When I was under the velvet-black skies of western Texas a few months ago, I had a magnificent view of the star-studded bulge of our galaxy in the direction of the summer constellation Sagittarius.
How many advanced alien civilizations might be in this crowded hub of the Milky Way, I pondered? The problem is that we are embedded in a thick forest of stars, and identifying the location of an extraterrestrial civilization – one that’s attempting to contact us – is the proverbial needle-in-a-haystack search, as the SETI scientists always say.
So instead of looking for signals, perhaps the way to find evidence of E.T. is to scrutinize the physical evidence in a neighboring “forest,” or rather nearby galaxy.
Because even the nearest galaxies are millions of light-years away, any idea of communicating with these aliens is unfeasible. Our observations would be made for purely identifying archeological evidence of the actions of a civilization.
For this to work you would have to look at the tallest trees in that forest, i.e. engineering activities on such a large scale they give an anomalous appearance to the galaxy that cannot be explained by known astronomical processes. The features would instead be the handiwork of super-duper civilizations that are leaving their ecological imprint on the galaxy at a mega-scale.
In 1964, the Soviet astronomer Nikolai Kardeschev hypothesized such extraterrestrial civilizations as Type II. They would surpass our energy production capabilities by a factor of approximately 10 billion. How? By capturing the total energy output of their parent star.
In the early 1960s, physicist Freeman Dyson proposed that a shell could be built around a star to trap much of its energy. The shell would be fabricated from dismantling a planet about the mass of Jupiter.
This so-called “Dyson sphere” is legendary, and there have even been searches for the signature of such artifacts in astronomical infrared databases. The problem is that a star enshrouded in dust would look pretty much like a Dyson sphere. In a survey of 250,000 infrared sky sources cataloged in the 1970s, 17 “quasi-plausible” Dyson sphere signatures came up, according to Richard Carrigan of Fermilab.
It’s imaginable that a super-civilization would begin a wave of colonization that spread out to neighboring solar type stars from its home base. Each offshoot would “astro-form” the colonized planetary system by constructing a Dyson sphere around the host star.
Carrigan envisions seeing “Dyson bubble” in nearby galaxies. These would be clusters of Dyson spheres that enclosed a grouping of stars colonized by a Type II Kardeschev civilization. The logic is that after you’ve built a backyard fence, you can start to conceptualize building the Great Wall of China and still hope to gain perspective on the process, Carrigan says.
These Dyson bubbles would be detected as anomalous dark voids in a galaxy’s disk. When these voids were observed in infrared light they would glow brightly with the heat radiation from the surfaces of Dyson spheres. This would show that they are not simply voids where solar-type stars are conspicuously missing.
The Hubble Space Telescope is conducting a multi-year survey across a swath of the neighboring Andromeda galaxy. The images are filled with so many resolved stars that they look like grains of sand on a beach. This could make an excellent citizen science project, to scour the Andromeda fields for anomalous-looking regions.
The magnificent face-on Whirlpool galaxy, M51, is an ideal place to go looking for Dyson bubbles. Hubble has photographed the entire galaxy down to a resolution of roughly 15 light-years across. Present Hubble and Spitzer Space Telescope infrared photos of the Whirlpool reveal the typical galaxy’s intricate cobweb tracing in dusty filaments.
However, a rough qualitative estimate by Carrigan suggests that there are no unexplained bubbles or voids in M51. This analysis is complicated by the fact that the infrared light skeletal pattern of a spiral galaxy pattern itself is shaped by voids.
Gigantic elliptical galaxies, which are completely devoid of light-blocking dust, would look very odd indeed if dark voids were detected. However, the nearest ellipticals are 60 million light-years away and so would require a space telescope much larger than Hubble to yield enough resolution to detect anomalies.
An apparent lack of any evidence for large-scale artifacts in galaxies as old as ours begins to set an upper limit on just how technologically advanced alien civilizations can evolve.
Kardeschev hypothesized about Type III civilizations that would harness the entire energy of a galaxy. The observational evidence for astro-engineering an entire galaxy is lacking, and so it’s fair to say that Type III civilizations just don’t exist at all – or at least not yet.
The universe has had 12 billion years to evolve a Type II or Type III civilization. If there’s no obvious archeological evidence, than maybe intelligent beings don’t evolve all that far beyond our projected capabilities of perhaps mega-engineering on the scale of a single solar system.
Maybe extraterrestrials simply don’t have the motivation, know-how, or the budget.