6 ms·

It's actually one of the sharpest images ever made - in terms of angular resolution. The Sag.A* ring is about 51 microarcseconds in diameter. The EHT has a the

by kloch 4y ago

It's actually one of the sharpest images ever made - in terms of angular resolution. The Sag.A* ring is about 51 microarcseconds in diameter. The EHT has a theoretical resolution of ~25 micro arcseconds. For comparison NirCam on Webb has a pixel resolution of 70 miliarcseconds (about 2800 times worse resolution than EHT). The reason it looks blurry is that the black hole features are close to the resolution of EHT so it's only a dozen or so pixels worth of information enlarged to typical image size. EHT is essentially a radio telescope with a dish the size of the Earth. The only way to get higher angular resolution is to use higher frequencies (which they are working on) or use radio telescopes in space to get longer baselines than the diameter of the Earth.

mabbo 4y ago
> The only way to get higher angular resolution is to use higher frequencies (which they are working on) or use radio telescopes in space to get longer baselines than the diameter of the Earth. Would it be possible to use the same trick in space? IE: get a baseline the diameter of Earth's orbit (roughly)?
- kloch 4y ago
  For Interferometry to work the data from different baselines has to be collected at the same time so waiting 6 months does not help. Spacecraft could theoretically be used to extend the baselines but the volume of data to be transferred is prohibitive with current spacecraft comm tech. Even on Earth they resort to shipping cases of hard drives instead of transferring over the Internet. One technique where simply waiting 6 months works very well is in measuring parallax. The Gaia spacecraft takes advantage of this.
  - bell-cot 4y ago
    I wonder what sort of range/throughput you could get with "Heavy" versions of the inter-satellite communications lasers which SpaceX is putting on their Starlink satellites...
  - privong 4y ago
    > Spacecraft could theoretically be used to extend the baselines but the volume of data to be transferred is prohibitive with current spacecraft comm tech. Space-based very long baseline interferometry (VLBI) has been done at lower frequencies, most recently with the RadioAstron satellite[0]. There hasn't yet been a VLBI satellite observing at the same frequencies that the EHT uses, but there are mission concepts being discussed. [1] discusses some of the technical challenges. [0] http://www.asc.rssi.ru/radioastron/ http://www.asc.rssi.ru/radioastron/ [1] https://arxiv.org/abs/2204.09144 https://arxiv.org/abs/2204.09144
  - Valgrim 4y ago
    Why not ship cases of hard drives then? With the plummeting cost of space launches, it seems reasonable to include enough ΔV(1) for a return mission. (1) https://www.smbc-comics.com/comic/delta-v https://www.smbc-comics.com/comic/delta-v edit: We could also send the (super)computer that will process these images in LEO, so we don't even have to worry about atmospheric re-entry.
  - KAMSPioneer 4y ago
    So I work at one of the participating institutes, and you're very much dead-on about transfer speeds/logistics limiting options here. I'm not an astronomer, so grain of salt, but the data is generated at a bit of an unwieldy pace: there are four collector nodes at each site, each of which generates ~16Gbps of raw data (though read speeds from disk after observation is more like 8Gbps). This, as you say, forces most locations to ship physical drives, and also makes centrally planning these observations rather tricky, as there's very little visibility into each station's observations until some time afterwards. But I'm optimistic that some institutions (hopefully including mine!) will be able to transfer these data over the network after the next run of EHT observations. Exciting stuff for sure.
