Solving the longstanding mystery of the evolution of the universe

Astronomers claim to have solved a longstanding mystery about how the Universe evolved: the spatial distribution of faint satellite galaxies around the Milky Way.

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

These satellite galaxies have an unusual alignment in that they appear to reside on a huge, thin rotating plane known as the “satellite plane.”

For more than 50 years, astronomers have been stumped by this seemingly unlikely arrangement, causing many to question the validity of the conventional cosmological model, which aims to reveal how the Universe came to look as it does today.

Now, a new study led collaboratively by the Universities of DurhamThe United Kingdom, and Helsinki, Finland, has discovered that the plane of the satellites is a cosmological peculiarity that will disappear over time in the same way that constellations of stars gradually alter.

Their findings remove the threat that the plane of the satellites poses to the dominant model of cosmology.

This concept describes how the Universe began and how the galaxies we witness today gradually grew among clumps of cold dark matter, 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 clustered in an incredibly thin plane that runs through the galaxy, as well as circling in a long-lived, coherent disk.

There is no known physical mechanism capable of transforming satellite planes. Instead, the satellite galaxies were expected to clump together in a nearly circular configuration, tracking dark matter.

Since the discovery of satellite blueprints in the 1970s, astronomers have searched and failed to locate similar structures in realistic supercomputer simulations of the evolution of the Universe from the Big Bang to the present day.

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

However, the astronomers used new data from the European Space Agency’s GAIA space observatory in this current study. GAIA is creating a six-dimensional map of the galaxy, including the exact locations and velocity measurements of about a billion stars (about 1% of the total) and their companion systems.

Scientists were able to project the orbits of satellite galaxies into the past and future and witness the shape and dissipation of the plane in a few hundred million years, a mere blink of an eye in cosmic time.

The researchers also looked for indications of satellite planes in new custom cosmological models.

They understood that previous simulation-based analyzes had been misled by not taking into account the satellites’ distances from the center of the galaxy, which had caused virtual satellite systems to appear considerably rounder than real ones.

Taking this into consideration, the scientists discovered numerous virtual Milky Ways, each with a plane of satellite galaxies similar to that visible through telescopes.

This, according to the researchers, removes one of the main challenges to the validity of the standard model of cosmology and confirms that the idea of ​​dark matter remains fundamental to understanding the Universe.

The strange alignment of the Milky Way’s satellite galaxies in the sky has perplexed astronomers for decades, so much so that it was seen as posing 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 alignment, a matter of being in the right place at the right time, just like the constellations of stars in the sky..

Carlos Frenk, study co-author and Ogden Professor, Fundamental Physics, Institute for Computational Cosmology, Durham University

Carlos Frenk adds, “Come back a billion years from now and the plane will have disintegrated, just like the constellations today. We have been able to eliminate one of the main remaining challenges of the cold dark matter theory. It goes on to provide a remarkably accurate description of the evolution of our Universe..”

The plane of the satellites was really amazing. Perhaps not surprisingly, a puzzle that has endured for nearly fifty years required a combination of methods to solve, and an international team to come together..

Dr. Till Sawala, lead study author, University of Helsinki

The study was financially supported by the European Research Council and the UK Science and Technology Facilities Council and made extensive use of the Cosmology Machine (COSMA) supercomputer at Durham University. COSMA is hosted in Durham as part of the DiRAC High Performance Computing Facility funded by the Science and Technology Facilities Council to support researchers across the UK.

journal reference

Sawala, T. et al. (2022) The satellite plane of the Milky Way is consistent with ΛCDM. nature astronomy.


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