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Gravitational Lensing: Untangling an Image

The behavior of distant galaxies may tell us much about our own Milky Way’s evolution, as well as alerting us to the differing outcomes possible as galaxies mature. This morning we look at a galaxy labeled eMACSJ1341-QG-1, one that puts on display the phenomenon of gravitational lensing. We may one day use the distortion of spacetime caused by massive objects much closer to home to study nearby stars and their planets, assuming we can learn to exploit the natural gravitational lensing effect that occurs at 550 AU from the Sun.

But back to the galactic perspective. Lined up with a massive galaxy cluster called eMACSJ1341.9-2441, the light from the much more distant galaxy is magnified by 30 times as the gravity of the intervening cluster — its presumed dark matter, gas and thousands of individual galaxies — distorts spacetime. Gravitational lensing was confirmed during a solar eclipse in 1919, when background stars were found to be offset in precisely the way Albert Einstein had predicted. Astronomers now rely on such lensing to produce information about objects that would otherwise be all but invisible.

Image: The quiescent galaxy eMACSJ1341-QG-1 as seen by the Hubble Space Telescope. The yellow dotted line traces the boundaries of the galaxy’s gravitationally lensed image. The inset on the upper left shows what eMACSJ1341-QG-1 would look like if we observed it directly, without the cluster lens. The dramatic amplification and distortion caused by the intervening, massive galaxy cluster (of which only a few galaxies are seen in this zoomed-in view) is apparent. Credit: Harald Ebeling, UH IfA.

Discovery of the quiescent galaxy, identified as a gravitationally lensed triple image, was confirmed by the ESO/X-Shooter spectrograph, mounted at the European Southern Observatory’s Very Large Telescope site at Cerro Paranal in Chile. Harald Ebeling (University of Hawaii, Honolulu), lead author of the paper on this work, describes the effort, which has now produced a new record for magnification of this type of galaxy:

“We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing. This discovery stands out though, as the huge magnification provided by eMACSJ1341 allows us to study in detail a very rare type of galaxy.”

Quiescent galaxies — those in which star formation has all but ceased — represent the endpoint of galaxy evolution, which makes this one somewhat unusual. Objects at this redshift should be young enough not to have used up their gas supply. Hence learning why eMACSJ1341-QG-1 has stopped forming stars is a significant quest.

Working with data from the Hubble Space Telescope, Ebeling and colleagues now continue the study through HST imaging as well as ground-based instruments, and further analysis of the lens model that allows them to remove distortion from the magnified image. From the paper;

Although ground-based spectroscopy with facilities in Chile and on Maunakea will allow the characterization of the stellar populations of eMACSJ1341-QG-1, an analysis of its spatial profile and any radial dependencies of its properties relies on the availability of resolved colors and a robust lens model that allows the reconstruction of the galaxy in the source plane. HST imaging in multiple filters will be critically important to achieve either of these goals.

There is much to learn:

While it is widely accepted that already at z∼1.5 a majority of the most massive galaxies had evolved stellar populations and form few stars, the observational evidence behind this picture is not conclusive, in particular regarding the puzzlingly compact size of some of these galaxies, the quenching mechanism, and the impact of dust on the apparent prominence of the old stellar population.

Centauri Dreams’ take: Fascinating in its own right, gravitational lensing studies like these remind us that when we do become capable of sending spacecraft to 550 AU and beyond to explore the uses of the Sun’s lens to study possible mission targets, we’re faced with huge questions of how to remove the massive distortion of the image, untangling it to produce workable information. The rapidly advancing field of deep-sky gravitational lensing should produce numerous insights into how we approach lensed images from future space missions.

Let me also note this: Gravitational focus lensing in the context of space missions was discussed by Geoff Landis (NASA GRC) as well as Slava Turyshev (JPL) at the most recent Tennessee Valley Interstellar Workshop. You can see the video of both presentations here.

The paper is Ebeling et al., “Thirty-fold: Extreme Gravitational Lensing of a Quiescent Galaxy at z = 1.6,” Astrophysical Journal Letters Vol. 852, No. 1 (abstract / preprint).

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{ 31 comments… add one }
  • John walker February 2, 2018, 15:49

    For Landis and Turyshevs 2017 presentations go to TVIW youtube channel. They are videos 20. and 21.

