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Thread: 2018 - Directly 'Sees' Our First Black Hole

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    2018 - Directly 'Sees' Our First Black Hole

    (I apologize if I felt into temptation in my previous posts; now I'll keep my threads short & sweet with 1 or 2 posts)

    They are stating here that in 2018 we'll see the first black hole:

    https://www.forbes.com/sites/startsw.../#1dc8c39c3a16

    Does that mean they'll be able to see what's going on at the event horizon? If so will they be able to prove or disprove GR with the observed orbital velocities of the stars at the event horizon or is that already confirmed?


    Thanks a lot in advance,
    philippeb8

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    2018 Will Be The Year Humanity Directly 'Sees' Our First Black Hole
    All told, we expect the event horizon to appear, from our point of view, 250% as large as the mass predictions would imply.
    We have been detecting black holes for decades. They now have the data to directly see a specific black hole.
    They will be able to see the effects of the event horizon on light from stars around the supermassive black hole. No star orbits will be measured.
    The closest star we have found is S0–102 which gets to within 38.9 billion km. The event horizon is 44 million kilometers.
    Last edited by Reality Check; 2018-Jan-11 at 08:38 PM.

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    Quote Originally Posted by Reality Check View Post
    No star orbits will be measured.
    (Sadly...) Thank you Reality Check for the clarifications.

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    The orbits of several stars around the black hole have already been measured, which provides a lot of information about the mass and location of the black hole.

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    Should the word direct be used in this case? Is it not still indirect, though very strong, evidence?

    Have we not "seen" (including IR) an EH before, such as the Milky Way's BH?
    Last edited by George; 2018-Jan-11 at 02:42 PM.
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    I think that the idea is that the observations were already made (a year ago), and that the analysis will be complete this year... and that all that really happened was that they had sufficient resolution (in theory, not reported success yet) that the event horizon is more than one pixel across. Don't hope for detail on this one, it is just our first look. If this works then we may be able to get better looks in the decades ahead, especially if some of the interferomtric contributions can be made from the Moon, or other deeper space locations off the planet.
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    I think that the idea is that the observations were already made (a year ago), and that the analysis will be complete this year... and that all that really happened was that they had sufficient resolution (in theory, not reported success yet) that the event horizon is more than one pixel across. Don't hope for detail on this one, it is just our first look. If this works then we may be able to get better looks in the decades ahead, especially if some of the interferomtric contributions can be made from the Moon, or other deeper space locations off the planet.
    The Youtube link I gave allows us to see the EH, right? It's more than a computed size as they state for Sag. A.
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by Strange View Post
    The orbits of several stars around the black hole have already been measured, which provides a lot of information about the mass and location of the black hole.
    Ok so the mass of the black hole is determined by the orbit of the stars, which assumes GR is right. I was talking about the other way around: predicting the orbit of the stars knowing in advance the mass of the black hole and which should confirm or refute GR. But we don't know the mass of the black hole so this answers my question, thanks a lot.

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    Quote Originally Posted by philippeb8 View Post
    Ok so the mass of the black hole is determined by the orbit of the stars, which assumes GR is right. I was talking about the other way around: predicting the orbit of the stars knowing in advance the mass of the black hole and which should confirm or refute GR. But we don't know the mass of the black hole so this answers my question, thanks a lot.
    Accurate measurements of the orbits of those stars do give some confirmation of GR.
    https://www.newscientist.com/article...al-black-hole/
    https://arxiv.org/abs/1512.03818

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    Quote Originally Posted by Strange View Post
    Accurate measurements of the orbits of those stars do give some confirmation of GR.
    https://www.newscientist.com/article...al-black-hole/
    https://arxiv.org/abs/1512.03818
    Interesting. One last question: how did they solve the mass of the black hole beforehand?

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    Sagittarius A*
    Firstly from the orbits and masses of the stars around the supermassive black hole.
    The Third law of Kepler is "The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit" and Newtonian gravitation gives a value for that proportionality related to the sum of the planet and primary masses (star and black hole in this case). Measure the period P and semi-major axis a of an orbit and the mass m of a star, plug the values into the equation and out pops the mass M of the black hole. This is something even we can do for ourselves, e.g. P, a and m are listed for S2 in Wikipedia. Note that the star mass m is optional if we assume that M >> m and set m = 0.

