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THE ELECTRONIC JOURNAL OF
THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
Volume 5, Number 5 - December 1993
The Electronic Journal of the Astronomical Society of the Atlantic
(EJASA) is published monthly by the Astronomical Society of the
Atlantic, Incorporated. The ASA is a non-profit organization
dedicated to the advancement of amateur and professional astronomy
and space exploration, as well as the social and educational needs
of its members.
DETECTABILITY OF EXTRATERRESTRIAL TECHNOLOGICAL ACTIVITIES
Guillermo A. Lemarchand [1]
Center for Radiophysics and Space Research
Cornell University, Ithaca, New York, 14853
1 - Visiting Fellow under ICSC World Laboratory scholarship
Present address: University of Buenos Aires,
C.C.8-Suc.25,
1425 - Buenos Aires,
Argentina
This paper was originally presented at the Second United
Nations/European Space Agency Workshop on Basic Space Science
Co-organized by The Planetary Society in cooperation with
the Governments of Costa Rica and Colombia, 2-13 November 1992,
San Jose, Costa Rica - Bogota, Colombia
Introduction
If we want to find evidence for the existence of extraterrestrial
civilizations (ETC), we must work out an observational strategy for
detecting this evidence in order to establish the various physical
quantities in which it involves. This information must be carefully
analyzed so that it is neither over-interpreted nor overlooked and
can be checked by independent researchers.
Page 1
The physical laws that govern the Universe are the same everywhere,
so we can use our knowledge of these laws to search for evidence
that would finally lead us to an ETC. In general, the
experimentalist studies a system by imposing constraints and
observing the system's response to a controlled stimulus.
The variety of these constraints and stimuli may be extended at
will, and experiments can become arbitrarily complex. In the
problem of the Search for Extraterrestrial Intelligence (SETI), as
well as in conventional astronomy, the mean distances are so huge
that the "researcher" can only observe what is received. He or she
is entirely dependent on the carriers of information that transmit
to him or her all he or she may learn about the Universe.
Information carriers, however, are not infinite in variety. All
information we currently have about the Universe beyond our solar
system has been transmitted to us by means of electromagnetic
radiation (radio, infrared, optical, ultraviolet, X-rays, and gamma
rays), cosmic ray particles (electrons and atomic nuclei), and more
recently by neutrinos.
There is another possible physical carrier, gravitational waves, but
they are extremely difficult to detect.
For the long future of humanity, there have also been speculations
about interstellar automatic probes that could be sent for the
detection of extrasolar life forms around the nearby stars.
Another set of possibilities could be the detection of
extraterrestrial artifacts in our solar system, left here by alien
intelligences that want to reveal their visits to us.
Table 1 summarizes the possible "information carriers" that may let
us find the evidence of an extraterrestrial civilization, according
to our knowledge of the laws of physics. The classification of
techniques in Table 1 is not intended to be complete in all
respects.
Thus, only a few fundamental particles have been listed. No attempt
has been made to include any antiparticles. This classification,
like any such scheme, is also quite arbitrary. Groupings could be
made into different "astronomies".
Page 2
TABLE 1: Information Carriers
|-
| Radio Waves
| Infrared Rays
|- | Optical Rays
| Photon Astronomy| Ultraviolet Rays
| | X-Rays
Boson | | Gamma Rays
Astronomy | |-
| Graviton Astronomy: Gravity Waves
|- |-
| Neutrinos
|- |- Fermions| Electrons |-
| Atomic | | Protons | Cosmic
| Microscopic| |- | Rays
| Particles | Heavy Particles |-
Particle | |-
Astronomy | |-
| Macroscopic Particles| Meteors, meteorites,
| or objects | meteoritic dust
|- |-
|-
| Space Probes
Direct | Manned Exploration
Techniques | ET Astroengineering Activities in the Solar
System
|-
The methods of collecting this information as it arrives at the
planet Earth make it immediately obvious that it is impossible to
gather all of it and measure all its components. Each observation
technique acts as an information filter. Only a fraction (usually
small) of the complete information can be gathered. The diversity
of these filters is considerable. They strongly depend on the
available technology at the time.
