At a distance of 2.5 million light-years from Earth, the Andromeda Galaxy looks like a pale sickle-shaped object to the naked eye. However, this object is almost twice as big as our Milky Way and three times as massive. Moreover, this grandeur hides a whole “family” of nearly 30 dwarf satellite galaxies that circle their host like bees around a hive.
Photo: NASA
The Hubble Space Telescope studied this dynamic system with incredible precision, spending more than 1000 orbital hours creating a 3D map of the satellites and analyzing their evolution over billions of years.
Why is Andromeda not like the Milky Way?
A comparison with our galaxy revealed striking differences. Whereas the Milky Way has a relatively stable history, Andromeda underwent a large-scale merger with another galaxy billions of years ago. This event, along with Andromeda’s twice the mass, explains its “turbulent nature” and the diversity of its satellites. Unlike our galaxy, where the satellites are scattered randomly, half of Andromeda’s satellites move in the same plane and direction.
“This discovery is a complete surprise to us. We still don’t understand why they formed such a strange configuration,” admits study leader Daniel Weisz.
Dwarf galaxies with a stormy past
The brightest satellite of Andromeda is Messier 32 (NGC 221). It is believed to be the core of a galaxy that once collided with Andromeda. After the collision, M32 lost most of its stars and gas, but continued to orbit. This galaxy contains old stars, but evidence of violent star formation billions of years ago raises new questions.
In addition to M32, Andromeda has unique dwarf galaxies that have been forming stars for much longer than the models predicted. “This contradicts all the simulations!” emphasizes Alessandro Savino, author of the study.
Forecasting the future with a look into the past
Thanks to Hubble, scientists have obtained data on the movement of satellites for the first time. Subsequent observations in five years using the James Webb telescope will allow us to reconstruct the trajectories of all 36 dwarfs and review their history billions of years ago.
So far, most of the knowledge about galaxies has been based on studies of the Milky Way. However, Andromeda has shown that the rules of cosmic evolution may be different.
“We realized that small galaxies in different systems evolve differently. This changes our understanding of the Universe,” Weisz summarizes.
Earlier, we reported how Hubble had completed a ten-year-long creation of a 417-megapixel panorama of the Andromeda galaxy.
Provided by NASA
