1998A&A...337...69O

We present the results of multi-epoch global VLBI observations of the Compact Symmetric Object (CSO), 0710+439 at 5GHz. Analysis of data spread over 13 years shows strong evidence for an increase in the separation of the outer components at a rate of 0.251±0.029h^–1c. Dividing the overall size of 86.8h^–1pc by this separation rate implies an estimated kinematic age of only 1100±100yrs. After taking into account possible temporal variations in hotspot advance speeds due to cloud collisions or hydrodynamic instabilities we argue that the upper limit to the age of 0710+439 is most likely within a factor of 2 of this estimate and certainly within a factor of 10 (i.e. <11000yrs). This result therefore strongly supports the idea that Compact Symmetric Objects are very young radio-loud sources. Furthermore the large radiative efficiency we calculate for 0710+439 is consistent with strong negative luminosity evolution as CSOs grow in size and with them evolving into classical double sources.