In case anyone was wondering, like me, what the MJy unit in the lower diagram is: It's Mega-Jansky. Just funny that it's then being rescaled by 10^-9. Why didn't they use Milli-Jansky in the first place?
One fun thing think about is that these two galaxies are only aligned from our perspective in the universe. Viewed from a different location, and they're just two normal galaxies.
Also, imagine having the technology to send signals through the lens and get the attention of intelligent life on the other side.
Even assuming a civilization can predict the alignment of the lenses (galaxies), they'd still need quite a powerful signal just to reach the first lens, let alone the second, and then a potential civilization who may be listening at just the right time on the other side. Hard to beat background noise even at distances of a few light years.
It's kind of interesting in terms of analytics... can we predict when lenses will appear and disappear, from our perspective? What might we do with that information once we are more advanced?
1. Yes it would be somewhat predictable to find these lenses for a civilization more advanced than ours.
2. Unless we find faster than light communication (which, with our current understanding of physics is about as likely as humans jumping to the moon) there is nothing we could use it for other than definite proof that other life has evolved in the universe. Interesting data, but they're most likely extinct for billions of years already and even if they're not, the compound gravity lens will have moved out of alignment by then so we have no means to send a message back.
And technically they are only temporarily so, given enough millions of years they will drift apart and lose the alignment.
Also, other stars can come to align in the future. Makes me wonder if we can antecipate other cases like this and create a future schedule of "To Observe" so future generations can look at them. Although, these generations might be so distant from ours that might not even be considered of the same species
> ... This search would have revealed optical laser light from the directions of Alpha Cen B if the laser had a power of at least 1.4–5.4 MW (depending on wavelength) and was positioned within the 1 arcsec field of view (projecting to 1.3 au), for a benchmark 10-m laser launcher
For comparison, with our measly human technology...
> The Vulcan 20-20 laser is so named because it will generate a main laser beam with an energy output of 20 Petawatts (PW) alongside eight high energy beams with an output of up to 20 Kilojoules (KJ). This is a 20-fold increase in power which is expected to make it the most powerful laser in the world.
> The entire message consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW.
> The broadcast was particularly powerful because it used Arecibo's megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo's.
A perfectly parallel source wouldn't fall off with inverse square, but all real sources are not — and cannot be — perfectly parallel.
What you get from lasers is very high gain in the direction it is pointed in, but it's still subject to the inverse square law.
It's capable of being enough gain to be interesting, to be seen from a great distance.
If you engineer it so the gain is enough to outshine the rest of the parent galaxy in the direction it is pointed, then that's effectively good enough because the galaxy is also following inverse-square and you'll continue to outshine the parent galaxy even as you and it both get weaker, but it's still falling off inverse-square.
The energy density drops off as inverse square law, but the photons go forever. Radio is just photons (light) so it goes forever until it interacts with something it hits. The expanding universe will stretch it's wavelength slightly however.
Sure, but the amount of photons as a percentage of the background radiation drops as a function of the distance. It's not all that far away in cosmic distances when any signal from Earth is millions of times less powerful than the noise level.
Yes in a vague sense. And No in a strong practical sense.
Lensing works in reverse except for time delays which make the idea much more complex. The object's past is projected to us now, but our past would be projected to somewhere that the far object no longer occupies. Double lensing makes this even less reversible.
When the light we are now seeing was emitted, the lensing wasn't in place. In fact, the galaxies doing the lensing hadn't even evolved to the state that we see them in.
So if we sent a response to what we see now, it wouldn't make it back to the lensed objects.
That's just for single lensing. Double lenses are a massive coincidence of events at 4 points in time and space (emission, first deflection, second deflection and observation). That means that light going the other way wouldn't have the two intermediate points in the right place at the right times so it all breaks down for us and the object we see. There are some points that would be double lensed in the reverse direction but the locations and times for the source and observer have only very vague correlation to our location and the location of the object we see.
