The Andromeda Galaxy, captured in this image by NASA's Spitzer Space Telescope, is the closest major galaxy to the Milky Way, but new Hubble data suggest it evolved very differently. (Image credit: NASA/JPL-Caltech)
A major new study by the Hubble Space Telescope provides the first bird's-eye view of all the known dwarf galaxies orbiting the Andromeda Galaxy.
The results show that over billions of years, Andromeda and its family of dwarf galaxies have undergone significantly chaotic interactions – reminiscent of a game of cars – compared to the relatively calm evolution of galaxies surrounding the Milky Way.
The study's authors say the findings, published in The Astrophysical Journal, show that we may not be able to extrapolate data about other galaxies based on our understanding of our own.
“There have always been concerns about whether what we learn about the Milky Way applies more broadly to other galaxies,” study co-author Daniel Weiss, an assistant professor of astronomy at the University of California, Berkeley, said in a statement. “Our work has shown that low-mass galaxies in other ecosystems have followed different evolutionary paths than what we know from the Milky Way’s satellite galaxies.”
At about 2.5 million light-years away, Andromeda is the closest major galaxy to us and getting closer; Andromeda and the Milky Way are expected to collide and merge in about 5 billion years. To the naked eye, it appears as a faint spindle-shaped object, taking up about as much of the sky as the full Moon. What is invisible without powerful telescopes and poorly understood is a swarm of about three dozen smaller galaxies scattered around Andromeda like bees around a hive.
Beginning in late 2019, Hubble spent two years cataloging images — and measuring the locations and motions — of three dozen galaxies orbiting within 1.63 million light-years of Andromeda. The data gave Weiss and his team the first complete 3-D map of our galactic neighbor’s ecosystem. Using this information, the researchers studied the processes that governed the evolution of these dwarf galaxies over nearly 14 billion years of cosmic time.
“Everything that's scattered around the Andromeda system has a significant asymmetry and perturbation,” said Weiss, the lead investigator for the Hubble program. “It's likely that something significant has happened recently.”
That “something,” the researchers say, was a collision between Andromeda and a larger galaxy billions of years ago. A possible culprit is Messier 32, Andromeda’s satellite galaxy and its brightest companion. Astronomers suspect that M32, visible in Andromeda’s lower left, is the remnant core from the merger.
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