Complex sentence: A theoretical study shows the system started off with solar masses of 3.0 and 2.5, but the latter star lost its mass in becoming a white dwarf and sent half a solar mass to Zeta Cygni, along with the heavy chemical elements it possesses today.
Split into simpler sentences: A theoretical study shows the system started off with solar masses of 3.0 and 2.5, but the latter star lost its mass in becoming a white dwarf. It sent half a solar mass to Zeta Cygni, along with the heavy chemical elements it possesses today.