Andromeda's Star Formation Slows, Suspected Trigger: a Neighbor Named M32

Hubble observations show the Andromeda galaxy’s rate of turning gas into stars has dramatically slowed in the last ~40 million years, with the slowdown most pronounced on the side facing its tiny neighbor M32. While researchers acknowledge they can’t prove M32 caused the decline, it is the leading suspect, possibly due to a past collision. The study mapped Andromeda’s history across two-thirds of its disk, finding current star formation at about 0.2 solar masses per year (roughly one-fifth the Milky Way’s rate). The Nancy Grace Roman Space Telescope will help measure more of Andromeda’s stars to further test the M32-link in the coming years.