    • Paul Gilster February 2, 2018, 17:14

      Thanks, John. Somehow I missed #20, but I’ve changed the text above to reflect the fact that both presentations are now available.

  • jonW February 2, 2018, 17:34

    And holy camoley it was announced today that gravitational lensing (in this case, microlensing) had allowed researchers to find planets in a galaxy 3 billion light years away–is this legit?! https://www.eurekalert.org/pub_releases/2018-02/uoo-oad020218.php

  • DJ Kaplan February 2, 2018, 19:15

    “Mission targets” seems so blissfully optimistic. If a body is so far away that it requires GL to image it usefully, then it’s a “mission target” for a following century, sorry to say.

    • Paul Gilster February 2, 2018, 21:56

      You’ve missed my point, DJ. The mission targets I’m talking about would be planets around a nearby system like Proxima or Centauri A/B. The point being that Breakthrough Starshot is investigating how to use the Sun’s gravitational focus to study such mission targets close up before sending a mission. They’re also looking into the communications possibilities at 550 AU and further out, where lensing takes effect. I brought up all that because the overall topic of gravitational lensing can be useful in helping us work out how to study wildly distorted lensed images. We can use lensing for things much, much closer than distant galaxies.

      • Michael Fidler February 6, 2018, 19:19

        What about nearby red dwarfs being used for gravitational focusing?
        Take Barnard’s star for example, it has a low mass so very long focal length gravitational lensing, could it reach 6 light years in length? Many of these nearby red dwarfs are in the densely packed star fields of the Milky Way, it would be interesting to see if some of them may magnify background stars and the exoplanets around them, and maybe free floating exoplanets.

  • Michael Fidler February 2, 2018, 20:37

    Worlds Without End?

    Probing Planets in Extragalactic Galaxies Using Quasar Microlensing.

    Xinyu Dai, Eduardo Guerras (University of Oklahoma)
    (Submitted on 31 Jan 2018)
    Previously, planets have been detected only in the Milky Way galaxy. Here, we show that quasar microlensing provides a means to probe extragalactic planets in the lens galaxy, by studying the microlensing properties of emission close to the event horizon of the supermassive black hole of the background quasar, using the current generation telescopes. We show that a population of unbound planets between stars with masses ranging from Moon to Jupiter masses is needed to explain the frequent Fek line energy shifts observed in the gravitationally lensed quasar RXJ1131-1231 at a lens redshift of z=0.295 or 3.8 billion light-years away. We constrain the planet mass fraction to be larger than 0.0001 of the halo mass, which is equivalent to 2,000 objects ranging from Moon to Jupiter mass per main sequence star.

    “This planet to star mass ratio is equivalent to >∼ 2000 objects per main sequence star in the mass range between Moon and Jupiter, or >∼ 200 objects in Mars to Jupiter range including 0.08 jupiters!”

    https://arxiv.org/abs/1802.00049

    • Michael Fidler February 2, 2018, 23:07

      Astrophysicists discover planets in extragalactic galaxies using microlensing.

      https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2018/ouastrophysi.jpg

      The gravitational lens RX J1131-1231 galaxy with the lens galaxy at the center and four lensed background quasars. It is estimated that there are trillions of planets in the center elliptical galaxy in this image. Credit: University of Oklahoma

      Read more at: https://phys.org/news/2018-02-astrophysicists-planets-extragalactic-galaxies-microlensing.html

    • Harry R Ray February 5, 2018, 10:38

      Does this mean that the VAST MAJORITY of free-floating “planets” in this galaxy(>~1800) are LESS MASSIVE THAN MARS? The good news about this claim is that it CONFIRMS a recent study’s claim about the PAUCITY of free-floating Jupiter mass objects in the Milky Way. The bad news is that it fact the we have NOT detected EVEN ONE free-floating object in our galaxy with a mass signifigantly LESS than Saturn’s! Unless this is due to the insensitivity of our microlensing surveys to detect such objects, I would take this new claim with a SERIOUS grain of salt.

