Are Radio Pulsars Extraterrestrial Communication Beacons?
01.05.2014 11:23
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Are Radio Pulsars Extraterrestrial Communication Beacons?
Paul A. LaViolette
The Starburst Foundation
Niskayuna, New York
plaviolette@starburstfound.org
February 2, 2014
Abstract: Evidence is presented that radio pulsars may be artificially engineered beacons of
extraterrestrial intelligence (ETI) origin. It is proposed that they are beaming signals to
various Galactic locations including our solar system and that their primary purpose may be
for interstellar navigation. More significantly, about half a dozen pulsars appear to be
conveying a message intended for our Galactic locale by marking key positional sky locations.
They appear to make reference to the center of our Galaxy, which is a logical shared reference
point for interstellar communication. The Millisecond Pulsar (PSR1937+21) is noted to be
the closest pulsar to the point that lies one-radian from the Galactic center along the galactic
plane. The chance that a pulsar would be positioned at this key location and also display the
highly unique attention-getting characteristics of the Millisecond Pulsar is estimated to be one
chance in 7.6 trillion. Other pulsars that appear to be involved in conveying this message
include the Eclipsing Binary Millisecond pulsar (1957+20) and PSR 1930+22, both of which
make highly improbable alignments relative to the Millisecond Pulsar position, the Crab and
Vela pulsars, and PSR 0525+21. All display one or more unusual attention-getting
characteristics. A method is proposed whereby a civilization magnetically modulates the
cosmic ray flux of a neutron star to produce stationary, broadband, targeted synchrotron
beams having pulsar-like signal characteristics. Also a lower tech approach is proposed that
instead modulates the relativistic electron beam from a linear particle accelerator to produce a
free electron laser beam.
keywords: pulsars, neutron stars, CETI, extraterrestrial communication, astro-engineering
1. Introduction
The following intends to demonstrate here that radio pulsar signals are likely of artificial
origin, hence that the standard assumption that pulsar signals arise naturally is in error. Here, a
distinction should be made between the neutron stars, which provide the cosmic ray energy
powering pulsar signals and which are of natural origin, and the pulsar signals themselves which
appear to be purposely engineered from this cosmic ray flux for purposes of communication.
While the same name, "pulsar," is used to refer to all types of pulsars, it is advisable to
distinguish here between the radio-quiet X-ray and gamma ray pulsars and those that belong to
the radio pulsar category. I propose that the first category indeed are of natural origin and that
their pulsed signals can be adequately explained by means of Thomas Gold's lighthouse model or
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some variation of it. That is, such a source may be modeled as being a cosmic-ray-emitting
neutron star that has a strong polar magnetic field and in which the interaction of its cosmic rays
with its polar magnetic field causes it to beam synchrotron or bremstrahlung radiation from one
or both of its poles. As the star rotates, it periodically flashes its X-ray (or gamma ray) beam in
our direction creating a continuous train of pulses.
Examples of such pulsars include the matter accreting millisecond x-ray pulsars and slow
pulsars found in accreting X-ray binaries such as those reviewed by Patruno and Watts (2012).
The well known x-ray pulsar Hercules X-1 is an example of a pulsar that is admittedly a natural
source. Generally the integrated X-ray or gamma ray pulse profile of such sources has noticeable
random variation, making the profile's shape and timing rather imprecise. Adding up successive
pulses produces an integrated profile that still embodies a significant amount of random variation.
Such timing variability is what one would expect if one were observing a synchrotron-emitting
neutron star that was producing electromagnetic emissions through natural processes. Moreover
pulsars in this class normally are not seen to have a radio counterpart to their pulses. Radio
emission, if observed, is seen during transient flare events associated with matter accretion
episodes and is assumed to come from a radio jet associated with the accretion event, for
example, see Jonker, et al. (2008).
Radio pulsars, on the other hand, seem to be an entirely different type of phenomenon. Since
the time they were discovered, they hold the unique status of being the most complex and most
highly ordered phenomenon known to astronomy. Besides exhibiting very high precision in the
timing, shape, and polarization pattern of their integrated pulse profile, they also exhibit a variety
of subpulse and pulse profile ordering characteristics which give each pulsar a unique signal
signature. Some of these ordering characteristics include:
1. subpulse amplitude modulation
2. subpulse phase drifting
3. multicomponent correlated subpulse phase drifting
4. quantization of subpulse phase drift rate
5. pulse profile mode shifting
6. pulse profile mode switching grammar
7. pulse profile mode switching with mode memory
8. sporadic nulling of the pulse emission
These ordering characteristics are so varied and unique that efforts to model them have
proven futile. For example, radio astronomers Alexei Filippenko and V. Radhakrishnan (1982)
state:
"The standard polar cap model of pulsar radio emission provides acceptable explanations for
a wide variety of observed pulsar characteristics. Nevertheless, we show that it has difficulty
accounting for certain details pertaining to drifting subpulses, nulling, and mode changing. In
particular, the persistence of drifting subpulse phase memory observed during pulsar nulling,
as well as the phenomenon of nulling itself, seem to defy simple explanation."
Radio astronomers N. Bartel, et al. (1982) are also perplexed about mode-switching phenomenon
in radio pulsars. They write:
"Despite the fact that the mode-switching phenomenon has such an important effect on pulse
emission, no elaborate theory as yet exists as to how to interpret it."
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Radio astronomers J. Taylor, R. Manchester, and G. Huguenin (1975) also admit the confused
status of this area of astronomical research. They state:
"There exists an extensive literature of observational details which, although well
substantiated by repeated measurements, remain unexplained and unassimilated into pulsar
models."
Pulsar astronomers J. Gil, A. Krawczyk, and G. Melikidze (1997), state:
"Although almost 30 years have past since discovery of pulsars, their radiation still remains a
mystery. This concerns both the fundamental problem of the coherent radio emission as well
as the specific modulation of pulsar radiation in the form of individual pulses and the
characteristic stable mean profiles."
More recently, pulsar astronomers J. Gil, et al. (2007) state:
"40 years after discovery of pulsars the actual mechanism of their coherent radio emission is
still a mystery. Drifting subpulses, which seem to be a common phenomenon in pulsar
radiation, is also a puzzle."
This modeling difficulty continues to be a problem even today, e.g., as seen with the
discovery that mode switching pulsar PSR 0943+10 exhibits abrupt synchronous switching of its
radio and X-ray emission with X-ray emission being strongest when radio emission is weakest
(Hermsen, et al., 2013). Also a paper by Andersson, et al. (2012) overturns a 40 year old theory
that attempts to explain the phenomenon of period glitching leaving a natural cause explanation
for the phenomenon to be an open question. It is apparent that radio pulsar signals are so
complex as to elude all efforts to model them in a natural way as emissions produced by a
rotating neutron star. This leaves open the possibility that they may in fact be astro-engineered
beacons of intelligent origin.
I began studying pulsars in 1979, at a time when only a few hundred were known. To date
over 2267 have been discovered. The discoveries made in the past 35 years appear only to
further support the conclusion I had come to in 1979 that pulsars are likely of ETI origin. I
believe their main function is to serve as navigation beacons for interstellar travel (LaViolette,
2000a, 2006). Collectively they may serve as a kind of galactic GPS system, allowing space
travelers to triangulate their ship's position during interstellar flight. I have shown that pulsar
signals could be used not only to triangulate a ship's position in the Galaxy, but also to determine
its relative velocity and even to correct for any time dilation that might occur in cases where
travel speeds might reach a substantial fraction of the speed of light. Others later independently
suggested thoughts along similar lines, that future terrestrial space travelers might use X-ray
pulsars for interplanetary and interstellar navigation.