    - kloch 4y ago
      How many seconds of observation data are required for one of these images?
      - KAMSPioneer 4y ago
        For the entire image? I'm not sure, but a lot. Usually an EHT observing session is days in length, and the responsible astronomer(s) will reside at the telescope for a week or so...but I don't believe that 100% of that time is spent feeding data into the collectors. I can ask my coworker tomorrow for clarification on the actual observing time and post an update.
    - whoopdedo 4y ago
      Where can I read more about how that volume of data is generated? I'm looking at the description of ALMA right now. So is each "node" a cluster of antennas? And each antenna is collecting a high-resolution snapshot across a wide frequency band. And each snapshot has to be timestamped. What's the sampling rate? It says the frequency range is 31GHz to 950GHz but how wide can a single snapshot be? Then to move it around are you using InfiniBand or something even faster?
      - adgjlsfhk1 4y ago
        much faster than infiniband. A suitcase full of hard drives.
exhilaration 4y ago
I also want to point out that the mass around Sagittarius A* is rapidly shifting which makes getting a sharp image still harder. From the NYT: Sagittarius A*, the black hole in the Milky Way galaxy, is a harder target. It is less than one-thousandth the mass and size of the M87 hole and, therefore, evolves a thousand times faster. The M87 black hole barely budges during a weeklong observing run, but Sagittarius A* changes its appearance as often as every five minutes. https://www.nytimes.com/2022/05/12/science/black-hole-photo.html https://www.nytimes.com/2022/05/12/science/black-hole-photo....
- bjelkeman-again 4y ago
  M87, according to the original link is 1000x the mass of Sag A, which has a diameter 17x that of our sun. It is mind (and space) bending.
- JohnBooty 4y ago
  Wow, that's incredible. Is that because of all the material the black hole is "devouring?"
  - deleted 4y ago
    [deleted]
- brandmeyer 4y ago
  > all while compiling an unprecedented library of simulated black holes to compare with the observations It also sounds like this is the combination of an image-generating model hypothesis as well as the raw data itself. Ie, this is the image that the model produces which best-fits the sparse interferometry data.
deleted 4y ago
[deleted]
VikingCoder 4y ago
Can someone do the math for me? Let's say I'm 6 feet tall... what object would I have to hold out at arm's length, to have the same angular width as the entirety of this image? A bacteria? A virus?
- Dave_Rosenthal 4y ago
  https://www.wolframalpha.com/input?i=50+microarcseconds+*+%282.5ft+%2F+1+radian%29 https://www.wolframalpha.com/input?i=50+microarcseconds+*+%2... The answer is ~200 picometers. Wolfram lists some helpful comparisons: 1/2 the distance between base pairs in DNA 3x the atomic diameter of helium (the smallest atom) Suffice to say you'd have a hard time seeing it as it would be 3,000x smaller than the wavelength of visible light.
  - VikingCoder 4y ago
    Thank you! That's freaking bonkers.
  - devoutsalsa 4y ago
    Hydrogen isn’t smaller than helium? Or hydrogen isn’t an atom?
    - edgyquant 4y ago
      Helium has the smallest atomic radius
deleted 4y ago
[deleted]

