DISCOVERY OF MICROWAVE EMISSION FROM 4 NEARBY SOLAR-TYPE-G STARS

Radio waves from the sun were detected 50 years ago, but the microwave detection of other single solar-type stars has remained a challenge. Here, the discovery of four solar-type radio stars is reported. These ''solar twin'' G stars are radio sources up to 3000 times stronger than the quiet sun. The microwaves most likely originate from a large number of relativistic electrons, possibly produced along with coronal heating, a process that is not understood. Two of the stars are younger than the sun and rotate more rapidly; the dynamo process in the stellar interior is therefore presumably more vigorous, resulting in enhanced coronal activity. One of the detections, however, is an old, metal-deficient G dwarf.