A simpler answer is just what happens if you look thru a telescope or binoculars "the wrong way" (backwards). The correct way shows a "zoomed in" view of that you're viewing, but looking the wrong way shows a "zoomed out" view.
So lifeforms on the other end of this cosmic "lens[es]" cannot use it to see us better, because in fact it makes us look further away from them than we are, from their perspective.
If I understand right, objects further than a redshift of z ~= 1.8 can't be reached by any signal we emit, and the second galaxy is at a redshift of z = 1.885. But I don't know how precisely (standard deviations rather than decimal places) the distance to the outbound cosmological horizon is being approximated, so it might be reachable by a signal sent by us:
The question I addressed is "does the lensing work the same from the other end". It's a very specific and clear question, and the answer is "no it does not", because if you reverse a telescope lens you get the opposite effect (from zoom-in to zoom-out)
The question of at what distance and relative velocity are the two locations so far apart that light can never make it from one to the other (due to expanding universe) is a completely separate issue.
Not really, its premise is using our Sun, not some lens composed of 2 galaxies (that would probably misalign well before our signal would reach them), not sure how you came up with such an idea.
It would be cool if we some day had special days of astronomy where every telescope is turned to galactic eclipses the way they once did for solar eclipses.
The sky is huge and we are moving, so surely some would happen in our lifetimes?
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is.
It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way.
The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years.
So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
No, because the light requires twice the time to travel there then back. If Earth did not move relative to the lens, it would work. Sadly we move, a lot, so what was here 2x ago was something not-earth.
To see earth, the lensing would been to be focused on where Earth was 2x ago. Still possible in theory, and you might even argue just as likely as a fully reflecting curve. But you'd not call it "back towards us". It would need to be "curved to where earth was".
Technically? But the image would be very very very small, so we'd need a detector bigger than the solar system (guesstimate) to see it. That's to see it: I can't imagine what it would take to resolve the image. The tricks in this paper are a start.
> The first lens is relatively close to the source, with a distance estimated at 10.2 billion light-years. What happens is that the quasar’s light is magnified and multiplied by this massive galaxy. Two of the images are deflected in the opposite direction as they reach the second lens, another massive galaxy. The path of the light is a zig-zag between the quasar, the first lens, and then the second one, which is just 2.3 billion light-years away
So, given a simplistic model with no relative motion between earth and the presumed constant location lens:
Earth formation: 4.54b years ago
2.3b * 2 = 4.6b years ago
10.2b * 2 = 20.4b years ago
Does it matter that our models of the solar systems typically omit that the sun is traveling through the universe (with the planets swirling now coplanarly and trailing behind), and would the relative motion of a black hole at the edge of our solar system change the paths between here and a distant reflector over time?
With all the galaxies out there, it seems likely that Earth should be in the focus of lots of systems of this kind. Hopefully in the future we'll be able to find and use these galactic telescopes!
I made this comment before but someone on HN made a good argument is way harder than it sounds and given it's size/cost/function it'd basically have to point in one direction, it's not like an easily moveable telescope you can scan around with.
This is true, but also, keep in mind that the JWST was insanely hard and almost cancelled a few times :)
The SGL would be much, much harder than the JWST would be, and the JWST was already stretching our capabilities.
The SGL needs to be 650AU away from us.
Voyager 1 and 2 are currently 165AU and 120AU away.
The JWST is 0.01 AU from us.
And you can only look in one direction after the probe finally gets into position. Once you're 650AU away, it's not really feasible to move "sideways" far enough to look at something else.
The ratios between 650AU, 165AU, and 0.01AU are somewhat moot.
In 1957 Sputnik 1 had an apogee of ~900km from the Earth.
By 1969 NASA was sending rockets ~385000km to the moon.
By 1979 Voyager 1 & 2 were reaching Jupiter ~5AU from Earth.
We went from 900km to 5AU in 22 years.
If SpaceX achieves their stated goals of lowering $/kg to orbit and rapid re-usability with Starship it will unlock things like asteroid/lunar mining and space based manufacturing which will allow the construction of the kind of infrastructure needed to make distances like 650AU achievable in reasonable time frames.