I have also proposed that a small subset of these radio pulsars, about half a dozen, may be
conveying a message specifically intended for us (LaViolette, 2000b, 2006). Some observations
about the sky positions of a few of these unique message-conveying pulsars are summarized in
the sections that follow. As is shown, the evidence is difficult to explain in any way other than
by assuming that pulsars are artificial beacons.
2. Our Assumptions About Extraterrestrial Intelligence: Are They Too Restrictive?
In arriving at this ETI interpretation, it is best not to be fettered by restrictive, preconceived
notions about the possible technological advancement of extraterrestrial life, for example, the
assumption that if intelligent beings live elsewhere in the Galaxy that they should not be much
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more advanced than we are. Or, the assumption that, because our own civilization does not
intercommunicate with extraterrestrial civilizations (at least openly), that one should not expect
there to exist multiple civilizations in the Galaxy that intercommunicate with one another, visit
one another, or even be mutually organized among themselves in some manner.
The process of interpreting whether or not a deep space signal is of intelligent origin is
difficult to separate from the assumptions that we, the message recipients, hold about life
possibly existing elsewhere in our Galaxy. Take as an example the sequence of events that
surrounded the first discovery of pulsars. The first radio pulsar was discovered in July 1967 by
the British radio astronomy graduate student, Jocelyn Bell. This source recorded in her data
initially attracted her attention because of it produced unusually regular broadband radio pulses,
something not seen before in modern astronomy. When she and her Cambridge University
research team combined successive pulses from this source to compose an integrated pulse
profile, they found that the source's pulse repetition rate was exceedingly precise and that the
shape and polarization pattern of its pulse profile was highly invariant. Because astronomical
sources do not exhibit such precision, they initially became convinced that they had discovered
what could very well be a message being sent from a civilization elsewhere in our Galaxy. Her
research team, led by professor Anthony Hewish, later labeled the radio source LGM-1, the
initials being jokingly chosen as an abbreviation for "little green men".
As their radio observations continued, the Cambridge group later discovered additional
pulsars which they labeled LGM-2, LGM-3, and LGM-4. But at this point, with so many
sources of similar character being discovered in different part of the sky, doubts began to emerge,
and after some deliberation, they chose to reject their initial hypothesis of this being a source of
artificial origin. The reason they gave for their reassessment was that they felt it was highly
unlikely that more than one civilization would be transmitting a message to us at the same time.
Also they did not believe that different civilizations would use a similar transmission method,
one utilizing a broadband radio synchrotron emission beam to produce its pulses. As a result,
they concluded that the sources, although highly unusual, must be a natural phenomenon. So
efforts were begun to devise stellar models that would account for the signals in natural terms,
and this natural source interpretation has stuck ever since.
In rejecting the extraterrestrial intelligence (ETI) hypothesis, the Cambridge astronomers were
in effect adopting the anthropomorphic assumption that a communicating ETI civilization would
be technologically similar to our own, that they probably would not have the ability to travel far
from their home planet and that they would be acting alone in their communication effort to make
contact with civilizations outside their solar system. Based on this assumption, they saw the
probabilities were very small that more than one independently acting civilization would be
making contact with us at this particular period of time.
Now, half a century later, with the advancement of our own technology and with our
discovery that stars in the Galaxy are more often than not orbited by planets, many of which
could sustain life, our views about the possibility of extraterrestrial life have changed. The idea
that there might be many advanced civilizations in the Galaxy, interacting, intercommunicating,
engaging in interstellar space travel between their worlds, cooperating with one another, and
possibly even organized into a kind of "Galactic federation" does not sound so far fetched to
many astronomers any more. If pulsars had been discovered today, rather than 47 years ago, the
ETI interpretation may not have been so readily rejected. This example shows us that there is in
fact an inherent psychological dimension or interpretive bias embedded in the search for
extraterrestrial intelligence.
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If one chooses to interpret the pulsar findings presented here and elsewhere (LaViolette,
2006) in an ETI context, and not as some extreme improbability of nature, one is inevitably led to
adopt a set of assumptions about the nature of Galactic extraterrestrial intelligence. These
assumptions, which are listed in Table 1, differ radically from those that were held by the
Cambridge University discoverers years ago.
Table 1. Some Assumptions about the Existence of Intelligent Life in the Galaxy
1) That there may be a multiplicity of advanced civilizations inhabiting our Galaxy that
intercommunicate with one another, that a large number of these may be communicating with
us at this point in time and may be using the same or similar method for interstellar
communication.
2) That these communicating extraterrestrial civilizations engage in interstellar travel. That is,
they are not merely residents in their own planetary system, but voyagers as well, capable of
traveling to other stars in the Galaxy. So, in this example we are assuming that they might
not be homebound like us, but have reached a more advanced stage of development.
3) That these communicating extraterrestrial civilizations have technologies that allow them to
send superluminal communications across the Galaxy (possibly by a mode other than pulsar
transmissions) and that they may even be able to travel through the Galaxy at superluminal
speeds using craft that are able to power their flights over distances of hundreds of light years
or more.
4) That civilizations living in differing parts of the Galaxy may be organized into a "Galactic
Federation" and may cooperate with one another to orchestrate a message sent from various
Galactic locations so that when these various communication beacons are considered together
by the recipient civilization they are seen to convey a message with a particular meaning. For
example, a series of communication beacons might be located at specific Galactic locations
which when considered together convey a particular geometrical meaning or exhibit alignments
that are difficult to explain in terms of random arrangements. Another possibility is that one
civilization, rather than an organized group of civilizations, has achieved the ability to travel
throughout the Galaxy and set up interstellar communication beacons at many outposts
throughout the Galaxy.
5) That the communicating civilization (or civilizations) have developed the ability to
engineer the cosmic ray flux from a neutron star so as to produce a series of nonrotating,
broadband, synchrotron emission beams targeted at specific Galactic locations and have the
ability to modulate these beams so as to produce pulsar-like radio emission pulses.
6) That the communicating civilization (or civilizations) might make reference to the Galactic
center (GC) in the message they direct to us. The GC is one Galactic location that all
civilizations share in common and hence would be a likely reference point in any interstellar
communication.
7) That communicating civilizations may make use of geometric relations in interstellar
communications they may be directing towards us, geometry being a universal language that
should be known to any advanced civilization.
It is not necessary to consider these seven assumptions or hypotheses as being proven in
advance. Instead, consider them as a context which allows one to better understand the pulsar6
ETI interpretation, namely the suggestion that radio pulsars may have an artificial origin, and that
a subset of these may be intentionally communicating a message to us. It is useful to present the
following analogy. Suppose that a forester has planted a forest of pine trees in a series of rows
where the trees in a given row are not necessarily equally spaced. An uninformed observer
looking at this forest for the first time from an arbitrary viewing perspective will think that he is
seeing a pine forest that grew by natural means. But when the person is allowed to walk
perpendicular to the rows, he will periodically adopt a viewing angle that allows him to see that
the trees grow in regular rows. In the case where all trees are exposed to the same soil conditions
and rainfall, the chances of the pines adopting such a highly ordered pattern by natural means is
vanishingly small. However, by knowing about the possibility of tree farming, our observer is
able to adopt a new perspective and to come to the more reasonable conclusion that this forest
has been engineered, that the trees were originally planted in this fashion by a forester.
So, let us think of radio pulsars as the trees and the unusually regular tree rows as
corresponding to the unusual positional locations exhibited by the subset of unique pulsars we
will be discussing. As in the case of the planted tree forest, the chance that these positional
locations arose due to a chance of nature will be shown to be vanishingly small. So, think of the
assumptions listed in Table 1 as a conceptual context that allows one a more plausible ETI
interpretation of radio pulsars.
