Stars, like humans, are more volatile when they’re young. As sunlike stars mature past their first billion years, they all tend to slow in their rotation, eventually converging to roughly the same period we see now in our sun: about 27 days for a star the same mass as our sun.
But when stars are young, they rotate more quickly and less predictably. Two stars of the same size may rotate at drastically different speeds. And stars that are fast rotators tend to shoot out more solar flares and coronal mass ejections, hurling powerful radiation and charged particles into their systems, often to the detriment of the planets around them.
