The Radio Supernebula in NGC 5253.

We present 1.3 cm and 2 cm subarcsecond resolution VLA images of the dwarf galaxy NGC 5253. Within the central starburst, we detect high-brightness [Tb&parl0;2 cm&parr0; approximately 100-12,000 K] radio continuum sources. These appear to be very dense, "compact" H ii regions. The dominant radio source is a nebula approximately 1-2 pc in size, requiring several thousand O stars within the volume to maintain its ionization. This nebula has no obvious optical counterpart. The number of ionizing photons we find for this cluster is nearly 2 orders of magnitude larger than indicated by Halpha fluxes, and the deduced stellar content accounts for a significant fraction of the total infrared luminosity of the galaxy. This cluster is a strong candidate for a globular cluster in the process of formation, perhaps the youngest globular cluster known.