INTRODUCTION

Why stellar engineering?

A song for occupations!

In the labor of engines and trades and the labor of fields I find the developments,

And find the eternal meanings.

Walt Whitman, from A Song of Occupations

Why, you might say, have the authors of this book ventured too close to the deep end? Are they mad: how can one engineer a star? And why would someone do it?

Yes, stars are huge. Our benevolent Sun is a run-of-the-mill star. It has a radius of about 700,000 kilometers and a surface temperature of about 6,000 Kelvin. Deep in its interior, the temperature and density is high enough for the thermonuclear conversion of ionized hydrogen (protons) into helium nuclei. A tiny fraction (less than one part in a billion) of the resulting energy warms the Earth, making life possible.

POTENTIAL APPLICATIONS

Gradually, as our star ages, it will expand and increase its luminosity. But no sweat: Earth will remain a comfortable abode for at least one billion years.

If humanity endures or evolves into some other form, our capabilities in space may expand. Someday humans, or their distant descendants, may be capable of rearranging the solar system. We may, in the near future, begin to alter the orbits of those asteroids and comets that might threaten the Earth. Unlike the non-feathered dinosaurs who became extinct about 65 million years ago due, at least in part, to the impact of a 10-kilometer space rock near what is now the Yucatan, humans have large brains and the capability to design ever-more-effective technologies.

If we can move these objects into safer solar orbits, why not do something useful with them? In the near-term, we may mine them for precious materials and export them to Earth or use them as resources in space. Such materials include water for life support and fuel, and rock for shielding against cosmic rays. Within the next century, thin-film power stations (Figure I.1) may be constructed in equatorial Earth orbits, at altitudes chosen to allow 24-hour orbits around our planet. Remaining in the same place above the Earth, these stations could beam down copious amounts of clean solar energy. The era of energy shortages would then be history. Other thin-film devices situated in stable locations between the Earth and Sun could serve as sunshades, reducing the effects of global warming in the near-term and maintaining our planet’s capability to support life in the distant future.

Figure I.1.Artist concept of an orbital beamed power station.

Courtesy: NASA

However, human civilization will still be tapping only a tiny fraction of the Sun’s radiant output. If the human population continues to grow, we may someday expand into Earth–Moon space, using asteroids or lunar resources to construct space habitats with Earth-like interiors that will be capable of supporting a human population greatly in excess of 10 billion people.

Such an expanding sphere of multi-kilometer space homes will need energy as well as living space (Figure I.2). Ultimately, we might disassemble unoccupied solarsystem bodies to construct more space habitats or solar-power collectors. In the distant future, there may be a sphere of these constructs circling our star. This might be detectable to alien astronomers circling distant stars.

Figure I.2.Artist’s rendering of the interior and exterior of an in-space habitat for thousands of residents.

Courtesy: NASA

As well as producing solar energy for the use of stay-at-home individuals, some of these power stations (Figure I.3) could be equipped with lasers or masers. A laser can produce a narrow beam of concentrated optical-frequency light. Masers do the same thing with microwaves. Such power beams could be projected farther into space than direct sunlight. One application of such devices is the propulsion of interstellar spacecraft. A technologically advanced civilization could thereby use solar collectors orbiting its star to expand to neighboring planetary systems.

Even when the star hosting such a civilization expands to the point that oceans on its habitable planet begin to boil, all is not hopeless. Another application of huge in-space constructs is the expansion of a planet’s distance from its star. This would extend the life of an advanced civilization’s planetary home. Ultimately, these techniques could be applied to free the planet from the confines of a dying star, to wander the galaxy endlessly as a rogue world.

Finally, a star itself could be used as an interstellar or intergalactic spaceship. Huge reflectors circling that star could directionally focus light and/or particles emitted from that star to produce thrust. This would not exactly be the faster-than-light ships of science-fiction, instead interstellar transits might take 100,000 years. Intergalactic trips might require a billion Earth years. However, instead of being cooped up inside the confines of a spacecraft, star voyagers would happily reside on their comfortable home world during the trip.

Figure I.3.Artist’s concept of a space solar power station.

Courtesy: NASA

THE SCALES OF SPACE AND TIME: IS ET BUILDING STELLAR CONSTRUCTS?

Humans have lived in villages or cities for about 10,000 years. Agriculture and animal husbandry are of the same vintage. At least some humans have been literate for 5,000 years or so. From the human perspective, these are enormous time intervals—more than 100 human generations. However, from the geological and biological perspectives, we have been civilized for the blink of a cosmic eye. Earth coalesced from the Sun’s birth nebula more than 4.5 billion years ago. The oldest life forms in the terrestrial fossil record are perhaps 4 billion years old. The universe emerged from the Big Bang about 13.7 billion years ago.