In this paper a review of the advantages and disadvantages of each
"physical carrier" is examined, including the case that the possible
ETCs are using them for interstellar communication purposes, as well
as the possibility of detection activities of extraterrestrial
technologies.
Classification of Extraterrestrial Civilizations
The analysis of the use of each information carrier are deeply
connected with the assumption of the level of technology of the
other civilization.
Kardashev (1964) established a general criteria regarding the types
of activities of extraterrestrial civilizations which can be
detected at the present level of development. The most general
parameters of these activities are apparently ultra-powerful energy
sources, harnessing of enormous solid masses, and the transmission
of large quantities of information of different kinds through space.
According to Kardashev, the first two parameters are a prerequisite
for any activity of a supercivilization. In this way, he suggested
Page 3
the following classification of energetically extravagant
civilizations:
TYPE I: A level "near" contemporary terrestrial civilization
with an energy capability equivalent to the solar
insolation on Earth, between 10exp16 and 10exp17 Watts.
TYPE II: A civilization capable of utilizing and channeling the
entire radiation output of its star. The energy
utilization would then be comparable to the luminosity
of our Sun, about 4x1026 Watts.
TYPE III: A civilization with access to the power comparable
to the luminosity of the entire Milky Way galaxy,
about 4x10exp37 Watts.
Kardashev also examined the possibilities in cosmic communication
which attend the investment of most of the available power into
communication. A Type II civilization could transmit the contents
of one hundred thousand average-sized books across the galaxy, a
distance of one hundred thousand light years, in a total
transmitting time of one hundred seconds. The transmission of the
same information intended for a target ten million light years
distant, a typical intergalactic distance, would take a transmission
time of a few weeks.
A Type III civilization could transmit the same information over a
distance of ten billion light years, approximately the radius of the
observable Universe, with a transmission time of just three seconds.
Kardashev and Zhuravlev (1992) considered that the highest level of
development corresponds to the highest level of utilization of solid
space structures and the highest level of energy consumption.
For this assumption, they considered the temperature of solid space
structures in the range 3 Kelvin s T s 300 K, the consumption of
energy in the range 1 Luminosity (Sun) s L s 10exp12 L(Sun),
structures with sizes up to 100 kiloparsecs (kpc), and distances up
to Dw 1000 mega-parsecs (mpc). One parsec equals 3.26 light years.
Searching for these structures is the domain of millimeter wave
astronomy. For the 300 Kelvin technology, the maximum emission
occurs in the infrared region (15-20 micrometers) and searching is
accomplished with infrared observations from Earth and space. The
existing radio surveys of the sky (lambda = 6 centimeters (cm) on
the ground and lambda = 3 millimeters (mm) for the Cosmic Background
Explorer (COBE) satellite) place an essential limit on the abundance
of ETC 3 Kelvin technology. The analyzes of the Infrared
Astronomical Satellite (IRAS) catalog of infrared sources sets
limitations on the abundance of 300 Kelvin technology.
Information Carriers and the Manifestations of Advanced
Technological Civilizations
Boson and Photon Astronomy
Electromagnetic radiation carries virtually all the information on
which modern astrophysics is built. The production of
electromagnetic radiation is directly related to the physical
Page 4
conditions prevailing in the emitter. The propagation of the
information carried by electromagnetic waves (photons) is affected
by the conditions along its path. The trajectories it follows
depend on the local curvature of the Universe, and thus on the local
distribution of matter (gravitational lenses), extinction affecting
different wavelengths unequally, neutral hydrogen absorbing all
radiation below the Lyman limit (91.3 mm), and absorption and
scattering by interstellar dust, which is more severe at short
wavelengths.
Interstellar plasma absorbs radio wavelengths of kilometers and
above, while the scintillations caused by them become a very
important effect for the case of ETC radio messages (Cordes and
Lazio, 1991).
The inverse Compton effect lifts low-energy photons to high energies
in collisions with relativistic electrons, while gamma and X-ray
photons lose energy by the direct Compton effect. The radiation
reaching the observer thus bears the imprint of both the source and
the accidents of its passage though space.
