Aliens and Interstellar Archaeology on the Kardashev Galactic Scale

Kardashev Type III and Its Traces
What would happen if a true galaxy-spanning civilisation went to work on astro-engineering?

We call this a Kardashev Type III civilisation, one that could exploit the power resources of an entire galaxy, and the assumption made has always been that such a culture would be very high profile, if not, blindingly obvious. It's projects would be so vast that our astronomers would be able to detect them by noting anomalies, outside of natural occurences.

Imagine, for example, a galactic culture that encloses each individual star in a Dyson sphere.

Image: M81, a spiral galaxy in Ursa Major. A ‘wavefront’ Dyson sphere culture might spread across such a galaxy, causing stars to drop out of visible light spectrum entirely, and then one by one, to be detected in the infrared. Credit and copyright: Giovanni Benintende.

A Dyson sphere or ‘shell’ would absorb all of the visible light from a star, re-radiating stellar energy at infrared wavelengths. A Dyson ‘ring’ would use planetary materials that would mask only part of the star’s light.

Scientists have used a list of very interesting infrared sources from the Infrared Astronomy Satellite (IRAS) in their searches, but have come up with no strong Dyson sphere candidates. Nonetheless, Dyson spheres remain interesting, if only because they vastly increase the habitable area around a star.

What would a Type III civilisation do with technologies that could create Dyson spheres not only in one place but across the galaxy?

Whatever the answer, you would think it would be clearly noticeable. Freeman Dyson himself has said that “…a type III (Kardashev civilisation) in our own galaxy would change the appearance of the sky so drastically that it could hardly have escaped our attention.”

James Annis, who has studied anomalous galaxies in a quest for signs of a Type III civilisation, reports: “It is quite clear that the Galaxy itself has not transformed into a type III civilisation based on starlight, nor have M31 or M33, our two large neighbours.” Nonetheless, we wonder whether we should take these statements as conclusive or definitive:

…what would happen for a civilisation that was on its way to becoming a type III civilisation, i.e. a type II.5 civilisation that is developing?

If it was busily turning stars into Dyson spheres the civilisation could create a “Fermi bubble” or void in the visible light from a patch of the galaxy with a corresponding upturn in the emission of infrared light.

This bubble would grow following the lines of a suggestion attributed to Fermi… that patient space travellers moving at 1/1000 to 1/100 of the speed of light could span a galaxy in one to ten million years.

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