Because cosmic timescales are so enormous compared to human timescales, it is fair to ask whether extraterrestrial civilizations much older than our own have engaged in stellar engineering. The Milky Way galaxy, our cosmic home, contains about 400 billion stars. If only 1% of these harbor Earth-like planets within stars’ habitable zones, then there are 4 billion opportunities for the development of advanced, technological life. We have a lot of ground to search for evidence of cosmic engineering.

Space is huge. Consider our Earth, which is a near-perfect sphere about 40,000 kilometers in circumference. If you have US$1,500 or so, you can book a flight that will circumnavigate the world in about 2 days, not including layovers. If you have got a bit more spare cash, you will soon be able to board a rocket to visit a space station or an orbital hotel. Circling the Earth at a low-orbit velocity of about 8 kilometers per second takes roughly 90 minutes.

In the not-too-distant future, our commercial space infrastructure may reach the Moon. Earth’s single natural satellite is at a distance of about 400,000 kilometers. Departing Earth orbit at 11 kilometers per second, a round trip to the Moon takes about a week—longer of course if you elect to descend to the surface and visit the Lunar Hilton.

Many near-Earth asteroids (NEAs) approach within a few million kilometers—space miners planning to tap this resource base will be away from home for about a year.

Mars approaches the Earth within 70 million kilometers or so. Since you have to stop when you arrive at the Red Planet and wait for the planets to align once again, humans bound for this destination must plan for a 2–3 year trip.

To avoid huge numbers, planetary scientists and mission planners use another unit in discussing distances within the solar system—the astronomical unit, the average Earth–Sun separation of 150 million kilometers. Earth is 1 astronomical unit from the Sun. The average distance of Mars from the Sun is 1.52 astronomical units. The most distant known solar system planet is Neptune, which is about 40 astronomical units from the Sun. Our fastest probes can fly past Neptune or dwarf planet Pluto on trajectories requiring travel times of about a decade.

Future stellar engineers can tap vast resources within our solar system if they can tolerate long stays in space. Many of the main-belt asteroids are within 3 or 4 astronomical units from the Sun, between Mars and Jupiter. The giant planets Jupiter, Saturn, Uranus, and Neptune have many natural satellites and thick atmospheres.

Beyond Neptune there are a host of comet-like Kuiper belt objects (KBOs). Dwarf planet Pluto is the second largest of the known KBOs. The Kuiper belt may contain thousands of rocky and icy bodies and extends to about 50 astronomical units from the Sun.

However, it does not end there. Beyond the Kuiper belt, reaching perhaps 50,000 astronomical units from the Sun is the Oort comet cloud. As many as a trillion comets, each in the 10–20-kilometer size range, reside in this spherical cloud. On occasion, some of these are driven toward the inner solar system by giant-planet alignments or passing stars. It is not impossible that a comet from the Oort cloud was the culprit that ended the reign of the non-feathered dinosaurs. However, these icy objects could also supply resources for stellar engineering projects.

Although humans may not visit the Oort cloud for centuries, five robotic probes from Earth are currently traversing this region. The fastest of these will require about 70,000 years to reach the 260,000 astronomical unit distance of our nearest extra-solar stellar neighbors, the triple-star system of Alpha and Proxima Centauri.

When you contemplate the vast reaches of galactic space, it is helpful to use a new unit. This is the light year—the distance that light travels in one year, moving at a velocity of 300,000 kilometers per second. There are about 60,000 astronomical units in one light year. The Alpha/Proxima Centauri system is about 4.3 light years from the Sun.

As part of the planning effort for an eventual probe to 200 astronomical units from the Sun, NASA has prepared a useful graphic (Figure I.4) which shows, on a logarithmic distance scale, the location of the major planets and the boundary of the Sun’s galactic influence, the heliopause. Galactic distances and travel times are daunting indeed.

Moving beyond our stellar neighborhood, future interstellar explorers must contend with the sheer size of our galaxy. The Milky Way is a spiral galaxy not dissimilar from the one shown in Figure I.5. The 400 billion or so stars in this star city are typically separated from their nearest stellar neighbors by a few light years. It takes light about 100,000 years to cross from one end of the galactic lens to the other.

