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Milky Way: ‘Impossible’ satellite mystery – supposed ring of dwarf galaxies is just a temporary effect

The Mysterious Ring of Galaxies: For decades, astronomers have puzzled over the arrangement of the Milky Way’s 11 small satellite galaxies, which goes against cosmological rules – they all seem to rotate in one plane. New analysis now reveals that the ring-shaped arrangement is deceptive and only the result of a temporary coincidence. In fact, dwarf galaxies are moving on completely different scales and will actually be spread out in a few hundred million.

The Milky Way does not move alone through space: over time it has encountered many smaller galaxies. It has some of these dwarf galaxies torn And catch up, others have become too Satellites Our home galaxy. These satellite galaxies include the Clouds of Magellanic, Fornax, Sagittariusthe sculptor, and the Leo I and Leo II dwarf galaxies.

The Milky Way and its satellite galaxies © Richard Powell/Public Domain

The ring puzzle of the dwarf galaxy

But the strange thing is that the 11 classic satellite galaxies appear to orbit the Milky Way neatly lined up. It forms a thin ring, also known as a satellite plane. But such a ring contradicts current cosmological models, especially the distribution of dark matter in our galaxy. This is because it is concentrated in the spherical halo of the Milky Way and thus exerts an almost uniform gravity on satellites in all directions.

Therefore, according to current models, satellite galaxies should also revolve around the Milky Way in a disorderly manner in a spherical sphere. Instead, they seem to form a tight belt. “There is no known mechanism that could explain such a jet orbiting the satellites,” says Till Swala and colleagues from the University of Helsinki. “This ‘satellite-level problem’ not only contradicts the ΛCDM cosmological model, but the entire dark matter concept.”

A New Look at Sagittarius, Fornax and Co

But how can this contradiction be explained? This question has preoccupied astronomers for more than 50 years. However, they have not yet been able to find a mechanism that would explain the oddly focused arrangement of dwarf galaxies. In search of an answer, Sawala and his team once again assessed the orbits and motions of 11 classic satellite galaxies using the latest data from the Gaia satellite.

The analyzes provided two new insights: on the one hand, the 11 dwarf galaxies were much less close together than previously assumed: the satellite plane covers 23.2° instead of just 16°. It corresponds to a real ring, as Swala and his team find. Instead, some of these dwarf galaxies, including Leo I and Leo II, are moving through the putative ring.

Dwarf galaxy positions
Arrangement of space galaxies in the past, present and future. © Sawala et al. / Natural Astronomy, Inc. CC by 4.0

random pairings in place of the common orbitals

But this means that the supposed belt of satellite galaxies is based on a purely chance meeting of satellite galaxies in the same plane. Similar to the way the planets of the solar system form conjunctions from time to time and line up in a line, this is also the case with dwarf galaxies in the Milky Way. “We now know that this satellite level is just a fluke – it’s the classic case of being in the right place at the right time,” explains co-author Carlos Frink of Durham University in England.

Just as the constellations we know are based on the random arrangement of stars that are far apart and not connected to each other, satellite galaxies only appear to form a unified ring. “If we looked at the whole thing again in a billion years, this episode would have disappeared long ago,” Frink says. According to calculations, the dwarf galaxies apparently diverged from each other in only a few hundred million years.

Fits the cosmic model again

Thus the mystery of the “satellite plane” of our Milky Way, which has existed for decades, has been solved. This also illustrates the alleged inconsistency of current cosmological models and the concept of dark matter: as assumed by these models, the gravitational influence of the Milky Way largely corresponds to the spherical distribution of dark matter in its halo.

“This has removed one of the biggest challenges to the cold dark matter theory,” Frink says. Thus, this cosmological model continues to be a remarkably accurate description of the evolution of our universe. (Nature Astronomy, 2022; doi: 10.1038/s41550-022-01856-z)

Source: Durham University