Hubble data show Andromeda’s star formation has slid for 500 million years, then dropped more sharply in the last 40 million, leaving the galaxy now producing only about one-fifth of a solar mass annually.
That decline traces back largely to a gas-and-dust ring 32,000 light-years from the center, which had driven about 60% of Andromeda’s star formation over the last 400 million years before fading.
M32 is the leading suspect for disrupting part of the disk: the region nearest the satellite fell below the galaxywide average about 60 million years ago and reached roughly one-third below average 10 million to 15 million years ago.
The interaction case remains unproven because astronomers do not know M32’s exact 3D distance from Andromeda, and proposed passage dates of 200 million or 20 million years ago do not neatly match the slowdown.
The study combined PHAT and PHAST surveys to map about 200 million stars across two-thirds of Andromeda’s disk, a baseline that NASA’s Roman telescope could soon extend to the galaxy’s full disk.