Extragalactic radio sources as lighthouses for SETI
The search for extraterrestrial intelligence (SETI) is one of the most ambitious scientific endeavors. It aims at detecting signals produced intentionally or unintentionally by extraterrestrial civilizations (Siemion et al., 2013). The Galaxy, however, is vast and finding suitable telescope targets for SETI is a critical task (Turnbull & Tarter, 2003).
We examine a strategy for selecting target areas for (active and passive) SETI aimed at improving chances for success. The aim is to search for and/or send electromagnetic signals towards and/or from notable extragalactic radio sources. Assuming that astronomy-wise civilizations are also involved in frequent multi-wavelength monitoring of conspicuous radio sources, the probability for interstellar observers to detect each other when observing in the same direction is increased. A similar idea was proposed by Lemarchand (1995) using Supernova 1987A. However, radio sources are constant "lighthouses" and exist all across the sky.
For illustration purposes, we calculate that a signal emitted in a ~1 degree beam in the opposite direction of Centaurus A, could reach ~200 stars, mostly M-dwarfs, at distances <600pc (stellar density model by Gould et al., 1996). Conversely if we search for ETI signals around Centaurus A, using the Allen-array (PFOV ~3 degrees, Deboer et al., 2006), ~200 stars at distances <300pc will be included in the field and the chance of detecting a message from a civilization using this strategy, is large.