How do astronomers use electromagnetic radiation?
Gamma radiation is used to generate electricity using RTG (radioisotope Thermoelectric Generator). But they must produce it using nuclear reaction because gamma radiation from space is insufficient for that purpose.
There are photovoltaic panels that utilize electromagnetic wave in the visible spectrum.
Meanwhile, there are many different electromagnetic radiation sources in outer space. This radiation provides information about the nature of various stars neutron stars, black holes or astronomical bodies.
For example, different stars emit characteristic set of discrete spectral lines which tells the information of elemental composition of the star.
Satellites also gets signals from earth. Vela satellite , for example, contains X-ray sensors that can detect detonations of nuclear ammunitions. This allows monitoring ad control to prevent illegal nuclear testing.