Low hanging fruit is easier to pluck. It might be that we cannot progress much further without consuming so many resources that Earth is left an uninhabitable husk.
That is precisely why we must transition to space based resource extraction and manufacturing.
There are practically infinite resources at our fingertips on the moon, the asteroid belts and eventually the gas giants.
What we need to unlock this are the means to economically launch a minimum viable self replicating infrastructure into space to take advantage of this.
The feedback loops that will ensue should we succeed will allow us to save Earth ecology, radically transform the human condition, and unlock the ability to explore the universe in ways that we can only imagine.
I'd think to make it practical you'd have to have kind of (semi-) automatic space based assembly infrastructure that builds them and launches them. Launching these probes individually seems like it would be impractical. Building that infrastructure wouldn't be easy at all and I don't see that happening in the next 50 years.
The neat thing about a how an Einstein ring works is that you don't need to stop, because rather than there being a focal point, there is a focal line, moving directly outward from the Sun. This means a probe could spend potentially decades imaging the same target on its outward path, if it had sufficient power.
> This unique configuration offers the opportunity to combine two major lensing cosmological probes: time-delay cosmography and dual source-plane lensing since J1721+8842 features multiple lensed sources forming two distinct Einstein radii of different sizes, one of which being a variable quasar. We expect tight constraints on the Hubble constant and the equation of state of dark energy by combining these two probes on the same system. The z2=1.885 deflector, a quiescent galaxy, is also the highest-redshift strong galaxy-scale lens with a spectroscopic redshift measurement.
Not an expert, just trying to add some more context.
With time-delay cosmography[1] one exploits that unless the source is perfectly in the center of the line of sight, then the photons that make up one lensed copy have traveled a different distance from the source than photons that make up a different lensed copy. This effect can be used to measure absolute distance and give an accurate measure of the Hubble constant.
With dual source-plane lensing[2] one exploits that if two different sources lensed by the same lens, one can take the ratio of the measurements between the two sources and get results that are significantly less affected by the lens itself and is completely independent of the Hubble constant.
Disclaimer: I am a layman, not trained at all. But I am interested in this stuff.
Our most powerful telescopes can see "back in time", by looking at stuff far enough away that it took nearly the entire age of the universe for the light to reach us.
I would guess that we can use this natural compound lens to "see farther" with our current telescopes than we might otherwise be able to see.
Our current best telescope, the JWST, can almost see to the very beginning of when it was possible to see, somewhere between 300k and 200M years after the big bang [0].
Somewhere in this time period, the universe cooled enough for normal matter to form.
The JWST still cannot see the actual 'edge' of when this occurred.
Maybe with this natural compound lens, we can see all the way to the edge.
And if we could see where the edge actually is, then maybe we can refine the estimate to a tighter range than [300k,200M], which would give us a better estimate of the expansion rate of the earlier universe.
Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images.
In case anyone was wondering, like me, what the MJy unit in the lower diagram is: It's Mega-Jansky. Just funny that it's then being rescaled by 10^-9. Why didn't they use Milli-Jansky in the first place?
https://en.wikipedia.org/wiki/Jansky
One fun thing think about is that these two galaxies are only aligned from our perspective in the universe. Viewed from a different location, and they're just two normal galaxies.
Also, imagine having the technology to send signals through the lens and get the attention of intelligent life on the other side.
In order to use them as a signaling platform (how?) the signal would have needed to have been sent several billion years ago.
At 10 billion light years away from the most distant lens it is 100% certain that they are no longer in a gravitational lensing configuration.
For a frame of reference, the Milky Way will be in the middle of its epic merger with Andromeda in about 5 billion years.
Even assuming a civilization can predict the alignment of the lenses (galaxies), they'd still need quite a powerful signal just to reach the first lens, let alone the second, and then a potential civilization who may be listening at just the right time on the other side. Hard to beat background noise even at distances of a few light years.
