Search for temporal coherence in the sky

摘要

A new observation mode, a survey of temporal coherence in large fields, is described. Longitudinal coherence can arise in many astrophysical scenarios and at different wave lengths, from plasma effects, scattering of electrons on periodic electromagnetic volumes, to Einstein rings and even extraterrestrial unintended signaling. There is a plurality of coherence seeking devices, developed for military purposes, which can be easily adopted for this task. Many are based on unbalanced interferometers, with a path difference that exceeds the white light envelope. They were shown to be able to discern very weak coherent sources in a heavily cluttered environment. For searches where the coherent wave length was unknown, a signal to background ratio of 1:10,000 was demonstrated. At a known wave length (e.g. molecular lines) one can even expect 1:1,000,000 detection ratio. Once such sources are found, they can be better monitored by most astronomical interferometers, whose field of view is usually rather narrow.