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Pulsar Navigation: Exploring an ETI Hypothesis

Pulsar navigation may be our solution to getting around not just the Solar System but the regions beyond it. For millisecond pulsars, a subset of the pulsar population, seem to offer positioning, navigation, and timing data, enabling autonomous navigation for any spacecraft that can properly receive and interpret their signals. The news that NASA’s SEXTANT experiment has proven successful gives weight to the idea. Station Explorer for X-ray Timing and Navigation Technology is all about developing X-ray navigation for future interplanetary travel.

At work here is NICER — Neutron-star Interior Composition Explorer — which has been deployed on the International Space Station since June as an external payload. NICER deploys 52 X-ray telescopes and silicon-drift detectors in the detection of the pulsing neutron stars called pulsars. Radiation from their magnetic fields sweeps the sky in ways that can be useful. A recent demonstration used four millisecond pulsar targets — J0218+4232, B1821-24, J0030+0451, and J0437-4715 — to track NICER within a 10-mile radius as it orbited the Earth.

X-ray Pulsar Navigation (XNAV) has become an active area of research, pursued not just at NASA but by Chinese satellite testing and by conceptual studies at the European Space Agency. Having barely left our own planet, we are far ahead of ourselves to talk about a galactic positioning system for future spacecraft, but there is reason to believe that the principles of pulsar navigation can be extended to make accurate deep space navigation a reality.

Pulsars as Navigational Matrix

The SEXTANT experiment dovetails with a new paper from Clément Vidal (Universiteit Brussel, Belgium), whose work falls into the broader context of recent studies of unusual astrophysical phenomena. The author of the ambitious The Beginning and the End (Springer, 2014), Vidal’s work has been the subject of several articles in these pages (see, for example, A Test Case for Astroengineering and related entries accessible in the archives). In this era of the enigmatic KIC 8462852 and the interstellar object ‘Oumuamua, we have begun to ask how to address possible extraterrestrial engineering within the confines of rigorous astrophysics.

Millisecond pulsars may offer a way to examine such questions, but it is important to point out at the outset the Vidal is not arguing that this type of pulsar is evidence of extraterrestrial engineering. What he is trying to do is ask a question with broader implications. How do we study unusual astrophysical phenomena in ways that include an extraterrestrial hypothesis? How, in fact, do we conclude when that hypothesis is remotely relevant? And are there ways to make observable and refutable predictions that would help us distinguish purely astrophysical phenomena from what Vidal calls ‘astrobiological’ phenomena that imply intelligence?

Image: An artist’s impression of an accreting X-ray millisecond pulsar. The inflowing material from the companion star forms a disk around the neutron star which is truncated at the edge of the pulsar magnetosphere. Credit & copyright: NASA / Goddard Space Flight Center / Dana Berry.

We’ve seen in the analysis of KIC 8462852 how many hypotheses have been put forward to explain that star’s unusual light curves, with more and more attention now being paid to a natural explanation involving dust in the system. Vidal’s lengthy paper examines the question of millisecond pulsars being useful for navigation, as with our own civilization’s global navigation satellite systems, like the Global Positioning System (GPS) or the Russian GLONASS (GLObal NAvigation Satellite System).

If we can derive a navigational methodology out of astronomical objects found throughout the galaxy, it seems reasonable to believe that more advanced civilizations would have deduced the same facts and might be using a pulsar positioning system (PPS) in their own activities. Pulsar navigation might thus have SETI potential — might some future SETI candidate signal contain timing and positioning metadata? Might some astrophysical phenomena like pulsars be modified by advanced cultures for use as beacons?

And if we push the issue to its conclusion, is it conceivable that what we see as a pulsar navigation capability is the result of deliberate engineering on a vast scale, the sort of thing we’ve imagined the builders of Dyson spheres and Kardashev Type II civilizations engaging in? Vidal does not argue that this is the case, but calls instead for using pulsar navigation as a way into what he calls SETI-XNAV, a program of research that would use existing and future astronomical data to examine millisecond pulsars in the context of testable predictions.

Vidal sees this as a way to “join pulsar astrophysics, astrobiology and navigation science,” one whose benefits would include developing new methods to design more efficient global navigation satellite systems here on Earth even as we explore how to refine our early XNAV experiments. Not incidentally, we would also be examining our methods when, as seems inevitable, we are confronted with another case of an astrophysical object that raises questions about possible artificial origins.

