Astronomers have observed the star formation history of 36 galaxies that are satellites of Andromeda.

The Andromeda satellite system (M31) serves as a genuine "laboratory" for studying the formation and evolution of dwarf galaxies that interact with their massive "host." Scientists are aware of approximately 40 satellites, most of which exhibit low luminosity and mass, a limited amount of gas, and ancient stellar populations. However, there are exceptions: some galaxies (notably IC 10 or Peg DIG) contain gas and continue to form stars.

To gain further insights into the formation and evolution of this system, an international research team led by Alessandro Savino from the University of California (USA) combined archival and new observational data obtained using the Hubble Space Observatory.

Subsequently, by creating detailed diagrams for each of the 36 satellite galaxies, astronomers "sorted" the stars by age and brightness, effectively "reading" the entire star formation history of each galaxy. The results of this new scientific work have been published in the journal Astrophysical Journal.

Since the Andromeda satellites are located nearly twice as far from their "host" than most of the Milky Way's satellites, observing the oldest stellar populations became key to understanding when and how rapidly the 36 studied galaxies initiated and halted their star formation processes.

The results indicated that the more massive a dwarf galaxy was and the farther it was from the center of Andromeda, the longer it continued to form stars. Conversely, compact and nearby satellites "burned out" more quickly, ceasing star formation at earlier stages. 

About half of the dwarf galaxies began forming stars more than 12 billion years ago, with their activity tapering off 8-10 billion years ago. Such a pattern is less common among the satellites of our Galaxy, suggesting possible differences in the evolution of the Milky Way and Andromeda.

The key factors determining the duration of star formation were the mass of the dwarf galaxy itself and the conditions in Andromeda's halo. Thus, the researchers were able to peek into the history and dynamics of one of the largest systems beyond the Milky Way and understand how the neighboring galaxy formed and evolved on cosmic scales.

Despite the impressive results, the work is far from complete: to refine the masses, orbits, and chemical compositions of each satellite galaxy, observations must be conducted using other observatories, including the James Webb Space Telescope.

The study of satellite galaxies is considered a crucial part of addressing the dark matter problem. Most large galaxies have fewer satellites than expected (the so-called missing dwarf galaxy problem). Therefore, astronomers are paying increased attention to studying the Andromeda satellite system, as it is the largest of the galaxies close to us.