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Your support = more science, more stars, more wonder. Donate to EarthSky and be part of something bigger.<\/strong><\/p>\n The Andromeda Galaxy is our next door neighbor. It\u2019s the closest large spiral galaxy to the Milky Way, 2.5 million light-years away. And on July 27, 2026, NASA said star formation in Andromeda is winding down.<\/p>\n A new study showed that over the past 500 million years, the rate of star formation has been slowing. Plus, there\u2019s been a particularly steep drop over the past 40 million years.<\/p>\n The Andromeda Galaxy and our Milky Way are the two most massive and dominant galaxies within the Local Group of galaxies. Andromeda is about twice as large as the Milky Way, though, and it\u2019s a bit younger than our galaxy. But observing Andromeda provides valuable insight into our Milky Way.<\/p>\n The researchers published their peer-reviewed study in The Astrophysical Journal<\/em> on July 27, 2026.<\/p>\n Andromeda is absolutely teeming with stars. Estimates are that it contains some 1 trillion stars. The Hubble Space Telescope has mapped much of the galaxy. Two surveys alone mapped 2\/3 of Andromeda\u2019s disk. And these data allowed astronomers to take measurements of 200 million individual stars.<\/p>\n Co-author Ben Williams of the University of Washington said:<\/p>\n We need to measure the individual stars because they are the fossil record of the galaxy\u2019s formation. Hubble is the only telescope that can give you high enough spatial resolution over a large enough area to be able to do that in Andromeda.<\/p>\n<\/blockquote>\n Using the data from Hubble, the team divided these ultra-sharp images into thousands of squares. The length of each side of the square measured 300 light-years. Then they analyzed each of these squares to determine how much star formation was occurring within it.<\/p>\n Astronomers can tell a star\u2019s general age by assessing its color. Younger and more massive stars are short-lived and bluer. Older and less massive stars that live longer are redder. So, redder squares contain older stars and bluer squares show more star formation.<\/p>\n Astronomers have calculated that the last time Andromeda saw a big burst of star formation was about 2 billion years ago. It likely happened after an interaction or merger with another galaxy. The tidal forces push gases together, which can then coalesce and trigger star formation.<\/p>\n So astronomers can calculate the rate of star formation by how much gas and dust can convert into stars. And they found that, 500 million years ago, Andromeda was forming stars at a rate of about one solar mass per year. That might not seem like much. But it fell even lower around 40 million years ago, to about half that rate. And now, scientists said, Andromeda is only cooking up stars at a rate of about 1\/5 the mass of our sun per year.<\/p>\n Most of the star-forming activity has been in a ring about 32,000 light-years from the galaxy\u2019s center. It\u2019s that activity that is now slowing over time. <\/p>\nStar formation in Andromeda is winding down<\/h3>\n
Hubble\u2019s view of Andromeda\u2019s stars<\/h3>\n
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Star formation in Andromeda<\/h3>\n