Afterwards,   Spiegel's work focused on models of the solar cycle and radiative processes in hot stars. He authored or co-authored more than 100 papers involving collaborations with over 60 individuals; these papers have been cited well in excess of 3000 times.
Following this, Spiegel's research focused on solar cycle models and radiative processes in hot stars. He authored or co-authored more than 100 papers that collaborated with over 60 people; these papers received citations significantly exceeding 3000 times.