Humanity is continuously striving to make a contact with potentially existing extraterrestrial civilizations. These attempts include the famous SETI project for analysis of astronomical radio signals, and Voyager space probes sent to become the first human-made objects that transited the limits of our Solar system. But what advanced technological ideas could so-called aliens use to achieve a similar aim?

How about the stellar-scale engineering?

This idea has been presented in a scientific paper published on arXiv.org. A joint team of astronomers from the West Virginia University (USA), University of California, Berkeley (USA), ASTRON (The Netherlands), Radboud University (The Netherlands) and the Green Bank Observatory (NRAO, USA) raised the idea of theoretically possible intentional modification of pulsar signals.

This task could be used to transmit immensely strong radio-frequency or light-based signals to inform all the neighbors about the presence of intelligent creatures that are able to accomplish cosmic-scale engineering projects, or at least who are able to tweak the pulsar’s signal.

The authors of this theoretical study argue that a sufficiently advanced civilization (compared with ours) could possess energy resources, which are necessary for stellar radio beacons construction. The team made this assumption based on the Kardashev scale introduced back way in 1964. This scale theoretically classifies civilizations according to their ability to consume energy. The energy consumption rate is about 4×1019 erg/s for humans – a Type-I civilization. Meanwhile, this rate rises up to ~4×1033 erg/s for Type-II, and up to 4×1044 erg/s for Type-III civilizations. Since that amount of energy is similar to the luminosity of galaxies, it would be absolutely enough to generate exceptionally strong radio signal, or to control another cosmic source in order to produce modulated signal.

The astronomers verified this idea using relatively simple mathematical calculations which considered the bandwidth of such signal, the distance of transmission, potential modulation mechanisms and the signal-to-noise ratio. They noted that even ultra-narrow-band signals (~1 Hz) require approximately 100 000 times more energy than the humankind is currently capable of producing in order to transmit these signals across the galaxy. And there is a high probability that other civilizations would simply miss the chosen ‘special’ frequency.

The solution is to use larger bandwidth. However, in this case the power requirements increase significantly (P ~ 1033 erg/s for 1GHz bandwidth). It is obvious that less-advanced civilizations could use naturally-occurring radio transmitters to overcome this energy-related obstacle.

The authors note that even Type-I civilization may be capable to implement this feature, as the only (minimum) requirement would be an ability to build and launch a modulating satellite to a nearby pulsar. Typical radio luminosity of a pulsar is approximately 7.4×1027 erg/s. This pulsar would therefore correspond to a radio-beacon built by civilization between Type-I and Type-II on the Kardashev scale

If the fastest pulsars and the best available modulation schemes are used, the information content transmission rate will possibly reach 1 Kbps or slightly more due to natural frequency limitations of this type of neutron stars. Also, at least five pulsars with solid beaming angle of 20 degrees would be required to cover the entire sky. Anyway, if we could do that with one pulsar, five wouldn’t be more difficult, would it?

By Alius Noreika, Source: www.technology.org