What is the center mass of a solar system?
The centre of mass of a solar system is the solar system barycentre.
The centre of mass of a solar system can vary greatly. In the case of our solar system it moves continuously and can be anywhere between near the centre of the sun and about 100km outside of the sun.
Here is a graph of the position of the solar system barycentre from 1940 to2028. The units are solar radii 696,000km.