Implications of Galactic Navigation

An ETI hypothesis has played around the idea of pulsars from the beginning, with a brief interest in extraterrestrial technologies leading to the objects being nicknamed ‘LGM stars,’ for ‘Little Green Men.’ But as Vidal explains, models explaining pulsar behavior are available that invoke nothing but natural processes. It’s fascinating to see that Italian astrophysicist Franco Pacini predicted pulsars based on his studies of neutron stars some months before their discovery was announced by Jocelyn Bell and Anthony Hewish in 1967. Vidal goes on to say:

Pacini’s and [Thomas] Gold’s models were the very first modeling attempts. Pulsar astronomy has immensely progressed since then, and pulsars display a phenomenology that requires much more advanced models (see the section Pulsar behavior). There is no single unified pulsar model that can explain all the variety of observations… nobody predicted that our Galaxy would host some pulsars with pulsations rivaling atomic clocks in stability, or that their distribution would make them useful for an out-of-the-spiral galactic navigation system.

It’s a system we’ve begun to explore because of the need for autonomous navigation, in which a spacecraft is capable of navigating without recourse to resources on Earth or in nearby space. Homing in on millisecond pulsars (MSPs) as a unique subset of the broader population of pulsars, Vidal asks what observable predictions we might make that could help us distinguish natural phenomena from artificial. Galactic distribution turns out to be one such marker.

The distribution of MSPs is isotropic, while normal pulsars appear to be concentrated in the galactic plane. Because they are formed in binary systems, this distribution of MSPs causes us to ask why there would be more binary star systems outside the galactic disk than in it.

Image: Figure 7 from the Vidal paper. Caption: The distribution of MSPs in Galactic coordinates, excluding those in globular clusters. Binary MSPs are shown by open circles. From Lyne & Graham-Smith (2012, 116). Credit: Clément Vidal.

Bear in mind that while pulsar navigation became an early topic, proposed as far back as 1974 by JPL’s George Downs, it was the proposal to use X-ray pulsars instead of radio pulsars (Chester and Butman, 1981) that demonstrated both improved accuracy and the ability to use the kind of small detectors that would be feasible for inclusion in a spacecraft payload.

The discovery of X-ray millisecond pulsars shortly thereafter illustrated the difference between ‘normal’ pulsars and MSPs (for more on this, see Duncan Lorimer’s “Binary and Millisecond Pulsars,” Living Reviews in Relativity December 2008, 11:8; abstract here). Although there is much to say about this issue, for now keep in mind the key difference noted above: MSPs accrete matter from a companion. They are generally found in binary systems.

Now we enter the realm of prediction. If there is a case to be made for MSPs as evidence of engineering, we would expect them to be distributed in ways that would appear non-random. We would expect few redundancies in their coverage areas, and in terms of their numbers, there should be enough for galactic navigation but not necessarily more. Moreover, we would expect artificial navigation sources like X-ray millisecond pulsars to beam preferentially in the galactic plane. If we do not find these things, the astrophysical model is supported.

What emerges in this paper is a series of such predictions that can be used to examine our growing data about pulsar, and in particular MSP, behavior. The data offer a rich enough hunting ground that we can look at such things as MSPs in globular clusters as opposed to elsewhere in the galaxy. We find that about half of MSPs appear in globular clusters, a fact that supports an astrophysical explanation, since stellar encounters are likely in such quarters and thus the formation of the binary star systems that produce MSPs in the first place is to be expected.

If MSPs are engineered objects, we would expect different properties between cluster MSPs and those in the disk. We should examine such questions as beaming direction, which an astrophysical explanation would find to be random. We would study as well whether pulsar beaming overlaps with other pulsar beaming within such clusters. Such a study under the SETI-XNAV rubric might help us uncover new binary MSPs, Vidal asserts, by modeling the coverage areas of MSPs and searching in places where coverage would be non-existent. The prediction would then be that we should find an MSP filling in the putative coverage gap.

Vidal’s paper offers numerous areas for such investigation. SETI-XNAV, he writes:

…draws on pulsar astronomy, as well as navigation and positioning science to make SETI predictions. This concrete project is grounded in a universal problem and needs: navigation. Decades of pulsar empirical data is available and I have proposed nine lines of inquiry to begin the endeavor… These include predictions regarding the spatial and power distribution of pulsars in the galaxy; their population; their evolutionary tracks; possible synchronization between pulsars; testing the navigability near the speed of light; decoding galactic coordinates; testing various directed panspermia hypotheses; as well as decoding metadata or more information in pulsar’s pulses.