But if you can do that, you know you have plenty of time for a civilization to develop on the other end to listen.
Might just not be us.
It's kind of interesting in terms of analytics... can we predict when lenses will appear and disappear, from our perspective? What might we do with that information once we are more advanced?
1. Yes it would be somewhat predictable to find these lenses for a civilization more advanced than ours.
2. Unless we find faster than light communication (which, with our current understanding of physics is about as likely as humans jumping to the moon) there is nothing we could use it for other than definite proof that other life has evolved in the universe. Interesting data, but they're most likely extinct for billions of years already and even if they're not, the compound gravity lens will have moved out of alignment by then so we have no means to send a message back.
And technically they are only temporarily so, given enough millions of years they will drift apart and lose the alignment.
Also, other stars can come to align in the future. Makes me wonder if we can antecipate other cases like this and create a future schedule of "To Observe" so future generations can look at them. Although, these generations might be so distant from ours that might not even be considered of the same species
I’m sure there are plenty of civilizations that have done this, but on the time scale of the universe no one happens to look at just the right moment.
But wouldn't the size and age of the universe also imply that someone has looked at just the right moment somewhere somewhen.
Don’t radio waves weaken proportionally to the square of the distance? No one would be able to detect them past a (relatively) small distance.
Omnidirectional source, yes.
However, beamed sources don't fall off that way.
A search for optical laser emission from Alpha Centauri AB - https://academic.oup.com/mnras/article/516/2/2938/6668809
> ... This search would have revealed optical laser light from the directions of Alpha Cen B if the laser had a power of at least 1.4–5.4 MW (depending on wavelength) and was positioned within the 1 arcsec field of view (projecting to 1.3 au), for a benchmark 10-m laser launcher
For comparison, with our measly human technology...
https://www.ukri.org/news/uk-science-facility-receives-85m-f...
> The Vulcan 20-20 laser is so named because it will generate a main laser beam with an energy output of 20 Petawatts (PW) alongside eight high energy beams with an output of up to 20 Kilojoules (KJ). This is a 20-fold increase in power which is expected to make it the most powerful laser in the world.
Or even five decades ago (TODAY!) ... https://en.wikipedia.org/wiki/Arecibo_message
> The entire message consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 450 kW.
https://www.seti.org/seti-institute/project/details/arecibo-...
> The broadcast was particularly powerful because it used Arecibo's megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo's.
A perfectly parallel source wouldn't fall off with inverse square, but all real sources are not — and cannot be — perfectly parallel.
What you get from lasers is very high gain in the direction it is pointed in, but it's still subject to the inverse square law.
It's capable of being enough gain to be interesting, to be seen from a great distance.
If you engineer it so the gain is enough to outshine the rest of the parent galaxy in the direction it is pointed, then that's effectively good enough because the galaxy is also following inverse-square and you'll continue to outshine the parent galaxy even as you and it both get weaker, but it's still falling off inverse-square.
I stand corrected on the inverse square.
I still hold that it would be possible to send and detect signals set with intention with not too much more advanced technology than what we have.
Anywhere in the galaxy within the super narrow beam that the Arecibo antenna happened to cover at the time, at least.
The energy density drops off as inverse square law, but the photons go forever. Radio is just photons (light) so it goes forever until it interacts with something it hits. The expanding universe will stretch it's wavelength slightly however.
Sure, but the amount of photons as a percentage of the background radiation drops as a function of the distance. It's not all that far away in cosmic distances when any signal from Earth is millions of times less powerful than the noise level.
> amount of photons as a percentage of the background
That's what "density" means. (i.e. the amount of something per unit volume)
> noise level
A photon will travel thru space forever without losing energy, unless it hits something. What noise are you talking about?
Is it only one direction or does it work the same from the other side?
Should work the other way too. Physics and symmetry:)
Yes in a vague sense. And No in a strong practical sense.
Lensing works in reverse except for time delays which make the idea much more complex. The object's past is projected to us now, but our past would be projected to somewhere that the far object no longer occupies. Double lensing makes this even less reversible.
