Having exhausted the supply of hydrogen at its core, the star cooled and expanded to 23 times the Sun's radius. The star is spinning slowly, taking  to complete its sidereal rotation.
The star's exhaustion of hydrogen led to a dramatic change in its state, causing it to expand to 23 times the Sun's diameter. As a result, the star's rotation period has increased significantly, taking a considerable amount of time to complete one rotation on its axis.