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THE ELECTRONIC JOURNAL OF

THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

Volume 5, Number 5 - December 1993

###########################

TABLE OF CONTENTS

###########################

* ASA Membership and Article Submission Information

* Detectability of Extraterrestrial Technological Activities,

Part 1 - Guillermo A. Lemarchand

###########################

ASA MEMBERSHIP INFORMATION

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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.

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 specula-

tions 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".

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 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 communica-

tion 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 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 trans-

missions 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)).

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 detecta-

bility 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 trans-

mission 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)

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 communi-

cations between an ETC planet and possible space vehicles. Vallee and

Simard-Normandin (1985) carried out a search for these kind of signals

near the galactic center. Because one of the characteristics of arti-

ficial 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)

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.

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 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 , 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 rela-

tively 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 geolo-

gical time periods, provided that the star has a sufficiently shallow

outer convective zone. They have estimated that the abundance anoma-

lies resulting from the slow neutron fission of plutonium-239 and

uranium-233 could be duplicated (compared with the natural nucleosyn-

thesis 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 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 character-

istic 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.

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