The Universe observable with electromagnetic radiation is five-
dimensional. Within this phase, four dimensions - frequency
coverage plus spatial, spectral, and temporal resolutions - should
properly be measured logarithmically with each unit corresponding to
one decade (Tarter, 1984). The fifth dimension is polarization,
which has four possible states: Circular, linear, elliptical, and
unpolarized.
This increases the volume of logarithmic phase space fourfold.
It is useful to attempt to estimate the volume of the search space
which may need to be explored to detect an ETC signal. For the case
of electromagnetic waves, we have a "Cosmic Haystack" with an eight-
dimensional phase space. Three spatial dimensions (coordinates of
the source), one dimension for the frequency of emission, two
dimensions for the polarization, one temporal dimension to
synchronize transmissions with receptions, and one dimension for the
sensitivity of the receiver or the transmission power.
If we consider only the microwave region of the spectrum (300
megahertz (MHz) to 300 gigahertz (GHz)), it is easy to show that
this Cosmic Haystack has roughly 10exp29 cells, each of 0.1 Hz
bandwidth, per the number of directions in the sky in which an
Arecibo (305-meter) radio telescope would need to be pointed to
conduct an all-sky survey, per a sensitivity between 10exp(-20) and
10exp(-30) [W m-2], per two polarizations. The temporal dimension
(synchronization between transmission and reception) was not
considered in the calculation. The number of cells increase
dramatically if we expand our search to other regions of the
electromagnetic spectrum. Until now, only a small fraction of the
whole Haystack has been explored (w 10exp(-15) - 10exp(-16)).
Page 5
TABLE 2: Characteristics of the Electromagnetic Spectrum
(All the numbers that follows each 10 are exponents.)
==================================================================
Spectrum Frequency Wavelength Minimum Energy
Region Region [Hz] Region [m] per photon [eV]
==================================================================
Radio 3x106-3x1010 100-0.01 10-8 - 10-6
Millimeter 3x1010-3x1012 0.01-10-4 10-6 - 10-4
Infrared 3x1012-3x1014 10-4-10-6 10-4 - 10-2
Optical 3x1014-1015 10-6-3x10-7 10-2 - 5
Ultraviolet 1015-3x1016 3x10-7-10-8 5 - 102
X-rays 3x1016-3x1019 10-8-10-11 102 - 105
Gamma-rays r3x1019 s10-11 r105
==================================================================
Radio Waves
In the last thirty years, most of the SETI projects have been
developed in the radio region of the electromagnetic spectrum. A
complete description of the techniques that all the present and
near-future SETI programs are using for detecting extraterrestrial
intelligence radio beacons can be found elsewhere (e.g., Horowitz
and Sagan, 1993). The general hypothesis for this kind of search is
that there are several civilizations in the galaxy that are
transmitting omnidirectional radio signals (civilization Type II),
or that these civilizations are beaming these kind of messages to
Earth. In this section we will discuss only the detectability of
extraterrestrial technological manifestations in the radio spectrum.
Domestic Radio Signals
Sullivan et al (1978) and Sullivan (1981) considered the possibility
of eavesdropping on radio emissions inadvertently "leaking" from
other technical civilizations. To better understand the information
which might be derived from radio leakage, the case of our planet
Earth was analyzed. As an example, they showed that the United
States Naval Space Surveillance System (Breetz, 1968) has an
effective radiated power of 1.4x10exp (10) watts into a bandwidth of
only 0.1 Hz. Its beam is such that any eavesdropper in the
declination range of zero to 33 degrees (28 percent of the sky) will
be illuminated daily for a period of roughly seven seconds. This
radar has a detectability range of leaking terrestrial signals to
sixty light years for an Arecibo-type (305-meter) antenna at the
receiving end, or six hundred light years for a Cyclops array (one
thousand dishes of 100-meter size each).
Recently Billingham and Tarter (1992) estimated the maximum range at
which radar signals from Earth could be detected by a search similar
to the NASA High Resolution Microwave Survey (HRMS) assumed to be
operating somewhere in the Milky Way galaxy. They examined the
transmission of the planetary radar of Arecibo and the ballistic
missile early warning systems (BMEWS). For the calculation of
maximum range R, the standard range equation is:
R=(EIRP/(4PI PHImin))exp(1/2)
Page 6
Where PHImin is the sensitivity of the search system in [W m-2].
