The starburst in the central kiloparsec of Markarian 231

We present VLBA observations at 0.33 and 0.61 GHz, and VLA observations bet ween 5 and 22 GHz, of subkiloparsec-scale radio emission from Mrk 231. In a ddition to jet components clearly associated with the active galzctic nucle us, we also find a smooth extended component of size 10-1000 pc most probab ly related to the purported massive star-forming disk in Mrk 231. The diffu se radio emission from the disk is found to have a steep spectrum at high f requencies, characteristic of optically thin synchrotron emission. The requ ired relativistic particle density in the disk can be produced by a star fo rmation rate of 220 M-circle dot, yr(-1) in the central kiloparsec. At low frequencies the disk is absorbed, most likely by ionized gas with an emissi on measure of 8 x 10(5) pc cm(-6). We have also identified four candidate r adio supernovae that, if confirmed, represent direct evidence for ongoing s tar formation in the central kiloparsec.