When the light we are now seeing was emitted, the lensing wasn't in place. In fact, the galaxies doing the lensing hadn't even evolved to the state that we see them in.
So if we sent a response to what we see now, it wouldn't make it back to the lensed objects.
That's just for single lensing. Double lenses are a massive coincidence of events at 4 points in time and space (emission, first deflection, second deflection and observation). That means that light going the other way wouldn't have the two intermediate points in the right place at the right times so it all breaks down for us and the object we see. There are some points that would be double lensed in the reverse direction but the locations and times for the source and observer have only very vague correlation to our location and the location of the object we see.
A simpler answer is just what happens if you look thru a telescope or binoculars "the wrong way" (backwards). The correct way shows a "zoomed in" view of that you're viewing, but looking the wrong way shows a "zoomed out" view.
So lifeforms on the other end of this cosmic "lens[es]" cannot use it to see us better, because in fact it makes us look further away from them than we are, from their perspective.
If only relativity were so simple :)
If I understand right, objects further than a redshift of z ~= 1.8 can't be reached by any signal we emit, and the second galaxy is at a redshift of z = 1.885. But I don't know how precisely (standard deviations rather than decimal places) the distance to the outbound cosmological horizon is being approximated, so it might be reachable by a signal sent by us:
https://upload.wikimedia.org/wikipedia/commons/8/88/Home_in_...
Not sure what the practical analogy would be. You can't use an exploding telescope?
The question I addressed is "does the lensing work the same from the other end". It's a very specific and clear question, and the answer is "no it does not", because if you reverse a telescope lens you get the opposite effect (from zoom-in to zoom-out)
The question of at what distance and relative velocity are the two locations so far apart that light can never make it from one to the other (due to expanding universe) is a completely separate issue.
> Is it only one direction or does it work the same from the other side?
The relationship is (must be) symmetrical. Were this not so, it would violate a principle called "Maxwell's Daemon" (https://en.wikipedia.org/wiki/Maxwell%27s_demon).
Thats probably not happening at that scale. I know this is the premise of interstellar communication in the three body problem. It's not real.
Not really, its premise is using our Sun, not some lens composed of 2 galaxies (that would probably misalign well before our signal would reach them), not sure how you came up with such an idea.
Using things at that scale to talk? It's not a thing in either case.
This Wikipedia page suggests otherwise - https://en.wikipedia.org/wiki/Gravitational_lens
This is seriously cool. One lens galaxy is amazing, but two! (Too bad that this is not steerable.)
Underlying paper: https://arxiv.org/abs/2411.04177
It would be cool if we some day had special days of astronomy where every telescope is turned to galactic eclipses the way they once did for solar eclipses.
The sky is huge and we are moving, so surely some would happen in our lifetimes?
Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is.
It takes light, the fastest thing that can be, 100,000 years to cross the Milky Way.
The Sagittarius Dwarf Spheroidal Galaxy is currently in the process of being consumed by the Milky Way and is expected to pass through it within the next 100 million years.
So, unless you're even more optimistic about life extension technology than I am, not in our lifetimes, no.
Surely any such eclipse lasts a long time. From the perspective of our lifetimes it is static.
Cool! Was hoping to see a magnification amount like 100x etc
If the lens curved light back toward us, could we see earth several million years ago?
No, because the light requires twice the time to travel there then back. If Earth did not move relative to the lens, it would work. Sadly we move, a lot, so what was here 2x ago was something not-earth.
To see earth, the lensing would been to be focused on where Earth was 2x ago. Still possible in theory, and you might even argue just as likely as a fully reflecting curve. But you'd not call it "back towards us". It would need to be "curved to where earth was".
@Dang is there a version of /best but for comments? The thought experiment in this comment broke my mind.
https://news.ycombinator.com/highlights
Technically? But the image would be very very very small, so we'd need a detector bigger than the solar system (guesstimate) to see it. That's to see it: I can't imagine what it would take to resolve the image. The tricks in this paper are a start.