For the NASA HRMS Target Search PHImin = 10exp (-27) and for the
NASA HRMS Sky Survey PHImin w 10exp(-23) (f)exp(1/2), where f is the
frequency in GHz. Table 3 shows the distances where the Arecibo and
BMEWS transmissions could be detected by a similar NASA HRMS
spectrometer.
TABLE 3: HRMS Sensitivity for Earth's Most Powerful Transmissions:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
ARECIBO PLANETARY RADAR
(1) TARGETED SEARCH MAXIMUM RANGE (light years)
Unswitched
With CW detector 4217
With pulse detector 2371
Switched
With CW detector 94
With pulse detector 290
(2) SKY SURVEY
Unswitched
CW detector 77
Switched
CW detector 9
BMEWS
(1) TARGETED SEARCH
Pulse transmit CW detector 6
Pulse transmit pulse detector 19
(2) SKY SURVEY
Pulse transmit CW detector 0.7
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
All these calculations assumed that the transmitting civilization is
at the same level of technological evolution as ours on Earth.
Von Hoerner (1961) classified the possible nature of the ETC signals
into three general possibilities: Local communication on the other
planet, interstellar communication with certain distinct partners,
and a desire to attract the attention of unknown future partners.
Thus he named them as local broadcast, long-distance calls, and
contacting signals (beacons). In most of the past fifty SETI radio
projects, the strategy was with the hypothesis that there are
several civilizations transmitting omnidirectional beacon signals.
Unfortunately, no one has been able to show any positive evidence
of this kind of beacon signal.
Another possibility is the radio detection of interstellar
communications between an ETC planet and possible space vehicles.
Vallee and Simard-Normandin (1985) carried out a search for these
Page 7
kind of signals near the galactic center. Because one of the
characteristics of artificial transmitters (television, radar, etc.)
is the highly polarized signal (Sullivan et al, 1978), these
researchers made seven observing runs of roughly three days each in
a program to scan for strongly polarized radio signals at the
wavelength of lambda=2.82 cm.
Radar Warning Signals
Assuming that there is a certain number N of civilizations in the
galaxy at or beyond our own level of technical facility, and
considering that each civilization is on or near a planet of a Main
Sequence star where the planetoid and comet impact hazards are
considered as serious as here, Lemarchand and Sagan (1993)
considered the possibility for detecting some of these "intelligent
activities" developed to warn of these potentially dangerous
impacts.
Because line-of-sight radar astrometric measurements have much finer
intrinsic fractional precision than their optical plane-of-sight
counterparts, they are potentially valuable for refining the
knowledge of planetoid and comet orbits. Radar is an essential
astrometric tool, yielding both a direct range to a nearby object
and the radial velocity (with respect to the observer) from the
Doppler shifted echo (Yeomans et al, 1987, Ostro et al, 1991, and
Yeomans et al, 1992).
Since in our solar system, most of Earth's nearby planetoids are
discovered as a result of their rapid motion across the sky, radar
observations are therefore often immediately possible and
appropriate.
A single radar detection yields astronomy with a fractional
precision that is several hundred times better than that of optical
astrometry.
The inclusion of radar with the optical data in the orbit solution
can quickly and dramatically reduce future ephemeris uncertainty.
It provides both impact parameter and impact ellipse estimates.
This kind of radar research gives a clearer picture of the object to
be intercepted and the orientation of asymmetric bodies prior to
interception. This is particularly important for eccentric or
multiple objects.
Radar is also the unique tool capable for making a survey of such
small objects at all angles with respect to the central star. It
can also measure reflectivity and polarization to obtain physical
characteristics and composition.
For this case, we can assume that each of the extraterrestrial
civilizations in the galaxy maintains as good a radar planetoid
and/or comet detection and analysis facility as is needed, either on
the surface of their planet, in orbit, or on one of their possible
moons.
