Magnetic fields "central to creation of Milky Way"

Magnetic fields undoubtedly played a key role in the formation of the Universe, new research has revealed.

Scientists have tracked the growth of magnetic fields since the Big Bang and observed a strong correlation with the formation of planets and stars and other celestial features. The work, they say, confirms a more detailed ‘map’ of how light is affected by magnetic fields.

“This is the first time we have been able to reconcile theoretical models of galaxy formation with detailed structure of the Milky Way’s magnetic field as it is observed,” said Dr Robert Grand, Ernest Rutherford Fellow at the Astrophysics Research Institute at Liverpool John Moores University. 

“Our models contain a lot of physics covering a wide range of scales, including star formation, supernovae, and energy input from supermassive black holes.” 

The team found that magnetic fields that permeate the Milky Way are at least a million times stronger than they were just after the Big Bang. 

Magnetic fields surround magnetic materials and electric currents and exert forces on objects around them. In Space they shape how dust and other materials coagulate in planets, as the magnetic force is much stronger than gravity in proto-planetary discs.

Magnetism also funnels more gas into the galaxy providing more fuel for star formation. However, strong magnetic fields can conversely act against star formation by providing significant pressure opposite to gravity, which helps explain why stars form so inefficiently.

In a paper in Nature Astronomy, the team, which include the Max Planck Institute and Heidelberg University, show such fields grew exponentially in a short space of time in the early Universe as a product of the rapid accretion of cosmic gas in the nascent Milky Way.

“We know now that when many stars were formed in the early Universe, magnetic field lines became compressed in the centre of the Milky Way, and the more compressed they became the stronger the magnetic field and so on and so forth,” explained Stefan Reissl, of the University of Heidelberg. 

The paper includes a new detailed treatment for how starlight becomes polarised as it passes through different kinds of magnetised gas and dust (interstellar medium) strewn about the Galaxy on its way to the Earth. It confirms a map of the Faraday rotation measure which reveals a detailed structure on large and small scales. 

“This is new confirmation that the star formation and galaxy formation physics we simulate is comprehensive and accurate enough to be able to reproduce such a detailed map very well, which has never been done before,” added Dr Grand.  

“We also now have a firm theoretical understanding of the genesis of magnetic fields in our Universe across cosmic time and it is further confirmation that the standard model of the Universe (Lambda cold dark matter - LCDM) which requires the presence of dark matter and dark energy, is correct. 

“This also means that a full understanding of the Universe, including the nature of the mysterious and long sought after dark matter particle, needs to account for magnetism. 

“Only by understanding the role of magnetic fields can we comprehend high-energy astrophysics events such as supernovae and milli-second pulsars, which produce high energy particles like protons that interact with magnetic fields.”

-The study: 'A reproduction of the Milky Way’s Faraday rotation measure map in galaxy simulations from global to local scales' is published in Nature Astronomy on 21 August 2023.