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Thread: First image of a black hole on April 10, 2019

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    Quote Originally Posted by Strange View Post
    Rather a large step, unfortunately.
    I’ll finance it if I can...


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    Quote Originally Posted by Strange View Post
    Rather a large step, unfortunately.
    That's not what Neil Armstrong said.

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    Quote Originally Posted by Glom View Post
    Veritasium did a really good video explaining the architecture of these terrifying abysses.
    Finally managed to watch that. As he points out, because of space-time curvature the "shadow" is actually 2.6 times the Schwarzschild radius.

    Worth watching: https://www.youtube.com/watch?v=zUyH3XhpLTo

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    Quote Originally Posted by Strange View Post
    Rather a large step, unfortunately.
    Centimeter-wavelength interferometry was done routinely between Earth and Radoastron, which had a an apogee behind 300,000 km (a light-second!). Its limitations were (1) there was only one, so the image synthesis was very sparse due to lack of baselenes, and (2) its aperture was "only" 10 meters, although there is apparently existing technology to unfurl dish antenna in the 70-meter class applied to Other Uses.

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    Is this observation anything like an Einstein Ring with the black hole being the object with extremely large mass?

    If it was would the lack of 'light' make any difference in the gravitational lens?

    https://en.wikipedia.org/wiki/Einstein_ring
    In observational astronomy an Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring, is the deformation of the light from a source into a ring through gravitational lensing of the source's light by an object with an extremely large mass.
    Image below from Wikipedia.
    ALMA_image_of_the_gravitationally_lensed_galaxy_SDP.81..jpg

    Image below from EHT.
    20190410-78m-800x466.png
    Last edited by LaurieAG; 2019-Apr-11 at 04:08 AM. Reason: fix Wikipedia image

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    Quote Originally Posted by LaurieAG View Post
    Is this observation anything like an Einstein Ring with the black hole being the object with extremely large mass?
    Not really. In this case all the light is from the accretion disk around the black hole rather than a single object behind it being lensed. The Veritasium video linked above has a good description.

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    Quote Originally Posted by Roger E. Moore View Post
    1. If you are going to do anything original with a black hole, do it with the great-granddaddy of them all, M87.
    Scott Manley has a nice explanation of why they picked M87 rather than our own Sgr A*. It has to do with the variability issues Don Alexander mentions above, angular diameter, and brightness. There is some nice explanations of the technologies involved.
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    All we see of this black hole is the gravitational lensing near it, but that should tell us plenty.

    I tried to calculate the size of a black hole's shadow, and I found this: [1801.00860] Shadows and strong gravitational lensing: a brief review. I did a lot of curve fitting, and I found out that a black hole's shadow stays very close to circular, and within a few percent of its nonrotating size of 3*sqrt(3)*(mass). The main effect is the displacement of that circle toward the outward-going part of the limb, about (2*a) * ( (obs dir) x (ang mom dir) ), where a = (ang mom)/(mass). All multiplied by G/c^2.

    That is why it is so difficult to measure that black hole's spin from its shadow. Lensing effects may be more helpful there, however.

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    Quote Originally Posted by Swift View Post
    Scott Manley has a nice explanation of why they picked M87 rather than our own Sgr A*. It has to do with the variability issues Don Alexander mentions above, angular diameter, and brightness. There is some nice explanations of the technologies involved.
    There have been lists circulating of potential SMBHs for similar detections. The angular sizes of the event horizon (and silhouette) drop very rapidly past M87 and Sgr A*. By some lists the next best candidate would be NGC 1600 with a 17-billion solar mass SMBH, but AFAICT it is pretty inactive and might not have enough surrounding material to give the lensed radio emission. Centaurus A sort of disappoints with only a few x107-solar mass black hole, putting its angular size way down.

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    Quote Originally Posted by ngc3314 View Post
    There have been lists circulating of potential SMBHs for similar detections. The angular sizes of the event horizon (and silhouette) drop very rapidly past M87 and Sgr A*. By some lists the next best candidate would be NGC 1600 with a 17-billion solar mass SMBH, but AFAICT it is pretty inactive and might not have enough surrounding material to give the lensed radio emission. Centaurus A sort of disappoints with only a few x107-solar mass black hole, putting its angular size way down.
    Is this thought to be a case of consumed all mater close by?

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    One of the scientists involved with the work gave a talk today at the Andalusian Institute of Astrophysics in Granada, and mentioned a few interesting points. One of them was that they had four teams using three analysis pipelines all analyzing the data in parallel (and being totally hush-mouthed about any results to the other teams). They then fed their final results blindly into a computer which performed a correlation check and told them all four images are identical at better than 95% confidence!

    And later he added they do have data of Sgr A* which they analyzed in the same manner, and here the results of the four teams were completely uncorrelated. Whoops.

    There's some issue, likely connected with the rapid variability timescales, which is messing things up.

