of the black hole, although even that is stretching the word shadow a little. Basically the light that "would have" been coming to us from that direction has been bent away by gravity.






            share|improve this answer









            $endgroup$












            • $begingroup$
              The question was why don't we see the accretion flow in front of the black hole?
              $endgroup$
              – Rob Jeffries
              2 hours ago












            Your Answer





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            3 Answers
            3






            active

            oldest

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            3 Answers
            3






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            2












            $begingroup$

            The black hole image that you saw is not a photograph in the traditional sense. A traditional photograph is created when visible light strikes a digital sensor or film in a camera.



            The image of M87 that you saw was created by an elaborate, complex, globe-spanning and labor-intensive operation.



            To start with, the telescopes used were radio telescopes. These radio telescopes "see" radio waves with a 1.3mm wavelength like we see visible light, which has a wavelength from violet (380 nanometers) to red (700 nanometers). Think of it like infrared vision or night vision.



            Eight radio telescopes all over the globe were pointed toward the same black hole at the same time over the course of four days. Each radio telescope collected an enormous amount of data by observing the black hole in the radio spectrum, not the visible light spectrum. According to the Event Horizons Telescope website, each of the eight radio telescopes produced about 350 terabytes of data per day. This radio spectrum observation data was timestamped using an extremely accurate atomic clock at each location.



            The data was then shipped to supercomputing centers to be processed by an algorithm. The computer algorithms work by lining up the data from the different telescopes using the accurate timestamps and by aligning the observed data spatially. This process is called very-long-baseline interferometry (VLBI). The basic idea is that if you take two distinct observations of the same object from different locations and synchronize them. This helps to eliminate atmospheric noise by seeing what both different images have in common. While it may seem like a highly artificial process, it is very effective at eliminating noise.



            The image you see is therefore the result of a computer algorithm processing radio observations of the black hole from 8 different locations on earth. The choice of color was likely a choice made by the computer scientists who wrote the algorithm, but it appears to bear some relation to the intensity of the radio energies observed: more energy shows as brighter, while darker spots with less energy are deeper red or black. This choice of color might make sense because the strong gravity of a black hole will tend to redshift any light emanating from nearby or passing close to the black hole. On the other hand, black holes are said to be enormously energetic in a broad spectrum of electromagnetic energy. First-hand accounts of nuclear explosions, which unleash X Rays and Gamma Rays and other far-ultraviolet energy have been described as having all kinds of exotic color.



            While this may seem a bit disappointing, it's worth noting that visible light does not propagate through space as well as radio. Radio penetrates dust and gas and all the intervening detritus in space much better. Visible light tends to be blocked and re-absorbed. Think of Wifi signals (radio) versus visible light. The Wifi penetrates walls, while the visible light gets blocked by walls, curtains, etc. The EHT website has some helpful infographics on VLBI.






            share|improve this answer











            $endgroup$












            • $begingroup$
              So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
              $endgroup$
              – Cristian M
              6 hours ago










            • $begingroup$
              The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              There is no answer here to the question asked.
              $endgroup$
              – Rob Jeffries
              2 hours ago
















            2












            $begingroup$

            The black hole image that you saw is not a photograph in the traditional sense. A traditional photograph is created when visible light strikes a digital sensor or film in a camera.



            The image of M87 that you saw was created by an elaborate, complex, globe-spanning and labor-intensive operation.



            To start with, the telescopes used were radio telescopes. These radio telescopes "see" radio waves with a 1.3mm wavelength like we see visible light, which has a wavelength from violet (380 nanometers) to red (700 nanometers). Think of it like infrared vision or night vision.



            Eight radio telescopes all over the globe were pointed toward the same black hole at the same time over the course of four days. Each radio telescope collected an enormous amount of data by observing the black hole in the radio spectrum, not the visible light spectrum. According to the Event Horizons Telescope website, each of the eight radio telescopes produced about 350 terabytes of data per day. This radio spectrum observation data was timestamped using an extremely accurate atomic clock at each location.



            The data was then shipped to supercomputing centers to be processed by an algorithm. The computer algorithms work by lining up the data from the different telescopes using the accurate timestamps and by aligning the observed data spatially. This process is called very-long-baseline interferometry (VLBI). The basic idea is that if you take two distinct observations of the same object from different locations and synchronize them. This helps to eliminate atmospheric noise by seeing what both different images have in common. While it may seem like a highly artificial process, it is very effective at eliminating noise.