My interest is in seeing how Vidal makes the distinction between astrophysical and astrobiological — in other words, as with KIC 8462852 and the interstellar object ‘Oumuamua, are we making progress as we begin to investigate under what some have called the ‘Dysonian’ SETI paradigm? That approach takes its name from the postulated Dyson spheres that have been the subject of early work and continue to be studied through projects like the Glimpsing Heat from Alien Technologies (G-HAT) program at Penn State (see Jason Wright’s Glimpsing Heat from Alien Technologies for more). These issues will grow in relevance as our observational tools hasten the pace of discovery.

More thoughts on all this in my next post. The paper is Vidal, “Pulsar positioning system: a quest for evidence of extraterrestrial engineering,” published online in the International Journal of Astrobiology 23 November 2017 (abstract / preprint). Also of interest: Chennamangalam, Siemion, Lorimer & Werthimer, “Jumping the energetics queue: Modulation of pulsar signals by extraterrestrial civilizations,” New Astronomy Volume 34, January 2015, pp. 245-249 (abstract).

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Comments on this entry are closed.

  • Ron S. January 15, 2018, 13:44

    My understanding (I haven’t read the paper) is that position is easily determined by dead reckoning alone in interstellar space. It is only a problem within the solar system, and especially in close orbits, that it is insufficient for accurate positioning due to (usually very slight) errors in gravitational effects of those bodies and solar radiation pressure.

    Therefore being “lost” is unlikely unless we speculate on a mode of transportation that is by its nature unpredictable to a degree. But that may involve undiscovered physics, if any, of questionable utility.

    More interesting is the problem of orientation; that is, knowing direction. As examples, I precisely know where I am but what direction is Earth so that I can aim my antenna, or preparing for application of thrust. We currently use prominent stars and other mechanisms for this in our spacecraft. Are pulsars truly helpful as an alternative?

    In the broadest sense, if you were to find yourself in a random location in the galaxy the detection of pulsars may be unhelpful since the detection distance is limited, their periods vary over time (and therefore with your distance from each), and can vary unpredictably for various reasons, the emissions are directional, and they have a limited emissions lifetime.

    To me it all sounds like a solution in search of a problem.

    • Clément Vidal January 16, 2018, 1:11

      Ron,

      Thanks for your objections. Here are some elements to address them.

      Dead reckoning is subject to cumulative errors. So for interstellar travel likely to last hundreds of years, it wouldn’t fit the bill. By contrast, pulsar navigation accuracy does not decline with time, as constant correction is available from different pulsar sources.

      On large time scales, the galaxy is quite dynamic: it rotates, stars go supernova, new stars are born, so it would not be so trivial to keep an up-to-date map. Neutron stars (pulsars) should last billions of years, and are amongst the most stable astrophysical bodies.

      The problem of orientation (called “attitude” in navigation science) is solved by pulsar navigation.

      Actually, pulsar navigation scientists have already solved the thought experiment you mention, that they call “lost in space” or “cold start” problem, i.e. the determination of position and velocity without requiring external assistance. See Sheikh’s impressive PhD thesis (2005, 51) for details. The period of MSPs varies extremely little, and in a highly predictable manner, which is why they can be seen as macroscopic atomic clocks.

      The fact that the emission is directional could indeed be problematic. That is why I suggested to study the coverage of MSPs. If the coverage is full of gaps, then I agree it’s unlikely to have been engineered.

      Millisecond pulsar navigation appears to be a solution to the problem of … galactic navigation.

      Best regards,
      Clément Vidal.

      Reference:

      Sheikh SI (2005) The use of variable celestial X-ray sources for spacecraft navigation. http://drum.lib.umd.edu/handle/1903/2856.

      • Ron S. January 16, 2018, 20:09

        Clement, thanks for the response. I have a few additional observations to make.

        “Dead reckoning is subject to cumulative errors. So for interstellar travel likely to last hundreds of years, it wouldn’t fit the bill. By contrast, pulsar navigation accuracy does not decline with time, as constant correction is available from different pulsar sources.”

        All methods of position and velocity measurement have error. The questions is how much and whether it within tolerance to successfully complete the mission. The MSP method would have to be compared to dead reckoning, used of optical stars, etc.

        While I have not done the necessary work I will still question the MSP method’s utility in this case. Use of pulsars can be no better than triangulating off optical sources. Direction of a star can be more easily and accurately measured than a radio source. Regardless, either method will do a poor job of establishing position by better than hundreds of AU is not more, depending on the locale. Even with cumulative errors dead reckoning is likely not so bad in comparison!

        Besides which, galactic position is rarely of importance. What is important is position and velocity relative to home (Earth?) and the destination. The first for communication and the latter for mission success. The target’s location and motion also has error and that can only be refined as it is approached. MSP or triangulation to other objects helps not at all.

