HomeAstronomy & SpaceAstronomyCosmological enigma of Milky Way's satellite galaxies solved

Cosmological enigma of Milky Way’s satellite galaxies solved

Astronomers say they have solved an outstanding problem that challenged our understanding of how the universe evolved. They have observed the spatial distribution of faint satellite galaxies orbiting the Milky Way.

These satellite galaxies exhibit a bizarre alignment. They also seem to lie on an enormous thin rotating plane called the “plane of satellites.”

Astronomers have been perplexed themselves by this seemingly unlikely arrangement. This has led them to question the validity of the standard cosmological model. They seek to explain how the universe came to look the way it does today.

New research led by the Universities of Durham in the United Kingdom and Helsinki in Finland has discovered that the plane of satellites is a cosmological quirk. It will dissolve over time in the same way that star constellations do.

These findings eliminate the threat posed by the plane of satellites to the standard model of cosmology.

This model explains the formation of the universe and how the galaxies we see now formed gradually within clumps of cold dark matter. The cold dark matter is a mysterious substance that makes up about 27% of the universe.

The findings were published in Nature Astronomy.

The satellites of the Milky Way appear to be arranged in an implausibly thin plane piercing through the galaxy. It is circling in a coherent and long-lived disc.

There is no known physical mechanism capable of transforming satellites into planes. It was thought that satellite galaxies should be arranged in a roughly round configuration tracing the dark matter.

The satellite plane was discovered in the 1970s. Astronomers have tried and failed to find similar structures in realistic supercomputer simulations of the universe’s evolution from the Big Bang to the present day.

The inability to explain the satellite arrangement led researchers to believe that the cold dark matter theory of galaxy formation was incorrect.

Astronomers used new data from the European Space Agency’s Gaia space observatory in the new research. Gaia is creating a six-dimensional map of our galaxy. The map is providing precise positions and motion measurements for approximately one billion stars and their companion systems.

Positions and orbits of the 11 classical satellite galaxies of the Milky Way, projected “face-on” (top) and “edge-on” (bottom), integrated for 1 billion years into the past and future. The right panels are a zoom-in of the left panels. The black dot marks the center of the Milky Way, arrows mark the observed positions and the directions of travel of the satellites. While they currently line up in a plane (indicated by the gray horizontal line), that plane quickly dissolves as the satellites move along their orbits. Credit: Till Sawala / Sibelius collaboration

Scientists were able to project the satellite galaxies’ orbits into the past and future and see the plane form and dissolve in a few hundred million years in a mere blink of an eye in cosmic time.

The researchers also searched new and tailor-made cosmological simulations for evidence of planes of satellites.

They realised that previous simulation-based studies had been misled by failing to account for satellite distances from the centre of the Galaxy. It caused the virtual satellite systems to appear much rounder than the real one.

Scientists discovered several virtual Milky Ways. Each of them had a plane of satellite galaxies similar to the one seen through telescopes.

According to the researchers, this eliminates one of the main challenges to the validity of the standard model of cosmology. It ensures that the concept of dark matter remains the foundation of our understanding of the universe.

More information: Till Sawala, The Milky Way’s plane of satellites is consistent with ΛCDM, Nature Astronomy (2022). DOI: 10.1038/s41550-022-01856-zwww.nature.com/articles/s41550-022-01856-z


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