            The image you see is therefore the result of a computer algorithm processing radio observations of the black hole from 8 different locations on earth. The choice of color was likely a choice made by the computer scientists who wrote the algorithm, but it appears to bear some relation to the intensity of the radio energies observed: more energy shows as brighter, while darker spots with less energy are deeper red or black. This choice of color might make sense because the strong gravity of a black hole will tend to redshift any light emanating from nearby or passing close to the black hole. On the other hand, black holes are said to be enormously energetic in a broad spectrum of electromagnetic energy. First-hand accounts of nuclear explosions, which unleash X Rays and Gamma Rays and other far-ultraviolet energy have been described as having all kinds of exotic color.



            While this may seem a bit disappointing, it's worth noting that visible light does not propagate through space as well as radio. Radio penetrates dust and gas and all the intervening detritus in space much better. Visible light tends to be blocked and re-absorbed. Think of Wifi signals (radio) versus visible light. The Wifi penetrates walls, while the visible light gets blocked by walls, curtains, etc. The EHT website has some helpful infographics on VLBI.






            share|improve this answer











            $endgroup$












            • $begingroup$
              So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
              $endgroup$
              – Cristian M
              6 hours ago










            • $begingroup$
              The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              There is no answer here to the question asked.
              $endgroup$
              – Rob Jeffries
              2 hours ago














            2












            2








            2





            $begingroup$

            The black hole image that you saw is not a photograph in the traditional sense. A traditional photograph is created when visible light strikes a digital sensor or film in a camera.



            The image of M87 that you saw was created by an elaborate, complex, globe-spanning and labor-intensive operation.



            To start with, the telescopes used were radio telescopes. These radio telescopes "see" radio waves with a 1.3mm wavelength like we see visible light, which has a wavelength from violet (380 nanometers) to red (700 nanometers). Think of it like infrared vision or night vision.



            Eight radio telescopes all over the globe were pointed toward the same black hole at the same time over the course of four days. Each radio telescope collected an enormous amount of data by observing the black hole in the radio spectrum, not the visible light spectrum. According to the Event Horizons Telescope website, each of the eight radio telescopes produced about 350 terabytes of data per day. This radio spectrum observation data was timestamped using an extremely accurate atomic clock at each location.



            The data was then shipped to supercomputing centers to be processed by an algorithm. The computer algorithms work by lining up the data from the different telescopes using the accurate timestamps and by aligning the observed data spatially. This process is called very-long-baseline interferometry (VLBI). The basic idea is that if you take two distinct observations of the same object from different locations and synchronize them. This helps to eliminate atmospheric noise by seeing what both different images have in common. While it may seem like a highly artificial process, it is very effective at eliminating noise.



            The image you see is therefore the result of a computer algorithm processing radio observations of the black hole from 8 different locations on earth. The choice of color was likely a choice made by the computer scientists who wrote the algorithm, but it appears to bear some relation to the intensity of the radio energies observed: more energy shows as brighter, while darker spots with less energy are deeper red or black. This choice of color might make sense because the strong gravity of a black hole will tend to redshift any light emanating from nearby or passing close to the black hole. On the other hand, black holes are said to be enormously energetic in a broad spectrum of electromagnetic energy. First-hand accounts of nuclear explosions, which unleash X Rays and Gamma Rays and other far-ultraviolet energy have been described as having all kinds of exotic color.



            While this may seem a bit disappointing, it's worth noting that visible light does not propagate through space as well as radio. Radio penetrates dust and gas and all the intervening detritus in space much better. Visible light tends to be blocked and re-absorbed. Think of Wifi signals (radio) versus visible light. The Wifi penetrates walls, while the visible light gets blocked by walls, curtains, etc. The EHT website has some helpful infographics on VLBI.






            share|improve this answer











            $endgroup$



            The black hole image that you saw is not a photograph in the traditional sense. A traditional photograph is created when visible light strikes a digital sensor or film in a camera.



            The image of M87 that you saw was created by an elaborate, complex, globe-spanning and labor-intensive operation.



