How do astronimers use radio waves to learn about the compsison of stars

Radio electro-magnetic emissions are detected by radio telescope (Jordell Bank,England and in Arecibo,Purerto Rica) by astronomers who study thermal radiation from the hot gases ,synchrotron radiation from electrons spiralling in magnetic fields and lines specific waves lengths(hydrogen emit 21 cm line) emitted by atoms and molecules in the interstellar gases in the stars within our galaxy and beyond in radio galaxies and quasars that have helped in learning the composition of stars and also mapping our universe, the spiral structure of the milky way, the crab nebula and pulsars as remains of our universe, the short radio wavelengths from the dense clouds in star formation, and the weak background radiation thought to be the early big bang radiation during the origin of our universe. karl Jansky first detected radio waves from the centre of our Galaxy in 1932.