There are perhaps 100 billion galaxies beyond the Milky Way. The closest is at a distance of a few hundred thousand light years. The observable universe has a diameter of perhaps 20 billion light years.

Because light’s velocity of 300,000 kilometers per second is the speed limit of the universe, light from distant objects has been traveling toward our telescopes for billions of years. The most distant electromagnetic radiation (light) we receive was radiated a few hundred thousand years after the Big Bang.

Our cosmic home is enormous, by any standard we can imagine. However, it contains tremendous resources that can be tapped by sufficiently advanced civilizations. By our standards, a civilization engaged in stellar engineering may appear god-like.

Figure I.4.A map of the solar system and close stellar neighbors. The numbers below the celestial objects represent distances from the Sun in astronomical units.

Courtesy: NASA

Figure I.5.Photograph of a spiral galaxy.

Courtesy: NASA

ORIGIN OF THE CONCEPT

You might reasonably assume that the concept of stellar engineering originated in the fertile brain of a theoretical astrophysicist. Surprisingly, stellar engineering first appears in a novel.

Olaf Stapledon, a British philosopher with a Ph.D., learned in the years between the World Wars that it was easier to make a living as a novelist than as an academic. In 1937, the first edition of his masterwork, Star Maker, was published. As described later in this book, this short science-fiction novel garnered much attention among scientists and engineers.

In Star Maker, some advanced planetary civilizations involved in the spread of higher consciousness through the galaxy enclose their stars in spherical shells constructed of solar system resources. The dual purposes of these constructs is to provide additional living space for a growing in-space population and increase the amount of radiated energy from the host star that can be used for societal purposes.

Other advanced societies, desiring to expand beyond the confines of our Milky Way galaxy, apply star-sized constructs to focus and redirect radiant and particulate stellar output, thereby producing thrust. This thrust, operating like a rocket, allows the residents of the encapsulated star to slowly cruise through intergalactic space, on billion-year journeys to neighboring galaxies.

In 1960, Professor Freeman Dyson, a British scientist affiliated with the Institute of Advanced Studies in Princeton New Jersey, authored a paper in the prestigious journal Science, in which he presented the case for such constructs and discussed how terrestrial astronomers might detect infrared radiation emitted by these constructs in the galactic vicinity of the Sun.

Is it perhaps because of this short article that many subsequent authors refer to these constructs as Dyson spheres. It is interesting to note that Dyson has spent decades attempting to convince people (without much success) to call these hypothetical artificial celestial objects Dyson/Stapledon spheres or Stapledon Dyson spheres.

Since the publication of Dyson’s original paper, several science-fiction authors have featured Dyson/Stapledon spheres in their fiction. Notable among these are Greg Benford and Larry Niven.

Some astronomers interested in SETI (the search for extraterrestrial intelligence) have combed the copious observational data sets obtained by infrared-sensitive space telescopes. One of these, Richard Carrigan, has used data from IRIS (the Interface Region Imaging Spectrograph, which is an infrared astronomy satellite) to search for infrared emissions from Dyson/Stapledon spheres out to about 1,000 light years.

HAVE WE FOUND ONE?

The Kepler spacecraft (Figure I.6), a space telescope launched and operated by NASA, has been one of our most successful tools in the search for planets circling other stars. Kepler does not attempt to directly image extra-solar planets. Instead, it remains with its instruments fixed on a small region of sky to monitor small variations in stellar brightness.

If a star’s brightness periodically dips by 100 parts per million or so, this indicates that Kepler is probably observing the transit of an orbiting planet in front of a star. Because planetary-system orientations vary, less than 10% of extra-solar planets can be detected in this fashion.

To date, Kepler has detected thousands of planets orbiting stars in the constellations of Lyra and Cygnus. Some of these planets orbit within the habitable zones of their stars.

Because of the huge number of candidate planets detected by this spacecraft, NASA has organized a program of citizen scientists to help sift through the data. One organizer of this data-reduction project is Tabetha S. Boyajian, a post-doctoral researcher at Yale University.

In late 2015, Boyajian was the principal author of a paper entitled Where’s the Flux?, that considered the anomalous light curve of the main-sequence star KIC 8462852, which is commonly referred to as Tabby’s Star. One interpretation of the observed variation in radiant output from this star (which is about 1,500 light years from our solar system) is the presence of an object circling the star in or near the habitable zone that is larger in size than any planet. Some have suggested that the object is a partial Dyson/Stapledon sphere under construction.

