Astronomers have examined the unique characteristics of the Milky Way in comparison to other galaxies.

The Milky Way consists of hundreds of billions of stars in a gigantic "whirlpool": the galactic arms spiral around the center, where, within a relatively small diameter of Mercury's orbit (approximately 100 million kilometers), lies a supermassive black hole with a mass equivalent to four million Suns. The Galactic disk occupies a space of about a hundred thousand light-years or even more, and in a small region of the Orion Arm, located 26 thousand light-years from the Galactic center, is the Solar System.

Spiral galaxies make up a significant majority in the Universe—60-70%. For this reason, astronomers have often assumed that Earth exists in a fairly typical environment and that any other spiral galaxy is similar to ours. The Milky Way has been viewed as a "laboratory" for studying occurrences in the Universe. However, it is now becoming evident that we are situated in a rather unusual location.

Recently, astrophysicists sought to understand how the supposed halo, in which galaxies are thought to be embedded like pearls in an oyster, affects them. This halo is believed to be composed of so-called dark matter, which is estimated to exist in the Universe in quantities five times greater than ordinary matter, the kind we understand and is recorded in the periodic table.

It is this unknown, hidden mass that, according to calculations, "holds," or maintains the structure of nearly all galaxies. Without it, these galaxies would have disintegrated into a scattered collection of stars. It is likely that galaxies would not have formed at all without dark matter. At least, this is the belief of most cosmologists.

To unravel this "cocoon" of dark matter, scientists decided to observe the galactic surroundings where numerous dwarf satellite galaxies have accumulated. The Milky Way has been found to have over 50 of these. The largest of them weigh billions of Suns and are visible to the naked eye: these are the Large and Small Magellanic Clouds. However, there are others, such as the Pegasus I Galaxy or Cassiopeia III, which have a total mass of all their stars of only about a million Suns and a diameter of around a thousand light-years.

In the case of the satellites of our Galaxy, it is noteworthy that almost all of them are "dead": no new stars are being born in them. This process continues only in the Magellanic Clouds and only because they have accompanied the Milky Way for the last couple of billion years. There is a belief that star formation in satellite galaxies ceases precisely due to the influence of dark matter.

A team of astrophysicists from the United States compared the situation around the Milky Way with what occurs with the satellites of other galaxies. They selected 101 galaxies that are similar to ours in mass and structure. In total, they counted 378 satellite galaxies. The researchers shared their findings in three different articles published in The Astrophysical Journal.

Firstly, they discovered that our satellite "lifeless" small galaxies are not a typical situation at all. In most "copies" of the Milky Way, stars are successfully forming even in satellite galaxies with masses of tens of millions of Suns, which are relatively small.

Secondly, the holders of large satellites, such as our Magellanic Clouds, generally possess a far more numerous collection of "younger siblings" than the Milky Way.

And thirdly, based on the resulting picture, scientists proposed to modify the established model of galaxy formation and how the "fate" of their satellites unfolds: the role of dark matter in this process turned out to be even less understood than before.