We have imaged the nearby galaxy merger Arp 299 at arcsecond and milliarcsecond resolution , using both the Very Large Array and the Very Long Baseline Array .
The large-scale radio emission from the merger contains 5 bright , compact radio sources embedded in diffuse emission , with diameters less than 200 pc .
Supernova rates of 0.1 to 1 per year are required to produce the VLA-detected radio emission in these sources .
Two of the compact VLA radio sources , designated Source A and Source D , also have been detected and imaged at milliarcsecond scales .
Source A , which is associated with the nucleus of one of the merging galaxies , contains five milliarcsecond-scale sources , each with a radio power between 100 and 1000 times that of the Galactic supernova remnant Cassiopeia A .
Four of these have flat or inverted spectra and appear to be young supernovae .
Three of the VLBI-scale sources are located within 10 pc ( projected ) of one another , and two are separated by less than 3 pc , indicating that they all may be within the same super starcluster or complex of such clusters .
The brightest VLBI-scale source , A0 , has an extremely inverted spectrum , with \alpha \gtrsim + 2 at gigahertz frequencies .
It seems to be the youngest supernova , which has not yet broken out of its circumstellar shell .
The milliarcsecond radio sources within Source A appear to constitute a supernova factory , confirming the presence of an extreme starburst that peaked at least a few million years ago .