    Ah, another interesting point: The imaging of certain phenomena depends on the length of the baselines involved, i.e., the distance between telescopes. There are some extremely short baselines (within ALMA, or from JCMT to SMA, both on Mauna Kea), and very long baselines (IRAM in Spain to everything else etc.), the latter give the ultra-high resolution. But imaging the base of the jet, which has a dimension smaller than what can be resolved with cm-wavelength VLBI, but significantly larger than the event horizon/ISCO, needs baselines in the 100s of km range, which are just not available right now. Adding the NOEMA arry in the Pyrenees as well as a telescope on Kitt Peak will give them those, though, and allow imaging of the accretion disk/jet transition. So anyone who thinks this image somehow rules out jets... Nope!

    Another fascinating tidbit was that the main technological leap that made this image possible was that they were able to record data (on to hard drives, nothing was correlated via Internet connections!) at a rate of 32 Gbit/s, up from the typical 2 Gbit/s for cm VLBI. They amassed TWO PETABYTES of data to produce those four images... They are now updating the systems to 64 GBit/s!
    Last edited by Don Alexander; 2019-Apr-12 at 06:46 PM.

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    2 PB is not a lot of storage on a per kilogram basis to be fair.

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    List of most massive black holes - Wikipedia -- I used the list there and followed its links to pages on the galaxies and quasars mentioned.

    I found the angular diameter of each BH's shadow, about 3*sqrt(3) ~ 5.2 times its event-horizon radius. It is in microarcseconds.
    Where AD
    Milky Way Sgr A* 56
    Messier 87 45
    Andromeda Galaxy 30
    NGC 1600 29
    NGC 4889 23
    IC 1101 22
    NGC 6166 22
    NGC 3115 21
    NGC 1281 17
    NGC 1270 16
    Sombrero Galaxy 11
    NGC 3842 10

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    I would assume the jets (thus a disk) of M87 and their inclination would make it more appetizing a target even if it is ~ 1/3 (per Antoniseb) smaller in apparent size. [ I used 4 billion sol masses but perhaps 6 or so billion is the better figure, better matching the post of lpetrich above.]

    Does the now measurable circular dark diameter serve as a better distance tool? Or would disk velocities or temp. be also required?

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    Well, as I see it, the BH mass is derived (6.5 +/- 0.7 E9 M_sol) with use of a distance measure from elsewhere. Perhaps a long-term variability study would reveal the true orbital dynamics and allow a measurement deriving a consistent mass-distance measure.

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    The next step they seem to be contemplating is adding an Earth-orbiting telescope to the Event Horizon Telescope system. This could add tens of percent to its resolving power.

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    Quote Originally Posted by Don Alexander View Post
    Well, as I see it, the BH mass is derived (6.5 +/- 0.7 E9 M_sol) with use of a distance measure from elsewhere. Perhaps a long-term variability study would reveal the true orbital dynamics and allow a measurement deriving a consistent mass-distance measure.
    What impressed me is that if an angular measurement can be obtained for the radius, and it’s formula is well known for an actual distance given a determined mass, then it would seem we would have a unique meausuring stick, never one like it in history. Or am I too hasty here?
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    If one has an independent measurement of the black hole's mass, then one does indeed have a new method of measuring cosmic distances. But at this stage, I don't think that it has been checked well enough to use for that purpose.

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    Quote Originally Posted by lpetrich View Post
    If one has an independent measurement of the black hole's mass, then one does indeed have a new method of measuring cosmic distances.
    It might be useful on a few percent of galaxies, but I think it would be the most direct measurement method ever devised, right?

    But at this stage, I don't think that it has been checked well enough to use for that purpose.
    Yep, but I recall Galileo's "superior" telescope discovery of the "ears" of Saturn. But here we must also establish the mass of the SMBH then hope both this mass figure and the diameter can both be accurate enough to be useful. I assume only AGN's are likely candidates, right?
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    Quote Originally Posted by George View Post
    It might be useful on a few percent of galaxies, but I think it would be the most direct measurement method ever devised, right?

    Yep, but I recall Galileo's "superior" telescope discovery of the "ears" of Saturn. But here we must also establish the mass of the SMBH then hope both this mass figure and the diameter can both be accurate enough to be useful. I assume only AGN's are likely candidates, right?
    How do you propose estimating the mass?

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    Quote Originally Posted by George View Post
    It might be useful on a few percent of galaxies, but I think it would be the most direct measurement method ever devised, right?
    The current uncertainty on the mass of the black hole in M87 is something like 15% (as measured by the EHT), while the uncertainty on the distance to the galaxy from other methods is under 5%. So it would probably act as a sanity check on other methods rather than a viable way to measure distance more accurately.

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    FYI:
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    Quote Originally Posted by Hornblower View Post
    How do you propose estimating the mass?
    Keplerian velocities, but to get these would be very difficult, of course. Yet, I'm regularly amazed at what astronomers eventually manage to do.

    phillippeb8's link shows current resolution to be 15 uas (microarcsec) for Sag A at 345 GHz, but improvable to 3 - 5 uas if between 1 to 1.6 THz. With a futuristic Moon baseline, 0.05 uas, or a 300x potential resolution gain seems obtainable. If orbiting stars aren't available, for an AGN, then perhaps a radial velocity gradient could be obtained of the disk, though only imagined at this point. Wouldn't this define the central mass well enough to improve overall distance accuracy? This also assumes a well-defined diameter could be determined for the SMBH.