Of the assumptions listed in Table 1, assumption (3) may raise concerns for those who
maintain that nothing can exceed the velocity of light. Contrary to the opinion of relativists, one
can point to a number of laboratory experiments that unquestionably demonstrate the reality of
superluminal signal propagation. One example is an experiment performed by Carôt, et al. (2012)
which sends microwave signals through a copper tube at many multiples of the speed of light. In
2012, demonstrating their technology to a conference room of about 20 physicists and
mathematicians Guenter Nimtz and Alexander Carôt (2012) sent microwave signals at
superluminal speeds through a 50 meter long copper tube waveguide. Another example is an
experiment performed by Alexis Guy Obolensky in 2005 in which Coulomb ground waves
produced by a high-voltage shock discharges were measured to travel across the laboratory at
superluminal speeds with initial departure speeds as high as 5c; see LaViolette (2008) for a
summary. Another very interesting example is the experiment conducted by Podkletnov and
Modanese (2011) in which a high voltage pulse discharged from a superconducting anode was
observed to produce a collimated gravity impulse wave whose speed was measured at 64 c. In
other experiments they measured speeds in excess of several thousand c (LaViolette, 2008).
All these technologies have in common that they generate longitudinal waves. So it is
conceivable that technologies could be developed to send and receive such longitudinal wave
transmissions across interstellar distances in support of the suggestion that ETI civilizations may
intercommunicate superluminally. Also Podkletnov and Modanese (2003) have demonstrated
that their longitudinal impulses are able to gravitationally accelerate a variety of target masses,
which means that such a technology potentially could be employed to propel a vehicle to
superluminal speeds (LaViolette, 2008). The energy for powering such a vehicle over interstellar
distances could come not necessarily from controlled fusion, but from nonconventional
alternative energy sources capable of tapping into a virtually unlimited source of energy theorized
to permeate all space (LaViolette, 1991, 2008, 2013).
Assumption (5), the idea that a civilization might engineer the cosmic ray emission of a
neutron star to produce a series of broadband synchrotron communication beams targeted on
specific Galactic locations, was first suggested in 2000 (LaViolette, 2000a, 2000b, 2006), and is
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summarized in Sections 6 and 7. Other SETI researchers have also suggested the idea that the
emission from a natural stellar source might be engineered for the purpose of interstellar
communication. For example, a team of astronomers, calling themselves the "Stellar Lighthouse
group," plan to study stars in a particular field of the sky which are cataloged in the Kepler data
base to look in for unusual stellar emission patterns that might indicate evidence of intelligent
communication (Walkowicz, et al., 2012). Their data base, though, consists entirely of optically
visible stars. Hence they will not be examining neutron stars or radio pulsars.
The Stellar Lighthouse group likely plans to establish a priori what characteristics they would
consider as constituting evidence for an astro-engineered beacon and what statistical criteria they
will use before beginning to conduct their analysis of the Kepler data set. This, of course, is a
good approach. Pulsars, however, were not discovered as part of a SETI search. There was no
program set up beforehand having the objective of detecting pulsed broadband radio sources with
the aim of determining whether there might be sources with signal characteristics indicative of
alien intelligence or whether such sources might be showing alignments with key Galactic
benchmarks. The first radio pulsar was discovered through serendipity and subsequent
discoveries came about simply to discover whether similar sources might exist elsewhere in the
Galaxy.
As often is the case new discoveries are made after the data has already been collected and it
is only afterward that a pattern is recognized in that data. It was not until 1979, twelve years
after the first pulsar discovery, and after some 300 pulsars had already become discovered, that I
first noticed something unusual about two very unique pulsars, the Crab and Vela pulsars,
namely that they were aligned with or marking the two supernova remnants that happen to lie
closest to our solar system. The realization that these two highly unusual, attention-getting
pulsars should align with these two particular remnants caught my attention. Then, discovering
that the explosion dates for these two nearby supernova were separated by the time taken for a
radiation wave to travel from one to the other away from the Galactic center toward the
anticenter, I became alerted to the possibility that the supernova detonation events may have
been triggered by some sort of cosmic ray volley or gravity wave disturbance propagating away
from our Galactic core. This, along with other information, led me to hypothesize that these two
pulsars may be communication beacons of artificial origin alerting us to a Galactic core explosion
event, one that had passed through our solar system about 14,000 ± 2000 years ago. Checking
out the validity of this "superwave" hypothesis became the subject of my Ph.D. dissertation, and
the results proved to support this hypothesis. In the years that followed, more than 15
predictions of this superwave theory became subsequently confirmed.
One does not necessarily need to accept in advance the superwave hypothesis to see that
pulsar signals likely have an ETI origin and that a subset may be communicating a message. The
evidence reported here and in my book (LaViolette, 2006) stands on its own. But the superwave
hypothesis does provide a context which allows this interstellar message to be more easily
comprehended. Often researchers may believe they have perceived a pattern in their data and
will do an a posteriori statistical analysis of their a priori results to justify its presence. It is in
such situations that researchers must take a critical attitude of their own work and exercise
caution so as to not delude themselves. I have done my best not to fall into such a trap.
3. The Millisecond Pulsar: A Possible Astro-Engineered Communication Beacon
Let us for the present suppose that there exists a civilization that is able to travel far from its
home star system and that has the ability to engineer the cosmic ray flux of a neutron star so as
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to produce a collimated synchrotron radio beam directed towards our locale (Assumptions (2)
and (5)). Also let us suppose that a communicating civilization would likely make reference to
the location of the Galactic center (Assumption (6)). Carl Sagan and Frank Drake, for example,
saw fit to do so in their design of the Pioneer 10 space plaque message which was intended for
communication to other civilizations. Consider then that if a civilization did have the ability to
travel anywhere in the Galaxy and they wanted to communicate with our star system, where
would it be logical for them to place a beacon or beacons that would make explicit reference to the
Galactic center as seen from our viewing perspective?
It would be unlikely that they would place their marker beacon in exact coincidence with the
GC sky position as seen from our particular viewing direction since the strong broadband radio
flux emanating from the Sagittarius A* radio source would mask any such beacon, making it very
difficult to detect. An off center location would be a more likely choice. In fact, between 2002
and 2004, one very unusual bright transient pulsed radio source, GCRT J17445-3009, was
observed at a sky position about 1° of arc from the GC. This unique object is discussed further
in Section 5.
One alternative location would be to place their communication beacon at the galactic
anticenter location (l = 179.94, b = +0.05) where interference from background radio emission
would be particularly low. When examining a region around the galactic anticenter, the pulsar
that comes closest to this position is PSR J0538+2817. It lies 1.75° away at galactic coordinate
l = 179.72, b = -1.69. Significantly, its longitude coordinate lies just 0.22° from the anticenter
longitude. It is found to be embedded in a 105 year old supernova remnant S 147 and is believed
to have originated from the supernova explosion site at the remnant's center located at (l =
180.0°, b = -1.7°). Hence to within the accuracy of knowing the remnant's center, this supernova
explosion took place right on the galactic anticenter longitude coordinate, although the explosion
site deviates 1.7° in latitude. While it is within normal chance probability to find a pulsar lying
within 1.75° of the galactic anticenter, it is less probable to find one having a longitude coordinate
deviating by less than a quarter of a degree from the anticenter longitude. At the time of writing,
there are about 2267 known pulsars and statistics show that about 5% of these lie within ±5° of
the galactic plane in the outer part of the Galaxy spanning the longitude range from l = 90°
through 180° to 270°. So on the basis of chance occurrence, there should be odds of one in 7 that
a pulsar would be located within 0.22° of longitude of the galactic anticenter longitude; i.e.,
(0.22/180) X 2267 X 5% = 0.14. This is not an astoundingly statistic, but it does catch one's
interest, even considering that this pulsar has no unusual distinguishing characteristics that would
cause us to want to single it out from the other pulsars.
