Cosmological mystery of Milky Way satellite galaxies solved

Cosmological mystery of Milky Way satellite galaxies solved

One of the new high-resolution simulations of the dark matter enveloping the Milky Way and its neighboring galaxy Andromeda. The new study shows that previous failed attempts to find counterparts of the satellite plane surrounding the Milky Way in dark matter simulations were due to a lack of resolution. Photo credit: Till Sawala/Sibelius collaboration

Astronomers say they have solved a prominent problem that has challenged our understanding of how the Universe evolved – the spatial distribution of faint satellite galaxies orbiting the Milky Way.

These satellite galaxies have a bizarre orientation – they appear to lie on top of an enormously thin, rotating plane called the “satellite plane.”

This seemingly improbable arrangement has baffled astronomers for over 50 years, leading many to question the validity of the standard cosmological model that attempts to explain how the universe got into its present form.

Now, new research led jointly by the Universities of Durham (UK) and Helsinki (Finland) has found that the plane of the satellites is a cosmological quirk that will dissipate over time as stellar constellations change.

Her research removes the challenge that the satellite level poses to the standard model of cosmology.

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

The results are published in the journal natural astronomy.

The Milky Way’s satellites appear to be arranged in an incredibly thin plane that penetrates the galaxy, and oddly enough, they also orbit in a continuous and long-lived disk.

There is no known physical mechanism that would turn satellites into airplanes. Instead, it was thought that satellite galaxies should be arranged in a roughly circular configuration that traces dark matter.

Since the discovery of the satellite plane in the 1970s, astronomers have tried unsuccessfully to find similar structures in realistic supercomputer simulations that track the evolution of the Universe from the Big Bang to the present day.

The fact that the satellites’ arrangement could not be explained led researchers to believe that the cold dark matter theory of galaxy formation might be wrong.

In this latest research, however, astronomers used new data from the European Space Agency’s Gaia space observatory. Gaia is creating a six-dimensional map of the Milky Way, providing precise positions and motion measurements for about a billion stars in our galaxy (about 1% of the total) and their companion systems.

Cosmological mystery of Milky Way satellite galaxies solved

Positions and orbits of the Milky Way’s 11 classic satellite galaxies, projected face-on (top) and edge-on (bottom), integrated for 1 billion years past and future. The right panels are an enlargement of the left panels. The black dot marks the center of the Milky Way, arrows mark the observed positions and the flight directions of the satellites. While they currently line up in a plane (indicated by the gray horizontal line), that plane is rapidly dissolving as the satellites move along their orbits. Photo credit: Collaboration between Till Sawala and Sibelius

This data allowed scientists to project the orbits of the satellite galaxies into the past and future and see the plane forming and dissolving in a few hundred million years – a mere blink of an eye in cosmic time.

The researchers also looked for evidence of satellite planes in new, custom-made cosmological simulations.

They realized that previous studies based on simulations had been misled by not accounting for satellites’ distances from the center of the galaxy, making the virtual satellite system appear much rounder than the real one.

Taking this into account, they found several virtual Milky Ways that feature a plane of satellite galaxies very similar to that seen through telescopes.

The researchers say this removes one of the main objections to the validity of the Standard Model of cosmology and means the concept of dark matter remains the cornerstone of our understanding of the universe.

Study co-author Professor Carlos Frenk, Ogden Professor of Fundamental Physics at the Institute for Computational Cosmology, Durham University, UK, said: “The odd alignment of the Milky Way’s satellite galaxies in the sky has puzzled astronomers for decades so much that it is classified as a profound challenge to cosmological orthodoxy.

“But thanks to the amazing data from the Gaia satellite and the laws of physics, we now know that the plane is just a random orientation, a matter of being in the right place at the right time, just like the constellations of the stars in the sky.”

“Come back in a billion years and the plane will have dissipated, as will the constellations today.

“We have eliminated one of the greatest challenges to cold dark matter theory. It continues to provide a remarkably accurate description of the evolution of our Universe.”

The lead author of the study, Dr. Till Sawala from the University of Helsinki said: “The satellite plane was really amazing.

“Perhaps not surprisingly, a mystery that has persisted for almost fifty years required a combination of methods to solve it – and an international team to come together.”

More information:
Till Sawala, the satellite plane of the Milky Way coincides with ΛCDM, natural astronomy (2022). DOI: 10.1038/s41550-022-01856-z.

Provided by Durham University

Citation: Cosmological Mystery of the Milky Way’s Satellite Galaxies Solved (2022, December 19), retrieved December 20, 2022 from

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