            To start with, the telescopes used were radio telescopes. These radio telescopes "see" radio waves with a 1.3mm wavelength like we see visible light, which has a wavelength from violet (380 nanometers) to red (700 nanometers). Think of it like infrared vision or night vision.



            Eight radio telescopes all over the globe were pointed toward the same black hole at the same time over the course of four days. Each radio telescope collected an enormous amount of data by observing the black hole in the radio spectrum, not the visible light spectrum. According to the Event Horizons Telescope website, each of the eight radio telescopes produced about 350 terabytes of data per day. This radio spectrum observation data was timestamped using an extremely accurate atomic clock at each location.



            The data was then shipped to supercomputing centers to be processed by an algorithm. The computer algorithms work by lining up the data from the different telescopes using the accurate timestamps and by aligning the observed data spatially. This process is called very-long-baseline interferometry (VLBI). The basic idea is that if you take two distinct observations of the same object from different locations and synchronize them. This helps to eliminate atmospheric noise by seeing what both different images have in common. While it may seem like a highly artificial process, it is very effective at eliminating noise.



            The image you see is therefore the result of a computer algorithm processing radio observations of the black hole from 8 different locations on earth. The choice of color was likely a choice made by the computer scientists who wrote the algorithm, but it appears to bear some relation to the intensity of the radio energies observed: more energy shows as brighter, while darker spots with less energy are deeper red or black. This choice of color might make sense because the strong gravity of a black hole will tend to redshift any light emanating from nearby or passing close to the black hole. On the other hand, black holes are said to be enormously energetic in a broad spectrum of electromagnetic energy. First-hand accounts of nuclear explosions, which unleash X Rays and Gamma Rays and other far-ultraviolet energy have been described as having all kinds of exotic color.



            While this may seem a bit disappointing, it's worth noting that visible light does not propagate through space as well as radio. Radio penetrates dust and gas and all the intervening detritus in space much better. Visible light tends to be blocked and re-absorbed. Think of Wifi signals (radio) versus visible light. The Wifi penetrates walls, while the visible light gets blocked by walls, curtains, etc. The EHT website has some helpful infographics on VLBI.







            share|improve this answer














            share|improve this answer



            share|improve this answer








            edited 6 hours ago

























            answered 6 hours ago









            S. ImpS. Imp

            20618




            20618











            • $begingroup$
              So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
              $endgroup$
              – Cristian M
              6 hours ago










            • $begingroup$
              The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              There is no answer here to the question asked.
              $endgroup$
              – Rob Jeffries
              2 hours ago

















            • $begingroup$
              So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
              $endgroup$
              – Cristian M
              6 hours ago










            • $begingroup$
              The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
              $endgroup$
              – S. Imp
              6 hours ago










            • $begingroup$
              There is no answer here to the question asked.
              $endgroup$
              – Rob Jeffries
              2 hours ago
















            $begingroup$
            So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
            $endgroup$
            – Cristian M
            6 hours ago




            $begingroup$
            So, if I understood correctly, we can see a black disk because the matter in front was not "visible" in the wavelength used by the radio telescopes. If so, why?
            $endgroup$
            – Cristian M
            6 hours ago












            $begingroup$
            The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
            $endgroup$
            – S. Imp
            6 hours ago




            $begingroup$
            The ring-like appearance of the image is so exciting because it matches theoretical predictions so closely. These theoretical predictions are complex, but say that the visible appearance of the black hole is about 2.5 times the size of the black hole's event horizon. I won't pretend to know all the specifics, but suspect the black hole's gravity traps a lot of light, and at the sides we see more because we're looking at a deeper/thicker cross section of the black hole's surrounding mass. Kinda similar idea to the sun look red at sunrise/sunset because it's traveling through more atmosphere.
            $endgroup$
            – S. Imp
            6 hours ago












            $begingroup$
            Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
            $endgroup$
            – S. Imp
            6 hours ago




            $begingroup$
            Also keep in mind that the image has a certain dynamic range. If you've ever adjusted brightness/contrast on an image you might get what I mean. Or like when you take a picture with your phone. The phone adjusts the exposure to the subject of the photo. If your subject is bright, it adjusts to let less light in. If your subject is dark, it adjusts to let more light in. My guess is that the computer algorithm was configured to adapt its dynamic range to the immediate vicinity of the black hole, making the background black and the brightest spot white, so that other colors fall in between.
            $endgroup$
            – S. Imp
            6 hours ago












