The Very Long Baseline Array ( VLBA ) and the Very Large Array ( VLA ) have been used to image the continuum radio emission from Mrk 231 , a Seyfert 1 galaxy and the brightest infrared galaxy in the local universe .
The smallest VLBA scales reveal a double , or possibly triple , source less than 2 pc in extent .
The components of this central source have minimum brightness temperatures of 10 ^ { 9 } – 10 ^ { 10 } K , spectral turnovers between 2 and 10 GHz , and appear to define the galaxy nucleus plus the inner regions of a jet .
The strongest component is probably synchrotron self-absorbed , while the weaker component to the northeast may be either free-free absorbed or synchrotron self-absorbed .

On larger VLBA scales , the images confirm a previously known north-south triple source extending 40 pc and elongated perpendicular to a 350-pc starburst disk traced by H i and CO .
Both lobes of the triple show evidence for free-free absorption near 2 GHz , probably due to ionized gas with a density of 1–2 \times 10 ^ { 3 } cm ^ { -3 } in the innermost regions of the starburst disk .
This free-free absorption resembles that toward the counterjet of 3C 84 , but requires ionized gas at lower density located considerably farther from the central source .
The absorbing gas may be ionized by the active nucleus or by local regions of enhanced star formation , possibly in the inner part of the starburst disk .
The elongation position angle of the 40-pc triple differs by 65 \arcdeg from that of the 2-pc source .
Unless the radio source is seen nearly end-on , the different symmetry axes on different scales in Mrk 231 imply a dramatic curvature in the inner part of the Mrk 231 radio jet .

A comparison of VLBA and VLA flux densities indicates that the radio continuum from the 350-pc disk has a spectral index near -0.4 at frequencies above 1.4 GHz and is plausibly energized by a massive burst of star formation , with the overall spectrum flattened somewhat by a contribution from free-free absorption .
On VLA scales , asymmetric and diffuse emission extends for more than 25 kpc .
This emission has a steep spectrum , exhibits linear polarization exceeding 50 % at some locations , and shares the symmetry axis of the 40-pc triple , but on a scale larger by three orders of magnitude .
The large-scale radio emission extends beyond the bulk of the optical galaxy , but has an initial axis similar to a series of optical star-forming knots several kiloparsecs from the nucleus .
This diffuse radio source is probably generated by energy deposition from a slow-moving nuclear jet , which conceivably could help energize the off-nuclear starburst as well .