  • Ljk February 2, 2018, 21:11

    Planets have been discovered in other galaxies through microlensing:

    https://www.eurekalert.org/pub_releases/2018-02/uoo-oad020218.php

  • J. Jason Wentworth February 3, 2018, 6:42

    A question: How wide is the gravitational lensing “point” at 550 AU from the Sun? I’m guessing that it has some significant breadth, 550 AU +/- some fractional or greater number of Astronomical Units, with the “focusing” getting gradually worse as one moves away from the ideal focusing point, and:

    If so, it would seem that placing multiple observing spacecraft in a circular solar orbit, 550 AU out, would enable long-time exposure pictures–using CCD cameras (or even scanned-film “automated darkroom” Luna 3/Lunar Orbiter-type camera systems (although film ‘n scanner systems probably be impractical that far out there)–to be taken of other stars and their planets, with the highest possible image sharpness. The slow orbital motion of such spacecraft at that distance would enable long exposures without blurring, and having multiple vehicles would allow objects in all directions along the orbit to be observed in short order. For imaging objects far off the ecliptic, different solar orbit inclinations–even a polar one–could be utilized at the same 550 AU distance. Also:

    Since spacecraft on opposite sides of the orbit would be 1,100 AU apart, they could determine the distances of stars via their trigonometric parallax with a higher degree of accuracy than can be achieved from opposite sides of the Earth’s orbit. This would also enable the distances of stars more than 100 light-years away (about the limit for this method, from Earth) to be measured via their trigonometric parallax. To reach these orbits, the laser-powered ion drive (see: https://www.centauri-dreams.org/?p=38702 ) or NEP (Nuclear Electric Propulsion, a reactor-powered [or perhaps RTG-powered] ion drive), in conjunction with Jupiter gravity assist, should suffice.

  • Michael February 3, 2018, 7:22

    The beauty of the gravilensing effect is that we don’t have to get to the start of the effect ~550 AU to get an image. If we have a halo of craft with a central communication probe following the surface of the convergence we could get information back sooner, just not as much light is gathered.

    • J. Jason Wentworth February 3, 2018, 13:12

      Thank you, Michael–this sounds like an even more convenient phenomenon (that’s easier to make use of) than I had thought! That’s good, because we could put observatory spacecraft in numerous, differently-inclined solar orbits that could be spaced such that collisions between them (which would already be very unlikely) would be impossible. Except for very faint objects, the lower light-gathering abilities of “off-ideal” distances wouldn’t be a problem (and even very dim objects could be imaged using longer time exposures).

      • Michael February 5, 2018, 3:13

        Maybe we could have the halo of craft to get spectroscopic information to define the planet’s orbit and general composition to greater accuracy and then use the central craft as it goes onto the solar focus line for a more accurate image.

  • J. Jason Wentworth February 3, 2018, 8:16

    Well, polish my alicorn and cloven hooves! While even “just” detecting planets in other galaxies is astounding in and of itself, the detection range (3.8 BILLION light-years [‘Sagan number territory’ to be sure]) *and* planet sizes (from our Moon to Jupiter) that they have managed to detect would have been considered flatly impossible just a few years ago, and this has implications for SETI–in “both directions”:

    From our point of view, it suggests that optical (laser, including X-ray laser [the Chandra X-ray observatory made those detections]) and perhaps also radio SETI could have an enormously-expanded list of potential targets (and, just maybe, eventually we’ll be able to detect “passive” life signatures–such as those of forests or similar biota–on extra-galactic planets). While engaging in dialogues with civilizations in other galaxies would be out of the question (although for biological rather than technological reasons), their optical and/or radio signals would finally answer the question “Are we alone?”, and even such a one-way cultural contact would teach us much. It’s even possible that some race in another galaxy (or in ours) that’s aware of gravitational lensing might periodically broadcast their version of the “Encyclopedia Galactica,” or at least an Arecibo Message-like declaration that “We’re here,” and:

    From others’ vantage points (including anyone else in the Milky Way [who might be utilizing their local sun(s)’ gravitational lensing capabilities], especially if they could detect “passive” life signatures), they could have been aware that there has long been life on Earth (even among young technological races in other galaxies). While distant intra-galactic or (especially) extra-galactic observers wouldn’t see or hear signs of technological life here (unless they’re quite close in interstellar terms) due to the light-time delay, if life–or even “just” multi-cellular life–is rare in the universe, the Earth might well be on a relatively short list of gravitational lensing “regular observation” targets. Now:

