Hi, we are aliens and we have “pulsars”

Artist illustration of a pulsar (Credit picture University of Manchester).


Where are all the aliens?

This question received many answers, ranging from “they are home watching TV” to “long dead and gone”.

And if they are there how to listen to them, or more important on which frequency should we tune our receivers to detect them?

One clever mechanism to transmit a simple message across the Galaxy is to use a natural emission, one that would be investigated by scientists and not random frequencies. Add a modulation system on this natural emission and you have a perfect transmitter. This is the scenario considered by Jayanth Chennamangalam et al. in a recent article in which they use pulsar signal as signal carrier.

Here they discuss the modulation mechanism, the information content of the beacon, the potential observational signatures of artificial modulation and finally they analyse the energy considerations for this kind of signalling scheme.

The main idea is to install a satellite on the orbit of the pulsar or to use a Dyson shell in order to modulate the pulsar signal and to transmit a signal. Using a simple single-bit modulation system the transmission rate would be quite low, less then 1Kbps but this could be increase by a more complex system that could make use of frequency-dependent system.

To cover the entire sky one such system would require at least five pulsars, if we assume that the beaming solid angle of a such pulsar is about 20% of the entire sky and could in principle run on the entire radio life time of a pulsar which in the case of a normal pulsar is about 10^7 yr and around 10^9 yr for the millisecond pulsar.

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