Another alternative way of making reference to the Galactic center would be to mark its
position along the galactic equator at northern or southern longitudes using the geometrical
concept of the radian. Looking down on the galactic plane and representing the galactic equator
as a circle with the solar system at the circle's center and the galactic center as a point on the
circle's circumference (at l = -0.0558°), we may take a chord equal to the circle's radius and mark
off two one-radian arcs on either side of the GC, which would deviate from the center by the
angle 360°/2Q = 57.2958°; see Figure 1. The Galactic center location may in this way be
indirectly indicated by galactic longitudes lying on either side of the GC position, at l = 302.648°
and l = 57.240°.
Such one-radian markers have the advantage that they not only explicitly refer to the Galactic
center but also employ a method that indicates that the beacon is intelligently situated, i.e., that
its creators have a knowledge of geometry, and that they make reference to our particular viewing
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location in the Galaxy. That is, these particular longitude sky positions only have significance as
Galactic center markers when viewed from our particular Galactic neighborhood location. The
same would be true if a marker beacon were placed at the Galactic anticenter location. Such
marker locations have the advantage of informing the recipient civilization that a beacon placed at
these locations is likely an extraterrestrial intelligent communication signal and not a natural
stellar source. In all of these cases, a beacon placed at these locations would necessarily be
Figure 1. Illustration of the one-radian markers relative to the Galactic center
(GC), as viewed from Earth.
intentionally targeting our solar system or local group of stars, possibly using a stationary
radiation beam.
What do we find at these two one-radian marker locations? Consider the southern GC radian
point (l = 302.648°, b = 0°). The pulsar whose sky position comes closest to this location is
one that is found at l = 302.637°, b = -0.866°, hence deviating by around 0.87° from this
location. It has a period of average length (~0.2 seconds) and no unusual distinguishing features.
Of the known pulsars, which currently number to be 2267, about 60%, or 1360, lie within ±5° of
the galactic plane in the longitude range from l = 270° through l = 0° to l = 90°. Hence for a
pulsar without any unusual characteristics it would not be unusual to find one coming within
0.87° of this southern point; i.e., (2.37 square degrees/ 1800 square degrees ) X 1360 = 1.8.
However it is interesting to note that the longitude coordinate for this pulsar deviates by just
0.011° from the southern one radian point longitude meridian. The odds of this happening due to
random chance are less probable, one chance in 12; i.e. 0.011/180 X 1360 = 0.083. Again, this is
not enormously improbable, but perhaps it is worth paying attention to.
Now consider the northern GC radian point (l = 57.240°, b = 0°). The pulsar that comes
closest to this point is PSR 1937+21, the well known Millisecond Pulsar. It is located at l
=57.509, b= -0.290 and comes within 0.4° of this one-radian point. If this were a pulsar that had
no particular distinguishing characteristics, there would be a chance of about one out of three of
finding one this close to this one-radian position ((0.5 square degrees / 1800 square degrees ) X
1360 = 0.38. But, on the contrary, this pulsar is indeed very distinctive which requires that we
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recalculate its probability. Unlike the pulsars at the other two marker locations we have
considered, this pulsar is one that really gets our attention. This pulsar has the following unusual
characteristics that make it stand out from the average radio pulsar:
a) It is the second fastest pulsing pulsar. (The fastest millisecond pulsar is found in a globular
cluster located very close to the Galactic center);
b) At radio wavelengths, it is the most luminous of all 130 known millisecond pulsars. Also it
is second brightest millisecond pulsar, exceeded only by a millisecond pulsar that lies 25 times
closer to us;
c) It is one of 14 pulsars known to emit giant pulses and when it emits a giant pulse, it becomes
the most luminous pulsar in the sky. It has been found to emit giant pulses as bright as 65,000
Janskys, as compared with the Vela pulsar which normally is the brightest pulsar and which
emits 5 Janskys. The Millisecond Pulsar giant pulses have brightness temperatures as high as 5
X 1039 K, making this the brightest temperature observed in the universe;
d) It is one of only 5 pulsars out of 2267 that emit optical pulses and also is the only
millisecond pulsar found to emit optical pulses;
e) It has the lowest proper motion of any pulsar known. Out of 233 pulsars which have had
their proper motions determined as of 2005, it has the lowest of all, essentially zero to within
the error of observation (0.8± 2.0 milliarc seconds per year). This is of interest from the
standpoint of this pulsar serving as a position marker because, of all pulsars, the Millisecond
Pulsar does not move from the important sky location it appears to be marking.
Each of these unusual characteristics are ones that would tend to get the attention of a
recipient civilization, hence making the Millisecond Pulsar qualify as a marker pulsar. These
five rather rare characteristics may be considered as being independent of one another. For
example, 42 of 45 glitching pulsars do not exhibit giant pulses and 11 of 14 pulsars that exhibit
giant pulses do not exhibit optical pulses. So, given the large percentage of non-correlating pulsar
characteristics, one is led to conclude that these characteristics are not related to one another.
Furthermore, no one has proposed a model that predicts any mutual causal relation between
these various characteristics. In the case where there is overlap, for example where a pulsar that
undergoes glitching also exhibits giant pulses, such pulsars are predominantly found to be
members of the Galactic message subset described here. Employment of more than one unusual
behavioral characteristic on the same pulsar would be logical from the standpoint of attracting the
attention of the message recipient to this subset.
One may ask what is the probability that a pulsar would have all these unusual characteristics
and also come this close to marking this particular Galactic location? The probability for a pulsar
to have characteristic (a) is about one out of 1133, the probability to have characteristic (b) is one
out of 130, the probability to have characteristic (c) is one out of 162, the probability to have
characteristic (d) is one out of 453, and the probability to have characteristic (e) is one out of
233. Assuming that these characteristics are uncorrelated with one another, we can multiply their
probabilities to figure the rarity of having a pulsar with all of these unusual characteristics. This
calculates to be 1.3 X 10-13 (1/3 X 1/1133 X 1/130 X 1/162 X 1/453 X 1/233). So the chance
that a pulsar has all these unique characteristics and is located at this particular sky location
estimates to one chance in 7.6 trillion!
Even if this method of figuring the statistics is off by several orders of magnitude, most
would agree that finding such a unique pulsar at this particular sky position that has ETI
communication significance, particularly from our Galactic viewing perspective, is quite
11
extraordinary. Hence, it is worth paying attention to as a possible example of an artificially
engineered beacon. On the other hand, one who is unwilling to consider the seven assumptions
listed above as a context for its interpretation may be left to conclude that this is one of Nature's
statistical flukes, one that should be entered into the Guiness Book of Records.
The Millisecond pulsar is discussed here first, because it constitutes the clearest and easiest
to understand proof of the pulsar-ETI hypothesis. But, it should be pointed out that the
Millisecond Pulsar was discovered after this hypothesis had already been formed. As mentioned
in Section 2, I had first come to the conclusion that pulsars were likely ETI beacons in 1979 by
studying the characteristics and sitings of the Crab and Vela pulsars. I documented this two
years later, in 1981, in my doctoral program laboratory notebook which I was using to tabulate
data to test this core explosion theory . The Millisecond Pulsar was discovered in 1982 and the
Eclipsing Binary Millisecond pulsar in 1988. Since the Millisecond Pulsar marks a point about
one radian from the Galactic center, I interpreted this as signifying that it too conveys a message
that makes reference to the Galactic center, providing very strong support for my earlier
interpretation of the Crab and Vela pulsars. That is, the one-radian concept here makes reference
both to the Galactic center and to the distance from the Galactic center to Earth.
Because the pulsar-ETI hypothesis was already formulated prior to the Millisecond pulsar
discovery, this should rule out what is sometimes called the lottery fallacy. This is where one
seeks out the one person out of millions who had the good fortune of winning a lottery and then
calculating how improbable it was that they had won. In an analogous way, one might object that
in performing the above probability calculation I had consciously sought out the one pulsar that
had among the most unusual attention-getting characteristics of the entire pulsar population to
calculate the odds that a pulsar at this particular location would have them. Since the pulsar-ETI
hypothesis had already been formulated within a Galactic-center-to-Earth context and since this
one radian location makes similar symbolic reference to the Galactic center and Earth viewpoint
location, it cannot be said that we are choosing this one radian location simply because a very
unusual pulsar is located there. Besides, as noted earlier, it would be logical for a communicating
civilization to make some kind of reference to the Galactic center in their message.
