A new study using data from NASA’s Hubble Space Telescope has revealed that the Andromeda Galaxy, the Milky Way’s nearest large galactic neighbour, has experienced a steady decline in star formation over the past 500 million years, with the slowdown accelerating during the last 40 million years.

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• Researchers using observations from NASA’s Hubble Space Telescope found that the Andromeda Galaxy (M31) has been producing progressively fewer new stars over the past 500 million years, providing new insights into galaxy evolution.
• The study, published in The Astrophysical Journal, analysed nearly 200 million individual stars using data from the Panchromatic Hubble Andromeda Treasury (PHAT) and Panchromatic Hubble Andromeda Southern Treasury (PHAST) surveys.
• Scientists divided Andromeda into thousands of regions, each covering about 300 light-years, to reconstruct the galaxy’s star formation history with unprecedented detail.
• The research indicates that Andromeda experienced a major burst of star formation around 2 billion years ago, likely triggered by an interaction or merger with another galaxy, after which star formation gradually declined.
• Approximately 500 million years ago, Andromeda formed stars at a rate of about one solar mass per year. This declined to half a solar mass per year around 40 million years ago and has now dropped to around one-fifth of a solar mass annually.
• Most recent star formation has been concentrated in a ring located nearly 32,000 light-years from the galaxy’s centre, with scientists finding that reduced activity within this ring is the primary reason for the overall decline.
• Researchers concluded that the slowdown is not due to a shortage of gas and dust, but rather because the galaxy appears to be entering a natural phase of reduced star-forming activity.
• The findings enhance scientists’ understanding of the long-term evolution of spiral galaxies such as Andromeda and the Milky Way, offering valuable clues about how galaxies age and gradually transition into quieter phases.