To zoom into a reflection on a lens or a water droplet?
From "Hear the sounds of Earth's magnetic field from 41,000 years ago" (2024) https://news.ycombinator.com/item?id=42010159 :
> [ Redshift, Doppler effect, ]
> to recall Earth's magnetic field from 41,000 years ago with such a method would presumably require a reflection (41,000/2 = 20,500) light years away
To see Earth in a reflection, though
Age of the Earth: https://en.wikipedia.org/wiki/Age_of_Earth :
> 4.54 × 10^9 years ± 1%
"J1721+8842: The first Einstein zig-zag lens" (2024) https://arxiv.org/abs/2411.04177v1
What is the distance to the centroid of the (possibly vortical ?) lens effect from Earth in light years?
/? J1721+8842 distance from Earth in light years
- https://www.iflscience.com/first-known-double-gravitational-... :
> The first lens is relatively close to the source, with a distance estimated at 10.2 billion light-years. What happens is that the quasar’s light is magnified and multiplied by this massive galaxy. Two of the images are deflected in the opposite direction as they reach the second lens, another massive galaxy. The path of the light is a zig-zag between the quasar, the first lens, and then the second one, which is just 2.3 billion light-years away
So, given a simplistic model with no relative motion between earth and the presumed constant location lens:
Does it matter that our models of the solar systems typically omit that the sun is traveling through the universe (with the planets swirling now coplanarly and trailing behind), and would the relative motion of a black hole at the edge of our solar system change the paths between here and a distant reflector over time?"The helical model - our solar system is a vortex" https://youtube.com/watch?v=0jHsq36_NTU
So they were looking in the neighborhood, basically found light sources that looked like they might be duplicates and they were, therefore lensing.
Can we then find more lensing with even more compounding on purpose instead of accidentally if we sift existing data for such dupes?
With all the galaxies out there, it seems likely that Earth should be in the focus of lots of systems of this kind. Hopefully in the future we'll be able to find and use these galactic telescopes!
Fund the SGL Telescope!
https://www.universetoday.com/149214/if-we-used-the-sun-as-a...
Seriously, we could build that, it's at the limit of our tech but if it was either we walk on the moon again or build SGL, I'd pick SGL
I made this comment before but someone on HN made a good argument is way harder than it sounds and given it's size/cost/function it'd basically have to point in one direction, it's not like an easily moveable telescope you can scan around with.
"way harder than it sounds" is how we move forward
walking on the moon was beyond our limits when it was announced
JWST was insanely hard and almost cancelled a few times, look at it now
This is true, but also, keep in mind that the JWST was insanely hard and almost cancelled a few times :)
The SGL would be much, much harder than the JWST would be, and the JWST was already stretching our capabilities.
The SGL needs to be 650AU away from us. Voyager 1 and 2 are currently 165AU and 120AU away.
The JWST is 0.01 AU from us.
And you can only look in one direction after the probe finally gets into position. Once you're 650AU away, it's not really feasible to move "sideways" far enough to look at something else.
The ratios between 650AU, 165AU, and 0.01AU are somewhat moot.
In 1957 Sputnik 1 had an apogee of ~900km from the Earth.
By 1969 NASA was sending rockets ~385000km to the moon.
By 1979 Voyager 1 & 2 were reaching Jupiter ~5AU from Earth.
We went from 900km to 5AU in 22 years.
If SpaceX achieves their stated goals of lowering $/kg to orbit and rapid re-usability with Starship it will unlock things like asteroid/lunar mining and space based manufacturing which will allow the construction of the kind of infrastructure needed to make distances like 650AU achievable in reasonable time frames.
Low hanging fruit is easier to pluck. It might be that we cannot progress much further without consuming so many resources that Earth is left an uninhabitable husk.
I agree totally.
That is precisely why we must transition to space based resource extraction and manufacturing.
There are practically infinite resources at our fingertips on the moon, the asteroid belts and eventually the gas giants.