by kloch 4y ago

mabbo 4y ago

> The only way to get higher angular resolution is to use higher frequencies (which they are working on) or use radio telescopes in space to get longer baselines than the diameter of the Earth. Would it be possible to use the same trick in space? IE: get a baseline the diameter of Earth's orbit (roughly)?

kloch 4y ago
For Interferometry to work the data from different baselines has to be collected at the same time so waiting 6 months does not help. Spacecraft could theoretically be used to extend the baselines but the volume of data to be transferred is prohibitive with current spacecraft comm tech. Even on Earth they resort to shipping cases of hard drives instead of transferring over the Internet. One technique where simply waiting 6 months works very well is in measuring parallax. The Gaia spacecraft takes advantage of this.
- bell-cot 4y ago
  I wonder what sort of range/throughput you could get with "Heavy" versions of the inter-satellite communications lasers which SpaceX is putting on their Starlink satellites...
- privong 4y ago
  > Spacecraft could theoretically be used to extend the baselines but the volume of data to be transferred is prohibitive with current spacecraft comm tech. Space-based very long baseline interferometry (VLBI) has been done at lower frequencies, most recently with the RadioAstron satellite[0]. There hasn't yet been a VLBI satellite observing at the same frequencies that the EHT uses, but there are mission concepts being discussed. [1] discusses some of the technical challenges. [0] http://www.asc.rssi.ru/radioastron/ http://www.asc.rssi.ru/radioastron/ [1] https://arxiv.org/abs/2204.09144 https://arxiv.org/abs/2204.09144
- Valgrim 4y ago
  Why not ship cases of hard drives then? With the plummeting cost of space launches, it seems reasonable to include enough ΔV(1) for a return mission. (1) https://www.smbc-comics.com/comic/delta-v https://www.smbc-comics.com/comic/delta-v edit: We could also send the (super)computer that will process these images in LEO, so we don't even have to worry about atmospheric re-entry.
- KAMSPioneer 4y ago
  So I work at one of the participating institutes, and you're very much dead-on about transfer speeds/logistics limiting options here. I'm not an astronomer, so grain of salt, but the data is generated at a bit of an unwieldy pace: there are four collector nodes at each site, each of which generates ~16Gbps of raw data (though read speeds from disk after observation is more like 8Gbps). This, as you say, forces most locations to ship physical drives, and also makes centrally planning these observations rather tricky, as there's very little visibility into each station's observations until some time afterwards. But I'm optimistic that some institutions (hopefully including mine!) will be able to transfer these data over the network after the next run of EHT observations. Exciting stuff for sure.
  - kloch 4y ago
    How many seconds of observation data are required for one of these images?
    - KAMSPioneer 4y ago
      For the entire image? I'm not sure, but a lot. Usually an EHT observing session is days in length, and the responsible astronomer(s) will reside at the telescope for a week or so...but I don't believe that 100% of that time is spent feeding data into the collectors. I can ask my coworker tomorrow for clarification on the actual observing time and post an update.
  - whoopdedo 4y ago
    Where can I read more about how that volume of data is generated? I'm looking at the description of ALMA right now. So is each "node" a cluster of antennas? And each antenna is collecting a high-resolution snapshot across a wide frequency band. And each snapshot has to be timestamped. What's the sampling rate? It says the frequency range is 31GHz to 950GHz but how wide can a single snapshot be? Then to move it around are you using InfiniBand or something even faster?
    - adgjlsfhk1 4y ago
      much faster than infiniband. A suitcase full of hard drives.

exhilaration 4y ago

I also want to point out that the mass around Sagittarius A* is rapidly shifting which makes getting a sharp image still harder. From the NYT: Sagittarius A*, the black hole in the Milky Way galaxy, is a harder target. It is less than one-thousandth the mass and size of the M87 hole and, therefore, evolves a thousand times faster. The M87 black hole barely budges during a weeklong observing run, but Sagittarius A* changes its appearance as often as every five minutes. https://www.nytimes.com/2022/05/12/science/black-hole-photo.html https://www.nytimes.com/2022/05/12/science/black-hole-photo....

bjelkeman-again 4y ago
M87, according to the original link is 1000x the mass of Sag A, which has a diameter 17x that of our sun. It is mind (and space) bending.
JohnBooty 4y ago
Wow, that's incredible. Is that because of all the material the black hole is "devouring?"
- deleted 4y ago
  [deleted]
brandmeyer 4y ago
> all while compiling an unprecedented library of simulated black holes to compare with the observations It also sounds like this is the combination of an image-generating model hypothesis as well as the raw data itself. Ie, this is the image that the model produces which best-fits the sparse interferometry data.

deleted 4y ago

[deleted]

VikingCoder 4y ago

Can someone do the math for me? Let's say I'm 6 feet tall... what object would I have to hold out at arm's length, to have the same angular width as the entirety of this image? A bacteria? A virus?

Dave_Rosenthal 4y ago
https://www.wolframalpha.com/input?i=50+microarcseconds+*+%282.5ft+%2F+1+radian%29 https://www.wolframalpha.com/input?i=50+microarcseconds+*+%2... The answer is ~200 picometers. Wolfram lists some helpful comparisons: 1/2 the distance between base pairs in DNA 3x the atomic diameter of helium (the smallest atom) Suffice to say you'd have a hard time seeing it as it would be 3,000x smaller than the wavelength of visible light.
- VikingCoder 4y ago
  Thank you! That's freaking bonkers.
- devoutsalsa 4y ago
  Hydrogen isn’t smaller than helium? Or hydrogen isn’t an atom?
  - edgyquant 4y ago
    Helium has the smallest atomic radius

deleted 4y ago

[deleted]