    If so, that would put the issue of possible interstellar (not intergalactic, unless something like wormhole transit or Alcubierre’s warp drive is feasible) visitors in the distant geological past, prehistoric epochs, or ancient times in a different light, for our Earth wouldn’t have been just happened upon–like a needle in a whole field of haystacks!–by interstellar explorers, but would instead be the selected target of planned and possibly periodic explorations. In this case, even the possibility of recent or future visitations in our time, while it’s unlikely, couldn’t be ruled out. The breathtakingly rapid improvements in our own abilities to see–and in detail–farther and farther into even the distant universe, as the article demonstrates, suggests (as does our approaching ability to send probes to other stars) that even moderately more advanced civilizations, just a century or two ahead of us, could have remote detection and direct examination (by space probes, including very small ones) capabilities that, to us, would be like something out of a J.R.R. Tolkien or Peter Beagle novel.

  • Tom Mazanec February 3, 2018, 9:51

    Maybe the reason extragalactic lensed views are so wonky is because the lensing galaxy is not spherically symmetrical, like the sun almost is?

    • Alex Tolley February 3, 2018, 13:24

      By assuming the shape of the target, you could infer the gravitational shape of the lensing object[s].

    • J. Jason Wentworth February 3, 2018, 13:28

      I can’t prove that, Tom, but it makes intuitive sense, and I had suspected that, too (that non-spherical gravity lensing objects would produce an image distortion effect analogous to astigmatism). Even oblate, rapidly-spinning massive stars (like Sirius and Pleione) might produce this effect–at least to an extent–when viewing objects behind/beyond them, if an oblate star’s “oval” cross-section is presented along our line of sight (if our line of sight is perpendicular–or nearly so–to the star’s rotational axis, that is). Also:

      I wonder if extremely fast rotation of extremely dense objects (such as white dwarfs, pulsars, or even black holes), which causes “space-time frame-dragging,” might also distort gravitationally-lensed images of more distant objects, even if the gravitational lensing objects are spherical, or nearly so?

  • Harold Shaw February 3, 2018, 19:08

    I imagine Breakthrough Starshot is looking at placing radio telescopes and not optical telescopes at our Sun’s focal.

    Gravitational lensing certainly has implications for SETI. Because gravitational lensing reduces the power required for communication between star systems, communication may not create detectable leakage. As well, the reduced power requirements would make it more affordable to use multiple channels, making it harder to detect signal since broadband communication would look natural. Hard to imagine an interstellar civilization not taking advantage of gravitational lensing.

  • Harold Shaw February 3, 2018, 19:32

    Gravitational lensing could also offer an alternative to exploring with Von Neumann probes. Find a quiescent black hole surrounded by material, convert that material into telescopes, identify promising targets and send probes directly to those targets.

  • J. Jason Wentworth February 4, 2018, 7:35

    It’s interesting that you’ve mentioned these things, Harold. The same thoughts (including regarding black holes) occurred to me last night:

    Maybe we don’t hear anyone else, and haven’t had visitors, because they can–rather like H.G. Wells’ Martians or Jonathan Swift’s Laputan astronomers–examine their spatial surroundings closely, and communicate with their peers using little power. Why go to the expense, complexity, and danger of traveling between stars (even *non-replicating* interstellar probes entail a small risk of hostile reactions [Von Neumann probes could become like rats or pathogens], if fast ones accidentally struck other stars’ planets, or even space colonies, stations, or spaceships) if one can “see the neighbors up close” and even easily talk with them without leaving the comforts of home? Also:

    Von Neumann probes may be harder to make work than we think (even a device that, if emplaced on the Moon’s surface, would separate out metals and start making nuts and bolts all by itself is beyond our capability, and a self-replicating probe would be far more complicated), so I don’t worry about an alien one arriving and turning us and our world–or even just a small asteroid or two–into more of its kind, but:

    I still favor probes because just looking from afar is never enough (our drive to explore space is emotional as well as rational, and I whole-heartedly embrace both aspects of it–and one day, personal visits will be possible). Plus, many kinds of analysis require physical contact, or at least close proximity (to scan celestial bodies with radar or lidar, to give just two examples). In addition:

    Bracewell interstellar messenger probes–which could also conduct “regular” investigations, and carry artifacts–would enable quick question-and-answer dialogues to exchange cultural and scientific information, and to learn each other’s languages (all of which would greatly benefit later, direct planet-to-planet communications). This rapid feedback would speed mutual understanding, *without* the long light-time delays that would otherwise result in decades or centuries between basic questions (such as those regarding what their–and our–languages are saying) and answers.

