Complex sentence: Its large mass (332,900 Earth masses) produces temperatures and densities in its core high enough to sustain nuclear fusion, which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation, peaking in the 400--700 nm band of visible light.
Split into simpler sentences: Its large mass (332,900 Earth masses) produces temperatures and densities in its core high enough to sustain nuclear fusion. This releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation peaking in the 400--700 nm band of visible light.