Could We Turn the Sun Into an Extremely Powerful Telescope? (space.com) 65
It's hypothetically capable of "delivering an exquisite portrait of the detailed surface features of any exoplanet within 100 light-years..." writes Space.com.
"It would be better than any telescope we could possibly build in any possible future for the next few hundred years..." While the sun may not look like a traditional lens or mirror, it has a lot of mass. And in Einstein's theory of general relativity, massive objects bend space-time around them. Any light that grazes the surface of the sun gets deflected and, instead of continuing in a straight line, heads toward a focal point, together with all the other light that grazes the sun at the same time... The "solar gravitational lens" leads to an almost unbelievably high resolution. It's as if we had a telescope mirror the width of the entire sun. An instrument positioned at the correct focal point would be able to harness the gravitational warping of the sun's gravity to allow us to observe the distant universe with a jaw-dropping resolution of 10^-10 arcseconds. That's roughly a million times more powerful than the Event Horizon Telescope.
Of course, there are challenges with using the solar gravitational lens as a natural telescope. The focal point of all this light bending sits 542 times greater than the distance between Earth and the sun. It's 11 times the distance to Pluto, and three times the distance achieved by humanity's most far-flung spacecraft, Voyager 1, which launched in 1977. So not only would we have to send a spacecraft farther than we ever have before, but it would have to have enough fuel to stay there and move around. The images created by the solar gravitational lens would be spread out over tens of kilometers of space, so the spacecraft would have to scan the entire field to build up a complete mosaic image.
Plans to take advantage of the solar lens go back to the 1970s. Most recently, astronomers have proposed developing a fleet of small, lightweight cubesats that would deploy solar sails to accelerate them to 542 AU. Once there, they would slow down and coordinate their maneuvers, building up an image and sending the data back to Earth for processing...
The telescope already exists — we just have to get a camera in the right position.
Thanks to Tablizer (Slashdot reader #95,088) for sharing the article.
"It would be better than any telescope we could possibly build in any possible future for the next few hundred years..." While the sun may not look like a traditional lens or mirror, it has a lot of mass. And in Einstein's theory of general relativity, massive objects bend space-time around them. Any light that grazes the surface of the sun gets deflected and, instead of continuing in a straight line, heads toward a focal point, together with all the other light that grazes the sun at the same time... The "solar gravitational lens" leads to an almost unbelievably high resolution. It's as if we had a telescope mirror the width of the entire sun. An instrument positioned at the correct focal point would be able to harness the gravitational warping of the sun's gravity to allow us to observe the distant universe with a jaw-dropping resolution of 10^-10 arcseconds. That's roughly a million times more powerful than the Event Horizon Telescope.
Of course, there are challenges with using the solar gravitational lens as a natural telescope. The focal point of all this light bending sits 542 times greater than the distance between Earth and the sun. It's 11 times the distance to Pluto, and three times the distance achieved by humanity's most far-flung spacecraft, Voyager 1, which launched in 1977. So not only would we have to send a spacecraft farther than we ever have before, but it would have to have enough fuel to stay there and move around. The images created by the solar gravitational lens would be spread out over tens of kilometers of space, so the spacecraft would have to scan the entire field to build up a complete mosaic image.
Plans to take advantage of the solar lens go back to the 1970s. Most recently, astronomers have proposed developing a fleet of small, lightweight cubesats that would deploy solar sails to accelerate them to 542 AU. Once there, they would slow down and coordinate their maneuvers, building up an image and sending the data back to Earth for processing...
The telescope already exists — we just have to get a camera in the right position.
Thanks to Tablizer (Slashdot reader #95,088) for sharing the article.
Caution! (Score:5, Funny)
Do NOT stare at Sun with remaining eye!
Probably okay to stare at sun ... (Score:3, Insightful)
... if you are that far away.
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Do NOT stare at Sun with remaining eye!
Great advice, though a little late for some people [ksat.com]... I'd recommend you as a future Science Advisor, but your username gives me pause in this case -- as either a caution or being too on-the-nose -- especially given someone else [politico.com] now on the team. :-)
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Explanation for our transatlantic friends: Staring at page 3 makes you blind :)
Well it is a gravitational lense (Score:2)
I mean in theory this can work. Obviously you'd need to block out the light from the sun, but that might be one of the small problems. It's more difficult to align the probe that captures the light that is lensed by the sun.
Re:Well it is a gravitational lense (Score:4, Funny)
I mean in theory this can work. Obviously you'd need to block out the light from the sun, but that might be one of the small problems. It's more difficult to align the probe that captures the light that is lensed by the sun.
Damn, there goes my plans to build a Dyson Sphere!
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The other problem is looking at other places. If your satellites are in one place relative to the Sun then observing anything not behind the Sun is difficult. 542 AU is really hard to maneuver around.