4. Related Pulsars in the Message Subset
If we choose to agree that the marking of this particular sky position is not a highly
improbable fluke of Nature, that the very unusual Millisecond pulsar might instead be a beacon
engineered by an intelligent civilization (or civilizations) in the Galaxy to intentionally mark this
key location which has extraterrestrial communication significance, then we are ready to consider
other unusual sitings of distinctive pulsars which together with the Millisecond pulsar appear to
synergize with one another to compose a symbolic message. The other pulsars in this
communicating subset include the Vulpecula pulsar (1930+22), the Eclipsing Binary Millisecond
pulsar (1957+20), the Vela pulsar, the Crab pulsar, and pulsar 0525+21.
The Vulpecula pulsar is the closest pulsar to the Northern one-radian longitude meridian,
deviating by just 0.1° of arc. Its position is collinear with the Millisecond Pulsar and the star
Gamma Sagittae; see Figure 2. Of stars that are visible to the naked eye, Gamma Sagittae, a 3.5
magnitude star, is the one that has the closest sky position to the Galaxy's northern one-radian
point longitude meridian. Consequently, it is a natural benchmark location for referencing the
Galactic center. The trajectory from the Vulpecula pulsar, through the Millisecond Pulsar
position currently projects within 0.01° of arc of Gamma Sagittae and would have been in exact
alignment about one millennium ago. A 0.01° deviation would have odds of one in 18,000 if due
12
to chance. If this alignment is instead interpreted as being intentional, it would imply that the
sending civilization knew the positions of stars visible from our particular viewing perspective
and that are bright enough to be easily seen by us. This implies that the sending civilization
either had traveled to our location some time in the past and learned the layout of the stars visible
in our sky, or that they have a highly accurate astronomical measurements of the locations and
relative distances of stars in the Galaxy and use of a highly sophisticated computer model capable
Figure 2. A sky diagram showing the location of the Millisecond Pulsar (PSR 1937+21),
Eclipsing Binary Millisecond Pulsar (PSR 1957+20), and the Vulpecula pulsar (PSR
1930+22) relative to the stars that form the constellation of Sagitta, the Celestial Arrow.
of projecting how the starry sky would look from any chosen point in the Galaxy.
The Eclipsing Binary Millisecond (EBM) pulsar, or "Black Widow pulsar" as it is commonly
known, is another that further calls our attention to the Galaxy's northern one-radian point. This
radio pulsar is unusual in that its pulse period comes closest of all pulsars to that of the
Millisecond Pulsar, deviating by just 3.184%, and yet it has a sky location just 4.5° away. This
alone beats the odds of random probability. To be the one pulsar that has a period closest to that
of the Millisecond Pulsar, the chances are one in 2267. The chance of a pulsar lying only 4.5°
away from the Millisecond Pulsar, yields one chance in 28; i.e. Q X (4.5)2 / (180° X 10°).
Furthermore the EBM pulsar is also distinctive in that it is one of only 14 eclipsing binary
millisecond pulsars. It is also the fastest pulsing millisecond pulsar of all eclipsing binary pulsars
and in addition has the most circular binary orbit of all. Its orbit deviates from perfect circularity
by less than one part in a billion! To date no one has offered an explanation as to how such
perfect circularity could be achieved by natural means. Moreover because it is eclipsing, its
13
orbital plane is aligned approximately in the direction of our solar system. So the chances of it
being such a unique eclipsing binary pulsar are one in 2267. In addition, the EBM pulsar is
unique in that it is one of only 14 pulsars known to emit giant pulses, giving a chance of one in
162. The chance of a pulsar having all of the above unique characteristics figures to be one chance
in 23 billion; i.e., 1/(2267 X 28 X 2267 X 162)
The galactic longitude of the EBM pulsar deviates from the longitude of the Millisecond
Figure 3. Positions of Millisecond Pulsar and EBM Pulsar in the vicinity of the
Galactic one-radian point showing how the layout of their longitudes depicts the
pi ratio.
Pulsar by an amount BC = 1.68807°; see Figure 3. Dividing this by the angular deviation of the
Millisecond Pulsar from the Galaxy's northern one-radian point, AB = 0.26895°, yields the ratio
6.2765, very close to the 2Q ratio 6.2832. Due to the proper motion of the EBM pulsar, the
ratio would have been exactly 2Q around 1775 C.E. Having established earlier that the
Millisecond Pulsar is associated with the one radian concept in a Galactic message context, it
follows logically to associate this pulsar's deviation from the Galaxy's northern one-radian point,
chord AB, also with the concept of one-radian. Then noting the unusual circularity of the EBM
pulsar's binary orbit, it is logical to associate this pulsar with the concept of the circumference of
a circle, and to associate the same metaphor with the longitudinal deviation of this pulsar from its
Millisecond Pulsar partner, chord BC, The above mentioned finding that the ratio of BC to AB
comes exceedingly close to 2Q, further validates this symbolism relating the EBM and
Millisecond Pulsar pair. Thus these two pulsars synergistically reinforce the one-radian
symbolism inferred for the Millisecond Pulsar. It is expected that an extraterrestrial
communication message would make use of geometrical relationships such as this since geometry
is a universal language that should be understood by all civilizations in the Galaxy.
The current sky position of the EBM pulsar deviates just 0.0018° from the galactic longitude
14
position that would allow the BC chord to make a perfect 2Q ratio with AB. For any pulsar to
come this close to this position, the odds are one chance in 74, i.e., (0.0018/180) X 1360 =
0.0136. For this particularly unique eclipsing binary millisecond pulsar to be so located, one
having the unusual characteristics mentioned above, the odds are one in 1.7 trillion (1/ (2.3 X 1010
X 74). When this is multiplied with the probability figured earlier for the siting of the
Millisecond Pulsar, one obtains odds of one chance in 1.3 X 1025.
There is also the additional observation that the sky position of the EBM pulsar is such that
trajectories drawn from it to the Galaxy's northern one-radian point and also to the star Gamma
Sagittae make an almost perfect 90° angle, deviating by just 0.15° of arc. We haven't included the
odds of this in our calculation. But hopefully odds as small as one in 1025 are sufficient to make
the point in favor of the ETI interpretation. Some may disagree with the particular numerical
value obtained here for these odds. But regardless of how they are figured, they are incredibly
small that the Millisecond Pulsar and Eclipsing Binary Millisecond pulsar would have such
unique attention-getting characteristics and be making these particular geometrical alignments.
Moreover the one-radian symbolism that they convey is relevant to their location.
The Crab and Vela pulsars also stand out as being quite unique. The Crab pulsar lies 6,585 ±
200 light years from us at a sky location that lies at galactic coordinate (184.56°, -5.78°), 7.5°
from the galactic anticenter; see Figure 4. It is associated with the Crab nebula, a remnant
produced by a supernova that was observed in 1054 CE. The Vela pulsar lies just 815 ± 100
light years from us toward galactic coordinate (263.55°, -2.79°) and overlies the Vela supernova
remnant which was produced by a supernova that would have been observed about 12,800 years
ago. Significantly, of all known 274 supernova remnants having ages less than 105 years, these
are the two that lie closest to our Sun.