    Secondly from the proper motions of thousands of stars around the black hole. That looks lie a modeling process in which they ask what distribution of matter would produce observed proper motions.

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    Quote Originally Posted by Reality Check View Post
    Sagittarius A*
    Firstly from the orbits and masses of the stars around the supermassive black hole.
    The Third law of Kepler is "The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit" and Newtonian gravitation gives a value for that proportionality related to the sum of the planet and primary masses (star and black hole in this case). Measure the period P and semi-major axis a of an orbit and the mass m of a star, plug the values into the equation and out pops the mass M of the black hole. This is something even we can do for ourselves, e.g. P, a and m are listed for S2 in Wikipedia. Note that the star mass m is optional if we assume that M >> m and set m = 0.
    Ok so they're using the observed orbital velocity of the stars to solve the mass of the black hole which is then used to predict the orbital velocity of the stars? I guess I would use a different technique to solve the mass of the black hole in the first place but if you say so then I won't argue (I wish there was another CQ forum for "constructive discussions").

    Secondly from the proper motions of thousands of stars around the black hole. That looks lie a modeling process in which they ask what distribution of matter would produce observed proper motions.
    Thanks again Reality Check I appreciate.

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    Quote Originally Posted by George View Post
    The Youtube link I gave allows us to see the EH, right? It's more than a computed size as they state for Sag. A.
    No, it doesn't. The event horizon disk as we would see it is about 1/100 of a pixel across in these images.
    Forming opinions as we speak

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    Quote Originally Posted by philippeb8 View Post
    Ok so they're using the observed orbital velocity of the stars...
    The first method measuring the mass M of the supermassive black hole uses the observed period P and semi-major axis a and mass of some stars in orbit around the black hole..
    The second method measuring the mass M of the supermassive black hole uses the proper motion of thousands of stars that are not in orbit around the black hole.
    Neither method uses orbital velocity.

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    Quote Originally Posted by Reality Check View Post
    Neither method uses orbital velocity.
    Aren't the period and the semi-major axis equivalent to the orbital velocity?

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    Quote Originally Posted by philippeb8 View Post
    Aren't the period and the semi-major axis equivalent to the orbital velocity?
    Period is a time and constant. Semi-major axis is a distance and constant. Orbital speed varies. For orbits with small eccentricity, the mean orbital speed is ~2pi* P/a.

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    Quote Originally Posted by Reality Check View Post
    Period is a time and constant. Semi-major axis is a distance and constant. Orbital speed varies. For orbits with small eccentricity, the mean orbital speed is ~2pi* P/a.
    Ok that answers my question, thanks.

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    would stars orbiting a SMBH show a similar orbit effect like Mercury, and its relativistic precession?
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    They would but very probably too small to measure from Earth since the closest SMBH is ~24,000 light years away.

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    Quote Originally Posted by antoniseb View Post
    No, it doesn't. The event horizon disk as we would see it is about 1/100 of a pixel across in these images.
    Ug! Wow, why did I say something that nuts? The first few seconds of the video seems to show, surprisingly, Einstein ring effects for the stars when close to the BH, and there seems to be a completely dark round disk in the image, if you allow one star or two to pass in front of it. It all combined to make me think we were actually seeing a BH.

    Doing the math, however, reveals that the diameter would be 3.7 trillionths of an arcsecond, so, in this case, seeing ain't believing. [My crunching gives me 30 million km for the Schwarzchild radius and I used 26,500 lyrs. distance.]
    Last edited by George; 2018-Jan-12 at 04:14 PM.
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    Quote Originally Posted by George View Post
    ... The first few seconds of the video seems to show, surprisingly, Einstein ring effects for the stars when close to the BH, and there seems to be a completely dark round disk in the image, if you allow one star or two to pass in front of it. It all combined to make me think we were actually seeing a BH.
    I saw the same thing. Not sure what the distortion is, or whether it is part of the data, or the rendering of the data.
    Forming opinions as we speak

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    Quote Originally Posted by antoniseb View Post
    I saw the same thing. Not sure what the distortion is, or whether it is part of the data, or the rendering of the data.
    I would guess atmospheric issues, but it is funny how I saw what I wanted to see. I know better. [Stars farther out also distort as well, when scrutinized.]
    We know time flies, we just can't see its wings.