What we need to unlock this are the means to economically launch a minimum viable self replicating infrastructure into space to take advantage of this.
The feedback loops that will ensue should we succeed will allow us to save Earth ecology, radically transform the human condition, and unlock the ability to explore the universe in ways that we can only imagine.
True but I'd be more convinced by an argument based on tech and engineering constraints than extrapolating a progress line.
>we move forward
Do you work in something related to Astro?
Yeah, you basically need to launch a new one for every target you want to image.
I'd think to make it practical you'd have to have kind of (semi-) automatic space based assembly infrastructure that builds them and launches them. Launching these probes individually seems like it would be impractical. Building that infrastructure wouldn't be easy at all and I don't see that happening in the next 50 years.
Probably even many, because it‘s energetically impractical to stop at the focal point.
The neat thing about a how an Einstein ring works is that you don't need to stop, because rather than there being a focal point, there is a focal line, moving directly outward from the Sun. This means a probe could spend potentially decades imaging the same target on its outward path, if it had sufficient power.
> the finding will allow other researchers to more precisely calculate the Hubble constant
How would a compound lens lead to a better estimate of the expansion rate of the universe?
From the abstract:
> This unique configuration offers the opportunity to combine two major lensing cosmological probes: time-delay cosmography and dual source-plane lensing since J1721+8842 features multiple lensed sources forming two distinct Einstein radii of different sizes, one of which being a variable quasar. We expect tight constraints on the Hubble constant and the equation of state of dark energy by combining these two probes on the same system. The z2=1.885 deflector, a quiescent galaxy, is also the highest-redshift strong galaxy-scale lens with a spectroscopic redshift measurement.
Not an expert, just trying to add some more context.
With time-delay cosmography[1] one exploits that unless the source is perfectly in the center of the line of sight, then the photons that make up one lensed copy have traveled a different distance from the source than photons that make up a different lensed copy. This effect can be used to measure absolute distance and give an accurate measure of the Hubble constant.
With dual source-plane lensing[2] one exploits that if two different sources lensed by the same lens, one can take the ratio of the measurements between the two sources and get results that are significantly less affected by the lens itself and is completely independent of the Hubble constant.
[1]: https://arxiv.org/abs/2210.10833
[2]: https://arxiv.org/abs/2204.03020
Disclaimer: I am a layman, not trained at all. But I am interested in this stuff.
Our most powerful telescopes can see "back in time", by looking at stuff far enough away that it took nearly the entire age of the universe for the light to reach us.
I would guess that we can use this natural compound lens to "see farther" with our current telescopes than we might otherwise be able to see.
Our current best telescope, the JWST, can almost see to the very beginning of when it was possible to see, somewhere between 300k and 200M years after the big bang [0].
Somewhere in this time period, the universe cooled enough for normal matter to form.
The JWST still cannot see the actual 'edge' of when this occurred.
Maybe with this natural compound lens, we can see all the way to the edge.
And if we could see where the edge actually is, then maybe we can refine the estimate to a tighter range than [300k,200M], which would give us a better estimate of the expansion rate of the earlier universe.
[0] https://www.universetoday.com/168872/webb-observations-shed-...
> ... "in a way where" ...
The elements of Style (https://en.wikipedia.org/wiki/The_Elements_of_Style) : "Make every word count."> ... "acts as a compound lens" ...
Not really -- not the sort of lens we're familiar with, one that concentrates light at a single focus. Technical methods can exploit these chance alignments to detect objects otherwise inaccessible, but not as coherent images.
I often see remarks like this one -- "Acts as a compound lens!" -- but that's not correct. It's more like this: https://arachnoid.com/relativity/graphics/curvature_diagram....
Such alignments are more likely to produce what's called an "Einstein ring" (https://en.wikipedia.org/wiki/Einstein_ring). Very useful, but not remotely a "compound lens".
See Figure 7 in (https://arachnoid.com/relativity/index.html#General_Relativi...) for an interactive gravitational lens simulator.