Also these two pulsars are very distinctive. Like the Millisecond Pulsar, they both have the
rare property of emitting optical pulses and giant pulses. Also they both exhibit pulsar period
glitches, and both produce pulses also in the X-ray and gamma ray spectral region making them
among the most easily detected of all pulsars. Furthermore they are distinctive because of their
luminosity and brightness. The Crab pulsar is the most luminous pulsar and is also the brightest
pulsar in the sky at optical, x-ray, and gamma ray wavelengths. At radio wavelengths it is the
second brightest, exceeded only by the Vela pulsar, which is located eight times closer. These
two pulsars may literally be called the "King and Queen of pulsars". One might ask then, what
15
Figure 4. The positions of the Crab and Vela supernova explosions relative
to the solar system.
are the chances of finding two highly unique pulsars and also the most luminous and brightest in
the heavens marking these two supernova remnants that are closest to the Sun?
Of the 279 known supernova remnants in the Galaxy, only 54, or about 19%, have pulsars
associated with them. So the odds that one of the two closest supernova remnants would have a
pulsar associated with it are about one in five. The odds that radio pulsars would be associated
with both of the two closest supernova remnants are one in 25 (i.e., 1:52).
But this grossly underestimates the probability of the Crab and Vela pulsar supernova
associations. We must consider also the uniqueness of these pulsars. Let us begin with the Crab
pulsar. The odds that the Crab nebula would be associated with a pulsar that has the attentiongetting
characteristic of being the most luminous radio pulsar in the sky when observed from the
radio through the gamma ray part of the spectrum) are one in 11,335; i.e., 1/(5 X (2267).
Considering that this pulsar also exhibits a large number of unique attention-getting properties
such as optical pulses (observed in 0.44% of pulsars), giant pulses (observed in 0.62% of
pulsars), interpulses (observed in 1% of pulsars), and period glitches (observed in about 3% of
pulsars), then the odds that a pulsar would be the most luminous of all, have all of the above
unusual features and also coincide with one of these two remnants is estimated at one in 611
million, [1/(5 X 2267)] X 0.0044 X 0.0062 X 0.01 X 0.03 = 1.6 X 10-9.
Vela shares all the same unusual attention-getting features that characterize the Crab pulsar,
except that it is instead the third most luminous pulsar. So the Vela pulsar association with the
Vela remnant may be calculated in a similar fashion except that it is two times more likely than
the Crab pulsar probability. Hence for Vela the odds are 1.2 X 109. The odds of both the Crab
and Vela pulsars coinciding with these two nearby supernova remnants, the closest to the Sun,
are then about one chance in 1018, i.e. 1.6 X 109 X 1.2 X 109.
Some may argue that young pulsars are among the more luminous hence that it would be
expected that a remnant as young as the Crab pulsar (~1000 years old) would have a pulsar that
would be unusually luminous. This reasoning, however, would not predict that the Crab remnant
16
would harbor the most luminous pulsar in the sky. Nor would it predict that its pulsar should
have emission at x-ray and gamma ray wavelengths. Moreover in the case of the Vela pulsar,
there is no evidence that it originated in a young supernova explosion. In fact, its ties to the
middle aged Vela remnant are quite shaky. It appears merely to be marking the Vela supernova
remnant through line-of-sight superposition. Its speed and trajectory indicate that, at the time of
the Vela supernova, its sky position was over 20 light years from the Vela explosion sky
position, hence indicating no reasonable association.
It is this sort of attention-getting coincidence estimated above, one chance in a billion billion,
that leads one to probe deeper to find out whether there might have been some important reason
to call our attention to these nearby supernova explosions. Looking into the history of these
supernova remnants and times when their explosions detonated at each location, one finds that
their explosions are temporally separated by the time taken for a light ray or high energy cosmic
ray to travel at the speed of light rectilinearly away from the Galactic center! We are given the
impression of an energetic disturbance issuing from the Galactic center as a result of a core
explosion, traveling radially out through the Galaxy at the speed of light, passing through our
solar system about 12,150 B.C.E., then causing the Vela supernova progenitor star to explode
about 11,570 B.C.E. (visible in 10,750 B.C.E.), and then causing the Crab supernova progenitor
star to explode about 5,530 B.C.E. (visible in 1054 AD); see Figure 4 (LaViolette, 1987). This
notion that the Crab and Vela pulsars may be part of an ETI message intentionally notifying us
of a light-speed cosmic ray volley, or superwave, that impacted our planet around 14,150 years
17
Table 2
Pulsar
Gamma
pulses
X-ray
pulses
Optical
pulses
Giant
pulses Interpulses
Period
glitches
Ultrashort
period
Crab x x x x x x
Vela x x x x x x
Millisecond x x x
EBM x x
Vulpecula x
PSR0525+21 x
ago becomes increasingly plausible when we note that the one-radian symbolism of the
Millisecond Pulsar implies a one-radian vector directed from the Galactic center to the Sun.
Curiously, of all pulsars the Millisecond Pulsar is the only one other than the Crab and Vela
pulsars to exhibit both optical pulses and giant pulses, thus inviting a mutual association of the
three; see Table 2.
A recent Galactic core explosion is a likely topic for interstellar discussion because core
explosions are a phenomenon that all civilizations in our Galaxy would be aware of and to
varying extents would be affected by. A check of the geologic record indicates that at the end of
the ice age 16,000 to 11,000 years ago the Earth did have a prolonged increase in its beryllium-10
production rate relative to the Holocene period, suggesting a higher than normal cosmic ray
exposure (LaViolette, 1983, 1987, 2005). Also a variety of astronomical evidence indicates that
an energetic cosmic ray volley did radiate isotropically from the Galactic center, pass through the
Solar System at about that time, and is currently in the vicinity of the Crab Nebula and
Cassiopeia A supernova remnants where it is energizing them (LaViolette, 1983, 1987, 2005).
There are other pulsars that appear to be part of this message, such as PSR 0525+21, a
glitching pulsar positioned just 1.3° of arc from the Crab pulsar. This one appears to be pointing
out the orientation of our solar system's ecliptic plane in the sky and the angular deviation of the
ecliptic plane from the Crab pulsar sky position (LaViolette, 2006).
5. Transient Pulsar GCRT J17445-3009
Another radio source that may be an artificial beacon calling our attention to the Galactic
center is the transient radio pulsar GCRT J17445-3009 (LaViolette, 2006). This source was
observed on three occasions between September 2002 and March 2004, and since that time has
not been seen again (Hyman, et al., 2005). This one may be considered a candidate for several
reasons. First, it was unusually bright. When it was observed between September 2002 and
September 2003, it shone with a radio brightness of 1.67 Janskys making it the second brightest
pulsed radio source in the sky, exceeded only by the Vela pulsar. Its brightness temperature was
estimated at about 1016 K implying an energy density vastly exceeding those of most other
classes of radio sources (Hyman, et al., 2005). This led its discoverers to conclude that it was
beaming coherent emission to us. Second, as a transient source, it was very unusual since no
other transient radio source has been observed to produce pulses with such regularity, unless one
wishes to interpret it as an extreme nulling pulsar as have Zhu and Xu (2014). A third unusual
feature is its unusually long period of 77 minutes. The longest period radio pulsar has a period of
11.7 seconds; so this one has a period that is longer by a factor of 395. Fourth, the radio pulse of
the transient source spanned 10 minutes, or 13 percent of its pulse period. Few pulsars exhibit a
18
pulse that spans such a large fraction of its pulse period. Others that do so include the Crab
pulsar, the Vela pulsar, and about three others. A fifth feature that prompts one to single out is
that the sky position of this source is so close to the Galactic center. The source lies just 1.1° of
arc southwest of the Sgr A* and is at about the same distance away as the Galactic center. Since
the time that it was discovered, only two pulsars have been found which have sky positions
closer to the GC by about 8 minutes of arc. But no unusual characteristics have been reported
that would make them stand out in a similar way.
