In this blogpost I shall review and briefly summarize the article by James Annis (1999) which is the first published work on the search for Kardashev Type III civilizations.
The 1964 work by Nikolai Kardashev established a scale for the technological development of intelligent civilizations based on their energy consumption. A Type III entity was posited to have the technological prowess to harness the energy of its entire galaxy. This would mean that it could capture energy from most of the stars in the galaxy and / or the supermassive black hole at the center of the galaxy. Potentially even Dark Matter and Dark Energy?
Annis theorizes that the if a entity could capture energy from most of the stars in its galaxy, it would give off signatures that should be observable by us. From the fundamental concepts of gravitation and thermodynamics he establishes relations between the observed intensity and the temperature of the galaxy. These relations should hold true for naturally occurring signals from galaxies. Therefore a potential way to find these ET civilizations is to look for outliers.
The cultivation of energy from stellar sources would lead to a dip in the stellar flux at the peak of its black body and increased emission at about 300 K since the absorbing objects would emit in the thermal region. Using the Tully Fisher relationship they plot the Luminosity vs Rotation Velocity (proxy for temperature) of the galaxies and try to find outliers or deviations from the trend. Doing this for a sample of about 130 Spiral and Elliptical galaxies they do not find any signals which can potentially be attributed to a Type III civilization.
Citing the results of his work, and the fact that we see that our (and our closest) galaxy/ies do not show such an anomaly, he tries to put constraints on the incidence rates for such a civilization. The upper limit on this rate is calculated to be about 300 Gyrs, which effectively means that such civilizations do not currently exist. However, an interesting point raised is the possibility of observer’s bias in the sample collected, and the fact that the outliers in the trend might have been excluded earlier on.
Further, if their technologies have evolved beyond stellar energy to more advanced forms such as exploiting the black hole at the center of the galaxy or generating energy from dark energy or dark matter then this technique would fail. This is further discussed in Wright et al. 2014b.