What is a radio telescope primarily used for?

A radio telescope is primarily used to gather radio waves or emissions from astronomical objects such as stars, galaxies, and other celestial phenomena. This type of telescope detects and analyzes the radio frequency emissions produced by various cosmic sources, allowing scientists to study objects that may not be visible in the optical spectrum. For example, many astronomical events and structures, like pulsars, quasars, and cosmic microwave background radiation, emit radio waves that can provide invaluable information about their nature and behavior.

The other choices describe different types of instruments or functions: measuring infrared light involves a different kind of telescope designed for a specific wavelength range; capturing visible light refers to optical telescopes that observe the light within the human-visible spectrum; and amplifying sound waves in the atmosphere pertains to devices unrelated to astronomical observations. Thus, gathering radio emissions is the unique and essential function of a radio telescope.