Abstract:
Electromagnetic waves will be absorbed when they pass through the atmo#2;sphere. Electromagnetic waves with some frequencies are absorbed more, while electromag#2;netic waves with other frequencies are absorbed less. The frequency range within which
the electromagnetic waves are less absorbed is called the atmospheric window of electro#2;magnetic waves. Similarly, the propagation of electromagnetic waves in the universe will be
absorbed by the galactic medium. This paper investigates the problem of the absorption
of electromagnetic wave when it propagates in the Milky Way. Our analysis shows that
there is a lower cut-off frequency for the electromagnetic waves which can reach the earth
passing through the Milky Way. Interestingly, the lower cut-off frequency is different respect
to different direction on the celestial sphere, which gives a distribution. This distribution
is closely related to the distribution of free electron gas in the Milky Way. We propose to
determine the distribution of free electron gas in the Milky Way by measuring the cut-off
frequency distribution.