Milky Way companion galaxies may be “newcomers”

(ORDO NEWS) — Data from the European Gaia mission could rewrite the history of our Galaxy, the Milky Way. Those small galaxies that we thought were “old friends” of the Milky Way, in fact, may turn out to be “aliens” who arrived in our Galaxy relatively recently.

Dwarf galaxies are groups of stars, numbering from several thousand to several billion luminaries. For several decades, it was thought that the dwarf galaxies surrounding our Milky Way galaxy were actually its satellites, that is, galaxies captured by the gravity of our larger galaxy many billions of years ago and since then orbiting it.

But now that the motion of these dwarf galaxies has been calculated with unprecedented accuracy, based on observations collected in the third release of data from the Gaia satellite, scientists have come to unexpected conclusions.

Fran├žois Hammer of the Paris Observatory, France, along with colleagues from Europe and China, used data from the Gaia satellite release to calculate the motion of 40 dwarf galaxies around the Milky Way. By calculating the three-dimensional velocities for each galaxy, the researchers then found the orbital energy and rotational (angular) momentum of the galaxy.

According to this calculation, the studied dwarf galaxies moved faster than the known giant stars and star clusters orbiting the Milky Way. So fast that they could not be in orbit around the Milky Way for a long time, where the powerful gravity of our Galaxy is rapidly “sucking” orbital energy and angular momentum.

This means that the dwarf galaxies studied in the study arrived in their orbits relatively recently, that is, in the next several billion years, the authors of the work concluded. This contradicts the generally accepted picture of the structure of our Galaxy, according to which most of the dwarf galaxies in the vicinity of the Milky Way were considered to be its satellites in stable orbits for a long time.

This may also imply that dwarf galaxies contain less dark matter than previously thought, since models have been proposed that include increased amounts of dark matter in dwarf galaxies to explain the integrity of dwarf galaxies that have long been under the powerful gravitational influence of the Milky Way. Dark matter appears like gravitational “glue”

The work was published in the Astrophysical Journal.

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