The threshold for the Equivalent Isotropic Radiated Power (EIRP) of
the radar signal could be roughly estimated by the size of the
object (D) that they want to detect (according to the impact hazard)
Page 8
and the distance to the inhabited planet (R), in order to have
enough time to avoid the collision.
One of the most important issues for the success of SETI
observations on Earth is the ability of an observer to detect an ETC
signal. This factor is proportional to the received spectral flux
density of the radiation. That is, the power per unit area per unit
frequency interval. The flux density will be proportional to the
EIRP divided by the spectral bandwidth of the transmitting radar
signals B.
The EIRP is defined as the product of the transmitted power and
directive antenna gain in the direction of the receiver as EIRP =
PT.G, where PT is the transmitting power and G the antenna gain.
This quantity has units of [W/Hz].
According to the kind of object that the ETC wants to detect (nearby
planetoids, comets, spacecraft, etc.), the distance from the radar
system and the selected wavelength, a galactic civilization that
wants to finish a full-sky survey in only one year, will arise from
a modest "Type 0" (w10exp13 W/Hz, Rw0.4 A.U., Dw5000 m, and lambdaw1
m) to the transition from "Type I" to "Type II" (w2x10exp24 W/Hz,
Rw0.4 A.U., Dw10 m, lambdaw1 mm).
Lemarchand and Sagan (1993) also presented a detailed description of
the expected signal characteristics, as well as the most favorable
positions in the sky to find one of these signals. They also have
compared the capability of detection of these transmissions by each
present and near future SETI projects.
Infrared Waves
There have been some proposals to search in the infrared region for
beacon signals beamed at us (Lawton, 1971, and Townes, 1983).
Basically, the higher gain available from antennas at shorter
wavelengths (up to 10exp14 Hz) compensates for the higher quantum
noise in the receiver and wider noise bandwidth at higher
frequencies.
One concludes that for the same transmitter powers and directed
transmission which takes advantage of the high gain, the detectable
signal-to-noise ratio is comparable at 10 micro-m and 21 cm. Since
non-thermal carbon dioxide (CO2) emissions have been detected in the
atmospheres of both Venus and Mars (Demming and Mumma, 1983), Rather
(1991) suggested the possibility that an advanced society could
construct transmitters of enormous power by orbiting large mirrors
to create a high-gain maser from the natural amplification provided
by the inverted atmospheric lines.
An observation program around three hundred nearby solar-type stars
has just begun (Tarter, 1992) by Albert Betz (University of
Colorado) and Charles Townes (University of California at Berkeley).
These observations are currently being made on one of the two 1.7-
meter elements of an IR interferometer at Mount Wilson observatory.
On average, 21 hours of observing time per month is available for
searching for evidence of technological signals.
Page 9
Dyson (1959, 1966) proposed the search for huge artificial
biospheres created around a star by an intelligent species as part
of its technological growth and expansion within a planetary system.
This giant structure would most likely be formed by a swarm of
artificial habitats and mini-planets capable of intercepting
essentially all the radiant energy from the parent star.
According to Dyson (1966), the mass of a planet like Jupiter could
be used to construct an immense shell which could surround the
central star, having a radius of one Astronomical Unit (A.U.). The
volume of such a sphere would be 4cr2S, where r is the radius of the
sphere (1 A.U.) and S the thickness. He imagined a shell or layer
of rigidly built objects Dw10exp6 kilometers in diameter arranged to
move in orbits around the star. The minimum number of objects
required to form a complete spherical shell [2] is about N=4
PIrexp2/Dexp2w2x10exp5 objects.
This kind of object, known as a "Dyson Sphere", would be a very
powerful source of infrared radiation. Dyson predicted the peak of
the radiation at ten micrometers.
The Dyson Sphere is certainly a grand, far-reaching concept. There
have been some investigations to find them in the IRAS database (V.
I. Slysh, 1984; Jugaku and Nishimura, 1991; and Kardashev and
Zhuravlev, 1992).
==================================================================
2 - The concept of this extraterrestrial construct was first
described in the science fiction novel STAR MAKER by Olaf
Stapledon in 1937.
==================================================================
Optical Waves
In the radio domain, there have been several proposals to use the
visible region of the spectrum for interstellar communications.
