LaViolette on Pulsars
The original discoverers of pulsar signals, Jocelyn Bell and Anthony Hewish of Cambridge University, thought at first that they might be observing artifacts of some extraterrestrial civilization (Sturrock and Rockefeller, 2000).
But a more acceptable if tentative explanation was soon found: the signals might be emanating from white dwarf stars that were contracting and expanding, or dimming and brightening (Hewish et. al., 1968). The radially-pulsing white dwarf model was itself soon discarded after two pulsars with periods less than 0.1 second were found in the Crab and Vela supernova remnants.
Out of some twenty different proposed theoretical models of possible sources of these pulsing signals, astronomers settled on the “neutron star lighthouse” put forward by Thomas Gold (1968). In that model, a neutron star emits two opposed beams of synchrotron radiation confined to a narrow cone about the star’s magnetic axis. We perceive pulses as the beams swing by us if we happen to be in the cone that they sweep out.
The original impression of pulsars (and other newly-discovered astrophysical objects and phenomena) as ETI beacons was not completely forgotten, however.
In a note added to his published proceedings of the 1971 USSR conference on Communication with Extraterrestrial Intelligence (CETI), Sagan (1973) wrote:
“The very serious current energy problems both in quasar and in gravity wave physics can be ameliorated if we imagine these energy sources beamed in our direction. But preferential beaming in our direction makes little sense unless there is a message in these channels. A similar remark might apply to pulsars.
There are a large number of other incompletely understood phenomena, from Jovian decameter bursts to the high time-resolution structure of X-ray emission which might just conceivably be due to ETI. Perhaps, in the light of Doctor Marx’s presentation, we must ask if the fine structure of some fluctuating X-ray sources is due to pulsed X-ray lasers for interstellar spaceflight. But Shklovsky’s principle of assuming such sources natural until proven otherwise, of course, holds. Extraterrestrial intelligence is the explanation of last resort, when all else fails.
“The pulsar story clearly shows that phenomena which at first closely resemble expected manifestations of ETI may nevertheless turn out to be natural objects – although of a very bizarre sort. But even here there are interesting unexamined possibilities. Has anyone examined systematically the sequencing of pulsar amplitude and polarization nulls? One would need only a very small movable shield above a pulsar surface to modulate emission to Earth. This seems much easier than generating an entire pulsar for communications.
For signaling at night it is easier to wave a blanket in front of an existing fire than to start and douse a set of fires in a pattern which communicates a desired message.”
Sagan’s suggestion was not taken up by the astronomical community. Astronomers were unwilling to (publicly) consider an ETI-based source for the signals they were receiving.
One reason they gave (Jastrow and Thompson, 1977), was that the pulse type of beacon was too wasteful of energy and wouldn’t be the method they would choose.
In The Talk of the Galaxy (2000), astrophysicist Paul LaViolette revives Sagan’s speculation.
Reviewing years of observations made since that CETI conference in 1971, with particular attention to high-resolution recordings of individual pulses, LaViolette finds significant support for considering pulsars as possible ETI beacons.
He of course notes the difficulties presented to the standard model by pulsars with millisecond periods.
But there have been many other challenges to the model in the form of quite interesting features of pulsar spatial distributions, and intricate behaviors seen in high-resolution recordings of individual pulses and pulse sequences.
Here is a brief listing of some behaviors found in the current literature and discussed by LaViolette:
Time-Averaged Regularity – Time-averaged pulse contours do not change over days, months, or years. Timing of averaged profiles is similarly precise.
Single-pulse Variability – Timing and shape of individual pulses vary considerably.
Pulse Drifting (certain pulsars) – Individual pulses occur successively earlier and earlier within the averaged profile (“drifting pulsars”). For certain drifting pulsars, drift rate abruptly shifts in value. Or drift may be random with occasional recurring patterns.
Polarization Changes – Polarization parameters vary within individual pulses, but time-averaged profile of polarization is constant.
Micropulses – About half of observed pulsars exhibit micropulses within individual pulses. Micropulses typically last a few hundred microseconds. Or they may have oscillatory periods.
Pulse Modulation – Signal strength may wax and wane over a series of pulses. Or this may be seen only when sampling every other pulse. Or maybe only at particular times in the profile.
Pulse Nulling – Pulse transmissions may be interrupted for seconds or hours. When resumed, varying parameters continue from where they had left off!
Mode Switching – More than one stable pulsation mode, with sudden switching between them.
Pulse Grammar – “Grammatical” switching rules.
Glitching – Pulse periods grow at a uniform rate (as though spinning pulsar is slowing down), but occasionally the period abruptly changes to a smaller value (pulsar instantaneously assumes a higher rotation rate?) and the sequence continues from there. When averaged over several minutes or so, these complexities disappear, leaving only extreme regularity.
The neutron star lighthouse model predicted that pulsars would be formed in supernova explosions and in fact several of them have been found near supernova remnants.
If that were truly how they were formed, one would expect to find pulsars concentrated toward the center of the galaxy where most supernovas occur. However, LaViolette has noticed that the distribution of observed pulsars in the galactic plane differs markedly from that. (He also cites studies of neutron stars associated with supernova remnants showing that the stars were not formed in the supernovas.)
In fact, there is a clumping of them near a point one radian north of the galactic center. He depicts a sharp fall-off of pulsars just beyond that point. He also noticed that some of the most unusual pulsars are found right at that edge in the distribution.
The position of these anomalies at a one-radian angular distance from the galactic center (g.c.) is especially odd because:
the radian is arguably a natural angular unit that would be recognized by many societies
this particular angular position would exist only from a point of view located exactly where we are – giving the impression of a deliberate signal or sign to our society or any society at our location
In the same vein, LaViolette points out that the two fastest known pulsars are located at the two one-radian positions.
These pulsars have other unique features that are listed by LaViolette. He also looks at the constellations in which the pulsars appear, and finds curious associations. The constellation Sagita (the “Celestial Arrow”) is located “adjacent” to a one-radian point. The arrow of Sagittarius’ bow (and the stinger of the Scorpion) designate the galactic center, and the cross of Crucis marks the southern galactic one-radian point.
These star formations all involve “marker” imagery.
Since the system of constellations was presumably invented here in our ancient cultural past, these oddly congruent associations suggest the constellations may have been devised in such a way as to embody and preserve knowledge of the significance of the pulsar signals for the benefit of future civilizations.
Pulsars as Artifacts
Unlike Sagan, who accepted the conventional model of a pulsar but wondered if ETI could be adding fine-grained modulation, LaViolette proposes a way in which the steady emissions of stars could be focused into the pulses we see. He explains that ETI might be using a nearly-collimated beam of synchrotron radiation, applying technology that we actually are developing today.
This dramatically offsets the effect of distance on the detectability of a beacon over interstellar distances.
Although we may now have or soon will have the capability to transmit focused synchrotron beams, LaViolette’s postulated transmitting society has access to energy on a scale far exceeding ours. Although pulsars are probably not neutron stars, they are still stars – white dwarfs modified to produce the pulsar signals.
The short of it is that we are observing a Kardashev/Kaku Type II civilization in terms of its ability to harness the total energy of a star.
Impact of LaViolette’s Hypothesis
LaViolette’s hypothesis has received some interest in the borderland science literature, but has not been taken very seriously by astrophysicists.
I am not aware of any that have taken the trouble to refute or even discuss his work; there also has been no follow-up in terms of:
reviewing the published data from which he drew his conclusions
obtaining and reanalyzing any of the original data on which the publications he used was based
searching for more of the kinds of patterns noted by LaViolette in fresh pulsar data