Stellar radio sources, radio source stars or radio stars are stellar objects that produce copious emissions of various radio frequencies, whether constant or pulsed. Radio emissions from stars can be produced in many varied ways.
Pulsars, a type of neutron star, are examples of radio stars. Rotation-powered pulsars are, as the name suggests, powered by the slow-down of their rotation. The rotation powers a magnetic field, which generates the radio emissions. Not all rotation-powered pulsars generate their pulses in the radio spectrum. Some of them, from the millisecond pulsars, generate X-rays instead. Aside from radio pulsars and X-ray pulsars, there are also gamma ray pulsars, which are mostly magnetars. Some radio pulsars are also optical pulsars.
Aside from pulsars, another type of neutron star is also characterized by radio emissions: the rotating radio transient (RRAT). As suggested by the name, the radio emission is erratic.
Some late-type stars can produce astrophysical masers from their atmospheres and beam out coherent bursts of microwaves.
The Sun, the nearest star to Earth, is known to emit radio waves, though it is virtually the only regular star that has been detected in the radio spectrum, because it is so close. It is not considered a radio star because it is not a strong radio source.
Quasars (quasi-stellar radio sources) are not radio stars. They also emit radio frequencies, but from the effects of supermassive black holes at the centre of galaxies. Although they appear to be stars, they are not stars, but the hyperactive heart of a galaxy.