            $begingroup$
            Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
            $endgroup$
            – S. Imp
            6 hours ago




            $begingroup$
            Actually, that sunset/sunrise example is probably not helpful. Think instead of how in pictures from the Int'l Space Station, you can only see the cloudy atmosphere when you look at the edge of the earth. If you look straight down, you're looking thru just a thin layer of atmosphere. If you look toward the edge of earth, you're looking through more atmosphere along the edge of the earth.
            $endgroup$
            – S. Imp
            6 hours ago












            $begingroup$
            There is no answer here to the question asked.
            $endgroup$
            – Rob Jeffries
            2 hours ago





            $begingroup$
            There is no answer here to the question asked.
            $endgroup$
            – Rob Jeffries
            2 hours ago












            2












            $begingroup$

            What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly.



            The disk is referred to as geometrically thick, but optically thin (see sections 1 and 2 of paper V issued by the Event Horizon Telescope collaboration on 10 April 2019). This is actually the opposite of the disk visualised in the film "Interstellar".



            Because the disk is geometrically thick, it covers the whole picture. Because it is optically thin, we can see through it to the black hole. That is the basic answer to your question.



            In an optically thin plasma, the brightness you will see is proportional to the optical path length (physical length multiplied by an absorption coefficient) along that sightline. The photon ring marks radiation travelling towards us that has been bent around the black hole, or has even orbited it several times. Hence those sight lines have larger optical path lengths and that is why we see it as a bright ring.



            Radiation travelling towards us from plasma in front of the black hole, has a small optical path length and is not very bright. In addition, the sight lines to plasma behind the black hole cannot travel through the black hole or even close to the event horizon. Hence the circular "shadow" inside the photon ring.






            share|improve this answer











            $endgroup$

















              2












              $begingroup$

              What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly.



              The disk is referred to as geometrically thick, but optically thin (see sections 1 and 2 of paper V issued by the Event Horizon Telescope collaboration on 10 April 2019). This is actually the opposite of the disk visualised in the film "Interstellar".



              Because the disk is geometrically thick, it covers the whole picture. Because it is optically thin, we can see through it to the black hole. That is the basic answer to your question.



              In an optically thin plasma, the brightness you will see is proportional to the optical path length (physical length multiplied by an absorption coefficient) along that sightline. The photon ring marks radiation travelling towards us that has been bent around the black hole, or has even orbited it several times. Hence those sight lines have larger optical path lengths and that is why we see it as a bright ring.



              Radiation travelling towards us from plasma in front of the black hole, has a small optical path length and is not very bright. In addition, the sight lines to plasma behind the black hole cannot travel through the black hole or even close to the event horizon. Hence the circular "shadow" inside the photon ring.






              share|improve this answer











              $endgroup$















                2












                2








                2





                $begingroup$

                What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly.



                The disk is referred to as geometrically thick, but optically thin (see sections 1 and 2 of paper V issued by the Event Horizon Telescope collaboration on 10 April 2019). This is actually the opposite of the disk visualised in the film "Interstellar".



                Because the disk is geometrically thick, it covers the whole picture. Because it is optically thin, we can see through it to the black hole. That is the basic answer to your question.



                In an optically thin plasma, the brightness you will see is proportional to the optical path length (physical length multiplied by an absorption coefficient) along that sightline. The photon ring marks radiation travelling towards us that has been bent around the black hole, or has even orbited it several times. Hence those sight lines have larger optical path lengths and that is why we see it as a bright ring.



                Radiation travelling towards us from plasma in front of the black hole, has a small optical path length and is not very bright. In addition, the sight lines to plasma behind the black hole cannot travel through the black hole or even close to the event horizon. Hence the circular "shadow" inside the photon ring.






                share|improve this answer











                $endgroup$



                What's going on here is that you have been misled into thinking the ring-like structure has anything to do with the accretion disk. It doesn't, or at least only indirectly.



                The disk is referred to as geometrically thick, but optically thin (see sections 1 and 2 of paper V issued by the Event Horizon Telescope collaboration on 10 April 2019). This is actually the opposite of the disk visualised in the film "Interstellar".



