Dwarf galaxies around the Milky Way shed light on its complex past

On the sidelines of the Gaïa mission, by studying the dwarf galaxies orbiting the Milky Way, American scientists noted that the majority of these galaxies had only recently arrived in the area. This discovery has implications for our understanding of the interplay between normal galaxies and dwarf galaxies, and raises questions about the “life expectancy” of a dwarf galaxy on the edge of a more massive galaxy.

The researchers involved in the study relied on data collected by the satellite Gaiafrom the European Space Agency (ESA), designed to observe and measure the characteristics of more than one billion celestial bodies to improve, among other things, our knowledge of the structure and evolution of our galaxy, The Milky Way. By bringing together the joint work of 20 countries, the mission has produced the most detailed three-dimensional mapping of our galaxy to date.

Gaïa, a satellite to explore our galaxy

We now know that the space around our galaxy is not empty, but abounds dwarf galaxies, of only a few thousand stars, thus forming a local subgroup. Today there are about fifty dwarf galaxies around The Milky Way, although not all of them are necessarily gravitationally bound to the latter. The largest galaxy confirmed in orbit around the Milky Way is the Sagittarius Dwarf Galaxy.

Neighboring galaxies recently arrived on the edge of the Milky Way

By studying the data collected by the Gaïa satellite, the researchers found that a large proportion of these galaxies had too large angular moments: in other words, most of the dwarf galaxies observed near the Milky Way move much faster than other objects that known to orbit our galaxy.

These dwarf galaxies would not have been close enough to the Milky Way long enough to interact gravitationally with it, leading scientists to believe that they would have only recently arrived in the area less than two billion years ago. (Age of the Milky Way). estimated at 13.5 billion years).

What would have happened to the first satellite galaxies?

We now know that Milky Way has swallowed other galaxies on several occasions over its history: for example, the galaxy Gaia-Enceladus would have been incorporated into the Milky Way about 10 billion years ago, as evidenced by a population of stars orbiting around 1 p.m. energies relatively weak. The Sagittarius dwarf galaxy is currently disturbed by gravitational forces of ours, and has been gradually integrated into it, and has been so for about 4 billion years.

In the light of all these observations, according to François Hammer, of the Paris Observatory, ” The simply gigantic gravitational force of the Milky Way would easily destroy a dwarf galaxy after one or two passes around it “. The dwarf galaxies orbiting the Milky Way would then have only one Life expectancy limited.

Dwarf galaxies orbiting the Milky Way would have only a limited life expectancy

But the researchers in the study go further: If the gravitational force of the Milky Way is too strong to allow a dwarf galaxy to survive on its approach in more than two passages, then how could a dwarf galaxy survive longer (as we had thought for the Milky Way’s dwarf galaxies)?

To explain this, scientists would bring in black fabric, which according to them would act as a glue that consolidates the dwarf galaxies. The possibility that these galaxies contain a certain amount black fabric is also much considered due to movement of their stars that could only be explained with “normal” matter.

The history of our Milky Way now appears to be far more complex than previously thought, and this research would further suggest an important role for dark matter in the evolution of our galaxy.

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