        Again, what really matter is orientation. There is no simple way to establish the spacecraft’s velocity (direction and speed) with respect to any object in the general case. That, too, is not perfectly stable over long periods, so relying on the final acceleration may be inadequate. Mission success relies on precisely knowing relative velocity and distance as the target is approached.

        Doppler of stellar spectra and perhaps a communications carrier from elsewhere can help but even the small error in those measurements will be cumulative.

        I remain unclear on exactly what kind of interstellar mission would benefit from MSP triangulation. Can you enlighten me with a specific example? The references I’ve been given are too long for me to peruse right now and in any case from reading the abstracts I doubt they will answer my questions.

        • Clément Vidal January 18, 2018, 4:40

          Ron,

          “The MSP method would have to be compared to dead reckoning, used of optical stars, etc.”

          The key issue with methods like dead reckoning is that it leads to *cumulative* errors. By contrast, GPS or pulsar navigation allow constant correction. The comparison with other methods has already been done, and pulsar navigation is a clear winner (see the section 2.3 “navigation with pulsars” for a detailed comparison, and references therein).

          Regarding accuracy, this is what I write in my paper: “For both GNSSs and pulsars, the accuracy is limited by the stability of the clocks employed. Typically, GNSSs have clocks with an accuracy of 3 nanoseconds (ns), while the interstellar medium leaves measurement uncertainties of the order of 100 ns for MSPs (Verbiest et al. 2009). Multiplied by the speed of light, this translates into errors of 90 cm and 30 m, respectively. This means that navigation with X-ray MSPs has the potential to be accurate down to 30 m on a galactic scale. Engineering and observational constraints make it hard to achieve such small error margins, but recent methods suggest that a range error of about 100 m may be achieved (e.g. Sheikh et al. 2007; Hanson et al. 2008).”

          So, we’re talking about meters or kilometers, definitely not AUs.

          As I already mentioned in my previous reply, the problem of orientation (called “attitude” in navigation science) is solved by pulsar navigation. It’s like the arrow’s direction on your GPS. It’s not much more difficult to determine than position or velocity. You can solve it with a Time-of-Arrival navigation method such as GPS or pulsar navigation.

          Obviously, I agree with your point that there is no absolute positioning, and we need to choose a reference frame. Logically, we tend to take the center of mass of the system we’re busy with. For Earth navigation, we take the center of the Earth, for solar-system navigation, the Sun, and it may be logical to choose the supermassive black hole for galactic navigation.

          Regarding, the changing environment, you’re right too that a positioning system is not the same as a map. You still do need maps. If you had no internet connection or no local map on your smartphone, your GPS would give you only your latitude and longitude, which is of limited use.

          Because of the pulsar navigation accuracy, it is directly relevant for space missions in the solar system (going to Mars, etc.). This explains the interest from space agencies around the globe. It is even more relevant for any deep space mission, such as the Breakthrough Starshot project, as many have already noticed in the comments.

          I hope this answers your questions.
          Best,
          Clément.

  • Michael January 15, 2018, 13:51

    ‘this distribution of MSPs causes us to ask why there would be more binary star systems outside the galactic disk than in it.’

    They may have been thrown randomly when one of the stars went supernova (Neutron remnant), asymmetrical supernovae can occur. This may be re-enforced if the companion has deformed the soon to go supernova star.

    Perhaps ‘Starshot’ could use these beacons as a navigational aid, however as any craft moves through space these beacons will go out of view but new ones will come into view.

    https://www.sciencedaily.com/releases/2011/02/110224145803.htm

  • Harold Shaw January 15, 2018, 14:12

    An engineered network of MSPs as a galactic positioning system would imply a lot of demand for navigation aids, that our galaxy has been colonized by one or many K2+ civilizations who spend a lot of time traveling between stars. I would be very curious to see if MSPs provide navigational benefits when traveling near the speed of light. Civilizations that spend much of their time in time dilation, near the speed of light or orbiting black holes, would leave room for abiogenesis and the evolution of civilizations like ourselves. For a time dilated civilization, slowing down to engage with non-time dilated civilizations would come at the cost of their life span relative to the age of the galaxy/universe.

    MSP beam coverage could overlap significantly and still be used as a navigation system. The population of MSPs would need to be modified only enough to provide full coverage and modification of the network could involve creating new MSPs rather than moving existing MSPs. Null or minimum beam overlap would occur only if the extra MSPs reduced the effectiveness of the network. Perhaps significant holes in coverage would counter indicate an engineered system.

