Unravelling the mystery of the Milky Way’s satellite galaxies

Our Milky way is orbited by a number of satellite galaxies that exhibit a bizarre alignment – they seem to lie on an enormous thin rotating plane – called the “plane of satellites”  

Standard cosmological model 

This seemingly unlikely arrangement had puzzled astronomers for over 50 years, leading many to question the standard cosmological model. 

This model seeks to explain the formation of the Universe and how the galaxies we see now formed gradually within clumps of cold dark matter – a mysterious substance that makes up about 27 per cent of the Universe.  

As there is no known physical mechanism that would make long-lived satellite planes, astronomers thought the cold dark matter theory of galaxy formation might be wrong. 

Cosmological quirk 

Our new research, carried out along with an international team of scientists, has now found that the plane of satellites in the Milky Way is a cosmological quirk. 

Using data from the European Space Agency’s GAIA space observatory the researchers used supercomputer technology to project the orbits of the satellite galaxies into the past and future. 

They saw the plane of galaxies form and dissolve in a few hundred million years – a mere blink of an eye in cosmic time.  

Virtual satellite systems 

They also realised that previous studies based on computer simulations had failed to consider the distances of satellites from the centre of the Milky Way, which made the virtual satellite systems appear much rounder than the real one.   

Taking this into account, they found several virtual Milky Ways which boast a plane of satellite galaxies very similar to the one seen through telescopes.  

They say this removes one of the main objections to the standard model of cosmology and means that the concept of cold dark matter remains the cornerstone of our understanding of the Universe.  

Find out more 

• The research was jointly led by Durham University’s Institute for Computational Cosmology, in our Department of Physics, and the Department of Physics at the University of Helsinki. 

• Read the full paper in the journal Nature Astronomy. 

• Discover more about the European Space Agency’s GAIA space observatory. 

• Our Department of Physics is a thriving centre for research and education. We are proud to deliver a teaching and learning experience for students which closely aligns with the research-intensive values and practices of the University. Feeling inspired? Visit our Physics webpages to learn more about our postgraduate and undergraduate programmes.  

• The research was funded by the European Research Council, the UK's 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.  

Main picture credit: Till Sawala / Sibelius collaboration (CC-BY).