    I'm intrigued by it because I see a potential yard-stick sitting out there at the center of many galaxies, and there has never been a "convenient" yard-stick available in the past, right?

    P.S. -- Are there metersticks these days, in lieu of yardsticks? I don't recall reading about metersticks.
    Last edited by George; 2019-Apr-16 at 05:58 PM.
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    Quote Originally Posted by George View Post
    Keplerian velocities, but to get these would be very difficult, of course. Yet, I'm regularly amazed at what astronomers eventually manage to do.

    phillippeb8's link shows current resolution to be 15 uas (microarcsec) for Sag A at 345 GHz, but improvable to 3 - 5 uas if between 1 to 1.6 THz. With a futuristic Moon baseline, 0.05 uas, or a 300x potential resolution gain seems obtainable. If orbiting stars aren't available, for an AGN, then perhaps a radial velocity gradient could be obtained of the disk, though only imagined at this point. Wouldn't this define the central mass well enough to improve overall distance accuracy? This also assumes a well-defined diameter could be determined for the SMBH.

    I'm intrigued by it because I see a potential yard-stick sitting out there at the center of many galaxies, and there has never been a "convenient" yard-stick available in the past, right?

    P.S. -- Are there metersticks these days, in lieu of yardsticks? I don't recall reading about metersticks.
    I understand how we can get information on orbital velocities by spectroscopic observations. How do we determine orbital radius without already knowing the distance to the galaxy by some other means?

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    Quote Originally Posted by Hornblower View Post
    I understand how we can get information on orbital velocities by spectroscopic observations. How do we determine orbital radius without already knowing the distance to the galaxy by some other means?
    Good question. Would the observed velocity profile be adequate?
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    Quote Originally Posted by George View Post
    Good question. Would the observed velocity profile be adequate?
    I'm pretty sure the answer is no. The calculations of the mass of Sgr A* using the orbits of stars nearby all appear to use both the orbital motion and the semi-major axis to do the calculation. The key equation is:



    If the period of a star going around black hole A is twice as long as a star going around black hole B (with the same angular separation in both cases), you can't tell whether that means the mass of A must be 4 times smaller, or if instead black hole A is 1.587 times closer than B (meaning that the semi-major axis is also that much larger), or some combination of a difference in mass and distance. I don't think it's possible to distinguish those cases without an independent distance measurement.
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    Quote Originally Posted by Grey View Post
    I'm pretty sure the answer is no. The calculations of the mass of Sgr A* using the orbits of stars nearby all appear to use both the orbital motion and the semi-major axis to do the calculation. The key equation is:



    If the period of a star going around black hole A is twice as long as a star going around black hole B (with the same angular separation in both cases), you can't tell whether that means the mass of A must be 4 times smaller, or if instead black hole A is 1.587 times closer than B (meaning that the semi-major axis is also that much larger), or some combination of a difference in mass and distance. I don't think it's possible to distinguish those cases without an independent distance measurement.

    It’s the gravity gradient at the EV that gives me hope the thought that extreme astronomy might reveal the difference: speghettification for small BHs vs a gentle pass for SMBHs. That gravity gradient difference could be helpful, but nano arcsecond resolution might be a pipe dream, if required.

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    Quote Originally Posted by George View Post
    It’s the gravity gradient at the EV that gives me hope the thought that extreme astronomy might reveal the difference: speghettification for small BHs vs a gentle pass for SMBHs. That gravity gradient difference could be helpful, but nano arcsecond resolution might be a pipe dream, if required.

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    I would guess the granddaddy of all pipe dreams. What sort of infalling object do you envision observing in any detail at distances beyond what we can determine with existing techniques? That is, far more distant than M87

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    Quote Originally Posted by Hornblower View Post
    I would guess the granddaddy of all pipe dreams. What sort of infalling object do you envision observing in any detail at distances beyond what we can determine with existing techniques? That is, far more distant than M87
    It was not about observing infalling objects. I was demonstrating the big difference in gravitational gradients between BH masses, thus a difference might be discernible for the velocity profile comparison. The question is whether or not, even with perhaps nano-arcsec resolution, what is observed for the BH diameter, along with a velocity profile, will improve distance determinations?
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    Quote Originally Posted by George View Post
    It was not about observing infalling objects. I was demonstrating the big difference in gravitational gradients between BH masses, thus a difference might be discernible for the velocity profile comparison. The question is whether or not, even with perhaps nano-arcsec resolution, what is observed for the BH diameter, along with a velocity profile, will improve distance determinations?
    Even taking in the relativistic corrections to the inverse square law, I don't think you can make this work.
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