Since the first proposal by Schwartz and Townes (1961), intensive
research has been performed on the possible use of lasers for
interstellar communication.
Ross (1979) examined the great advantages of using short pulses in
the nanosecond regime at high energy per pulse at very low duty
cycle.
This proposal was experimentally explored by Shvartsman (1987) and
Beskin (1993), using a Multichannel Analyzer of Nanosecond Intensity
Alterations (MANIA), from the six-meter telescope in Russia. This
equipment allows photon arrival times to be determined with an
accuracy of 5x10exp(-8) seconds, the dead time being 3x10exp(-7)
seconds and the maximum intensity of the incoming photon flux is
2x10exp4 counts/seconds.
In 1993, MANIA was used from the 2.15-meter telescope of the
Complejo Astronomico El Leoncito in Argentina, to examine fifty
nearby solar-type stars for the presence of laser pulses (Lemarchand
et al, 1993).
Other interesting proposals and analysis of the advantages of lasers
Page 10
for interstellar communications have been performed by Betz (1986),
Kingsley (1992), Ross (1980), and Rather (1991).
The first international SETI in the Optical Spectrum (OSETI)
Conference was organized by Stuart Kingsley, under the sponsorship
of The International Society for Optical Engineering, at Los
Angeles, California, in January of 1993.
There have also been independent suggestions by Drake and Shklovskii
(Sagan and Shklovskii, 1966) that the presence of a technical
civilization could be announced by the dumping of a short-lived
isotope, one which would not ordinarily be expected in the local
stellar spectrum, into the atmosphere of a star. Drake suggested an
atom with a strong, resonant absorption line, which may scatter
about 10exp8 photons sec -1 in the stellar radiation field. A
photon at optical frequencies has an energy of about 10exp(-12) erg
or 0.6 eV, so each atom will scatter about 10exp(-4) erg sec-1 in
the resonance line. If we consider that the typical spectral line
width might be about 1 ^O, and if we assume that a ten percent
absorption will be detectable, then this "artificial smog" will
scatter about (1A/5000A)x10exp(-1) = 2x10exp(-5) of the total
stellar flux.
Sagan and Shklovskii (1966) considered that if the central star has
a typical solar flux of 4x10exp33 erg sec-1, it must scatter about
8x10exp28 erg sec-1 for the line to be detected. Thus, the ETC
would need (8x10exp28)/10exp(-4) = 8x10exp32 atoms. The weight of
the hydrogen atom (mH) is 1.66x10exp(-24) g, so the weight of an
atom of atomic weight n is nxmH grams.
Drake proposed the used of Technetium (Tc) for this purpose. This
element is not found on Earth and its presence is observed very
weakly in the Sun, in part because it is short-lived. Tc's most
stable form decays radioactively within an average of twenty
thousand years. Thus, for the case of Tc, we need to distribute
some 1.3x10exp11 grams, or 1.3x10exp5 tons, of this element into the
stellar spectrum. However, technetium lines have not been found in
stars of solar spectral type, but rather only in peculiar ones known
as S stars. We must know more than we do about both normal and
peculiar stellar spectra before we can reasonably conclude that the
presence of an unusual atom in an stellar spectrum is a sign of
extraterrestrial intelligence.
Whitmire and Wright (1980) considered the possible observational
consequences of galactic civilizations which utilize their local
star as a repository for radioactive fissile waste material. If a
relatively small fraction of the nuclear sources present in the
crust of a terrestrial-type planet were processed via breeder
reactors, the resulting stellar spectrum would be selectively
modified over geological time periods, provided that the star has a
sufficiently shallow outer convective zone. They have estimated
that the abundance anomalies resulting from the slow neutron fission
of plutonium-239 and uranium-233 could be duplicated (compared with
the natural nucleosynthesis processes), if this process takes place.
Since there are no known natural nucleosynthesis mechanisms that can
qualitatively duplicate the asymptotic fission abundances, the
predicted observational characteristics (if observed) could not
easily be interpreted as a natural phenomenon. They have suggested
Page 11
making a survey of A5-F2 stars for (1) an anomalous overabundance of
the elements of praseodymium and neodymium, (2) the presence, at any
level, of technetium or plutonium, and (3) an anomalously high ratio
of barium to zirconium. Of course, if a candidate star is
identified, a more detailed spectral analysis could be performed and
compared with the predicted ratios.