    • Alex Tolley January 15, 2018, 15:21

      pp 11, 25 briefly address the relativistic question.

  • Alex Tolley January 15, 2018, 15:17

    I really liked the Vidal paper. Vidal both proposes the idea of MSP navigation (as well as communication and propulsion) and tests. He is not dogmatic. I like the 7 levels of artificiality (table 7, p17) and the answering of possible objections without dismissing them.

    Mobile organisms use a variety of techniques to locate themselves in space, and the scales adjust to allow long distance and local navigation. We humans may be improving our satnav location, but we still use other technques both technological and natural, to naviagte andlocate things on a local scale. One problem I see with pulsar navigation is that gravitational effects might distort the locational and timing aspects of pulsar navigation, although local signposts can also be used as navigational aids at smaller scales.

    • Harold Shaw January 15, 2018, 16:14

      The paper was compelling. I am going to read the paper about the ethics of directed panspermia. I just hope it doesn’t change my mind!

      The problem posed by gravitational effects could increase the minimum size of the PPS, require a greater density of MSPs. If a starship has an almanac of MSPs and their qualities, it could filter out the MSPs that display distortion.

      • Harold Shaw January 15, 2018, 16:44

        As well, MSPs located outside the galactic plane would be less likely to be distorted.

  • Douglas Loss January 15, 2018, 15:22

    Well, we should probably always keep in mind Occan’s Razor, although the idea has been around since at least Aristotle:

    “Aristotle writes in his Posterior Analytics, ‘We may assume the superiority ceteris paribus [other things being equal] of the demonstration which derives from fewer postulates or hypotheses.’ Ptolemy (c. AD 90 – c. AD 168) stated, ‘We consider it a good principle to explain the phenomena by the simplest hypothesis possible.'”

    • Alex Tolley January 15, 2018, 15:40

      Sometimes the simplest answer is elusive. For example, Aristotle’s explanation of why ice is found on the surface of a liquid was totally wrong (he thought flat objects could not penetrate water and hence stay on the surface rather than sink) because he was unaware of the true, simple, physics of density.

      Searching for simple, but unknown, phenomena is much of the basis for reductionist science.

      • Douglas Loss January 15, 2018, 17:11

        Yes, but when a simple, understood explanation describes the observed facts positing more complicated explanations is generally unneeded.

        • Clément Vidal January 16, 2018, 1:46

          Douglas,

          I agree Occam’s razor is a most serious objection. However, epistemologically the issue is not as clear as it seems. First, there are “anti-razor” principles: https://en.wikipedia.org/wiki/Occam%27s_razor#Anti-razors.

          Second, it’s easy to see the simplest explanation afterwards, but it took decades for the heliocentrism to be accepted (see Kuhn’s 1957 work on the Copernican Revolution), so simplicity also depends on pre-existing knowledge, other beliefs, a cultural context, etc.

          Also, I agree that single pulsar formation is well understood, but binary pulsar astrophysics is much richer and complicated, with many more open problems.

          I discuss at length this objection in section “3.5 Natural model” of my paper.

          Best,
          Clément.

          • Ron S. January 18, 2018, 22:09

            Clement, thanks again for taking the time to reply. At this point it’s obvious that I’ll need to read the paper when I have the time. It appears that it’s more interesting than I originally thought.

    • Harold Shaw January 16, 2018, 13:43

      The virtual model for a phenomenon must have the same dimensionality as the phenomenon. Some phenomenon appear as impossible tridents. I think we need to use a tool with Occam’s Razor on one end, anti-Occam’s razor on the other.

      Consider that the best argument against ETI is additive, that near everything about our history is required for us and us is the one and only.

  • Douglas Loss January 15, 2018, 15:29

    Disregarding the question of the potential artificiality of MSPs, do we have a good understanding on the accuracy of the positioning information we can derive from using them? I’m thinking about the Breakthrough: Starshot probes, which don’t include any capability for mid-course correction. Would it be feasible to incorporate this sort of position-finding, so we could at least know which probes are likely to fly through the Proxima system rather than missing it entirely?

  • Alex Tolley January 15, 2018, 15:30

    I would point out that global navigation systems are useful when traveling in areas where there is uniformity of view, like teh oceans. Coastal navigation is trivially easy and accurate compared to offshore dead reckoning. Similarly for jet aircraft flying well above landmarks and at night, whilst low level flying with propellers during the day allows for VFR navigation and landmarks.

