Scientists at Durham University have just solved a huge cosmological enigma about the Milky Way

The research places Durham firmly at the centre of fundamental physics

In huge news for the world of fundamental physics, scientists at Durham University have just announced they have solved an enigma about the Milky Way and how the Universe was formed.

The collaboration between Durham University and Helsinki University in Finland researched the spatial distribution of faint satellite galaxies orbiting the Milky Way. The researchers say the satellite galaxies appear in “a bizarre alignment” and seem to lie on “an enormous thin rotating plane”, which is called the “plane of satellites”.

Since its discovery in the 1970s, this “unlikely” configuration has perplexed astronomers for over 50 years and led many to challenge the standard cosmological model of how the Universe was formed, as no other planes of satellites could be found. Scientists also questioned the role of dark matter in the creation of the Universe because of this.

One of the new high-resolution simulations of the dark matter enveloping the Milky Way and its neighbour, the Andromeda galaxy. The new study shows that earlier, failed attempts to find counterparts of the plane of satellites which surrounds the Milky Way in dark matter simulations was due to a lack of resolution. Credit: Till Sawala / Sibelius collaboration. Free to use and distribute with attribution (CC-BY).

The scientists involved in the research explain the enigma of the Milky Way satellite planes as being appearing arranged in: “an implausibly thin plane piercing through the galaxy and, oddly, they are also circling in a coherent and long-lived disk.

“There is no known physical mechanism that would make satellites planes. Instead, it was thought that satellite galaxies should be arranged in a roughly round configuration tracing the dark matter”.

However, the joint research by the Universities of Durham and Helsinki has found that the plane of satellites is simply a “cosmological quirk”, and just as star constellations change over time, the plane of satellites will dissolve too.

The scientists used new data from the European Space Agency’s GAIA space observatory, which is currently creating a six-dimensional map of the Milky Way. The data meant scientists could project the orbits of the satellite galaxies into the past and future, and saw the how the plane formed and how it will dissolve, all in the space of a few hundred million years – “a mere blink in cosmic time”.

Therefore, the research has removed the challenge posed by the plane of satellites to the standard model of cosmology, and the findings are published in the journal Nature Astronomy. They say that the concept of dark matter “remains at the cornerstone of our understanding of the Universe”.

Caption: 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 centre 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 grey horizontal line), that plane quickly dissolves as the satellites move along their orbits. Credit: Till Sawala / Sibelius collaboration. Free to use and distribute with attribution (CC-BY).

Study co-author Professor Carlos Frenk, Ogden Professor of Fundamental Physics in the Institute for Computational Cosmology, at Durham University, UK, said: “The strange alignment of the Milky Way’s satellite galaxies in the sky had perplexed astronomers for decades, so much so that it was deemed to pose 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 chance alignment, a matter of being in the right place at the right time, just as the constellations of stars in the sky.

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

“We have been able to remove one of the main outstanding challenges to the cold dark matter theory. It continues to provide a remarkably faithful description of the evolution of our Universe.”

Study lead author Dr Till Sawala, of the University of Helsinki, said: “The plane of satellites was truly mind boggling.

“It is perhaps unsurprising that a puzzle which has endured for almost 50 years required a combination of methods to solve it – and an international team to come together.”

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

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