Astronomers want to look at 4pi
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No problem, just build a constellation of receptors forming a sphere around the sun, so they can pick up images from all angles. You know, kind of like Starlink.
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No problem, just build a constellation of receptors forming a sphere around the sun, so they can pick up images from all angles. You know, kind of like Starlink.
Well, with about 10k star systems within 100 light years it would take at least 10k telescopes unless you could start eliminating targets.
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Re:Well it is a gravitational lense (Score:5, Informative)
Normally, when gravitational lensing is talked about, we make these guesses what the matter distribution is in the focusing galaxy or cluster or what have you, and then what’s behind it is easier to unwarp. But we know the matter distribution in our solar system to a high degree of precision allowing for precise unwarping.
Seems like a big issue needs solving (Score:2)
You're talking about very little actual light you want collected, so filtering out ALL of the sun's light is essential. But, even after you block the sun's disk, the solar system is full of dust and rocks that'll be scattering a fair bit of that light towards your receiver in myriad ways.
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Station keeping at that kind of distance doesn't have impossibly high fuel requirements... assuming you can get your imaging device out there in the first place.
But you're not going to want to stay in the plane of the Solar system - by going above or below it you vastly reduce the amount of material between you and what you're trying to image.
Still... aiming precisely enough to catch an exoplanet's surface at that distance? I suspect that's difficult enough to make this idea a non-starter until we find a w
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Well, your caveat is definitely true. But I'm not sure you need to leave the plane of the solar system. At that distance, even the orbit of Pluto would shrink to a pretty small dot...and that orbit's pretty empty.
OTOH, observing more than one VERY small area would be quite time-consuming.
I think my idea of three 5-mile mirrors at the corners of an equilateral triangle in Neptune's orbit would be easier. You'd need REALLY accurate clocks, though to use them as a synthetic aperture. (But we've already out
obvious solution (Score:4, Funny)
Of course, there are challenges with using the solar gravitational lens as a natural telescope. The focal point of all this light bending sits 542 times greater than the distance between Earth and the sun. It's 11 times the distance to Pluto, ...
Place a few smaller suns in between to re-focus the light ...
A few smaller suns (Score:1)
It's been [er, will be] done [doctorwho.tv], albeit for a different purpose.
Pbs spacetime has a video (Score:5, Informative)
How about something smaller? (Score:4, Interesting)
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Jupiter (Score:2)
Why not use Jupiter instead? Smaller and more manageable but maybe you would burn too much fuel maintaining proper orbit.
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If it's a focal "point" (Score:2)
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If you were using glass, yes, it would be a point. But, since it's the Sun and its surface changes, the photons would be slightly deflected from a point.
Also, even in photography where there is a focal point, it's not a point like the tip of a pin. If you go down small enough you'd see the point is quite large. The same here. It's a point in the sense that it's where the most photons would end up, but not a literal point.
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You'll find in even regular photography that if your sensor is a single point you dont get much of an image.
That is, unless you play fancy games with illumination, but that's even harder with this setup.
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Exoplanets aren't point sources, and the sun is not a perfect sphere.
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a spherical lens does not actually focus light
its close to the right shape that focuses in a small approximating area, but not quite right
also true for spherical mirrors as seen in reflector telescopes
I am doubting any meaningful resolving power, as well as any meaningful magnification power, there is only so much you can do with a pinhole regardless of its shape
we dont marvel at telescopes systems of magnification, we marvel at their apertures - how mu
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Translating our pointlike detector across some miles the transverse direction, 50 billion miles from the focusing device (sun), changes the angle that light is received from by an amount equal to the angle subtended by a planet orbiting another star. The probe would literally build a
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The focal point is the point where a point is focused on a point. \
If you want to form an image of something, which consists of many points (both the image and the something), you need to bring each one into focus, which requires moving around.
Diffraction and Poisson noise are a bitch (Score:5, Interesting)
So let's say you had the magic camera hovering out there at 500-something AU.
It'll get flooded with photons from the Sun, which would be considerably closer and considerably brighter than your target 100ly away.
So now you need a sunshade, also magically hovering between your camera and the sun, just the right size to block out the Sun but not the annular region around the Sun where your target signal is coming from.
'cept now, you've got a problem. Because you can't completely block out the Sun. Diffraction means light will bend in around the edges of your sun shade and make a spot roughly (lambda/d)*r in size at your focal surface from the sun. The astute observer will note that for this to work, the r/d term for the occulter is roughly identical to the r/d term for the physical size of the spot made by the telescope defined by the gravitational lens.
Assuming you've made a perfect occulter.
So now you're back to the glare and stray light from a 1 Sun source at 500 AU vs a target at 100 ly. 100 ly/500 AU is about 1e4. Which is how much extra Poisson noise there is from stray light in your image relative to the signal from the target *Sun* nevermind the planet.