    In space, stars are always visible and therefore accurate star maps should be useful for navigation. I’m not sure I buy the idea that stars are too abundant, as they can be reduced by filtering for certain types or luminosities. Computers can do that easily at low cost. Knowledge of movements can overcome the non-static movement of stars. I would think that computers could also overcome the problem that Asimov used in a short story where a new supernova stranded a criminal in space as his navigational computer could no longer match the view with the onboard navigational maps.

  • Harold Shaw January 15, 2018, 16:18

    On Earth, lighthouses have unique patterns that distinguish them from other lighthouses, allowing sailors to confirm their position. Unique signals would serve the same purpose for a PPS. I just don’t know how to distinguish natural variability from engineered variability.

  • Paul Titze January 15, 2018, 21:04

    Hi Paul,

    Interesting paper. For another method to fix one’s position in interstellar space, see the following paper:

    http://vixra.org/abs/1106.0053

    Cheers, Paul.

  • Doug Muir January 16, 2018, 6:55

    Does anyone know why NICER was placed on the ISS? The ISS has a number of disadvantages as a platform: vibration, contamination, an orbit that regularly has Earth, Sun and Moon occultations. Presumably there must have been some countervailing advantages that caused NASA to put NICER there anyway, but brief googling hasn’t turned up exactly what. Does NICER need some sort of regular maintenance? Anyone?

    Thanks in advance,

    Doug M.

    • Bill January 16, 2018, 15:20

      This short blurb is on the NASA NICER fact sheet.

      PLATFORM AND DESIGN
      ESTABLISHED PLATFORM AND BENIGN
      ENVIRONMENT
      The International Space Station offers
      established infrastructure for transportation,
      power, and communication for the NICER
      payload. The stable platform and generous
      resources simplify NICER’s design, reducing
      cost and risk. NICER’s design is tolerant of
      the space station vibration, contamination,
      and radiation environments.
      NICER will launch in 2017 and operate from the International Space Station

  • Michael Fidler January 16, 2018, 7:42

    Has the Sun a companion star?
    Nature 270, 324–326 (24 November 1977)
    E. R. HARRISON

    “PULSARS are accurate timekeepers. They are believed to be rotating neutron stars, with strong magnetic fields, and the energy they radiate is at the expense of their rotational kinetic energy1. As each pulsar ages, its period P (relative to the Solar System barycentre) slowly increases, and its period derivative P( = dP/dt) slowly decreases. Certain interesting pulsars (displayed in Table 1) have anomalously small period derivatives, and rather surprisingly, are found grouped together in the same region of the sky (shown in Fig. 1). I suggest here, as an explanation of the peculiar properties of these pulsars, that the barycentre of the Solar System is accelerated, possibly because the Sun is a member of a binary system and has a hitherto undetected companion star”.

    Edward Robert Harrison.
    https://en.wikipedia.org/wiki/Edward_Robert_Harrison
    Cosmology by EDWARD HARRISON
    Five College Astronomy Department, University of Massachusetts
    Steward Observatory, University of Arizona
    http://physics.muni.cz/~novotny/-CSMLG/(Harrison%20E.-Cosmology_%20The%20Science%20of%20the%20Universe-Cambridge%20University%20Press%20(2000)).pdf

    The solar acceleration obtained by VLBI observations
    M. H. Xu1,2, G. L. Wang1, and M. Zhao1
    Accepted 11 July 2012

    “The hypothesis of a companion star orbiting the Sun should
    offer more room for explaining the vertical component of the
    acceleration, and indeed, normally stars are members of double
    star systems or multiple systems (Donnison 1984). Harrison
    (1977) firstly suggested that the Sun has an undetected companion
    star as an explanation of the decrease in the period of a small group of pulsars. Later this was discussed in more detail by Cowling (1983) and Thornburg (1985). However, these studies could only constrain the SSB’s acceleration to ∼32 mm s−1 yr−1, which is much higher than the value of our vertical component, 3.95 mm s−1 yr−1. Recently, Zakamska & Tremaine (2005) used the timing data of millisecond pulsars, pulsars in binary and pulsating white dwarfs to determine the acceleration. They used the theoretical Galactocentric acceleration aGal, to correct the observed period derivatives before the data analysis, and then they constrained the SSB’s remaining acceleration on the upper limit of 4.73 mm s−1 yr−1, comparable with our vertical component.
    So the vertical component we obtained may provide a direct observational evidence of the existence of the solar companion”.

    https://www.aanda.org/articles/aa/pdf/2012/08/aa19593-12.pdf

    THE SECULAR ABERRATION DRIFT AND FUTURE CHALLENGES
    FOR VLBI ASTROMETRY.

