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Claudio Maccone: A Deep Dive into Gravitational Lensing

Sorry for the server problems the last few days, which resulted in some tinkering under the hood by people far more skilled at such things than I am. Meanwhile, those experiencing deja vu at seeing this post should take heart — there is a simple explanation. Last week I posted an earlier article about Claudio Maccone’s upcoming presentation on gravitational lensing and the FOCAL mission to exploit it, but had to withdraw the post when I realized the live session, a ‘webinar’ organized by Ravi Kumar Kopparapu (NASA GSFC) and Jacob Haqq Misra (Blue Marble Space Institute of Science), might not be available beyond a restricted audience.

Once that was straightened out, the meeting had already occurred, but fortunately Dr. Maccone’s session was recorded and is now available here. I’m going to go ahead and run the rest of that earlier post now, because most people didn’t see it. Even so, and despite the fact that it was only up on the site for a few minutes, that turned out to be long enough for it to propagate, without my realizing it, to several thousand people on the email list, which is why I have to pause to explain all this.

As for Claudio Maccone, the FOCAL mission, and future uses of this resource, a few thoughts. The Sun’s gravitational lens became something of an obsession of mine when I first learned about it in the 1990s. Although the physics of gravitational lensing became apparent in Einstein’s work, and was indeed studied by him, it would take several decades before Sydney Liebes at Stanford worked out the mathematics and showed how a galaxy between us and a more distant quasar could focus the light of the quasar in ways astronomers could observe.

The Stanford connection persisted in the work of Von Eshleman, who as far as I know was the first to delve into whether our own Sun could be used in much the same way. As astronomers explored the concept in the 1980s, Dr. Maccone went on to conceive of a mission that could exploit lensing. The Sun bends the light of an object directly behind it (in terms of the observer) in such ways that potential magnifications are huge. Could we put a spacecraft into range of the gravitational lens (beginning at 550 AU and extending outward), to achieve unprecedented magnification at various wavelengths of another stellar system?

Image: Claudio Maccone, in a photo I snapped at one of the Breakthrough Discuss meetings in Palo Alto.

I hope you’ll watch the presentation, which ranges over all aspects of gravitational lensing that Dr. Maccone has addressed in his papers and books, including not only the implications for astronomy but also the potential for using lensing to boost communications from distant interstellar probes. Anyone interested in deep space astronomy and communications will find this a cutting-edge topic, and as you might expect, one that inspires controversy. The lensing effect is real. The key issue: Can we exploit it with near-term technologies?

The FOCAL mission that Dr. Maccone explores in his book Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer Praxis, 2009) and subsequent papers is a deep dive into the hardware required to find the answer.

You can imagine why an effort like Breakthrough Starshot would find gravitational lensing as interesting as it does. If we could coax huge gain out of this natural lens, we could examine a star system like Alpha Centauri at close range long before sending a spacecraft there. And once deployed, even the tiny craft envisioned by Breakthrough Starshot would have the potential for returning data to Earth via a communications ‘bridge’ enabled by lensing. Other astronomical uses of gravitational lensing are, as you might imagine, numerous (I for one would like to know what a FOCAL mission might achieve in studying the Cosmic Microwave Background).

Tomorrow I want to dig into some of these issues, beginning with memories of a breakfast at Princeton back in 2006 that I shared with Greg and C Matloff, where I first met Dr. Maccone.


Comments on this entry are closed.

  • David Jernigan December 9, 2020, 10:05

    I wonder if the lens could also be used for “aiming” an interstellar probe, by providing a laser line between a focal probe and the target. The craft would simply need to stay in the line to know it’s on course.

    One would have to “lead” the line to where the probe needs to be when it arrives, but that should be achievable.

    The line would have to be switched on months or years before the craft embarks, and the craft would need to be at least 550 AU along its journey in order to use the line for pre-acceleration aiming.

    There is the question of how wide the line would spread, but it seems that huge signal gain implies a tight lensing.

    Finally, since the line would be switched on to point to where the target object isn’t yet, it would need to communicate with *another* FOCAL probe that actually sees the target in question.

    But maybe it’s feasible and useful?

  • swage December 9, 2020, 11:25

    I think that is an extremely interesting idea – also one would assume that such natural “bridges” would be commonly exploited by a multitude of approaches by any species achieving the knowledge and the means 2 do it. It would be a rational thing to do, much more so than using the hydrogen wavelength to broadcast signals. I wonder if such signals could be detected, however as these would be highly focused and directional this would be rather complicated.

    • Mike Serfas December 9, 2020, 21:05

      Indeed, the bridges provide a potential solution to the Fermi paradox, because aliens might set their communications budget supposing that anyone with the wit to understand their signal is capable of using a receiver of size comparable to a star.