The probabilities for this pulsar calculate to be 2/2267 that it would be the second brightest
radio pulsar, 1/2267 that it would have the longest pulsar period, 6/2267 that it would be a pulsar
whose pulse occupies a substantial fraction of its pulse period, and 3/2267 that it would be the
third closest to the Galactic center. All together, the chances of having a pulsar with all of these
unique characteristics figures to one chance in 324 million.
Prior to the discovery of this source I had proposed that a subset of radio pulsars, those
discussed above, are making explicit reference to the Galactic center (LaViolette, 2000b). So
subsequently finding this very unique transient source positioned so close to the Galactic center
sky position, led me to conclude that it too is likely a beacon that was intentionally placed to call
our attention to the Galactic center (LaViolette, 2006), although since its discovery it has
remained radio quiet.
6. A Technology for Producing a Pulsar-like Communication Beam
The method of astro-engineering pulsar emissions that I have proposed presupposes that a
civilization has developed the ability to journey close to a cosmic ray emitting neutron star or Xray
star. Once positioned in its vicinity and properly shielded from its cosmic ray flux, a
properly equipped spaceship could project a maser beam to an ionized region in the star's corona
and phase conjugate microwaves reflected back to the maser to produce a self-amplified, phase
conjugate soliton beam between the ship's maser generator and the star's corona (LaViolette,
2000b, 2006). Such microwave phase conjugate resonator technology has been developed by the
military mainly for use as a directed energy weapon or for space propulsion (LaViolette, 2008),
although its application to radar signal amplification has also been explored (Chu, et al., 1993).
By interfering properly chosen microwave frequencies, it is possible to create a magnetic field
grating pattern in the star's coronal region that would locally decelerate its outgoing relativistic
electron (and proton) flux and produce an outward directed synchrotron beam. Due to the
relativistic beaming effect, this emitted radiation would be confined to a forward-directed conical
beam having an aperture of 2/γ radians and a luminosity that would scale as 8γ3, where γ is the
Lorentz factor of the cosmic ray electrons. The Crab pulsar neutron star is estimated to emit
cosmic ray electrons having Lorentz factors of up to γ ~ 107. In this case, the generated
synchrotron beam would have a divergence of ~10-7 radians, which would produce a beam target
diameter of about 40 AU at a distance of 6500 light years.
By modulating the magnetic field intensity of the grating pattern, the communication beam
intensity may be modulated in periodic fashion to produce highly precise, attention-getting
pulses. Grating fields oriented perpendicular to the outgoing cosmic ray flux would generate
linearly polarized synchrotron emission while fields oriented parallel to the outgoing flux would
be effective in generating circularly polarized emissions. Through proper manipulation of this
remote field grating pattern, pulsed signals could be produced having complexities comparable to
those observed to come from pulsars.
19
7. Synchrotron Particle Beam Communicators vs. Phased Array Antenna Communicators
The proposal of stationary broadband radiation beams targeted on distant stellar locations,
initially proposed 14 years ago (LaViolette, 2000a, 2000b), has more recently received indirect
support from the ideas presented by the Benford group. Benford, et al. (2010a, 2010b) have
shown that there is an economical advantage in using stationary targeted broadband
electromagnetic beams for communication with extraterrestrial intelligence (CETI) in that far less
power and operating cost is required to send one's signal as compared with more traditional
discrete-frequency, non-directed radio transmissions.* As an example of how such a
communicator beam might be constructed, they propose using a deployed array of microwave
antennas fed by high-power gyrotrons and networked to operate as a phased array so as to emit a
pulsed microwave beam in a particular direction. In one of their examples, they consider a 5.1 km
diameter antenna array consisting of 3000 gyrotrons, each capable of emitting a few megawatts of
power. They figure a total power requirement of 6.9 GW and antenna gain of ~109 to produce an
effective isotropic radiated power (EIRP) of 1019 watts. This is emitted as a beam having an
angular divergence of about 10-4 radians which is able to communicate over a distance of ~6000
light years and illuminate a region about 1 light year in diameter. They propose transmitting at a
frequency of ~1 GHz and estimate a bandwidth of about 1 megahertz for the oscillator power
levels they consider, the limited frequency spread of their beam being determined by the physics
of microwave oscillation in gyrotron cavities.
Ten years earlier a substantially different method was proposed for a "low-tech" terrestrialbased
device capable of producing a targeted interstellar communication beam, one that involved
modulating the output of a free-electron maser (LaViolette, 2000b, 2006, Appendix B). In this
design, a linear accelerator would generate a continuous beam of ultra relativistic electrons which,
in turn, would be directed into a wiggle field modulator consisting of transverse magnetic fields
generated by a series of superconducting magnets. These wiggle fields would cause the electrons
to emit a beam of synchrotron radiation. Another version of the device configures the imposed
magnetic field lines parallel to the particle trajectory so as to produce an electron cyclotron
maser. In either version, due to the relativistic beaming effect, this emitted radiation is confined
to a forward-directed narrow conical beam having an aperture of 2/γ radians and a luminosity that
would scale as 8γ3, where γ is the Lorentz factor of the cosmic ray electrons. By varying the
power to the imposed magnetic fields, the communication beam intensity may be modulated in
periodic fashion to produce highly precise, attention-getting pulses.
The radiation beam of this communicator was proposed to have a median frequency of f =
400 MHz and bandwidth of Δf = 400 MHz and an intensity sufficient to produce a 0.8 Jansky
signal at a distance of 6500 light years, hence a signal strength equal to that coming from the Crab
pulsar. Calculations indicate that this would require a particle accelerator capable of producing a
1 megawatt beam of 50 Gev electrons having a Lorentz factor of γ = 2 X 105. The particles
would produce a syncrotron beam whose divergence calculates to be 10-5 radians, which yields a
beam diameter of about 0.065 light years (4 AU) at a target distance of 6500 light years provided
that the particle beam cosmic rays have trajectories that are initially parallel to one another.
Choice of a lower γ for the particle beam increases the beam divergence and reduces the Doppler
boosting of the synchrotron emission but necessitates an increased relativistic particle energy flux
________________
* Thinking that the idea of a targeted broadband interstellar communication beam was novel, the
media stories that reported on the Benfords' papers labeled these as "Benford beacons." But, the idea
was not novel as this idea had been proposed 12 years earlier (LaViolette, 2000a, 2000b).
20
to maintain an equivalent target signal intensity. I had conservatively estimated an efficiency of
1% for converting electric power to relativistic electron power and in turn into synchrotron beam
power. Hence the proposed communicator would require an input power of 100 MW to
operate. So it would use about 70 times less power than what the Benfords estimate for their
phased array communicator and would produce a beam having a 50 fold lower EIRP.
I did not estimate a cost for constructing the proposed particle beam communicator, but it
should not cost much more than $5 billion, the cost of constructing the Large Hadron Collider.
Using an input power of 120 MW, the Large Hadron Collider generates 70 Gev electrons
(Lorentz factor γ ~ 2 X 105), hence comparable to this communicator example. One must
consider that the cost of accelerator technology is progressively dropping over the years with the
advent of beat wave and wake field accelerators used in producing free electron lasers. So the
construction cost could be substantially less than estimated here. Certainly, it would be an order
of magnitude less than the $41 billion that the Benfords estimate for their 6000 light-year pulsed
beam communicator.
The Benfords refer to their phased array communicator as broadband, as distinguished from
the prior notion of discrete frequency communication. I also had used the term broadband to
refer to the pulsar particle beam communicators (LaViolette, 2000b). However, these synchrotron
beacons would produce a much broader frequency spread than those that the Benfords have
considered (Δf > 100 MHz as compared with Δf ~ 1 MHz). Hence compared to the broadband
beams of the Benfords, these particle beam beacons would be ultra-broadband. It is generally
agreed that a beacon that spans a greater bandwith is desirable from the standpoint of ETI communication
since this increases the chance of the beacon being detected by a target civilization.