                Because the disk is geometrically thick, it covers the whole picture. Because it is optically thin, we can see through it to the black hole. That is the basic answer to your question.



                In an optically thin plasma, the brightness you will see is proportional to the optical path length (physical length multiplied by an absorption coefficient) along that sightline. The photon ring marks radiation travelling towards us that has been bent around the black hole, or has even orbited it several times. Hence those sight lines have larger optical path lengths and that is why we see it as a bright ring.



                Radiation travelling towards us from plasma in front of the black hole, has a small optical path length and is not very bright. In addition, the sight lines to plasma behind the black hole cannot travel through the black hole or even close to the event horizon. Hence the circular "shadow" inside the photon ring.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited 1 hour ago

























                answered 1 hour ago









                Rob JeffriesRob Jeffries

                54.4k4112175




                54.4k4112175





















                    1












                    $begingroup$

                    The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower than the intensity in the bright ring around it. So in that sense it really is a dark spot.



                    It is described in the papers as the "shadow" of the black hole, although even that is stretching the word shadow a little. Basically the light that "would have" been coming to us from that direction has been bent away by gravity.






                    share|improve this answer









                    $endgroup$












                    • $begingroup$
                      The question was why don't we see the accretion flow in front of the black hole?
                      $endgroup$
                      – Rob Jeffries
                      2 hours ago
















                    1












                    $begingroup$

                    The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower than the intensity in the bright ring around it. So in that sense it really is a dark spot.



                    It is described in the papers as the "shadow" of the black hole, although even that is stretching the word shadow a little. Basically the light that "would have" been coming to us from that direction has been bent away by gravity.






                    share|improve this answer









                    $endgroup$












                    • $begingroup$
                      The question was why don't we see the accretion flow in front of the black hole?
                      $endgroup$
                      – Rob Jeffries
                      2 hours ago














                    1












                    1








                    1





                    $begingroup$

                    The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower than the intensity in the bright ring around it. So in that sense it really is a dark spot.



                    It is described in the papers as the "shadow" of the black hole, although even that is stretching the word shadow a little. Basically the light that "would have" been coming to us from that direction has been bent away by gravity.






                    share|improve this answer









                    $endgroup$



                    The black part in the centre of the image genuinely represents some directions from which less energy is arriving at the telescopes. I believe the intensity in the middle of it is about 10 times lower than the intensity in the bright ring around it. So in that sense it really is a dark spot.



                    It is described in the papers as the "shadow" of the black hole, although even that is stretching the word shadow a little. Basically the light that "would have" been coming to us from that direction has been bent away by gravity.







                    share|improve this answer












                    share|improve this answer



                    share|improve this answer










                    answered 3 hours ago









                    Steve LintonSteve Linton

                    2,5231319




                    2,5231319











                    • $begingroup$
                      The question was why don't we see the accretion flow in front of the black hole?
                      $endgroup$
                      – Rob Jeffries
                      2 hours ago

















                    • $begingroup$
                      The question was why don't we see the accretion flow in front of the black hole?
                      $endgroup$
                      – Rob Jeffries
                      2 hours ago
















                    $begingroup$
                    The question was why don't we see the accretion flow in front of the black hole?
                    $endgroup$
                    – Rob Jeffries
                    2 hours ago





                    $begingroup$
                    The question was why don't we see the accretion flow in front of the black hole?
                    $endgroup$
                    – Rob Jeffries
                    2 hours ago











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                    ValueError: Expected n_neighbors <= n_samples, but n_samples = 1, n_neighbors = 6 (SMOTE) The 2019 Stack Overflow Developer Survey Results Are InCan SMOTE be applied over sequence of words (sentences)?ValueError when doing validation with random forestsSMOTE and multi class oversamplingLogic behind SMOTE-NC?ValueError: Error when checking target: expected dense_1 to have shape (7,) but got array with shape (1,)SmoteBoost: Should SMOTE be ran individually for each iteration/tree in the boosting?solving multi-class imbalance classification using smote and OSSUsing SMOTE for Synthetic Data generation to improve performance on unbalanced dataproblem of entry format for a simple model in KerasSVM SMOTE fit_resample() function runs forever with no result