Was thinking about the picture of the black hole in the, I think, Andromeda galaxy from a little while back. To achieve this, they used several telescopes located all over the globe (along with some whiz bang computing) to essentially make a telephoto lense with an appeture size Earth.
How difficult would it be to do this over the course of a year or two for a lense with an appeture size Solar System. It seems to me that if it can be done on a planetary scale then the same technology should work on a solar system scale.
My main question is if we can resolve a black hole some 15 million light years away with a planet sized lense, what could we see with a solar system sizes lense?
Yes, I know we didn’t actually get a snap shot of the black hole, rather its shadow and disk of stuff orbiting showing very much as predicted(as I understand it)
Well, what I meant was what if they did the same thing over a period of a couple years or so, using ground based telescopes, not deploying telescopes around the solar system.
My understanding was that collecting the images that went into the original took a period of some months, 2 or 3 I believe
That does raise an interesting idea, “drop off” a space based telescope every few months to create a lense that is truly earth year sized
Without checking, that would be something around 180 million mile appeture?
Close. About 185 million. But the light gathering ability would not be correspondingly enhanced. But I see no reason why, in principle, this could not be done.
The black hole imaged was actually messier 87, which is about 55 million light years away. It’s a really big black hole though, so it has about the same apparent size as the Milky Way’s. The galaxy is also on its side in relation to us, so we had a good unobstructed view to the black hole.
The amount of data collected was huge, on the order of petabytes or more, and the information was actually transported in hard drives, as it wouldn’t be practical to try to transmit it over the internet. You’d have to have some pretty good date transmitting technology to make this work.
You wouldn’t really “drop off” telescopes, as they would still be travelling in the same orbit as the Earth. Most likely you’d want to position them in the L4 and L5 points, as those would be the most stable positions. Not exactly the width of the Earth’s orbit, but a significant chunk of it. If you want bigger, you could put them in the Lagrange points of Jupiter, but that puts them further away, complicating data transmission as well as them not maintaining the same orientation compared to Earth over the course of a year.
And this is why the Milky Way’s black hole has not been resolved as well at this time. Too much changes over those couple of months, like taking a long exposure of a moving object.
It’s not about light gathering ability, it is about resolution.
You gather more photons with a larger collecting surface, but you get better resolution based on the width, or distance from one “side” of the telescope to the other. For the purposes of resolution, two telescopes on opposite sides of the globe act as one telescope the size of it.
The light has to reach the telescopes simultaneously (adjusting very slightly for different elevations as necessary). The two measurements can’t be 1/1,000,000th of a second seperated, much less 6 months.
As a somewhat analogy, imagine that you wanted a 3D stereoscopic image of something that isn’t a still-life—say a runner on a track. You would need two cameras with the necessary seperation triggering at the same time to get two shots of the same moment but with some paralax. If you had one camera, took one photo of the runner, then moved it a few inches and took a second photo of the runner a second later, you would still get the necessary paralax, but you would not get something that could be used to make a stereogram.
Also note that this process is much easier for lower frequencies of light: It’s done routinely for radio waves, for instance. Though even there, it’s more data than is practical to transmit over the Internet.
Note that the Event Horizon Telescope is a radio telescope. Or rather, about 10 of them which usually work independently.
Very long baseline interferometry in visible light is very difficult and I don’t think anyone is doing it right now. The twin Keck telescopes in Hawaii were meant to used for interferometry, but I don’t think they ever got that to work.
Aside from all the other limitations I didn’t know about/hadn’t considered, I’d forgotten about how much data went into that black hole image and that they physically transported the drives because that quantity was impractical to transmit.