    Take a look a figure 3, no mention of possible companion to Sun.
    https://arxiv.org/pdf/1301.0364.pdf

    THE VLBA EXTRAGALACTIC PROPER MOTION CATALOG AND A MEASUREMENT OF THE SECULAR ABERRATION DRIFT.
    October 6, 2017

    Take a look at figure 8 and 10.
    https://arxiv.org/pdf/1710.02099.pdf

    Could a civilization have built a Dyson Sphere around a white dwarf that has an orbit around the Sun, assuming that their stealth tech could cover up the IR signature? Well looking at these articles and making a educated guess I would say we need to look around R.A 17h 25m and -20.00 south in equatorial coordinates. Thanks for the tip Paul, the tip of a huge iceberg!

    • Michael Fidler January 18, 2018, 4:42

      Have been doing a little research on solar system orbits and dynamics in relation to a long period White Dwarf or Neutron Star Dyson Sphere. This makes the solar system 1/2 of a binary star system. (see image)
      http://3.bp.blogspot.com/-Lbhn-0J_9GU/TWKpHHTKiiI/AAAAAAAACrc/NsbHBoZvG6s/s1600/nemesis_orbit_02.gif

      What is interesting is that Winter Solstice and the Perihelion of the Earth to the Sun is also near that point in late December early January. (around R.A 17h 25m and -20.00 south) But what was very surprising is
      that Saturn’s rings are widest at that point and it is near its Aphelion. Fifteen years later it rings are widest again with the south pole facing us and is at its Perihelion. Since Nemesis is probable at its most distant point this seems to have caused a certain amount of aliment and inclination in our solar system when it is at perihelion to the sun.
      http://www.nakedeyeplanets.com/saturn-orbit-1993-2020.gif

      https://upload.wikimedia.org/wikipedia/commons/b/b8/Motion_of_Sun%2C_Earth_and_Moon_around_the_Milky_Way.jpg

      http://www.aoi.com.au/Extracts/Planet-Inclinations.png

      https://www.physicsforums.com/threads/orientation-of-the-earth-sun-and-solar-system-in-the-milky-way.888643/

      The illustrations below shows the Perihelion (Green) and Aphelion (Red) with the inclination below and above Earths ecliptic. What would be much better is a chart that shows the inclination in relation to the Sun’s equator of all the planets including Earth. There seems to be a general tilt that may have been caused by Nemesis passing nearby some
      170 times in the last 4.5 billion years.
      By the way the moons orbit passes directly over this area also.

      • Michael Fidler January 18, 2018, 4:48
        • Michael Fidler January 19, 2018, 6:25

          Some more surprising material relating to the planet Saturn:

          On the recently determined anomalous perihelion precession of
          Saturn.

          https://arxiv.org/pdf/0811.0756.pdf

          The Perihelion Precession of Saturn, Planet X/Nemesis and MOND.

          ” In particular, the resulting perihelion precession would be retrograde so that it would be able to explain the anomalous perihelion precession of Saturn recently determined from an analysis including radiotechnical data from Cassini. An investigation of the tidal parameter of X as a function of its ecliptic longitude and latitude showed that its maximum value occurs for X located perpendicularly to the ecliptic, while its minimum occurs for X lying in the ecliptic. Accordingly, it has been possible to determine the present-day distance of X for different postulated values of its mass. Rock-ice planets as large as Mars and the Earth would be at about 80 au and 150 au,
          respectively, while a Jupiter-like gaseous giant would be at
          approximately 1 kau. A typical brown dwarf (M = 80MJ)
          would be at about 5 kau, while Sun-sized body would be at
          approximately 10 kau. If it is difficult to believe that a mainsequence Sun-like star exists at just 10 kau from us, the
          distances obtained for terrestrial-type planets are
          substantially in agreement with theoretical predictions
          existing in literature about the existence of such bodies
          which would allow to explain certain features of the
          Edgeworth-Kuiper belt. Incidentally, let us note that our
          results rule out the possibility that the hypothesized Nemesis
          can be the Sun-like object X that may be responsible of the
          anomalous perihelion precessions of Saturn, also because, at
          approximately just 10 kau from us, its orbital period would
          amount to 1-10 Myr, contrary to the 26 Myr periodicity in
          extinction rates on the Earth over the last 250 Myr which
          motivated the Nemesis proposal. Moreover, our Sun-sized
          body X would not penetrate the Oort cloud which is believed
          to extend from 50 kau to 150 kau. The tidal parameter of
          Nemesis would be, instead, 2 – 4 orders of magnitude
          smaller than the present-day level of accuracy in measuring
          it ( 10-26 s-2 ). On the other hand, if our X had a distance of
          about 88 kau, as predicted for Nemesis, our result for its tidal
          parameter would imply a mass of 300M.
          For a particular position of X, i.e. along the direction of
          the Galactic Center, our results hold also for the recently
          proposed form of the External Field Effect in the framework
          of MOND in the sense that it would be able to explain the
          perihelion precession of Saturn in such a way that it mimics
          the existence of a body in the direction of the center of the
          Milky Way”.