  • wdk December 9, 2020, 11:57

    Thanks for bringing this up. As it turns out, this is perfect timing for
    some local activities. Of the existing methods to detect exoplanets – astrometric, doppler, transit and imaging within a spectral band – microlensing is the most complex and “transient” in nature, Yet it also has this magnification potential with deep space platforms.

    Now if we could only get such remote spacecraft to slew their view fields with alacrity…

  • Alex Tolley December 9, 2020, 15:56

    I am most interested in the use of 2 suns for interstellar communication. Unlike the receiver, I would imagine there are issues with a moving probe sending data – is it sent as a torus that must widen as the distance from the sun increases, or is this a minor issue at that distance? If ETIs use this approach for monitoring worlds, how should we search for these distant transmission hubs that must communicate with the lurker and the homeworld/system? What are the theoretical and likely real-world gains? How precise must pointing accuracy and positioning be? Etc, etc.

  • Robin Datta December 9, 2020, 19:28

    For each of the instances when and where the earth is graviationally lensed by some remote object, the mutual effect may offer useful data at wavelengths of particular interest, such as radio communications in proximity of the remote object. Perhaps the equivalent of local WOW signals or more.

  • torque_xtr December 10, 2020, 5:34

    There’s another thing about the gravitational lensing, which fascinates even more. Because of the Sun’s transparency to neutrinos and gravitational waves, the stronger lensing around dense solar core can be used, and this brings focal point to as close as 24 AU – entirely within the range of current spacefaring technology. (https://journals.aps.org/prd/abstract/10.1103/PhysRevD.61.083001)

    While it’s doubtful that neutrino amplification is sufficient for putting a detector on a spacecraft, gravitational waves are entirely different matter. GWs from tight binaries and maybe even relic background waves probably could be measured not only by eLISA-class antenna, but by a much more lightweight one. And since the focus is much closer, a considerable swath of the sky could be observed with a single spacecraft, not only one single arcsecond-wide spot.

    Bonus, the GW-X-raying of the Sun itself, if a suitable point source is found :-)

  • Cyril December 10, 2020, 7:04

    Wouldn’t a radio receiver at the Earth-Sun L3 point have even better resolution than one at the solar gravitational focus, if we put a similar receiver near the Earth and use the two as an interferometric array?

    Even if we started cold on the technology for an L3 mission (very daunting), and FOCAL were mature already, we would probably get results much sooner. My hair grows white just thinking of how long a mission to 550 AU would take.

  • wdk December 10, 2020, 12:16

    On the subject of gravitational lensing or microlensing, due to some correspondence resulting from a recent video conference, I had some
    discussion with a participant that observed what appeared to be a flare up of as follows:

    As my correspondent described it, it was 31 July 2020 2:22 am Pacific Time ( California around Sacramento).

    “The star Nunki …happens to be a twin-star system. What I saw that night at about 2:22AM Pacific Time, wasa momentary flash of light from that system that was probably ten times the brightness of the Planet Jupiter during its closest viewing from Earth.

    “The flash of light began as an initial burst of brilliant light, great enough to cast shadows on the night time ground before me, and the
    flashing brightness fluttered a bit over the course of about five to seven seconds before it returned to its usual brightness…”

    As suggested by my correspondent, I looked for additional information on Nunki and wrote back:
    “Nunki is also listed as Sigma Saggittarii, down the alphabet, but second brightest star in the constellation. But Saggittarius faces inward toward the center of the Milky Way. It is also a B on the main sequence. This has some implications. That it is relatively stable, but 3300 times brighter than the sun…”

    We ruled out nova or supernova because of proximity, left the flare instabilities as an open possibility, but more likely observed in a red dwarf. But then there was the possibility of a nearby event to Nunki between here and the center of the galaxy surround Saggittarius A.

    And that would include the possible gravitational lensing.

    I am not aware of additional witnesses to this particular event, but I see no harm in searching for a show of hands that might have heard of anything related to this. Obviously, it is not repeatable, but I suspect that micro lensing events generally are not blessed with being observed at regular intervals.

    The references to Sigma Sag’s secondary or B did not make clear how closely connected B was to A. But I suspect the answer is probably in the recent Gaia astrometry mission data dump.

    effective surface temperature about 19,000 K or 3 x that of the sun. It’s EUV shall we say. Significant Xray in the spectrum. The intense absolute luminosity is indicative of a short lifespan relative to the sun on the main sequence. Less than a billion years, maybe several hundred million. So, I don’t think it likely there was a planet with life and civilization nearby it. Several arc-minutes away there is another star, though its radial distance from us could be considerably different than 220 lys.

    • wdk December 10, 2020, 16:32

      On that comment about the Sigma Saggittarii sighting and the
      secondary ( B) in its vicinity, in all likelihood the new Gaia survey will have some higher resolution data on that ( 10 micro-arcsecond resolution). In parsecs that gives some information to 326000 light years, reduced to lower distances depending on what you are looking for. But it will be interesting to get a handle or data from the new
      database. If nothing else, just more definitive star guides.