    • Brett Bellmore February 4, 2018, 16:33

      I’m a bit more optimistic about Von Neumann probes. I’m a tooling engineer, and I’ve been watching automation come closer and closer to “closing the circle”, driven by business’ desire for greater efficiency and lower labor costs.

      It’s true nobody has built a device to extract iron from lunar soil and make bolts out of it. But, who’s had an economic incentive to? Nobody, yet.

      I think we’re close to having all of the pieces, and once somebody has a reason to put them together, self-reproducing machinery will appear faster than anybody expects.

    • Harold Shaw February 4, 2018, 19:37

      In the manner that it replicates, a self replicating probe wouldn’t have to be any more complex than a biological organism. Granted that is still complex but not out of reach, humanity is already experimenting with synthetic biology. A probe could arrive in a system as a small seed that plants itself, grows into a fully formed ‘life form’ that eventually creates other seeds. For a civilization that develops strong AI, robotics, and a version of transhumanism the resulting entities would mechanically be Van Neumann machines. It isn’t unimaginable that, given a few thousand years of development, individual transhumans could claim or settle entire star systems.

      Employing a local agent does make sense, though it does raise some interesting questions. If an immensely intelligent and industrially capable entity arrived in the solar system 10 million years ago, just who’s star system is this? If a dumb probe is found that is unable or unwilling to share information, do we take it apart?

      • Alex Tolley February 5, 2018, 16:46

        Self-replication in biology uses a lot of self-organization. While feasible with some machine components, most machine parts and processes are not. I am optimistic that we can get there eventually, but the technologies involved will be very different than are recognizable today.
        However, it is entirely possible that self-replication uses technologies we understand today, but encompasses a machine civilization to achieve, rather than a seed. While far less energy efficient, time is not a constraint, and so world ships slowly traveling and replicating at target stars is another approach that should work without any unknown or magical tech.

  • Andrew Wright February 4, 2018, 12:55

    I would think that correcting a lens image magnified by our own Sun would be fairly straightforward, since we know its shape very well.

    Is it a given that placing a probe at the focus point is the way to go? To get there in a reasonable time, it will have to travel very fast, and so it will be expensive in fuel to slow it down. Perhaps it is better to use multiple smaller probes that take data as they fly through the focus? Although I say ‘the’ focus, actually there will be a separate focus for every target, won’t there? A probe in an orbit that far out will move very slowly and isn’t likely to scan across very many interesting targets in a reasonable time. Better to send multiple probes to pass through the focal points relating to specific targets, and don’t bother slowing them down.

    • Paul Gilster February 4, 2018, 13:33

      Andrew, check Geoff Landis’ TVIW presentation (link in the article) for reasons why the image can be so difficult to sort out.

      • Patient Observer February 4, 2018, 23:40

        That was a sobering presentation. The physics/math was beyond me but he did, at one point in the presentation, seem to suggest an 80 meter telescope around here could achieve the same light gathering capability and resolving power as a 1 meter telescope at the solar gravitational lens when using, say, a 1 meter telescope. The 80 meter telescope would also do a much better job in imaging (I think).

        Perhaps that 80 meter telescope needs to be in space but it may be a tossup which approach is more challenging. For example, one could imagine a 100 meter liquid mirror telescope on the far side of the moon. The engineering difficulties and cost would be astronomical but it could be far more productively than the gravitational lens mission.

        • Michael February 6, 2018, 2:10

          I believe it was around 80 km’s for the diameter of the scope.

    • Michael February 4, 2018, 17:05

      If we had radioactive decay products coating small MEM actuators we could use them to slow down and maneuver a very light craft like Starshot.

  • Michael February 11, 2018, 2:00

    Perhaps a reverse Axicon lens could be used to correct the image.

    https://www.edmundoptics.com/resources/application-notes/optics/an-in-depth-look-at-axicons/

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