  • ljk January 16, 2018, 10:29

    Did I miss this? No mention of the pulsar maps on the Pioneer Plaques and Voyager Records?

    http://www.johnstonsarchive.net/astro/pulsarmap.html

    http://www.pbs.org/the-farthest/science/pulsar-map/

    • Paul Gilster January 16, 2018, 12:23

      Vidal shows the Pioneer plaque and mentions the 14 pulsars shown there in his paper.

  • Steve Bowers January 16, 2018, 10:36

    Pulsar GPS systems are most valuable over long distances (thousands of light years) within the Galaxy, but (assuming faster-than-light travel is impossible) travelling thousands of light years would take thousands, or tens of thousands of years. During that time the pulsars would move, making their positioning information increasingly unreliable.

    Now I come to think of it, the same effect would occur even if FTL travel were available. These pulsar systems are less reliable than one might think.

    • DJ Kaplan January 16, 2018, 14:36

      Steve, on a certain (highly speculative!) level, this would suggest that FTL travel is possible and that there are being who have accomplished this…

  • ljk January 16, 2018, 12:19
  • Harold Shaw January 16, 2018, 13:34

    For Cases of MSP/PPS 1-3,4, MS drift and distortions would be corrected by an almanac. For cases 4,5-6, I think there is a return on investment threshold that must be overcome and that threshold is most proportional to average travel distance. An almanac will compensate for an amount of natural imperfection and it is easier to maintain productive almanacs locally.

    Evidence of cases 5 and 6 would indicate general activity levels we can realistically expect to discover.

    Would MSPs above the galactic plane all pointed towards the plane be optimal? Would there be any natural explanation if enough of the population where optimally oriented?

  • Harold Shaw January 16, 2018, 13:49

    If there is a relationship between the qualities of what falls onto the surface of neutron star and the signal profile of a neutron star, then the ability to control what falls would allow writing a signal.

    • Harold Shaw January 16, 2018, 14:03

      Arguably, the most cost efficient way to manufacture a MSP would be to nudge a naturally occurring system into becoming an MSP. This would create a MSP with a limit to predictability. Injecting atypical to MSP mass onto the neutron star would stand out if you were looking for it.

  • Michael Fidler January 19, 2018, 7:21

    Looking up the position of the planets in the area mentioned above, on the celestial mapping software I came across a number of planetary nebula’s. That started thinking about what Paul mentioned in:
    SETI and Astrobiology: Toward a Unified Strategy:

    “Any sufficiently advanced technology is indistinguishable from magic.” In this case, the quote is used to explore how difficult it may be to find extraterrestrial life of any kind. If intelligent, such life might build enormous structures observable by our astronomy.
    Or perhaps not: Karl Schroeder has posited that advanced technologies may be indistinguishable not from magic but from nature”.

    Planetary nebula’s would be the perfect place to hide a Dyson Sphere.
    After looking around the internet I found several finder charts and photo images of a peculiar planetary nebula in that area: It has a number of names, PK6-8.1, Minkowski 1-20, ESO 588-3, Henize 2-235, Sanduleak 2-204. What caught me of guard is that different references and photos showed it at different locations! Now this is a star packed area, close to the center of the milky way and this object is not well known so it would be easy to confuse it with other objects. But the image taken of it by the Hubble scope show it with relatively starless field??? (see below image) /www.intergalacticsafari.com/uploads/5/5/1/6/55162991/3129363_orig.jpg

    But what is nice about the image is that it shows a globe surrounded by a atmosphere of plasma, just what you might expect from a Dyson Sphere!. Now your thinking if this is near by the parallax would be quit large, but with no central star it is much harder to find out its distance since measuring it from something like GAIA may be difficult.

    Actually I would be very surprised if this is anything unusual but it goes to show you just how much is going on out there. Just how little these objects are studied and how easy it would be to mimic something that is very common. After all look at natures ability to camouflage creatures in the wild from their predators.