“A positive result in a search for the pattern would be one of the great experiments in the history of science.” Unidentified point-like very high energy gamma ray sources in the Milky Way may actually be starships of hyper-advanced alien civilizations who are actively exploring interstellar space, proposes Louis Crane in Searching for Extraterrestrial Civilizations Using Gamma Ray Telescopes.

A pioneer in quantum gravity at Kansas State University, Crane, formerly with the Institute for Advanced Study in Princeton and an Assistant Professor at Yale University, says the concentration of gamma rays near the galactic center is a prime target, because it would be a favorable region for interstellar colonization, given its great density of stars.

A negative result in the search, says Crane, “would still explain enough of the nature of the gamma ray sources to be of scientific value. Aside from the mind boggling quality of the possible result, there is really no reason not to make the measurements. Actually the measurements may already be made so that it would be a question of sorting through data looking for the pattern.”

Searches using space-based telescopes, observes Crane, like the Fermi Gamma-ray Space Telescope (FGST), and ground-based facilities like the High Energy Stereoscopic System (HESS) and the Very Energetic Radiation Imaging Telescope Array System (VERITAS), could determine if these sources are artificial in nature.

The creation of artificial black holes (ABH’s) by an advanced civilization, as Crane proposes in the paragraphs that follow, would be the ultimate physical experiment, in that careful examination of the Hawking radiation as the ABH evaporated and heated, would reveal all the fundamental particles and forces all the way to the Planck scale at the Big Bang, allowing them to reach the limit of knowledge of matter.

It is widely believed, says Crane, that every black hole produces a new baby universe on the other side of its singularity. If this is true, ABH technology will involve the creation process of universes. A society that decided to build the laser and other machinery to implement the ABH proposal would have to allocate resources comparable to building the pyramids over a timescale comparable to building the cathedrals. The work would have its fruition long after the initial builders’ lifespans.

The builders would understand their work as part of the eternal recreation of the universe, having purpose in the sense that the organs of animals develop purpose as the result of an evolutionary process. Their entire lives would have a higher purpose in that they result in the creation of new universes and new life, as well as spreading their descendants throughout the universe. It would also imply that our own universe is fine tuned because it is the result of the activity of earlier intelligence.

Artist’s impression of a black hole starship.

Crane offers the possibility of searching for black hole starships using very high energy gamma ray telescopes.

A starship could be constructed using the Hawking radiation from an artificial nanoscopic black hole. The issue of whether such a ship or such a black hole could eventually be constructed, says Crane, “is extremely difficult; it is certainly far out of reach of current technology. The construction of a starship propelled by the radiation of such a black hole involves technical problems, such as focusing a gamma ray laser to nuclear dimensions and finding a way to reflect gamma radiation for which current technology has no solution. It is not possible to say whether an advanced civilization could ever solve them, or to describe a black hole starship in any detail.”

There is also the problem that Hawking’s computations depend on a semiclassical approximation. A full quantum theory of gravity coupled to matter is not developed by Earth-based physicists.

Recent advances in observational astronomy, however, have made it possible to search for extraterrestrial black hole starships in our galaxy. Interesting potential candidates have been observed, and tests to see if any of them are actual BHSs are not difficult to propose says Crane.

Detecting a Black Hole Starship

An ABH would be observed as a source of very high energy gamma radiation that would appear redshifted, and the red shift would increase in time. Midway through its voyage, the ship would turn around and begin deceleration. It would disappear to its previous observers, and a new image would appear in a forward cone. The new observers would see the source as blue shifted, and the shift would decrease over time. Detecting this distinctive pattern should be feasible.

From a observatory technology perspective, the study of very high energy gamma rays was frustratingly slow for many years. But great progress has been made in the last ten years, as a result of increases in computational power and the construction of batteries of multiple Cerenkov telescopes, says Crane. The Cherenkov Telescope Array (CTA) is the next generation ground-based observatory for gamma-ray astronomy at very-high energies. With more than 100 telescopes located in the northern and southern hemispheres, CTA will be the world’s largest and most sensitive high-energy gamma-ray observatory.

It has been discovered that there are some hundreds of very high energy gamma ray sources in our galaxy. Some of them seem to be associated with neutron stars or binary stars with infalling matter, but over half of them seem to lack any explanation. It is particularly difficult to explain why so many of them have no X ray component.

Another mystery is the overall excess of high energy gamma rays coming from the galactic center. It seems to be far greater than any known source such as pulsars could explain. It is also believed that the gamma ray sources are connected with the problem of the origin of the very high energy cosmic rays; which are still a puzzle.

Detectability

The many variables we do not know about a BHS would all affect its observability from current earth-based telescopes. Nevertheless, a rough calculation suggests that a BHS within 100 lightyears might be observable by the current generation of gamma ray telescopes. Varying our assumptions about the construction of a BHS could extend this to 1000 light years or more.

Black hole starships, would have one feature which would distinguish them from any natural phenomenon. They would accelerate up to relativistic velocities in a time frame from years to decades: a starship in the boost phase of its trajectory would appear redshifted to us, while a decelerating ship would appear blueshifted. In either case the rate of change of the red or blueshift would be on the order of a percent per year. Furthermore, the redshift would increase with time while the blueshift would decrease, with an accelerating starship visible to an observer behind it, while a decelerating ship would be visible ahead of it.

In addition, operating starships would appear and disappear on a time scale of decades or a century or so. This would also distinguish them from natural sources of radiation. The pattern of shifts, increasing red, decreasing blue, would be quite distinctive. It is extremely hard, Crane says, to imagine that any natural phenomenon would reproduce it. Natural bodies do not exhibit steady relativistic levels of changes in their velocities or gravitational fields.

This was the recent observation of Harvard’s Avi Loeb about that the interstellar object Oumuamua was in fact a probe sent to our solar system by an extraterrestrial civilization. Its extremely improbable trajectory along with its non-gravitational acceleration makes this suggestion plausible.

Reflections

If it is really true that black hole starships, or some similar high energy density drive ships exist, concludes Crane, they would play a more important role in the galaxy than would be apparent, because only a small number of their focused beams would reach us on earth.

As far as the existence of intelligent life elsewhere in the galaxy is concerned, says Crane, there is really no reason to rule it out. The answer to Fermi’s question he suggests “might simply have been that they were rather hard to see, paradoxically because their emissions were too energetic.”

The efforts to detect extraterrestrial civilizations via SETI are flawed by the fact that ordinary radio transmissions such as those produced on earth are only detectable over a radius of a relatively few light years, while the radiation

of a starship would be tightly beamed, extremely powerful, and in a very high frequency not common in nature. This would make it more detectable if, as in some recent estimates the nearest civilization were to be at a distance on the order of 1000 light years.

The image at the top of the page shows the entire sky at energies greater than 1 GeV based on five years of data from the LAT instrument on NASA’s Fermi Gamma-ray Space Telescope; the most prominent feature is the bright band of diffuse glow along the map’s center, which marks the central plane of our Milky Way Galaxy. NASA / DOE / Fermi LAT Collaboration.

The Daily Galaxy via Searching for Extraterrestrial Civilizations Using Gamma Ray Telescopes, FQXI.org and Universe Today