By 1950 it had become evident that many of the radio sources in the sky were compact (of small angular diameter). But astronomers still had no idea what most of them were. Bolton had identified Taurus A with the Crab Nebula, which was known to be a supernova remnant. Did this mean that most of the other radio sources were supernova remnants? It seemed unlikely. In fact, the other two sources that Bolton had identified were both galaxies. Furthermore, one of the strongest sources in the sky—Cygnus A—had still not been identified optically. Despite the controversy Bolton and his group began referring to all of the objects as “radio stars.”