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    <delurk>
    Here is a link to the video on the ESA website, with text describing when the video switches from real data to simulation. It seems to me the blurry B&W images are real data, not simulated. I'd be careful with evaluating my statement, I've been taking cold medicine.

    In the infrared, VLT is much nicer than Hubble, but it still deals with the atmosphere. One of these babies in space would be amazing (-ly expensive).

    </delurk>
    Solfe

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    Quote Originally Posted by Reality Check View Post
    Sagittarius A*
    Firstly from the orbits and masses of the stars around the supermassive black hole.
    The Third law of Kepler is "The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit" and Newtonian gravitation gives a value for that proportionality related to the sum of the planet and primary masses (star and black hole in this case). Measure the period P and semi-major axis a of an orbit and the mass m of a star, plug the values into the equation and out pops the mass M of the black hole. This is something even we can do for ourselves, e.g. P, a and m are listed for S2 in Wikipedia. Note that the star mass m is optional if we assume that M >> m and set m = 0.

    Secondly from the proper motions of thousands of stars around the black hole. That looks lie a modeling process in which they ask what distribution of matter would produce observed proper motions.
    Wouldn't light bending or lensing be a more precise approach to measure the mass of the black hole?

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    Quote Originally Posted by philippeb8 View Post
    Wouldn't light bending or lensing be a more precise approach to measure the mass of the black hole?
    How would you tell where the emitter of the lensed light would appear to be in the absence of the black hole?

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    Quote Originally Posted by Hornblower View Post
    How would you tell where the emitter of the lensed light would appear to be in the absence of the black hole?
    Well if there is a galaxy behind the black hole and the image we see is distorted by the lensing then we could interpolate the real shape of the galaxy with some simple computer algorithm. With the position we observe and the position we have interpolated we can then compute the mass of the black hole.

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    Quote Originally Posted by philippeb8 View Post
    Well if there is a galaxy behind the black hole and the image we see is distorted by the lensing then we could interpolate the real shape of the galaxy with some simple computer algorithm. With the position we observe and the position we have interpolated we can then compute the mass of the black hole.
    In better words, in CS there is a popular edge detection algorithm:
    https://en.wikipedia.org/wiki/Edge_detection

    So all you have to do is compare the shape of the edges in order to solve the mass of the black hole (that's an interesting project).

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    Quote Originally Posted by philippeb8 View Post
    In better words, in CS there is a popular edge detection algorithm:
    https://en.wikipedia.org/wiki/Edge_detection

    So all you have to do is compare the shape of the edges in order to solve the mass of the black hole (that's an interesting project).
    Except SagA* is in the middle of a large amount of dust and other matter. It is hard enough seeing it, let along seeing it, then past it, through the rest of our galaxy then on to the next galaxy that happens to be on that line of sight. If somehow we got through all that we'd then have to work out what the galaxy 'should' look like without directly observing it. Then we'd have to remove the effects of all that matter we were looking past.

    It is not a trivially, or likely even possible, observation to make with the level of precision required to estimate the mass of SagA*.

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    As I see it, we would still be guessing at the size and form of a background galaxy, provided we could see it. I can imagine two possibilities:
    1. A large, sparse galaxy slightly enlarged by a low mass foreground black hole.
    2. A more compact and dense galaxy greatly enlarged by a higher mass black hole.
    How could we tell which is which. How is this supposed to be more precise than measuring the angular positions and radial velocities of stars which we can see individually in orbit around the black hole, using suitable infrared imaging techniques?

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    Quote Originally Posted by Hornblower View Post
    How is this supposed to be more precise than measuring the angular positions and radial velocities of stars which we can see individually in orbit around the black hole, using suitable infrared imaging techniques?
    So they're using the angular positions and radial velocities of stars to determine the mass of the black hole which is then used to predict the orbital velocity of the stars (A -> B -> A).

    I think another well tested technique, such as light bending, should be used to determine the mass of the black hole in the first place (A -> B -> C) if you want to test the predictions of GR in regards to orbital velocities.

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