Why the most massive galaxies in the early universe stopped forming stars prematurely

Astronomical observations show that the most massive galaxies in the early universe formed approximately three to four billion years after the Big Bang and stopped producing stars very early in cosmic history, around one billion years after their formation. This strange behavior has puzzled experts in the field. For comparison, our galaxy, the Milky Way, is as old as the universe itself and continues to produce stars, albeit at a low rate, even 13.5 billion years after its formation.