Use of a natural cosmic ray source such as a neutron star, instead of a fabricated particle
accelerator, to power a synchrotron beam communicator has the advantage that one would have a
much greater spread of relativistic particle energies and hence would necessarily produce a much
broader spectrum synchrotron beam spanning many decades of the radio frequency spectrum and
in some cases could extend up to optical X-ray, and gamma ray wavelengths. Compared to the
more "low-tech" earth-based particle accelerator communication beam technology, this starengineered
beam technology would have a much lower energy demand. An initial investment of
energy would be needed to power up the maser phase conjugate resonator to create the projected
field grating pattern. But once the phase-conjugate beam was activated, no additional energy
would be needed to be added to it since the soliton beam would be able to entrain energy from the
impinging stellar cosmic ray flux. That is, energy from the outgoing cosmic rays would transfer
to the maser soliton beam within the wiggler field grating pattern established in the star's corona,
thereby allowing the maser beam to become self-powered. Also it is characteristic of phase
conjugate resonators that they confine their maser flux to their resonator beam which produces
relatively low energy losses.
Many such stationary pulsed synchrotron beams could be produced and pointed in various
directions away from a single neutron star to continuously target a large number of Galactic
locations. This would avoid the need to retarget a single beam to a series of different locations in
a repeating cycle as the Benfords' technique requires. Consequently, we would be aware only of
the existence of those beams being targeted directly towards us. What we have detected as pulsar
signals may be beams being aimed in the direction of our Galactic neighborhood.
Assuming that a phased microwave antenna array would be the only way a civilization would
be able to generate a targeted broadband communication beam, the Benfords (2010c) have chosen
to interpret pulsars as natural sources and have advised that SETI investigators should avoid
21
confusing pulsar signals with ETI communication sources. They state their belief that pulsars are
"clearly radiation from rotating star magnetospheres." However, on the contrary, a large number
of pulsar astronomers do not take such a confident stance about the explanatory power of the
lighthouse model. As a conceptual model it is useful for discussing and publishing various pulsar
observations, but many astronomers are far from satisfied with it, as was pointed out earlier.
As one example, the lighthouse model is easily disproved in the case of the Crab pulsar. The
Crab pulsar has a pulse that spans a large portion of its period, but it also exhibits an interpulse
about 145° after the main pulse. Pulsar modelers have attempted to explain the first feature as
indicating that the pulsar is aiming its pole towards us and precessing its hot spot around this
axis to create an extended pulse. But they attempt to explain the second feature by assuming that
the main pulse and interpulse come from opposite poles of the neutron star and that the pulsar's
axis is spinning end-for-end relative to our line of sight so that first one pole and then the other
shines in our direction. But these interpretations are completely incompatible with one another
leading one to conclude that the lighthouse model explanation for the Crab pulsar must be
incorrect.
Also the lighthouse model has difficulty accounting for the off-pulse constant background
emission observed in pulsars PSR B0525+21 and PSR B2045-16. In both of these pulsars radio
synchrotron emission has been detected at a pulse phase angle far from the main pulse (Basu, et
al., 2011, 2012). The pulse profile is typically sampled in the off-pulse phase range from 80° to
250° from the center of the main pulse, the main pulse spanning about 20° of the 360° pulse
phase. This low level emission prevails as a residual beamed flux that is emitted in between the
pulsar's main pulses at 5% of the main pulse intensity in PSR B0525+21 and 1.5% of the main
pulse intensity in PSR B2045-16. Observation has shown that the off-pulse emission has about
the same spectral index as the main pulse emission and hence must originate from the pulsar's
immediate vicinity as coherent beamed radio emission (Basu, et al., 2012). Hence emission from
a pulsar wind nebula has been ruled out. This phenomenon cannot be explained as emission
coming from the pulsar's magnetic pole because during this off-pulse interval its pole would be
expected to point away from the observer. Consequently, the lighthouse model has a difficult
time accounting for this. A beacon projecting a stationary targeted beam, however, could produce
this residual emission simply by decreasing the magnetic field intensity in the artificially
generated grating pattern and thereby diminishing the intensity of the emitted synchrotron flux to
a much lower level.
The Benfords state that one reason radio pulsars should not be considered as ETI beacons is
that they have a very large bandwidth of at least 400 MHz and that this is far larger than the 1
MHz bandwith limit imposed by the physics of their phased array antenna technology.
Apparently assuming that their method is the only conceivable method for generating targeted
radio beams and being convinced totally that pulsars are natural objects, they even suggest that a
communicating civilization would produce a signal that is not pulsar-like to ensure that their
transmission is not mistaken as coming from a natural source! This illustrates the point made
earlier that the assumptions that one holds, or paradigm that one adheres to in regard to CETI
capabilities plays a major role in one's decision as to whether an observed source might be or
might not be of ETI origin. It is my opinion that the Benfords' decision to rule out pulsars is
rooted in their restriction to the particular technology they have proposed for their broadband
communicator.
Take as an example their interpretation of the transient radio pulsar GCRT J17445-3009.
Four years after I had noted the possible ETI nature of this source (LaViolette, 2006, Ch. 5),
22
Benford, et al. (2010b) also discussed whether or not this source might be of ETI origin, noting
its extremely unusual nature. They conclude that it was likely not an engineered signal because it
would cost too much for an alien civilization like our own to build a powerful enough transmitter.
Here they consider that the transmitting civilization would use a phased array antenna
technology and presumably would be transmitting from the vicinity of their home planet. They
conclude that an antenna array large enough to produce the observed 1.67 Jansky radio signal
intensity from a distance comparable to a Galactic center distance of 26,000 light years would
cost about $20 trillion. They note that even if the transmitter were located as close as 1000 light
years, the cost would still be prohibitive at $730 billion. So they state that if it is an ETI beacon,
it must be much closer to us.
However, analysis of records of the GCRT J17445-3009 radio bursts indicate that their
coherent emission was predominantly circularly polarized (Roy, et al., 2010). This fits with the
particle beam communicator model suggested here in which the braking magnetic field is aligned
parallel to the cosmic ray electron flux, since the resulting electron cyclotron maser emission
would be characterized by a high degree of circular polarization. Beamed emission from a phased
antenna array, however, would have a rather small circular polarization component since any
circular polarization produced by adjacent microwave horns in the antenna array would oppose
and cancel out one another.
8. Conclusion
As discussed in section 3, besides the Galactic center, there are three principle sky positions
viewable from our solar system where a civilization could site a communication beacon and be
assured that their signal would be interpreted as an ETI message through its reference to the
Galactic center, these being the galactic anticenter location and the northern and southern
locations along the galactic equator that lie one radian from the Galactic center. One of these, the
Galaxy's northern one-radian point is clearly and unambiguously marked by an astoundingly
unique source. The unusually low chance probability of finding a pulsar as unique and attentiongetting
as the Millisecond Pulsar so close to the position that lies one-radian from the Galactic
center should by itself give strong support to the interpretation that this pulsar in particular is an
interstellar communication beacon. But in addition, there are several other unusual pulsars in this
vicinity which synergistically reinforce this interpretation. When considered together with the
strategic placement of the highly unique Crab and Vela pulsars which share many of the same
unique characteristics as the Millisecond Pulsar, the conclusion that they are communicating a
message involving reference to the Galactic center becomes even more convincing. Besides this
there is the temporary appearance of the radio pulsar transient source GCRT J17445-3009 which
also raises interest because of its close proximity to the Galactic center.
We are therefore led to conclude that this subset of pulsars, as well as other radio pulsars, are
artificial sources, and that Jocelyn Bell's first hunch was indeed the correct one. Of course, those
who choose not accept the ETI hypothesis and who also feel uncomfortable in accepting the
improbability of a natural explanation, always have the third option: namely that our Galaxy is
intelligent and is trying to communicate with us.
23
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