Following the same kind of ideas, Philip Morrison discussed
(Sullivan, 1964) converting one's sun into a signaling light by
placing a cloud of particles in orbit around it. The cloud would
cut enough light to make the sun appear to be flashing when seen
from a distance, so long as the viewer was close to the plane of the
cloud orbit. Particles about one micron in size, he thought, would
be comparatively resistant to disruption. The mass of the cloud
would be comparable to that of a comet covering an area of the sky
five degrees wide, as seen from the sun. Every few months, the
cloud would be shifted to constitute a slow form of signaling, the
changes perhaps designed to represent algebraic equations.
Reeves (1985) speculated on the origin of mysterious stars called
blue stragglers. This class of star was first identified by Sandage
(1952). Since that time, no clear consensus upon their origins has
emerged. This is not, however, due to a paucity of theoretical
models being devised. Indeed, a wealth of explanations have been
presented to explain the origins of this star class. The essential
characteristic of the blue stragglers is that they lie on, or near,
the Main Sequence, but at surface temperatures and luminosities
higher than those stars which define the cluster turnoff.
Reeves (1985) suggested the intervention of the inhabitants that
depend on these stars for light and heat. According to Reeves,
these inhabitants could have found a way of keeping the stellar
cores well-mixed with hydrogen, thus delaying the Main Sequence
turn-off and the ultimately destructive, red giant phase.
Beech (1990) made a more detailed analysis of Reeves' hypothesis and
suggested an interesting list of mechanisms for mixing envelope
material into the core of the star. Some of them are as follows:
o Creating a "hot spot" between the stellar core and surface
through the detonation of a series of hydrogen bombs. This
process may alternately be achieved by aiming "a powerful,
extremely concentrated laser beam" at the stellar surface.
o Enhanced stellar rotation and/or enhanced magnetic fields.
Abt (1985) suggested from his studies of blue stragglers that
meridional mixing in rapidly rotating stars may enhance their
Main Sequence lifetime.
If some of these processes can be achieved, the Main Sequence
lifetime may be greatly extended by factors of ten or more. It is
far too early to establish, however, whether all the blue stragglers
are the result of astroengineering activities.
Editor's Note: References to this paper will be published in Part 2
in the January 1994 issue of the EJASA.
Page 12
Related EJASA Articles -
"Does Extraterrestrial Life Exist?", by Angie Feazel
- November 1989
"Suggestions for an Intragalactic Information Exchange System",
by Lars W. Holm - November 1989
"Radio Astronomy: A Historical Perspective",
by David J. Babulski - February 1990
"Getting Started in Amateur Radio Astronomy",
by Jeffrey M. Lichtman - February 1990
"A Comparison of Optical and Radio Astronomy",
by David J. Babulski - June 1990
"The Search for Extraterrestrial Intelligence (SETI) in the
Optical Spectrum, Parts A-F",
by Dr. Stuart A. Kingsley - January 1992
"History of the Ohio SETI Program", by Robert S. Dixon
- June 1992
"New Ears on the Sky: The NASA SETI Microwave Observing Project",
by Bob Arnold, the ARC, and JPL SETI Project - July 1992
"First International Conference on Optical SETI",
by Dr. Stuart A. Kingsley - October 1992
"Conference Preview: The Search for Extraterrestrial Intelligence
(SETI) in the Optical Spectrum",
by Dr. Stuart A. Kingsley - January 1993
The Author -
==================================================================
Guillermo A. Lemarchand
Universidad de Buenos Aires
POSTAL ADDRESS: C.C.8 - Suc.25,
1425-Buenos Aires,
ARGENTINA
E-MAIL: lemar@seti.edu.ar
PHONE: 54-1-774-0667 FAX: 54-1-786-8114
==================================================================
THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
December 1993 - Vol. 5, No. 5
Copyright (c) 1993 - ASA
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