Re:Diffraction and Poisson noise are a bitch (Score:5, Informative)
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The minimum distance of 540AU is where parallel rays from infinity are focused to a point for light that just about grazes the Sun's surface, and coronal interference with the visibility of the Einstein ring would be a very real problem. If you move back even farther, rays from larger radii are focused.
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1979 Science paper
https://sci-hub.se/10.2307/174... [sci-hub.se]
2020 paper that I believe descibes a NASA NIAC project to study making such a thing:
https://arxiv.org/abs/2002.118... [arxiv.org]
NASA writeup:
https://www.nasa.gov/general/d... [nasa.gov]
Re: Diffraction and Poisson noise are a bitch (Score:2)
Ah NIAC. Famous for finally cracking faster than light travel and reactionless propulsion. Or throwing money at people promising to give it Serious Study.
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I forgot the paper by that noted crackpot Einstein:
https://sci-hub.se/10.1126/sci... [sci-hub.se]
Jupiter? (Score:1)
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Why not try this out using Jupiter first? The distances would be more manageable
The distances would be much greater.
Jupiter bends light less, so it has a much longer focal length.
You would be better off... (Score:2)
using a neutron star or black hole
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But unless "Moonfall" was a documentary, ...
I'm hard pressed deciding if the "science" was more ridiculous in the movie Moonfall or SyFy TV show The Ark ...
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Actually, I believe a neutron star could be quite close and not be seen if it was old enough. But I'm not sure the universe is old enough for the neutron star to be old enough.
Decelerate (Score:2)
So if it has to stay at the 542-ish distance, they'll need to ensure the spacecraft is sufficiently decelarated. There's two options .. travel there on a fucked up trajectory that will take centuries to get there. Or, get out there fast and decelerate. That would likely require a fucked-ton size rocket.
Re: Decelerate (Score:2)
I guess we now have a sketch of what the astrodynamics version of the "motherfucker" scene from The Wire ( https://m.youtube.com/watch?v=... [youtube.com]) would look like.
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The underlying idea is to make very inexpensive receivers that drift through the line of focus (it is no longer a point) for a few years and then are either abandoned, or become extra-solar probes. Every time we want to image a new planet, we send a new fleet of these micro-sats. So, no deceleration necessary.
Another poster recommended that there is a PBS video on the subject. I highly recommend it.
yeah.... (Score:2)
Hell yeah. Let's do it. (Score:2)
Re: Hell yeah. Let's do it. (Score:2, Interesting)
They're incalculable only because nobody bothers to calculate the value of something pointless.
Unless and until some kind of new physics actually lets you go to any of these places (spoiler alert: probably not happening at all and definitely not happening within your lifetime), knowing how many space gnats can dance on the head of a pin on Epsilon Eridani-b has no consequence, no value, and no purpose.
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You're right, all we need to do is get a few Voyager 1 type projects, one per pixel, and wait 3 times longer. Luckily you are willing to put all your money in the project, since this project is "Better than 99.999% of alternative uses for the money."
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I sort of agree with you, but only because the doing of it would require the development of a sustainable space manufacturing industry that could be turned to other purposes. Like rotating wheels 10 miles in diameter with decent radiation shielding and lots of living space. (Just add an engine and a controlled fusion generator and you've got a mobile space habitat that can [eventually] get anywhere in the galaxy. But don't get in a hurry, because ion-rockets don't have much thrust, and you need to scaven
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No, but it does require a lot of space-based industry, and that's a big step.
Sounds safer than my plan (Score:1)
I was going to turn an extremely powerful telescope into a sun.
A pinhole by any other shape (Score:3)
to re-collimate this light, you can only do so to light that was collimated to begin with, so only light that passes at the same radius of the gravity source can be focused
this infinitely thin ring with radius R=the magic value, is no better than a pinhole, the more finely you want to focus, the thinner the ring it is that you may collect from, tanking your effective aperture size to nothing, a pinhole
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You sound like a SME (subject matter expert) or close on this topic. I am not, I did get into astronomy a bit in the past, and I thought I knew a few things. So I ask - is it possible they are more concerned with the resolving power, as computed by Rayleigh's equation. Or am I wrong?
Wait 100 years for 5 seconds and hope. (Score:2)
At night (Score:1)
It doesn't need to be a single craft. (Score:2)
The premise is that there is a focal point where you place a single craft. One that jumps all over the place to scan an area.
No you don't need to do this. Instead you launch a lot of craft that can deploy a large collection surface. These craft can sit much further in the solar system. In a similar fashion to radio telescopes using arrays of antenna to make a virtual massive receiver you can do the same with visible light and a lot of math. As the lensing closer in and off centre would kinda like
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The math isn't horrendously difficult, it's a straightforward integral. The difficulty is that you need to cover an enormous area with reasonable sampling.