One alternative explanation proposed to date, that has a chance of being correct, is that a huge swarm of comets are circling Tabby’s Star. Critics have commented that huge comet swarms have never been detected. However, the same can be said for partial Dyson/Stapledon spheres.

However, the comet swarm proposal is currently in trouble. Bradley E. Schaefer of Louisiana State University has carefully investigated a century of photographs of this star in the Harvard College Observatory Archive. It appears that Tabby’s Star has dimmed by about 20% between 1890 and 1989. This is very unexpected because Tabby’s Star is a stable dwarf star which is a bit hotter than the Sun and somewhat more mature. At this stage in the star’s evolution, it should be increasing in luminosity, not decreasing.

Something very strange is indeed going on near this distant star. Hopefully, data from the next generation of space telescopes will resolve the issue. However, it is fascinating to consider the details and varieties of stellar-engineering constructions and realize that perhaps one of these may have been discovered. If the discovery is confirmed, we will finally know that humans are not alone in the universe.

As we examine Tabby’s Star and other similar anomalies, it is wise to keep an open mind. If these celestial megastructures actually exist, they may turn out to be more than physical constructs. It is not impossible that they are inhabited, a sort of living ring or sphere centered on the host star. Perhaps rather than being huge biospheres, they are instead integrated computing mechanisms or huge biocomputers composed of nanotechnological elements.

In this book, we discuss science-fiction speculations regarding these hypothetical structures and those who construct them. Of course, many, most, or all of these will not be correct. However, they may open our minds to the transcendent nature of the hyper-advanced cultures and civilizations who have partially or totally tamed the realms of their planetary systems.

Figure I.6.The Kepler spacecraft and its field of view.

Courtesy: NASA

It is wise to remember that in the community of extraterrestrials, if such a community exists, humans are the new kids on the block. As we remotely search the vast reaches beyond the sky, and perhaps eventually venture there, we should adopt the humble attitude of the explorer rather than the mindset of the conqueror.

FURTHER READING

Olaf Stapledon’s Star Maker has been reprinted numerous times. Greg Matloff’s edition is O. Stapledon, Last and First Men & Star Maker (Dover, NY, 1968). The text of this novel is now available online as well as in print.

The first or one of the first scientific papers on stellar engineering projects is Freeman Dyson’s Search for Artificial Sources of Infrared Radiation, Science, 131, 1667–1668 (1960). Dyson credits Stapledon with the concept in Disturbing the Universe (Harper & Row, NY, 1979). It is perhaps of sociological significance that most subsequent papers on the subject credit Dyson, not Stapledon.

Richard A. Carrigan Jr. has delivered the (so far unsuccessful) results of his search for infrared emissions from Dyson/Stapledon spheres in our galactic vicinity. He has also published these results in a paper entitled IRIS-Based Whole-Sky Upper Limit on Dyson spheres. This paper has been published in The Astrophysical Journal, 698, 2075–2086 (2009).

The initial paper presenting the unusual light curve of KIC 8462852 is T.S. Boyajian, D. M. LaCourse, S.A. Rapport, D. Fabrycky, D.A. Fischer, D. Gandolfi, G.M. Kennedy, H. Korhonen, M.C. Liu, A. Moor, K. Olah, K. Vida, M.C. Wyatt, W.M.J. Best, J. Brewer, F. Ciesla, B. Csak, H.J. Deeg, T.J. Dupuy, G. Handler, K. Heng, S.B. Howell, S.T. Ishikawa, J. Kovacs, T. Kozakis, L. Kriskovics, L. Lehtinen, C. Lintott, S. Lynn, D. Nespral, S. Nikbakhsh, K. Schawinski, J.R. Schmitt, A.M. Smith, Gy. Szabo, R. Szabo, J. Viuho, J. Wang, A. Weiksnar, M. Bosch, J.L. Connors, S. Goodman, G. Green, A.J. Hoekstra, T. Jebson, K.J. Jek, M.R. Omohundro, H.M. Schwengeler, and A. Szewczyk, Planet Hunters X. KIC 8462852—Where’s the Flux?, arXiv:1509.03622v2 [astro-ph.SR] (originally submitted September 11, 2015; revised version submitted January 25, 2016).

Another paper that excellently presents and discusses the various alternative explanations for this star’s anomalous light curve is J.T. Wright, K.M.S. Cartier, M. Zhao, D. Jontof-Hunter, and E.B. Ford, The G Search for Extraterrestrial Civilizations with Large Energy Supplies IV. The Signatures and Information Content of Transiting Megastructures, arXiv:1510.04606v1 [astro-ph.EP] October 15,