Magnetic fields can regulate disk formation , accretion and jet launching .
Until recently , it has been difficult to obtain high resolution observations of the magnetic fields of the youngest protostars in the critical region near the protostar .
The VANDAM survey is observing all known protostars in the Perseus Molecular Cloud .
Here we present the polarization data of IRAS 4A .
We find that with \sim 0.2 \arcsec ( 50 AU ) resolution at \lambda = 8.1 and 10.3 mm , the inferred magnetic field is consistent with a circular morphology , in marked contrast with the hourglass morphology seen on larger scales .
This morphology is consistent with frozen-in field lines that were dragged in by rotating material entering the infall region .
The field morphology is reminiscent of rotating circumstellar material near the protostar .
This is the first polarization detection of a protostar at these wavelengths .
We conclude from our observations that the dust emission is optically thin with \beta \sim 1.3 , suggesting that mm/cm-sized grains have grown and survived in the short lifetime of the protostar .