Are galaxies born magnetised? Astrophysicist, Professor Kandaswamy Subramanian talks about his recently published research paper

In this article, Professor Kandaswamy Subramanian, Visiting Professor of Astrophysics at Ashoka University, speaks about his work with a team of researchers from the International Centre for Theoretical Sciences, Tata Institute of Fundamental Research and Newcastle University titled “Turbulent Dynamos in a Collapsing Cloud.” The study explains the early development of coherent magnetic fields in galaxies in genesis, using dynamo theory adapted to gravitational collapse.

What is the dynamo process? 

Magnetic fields are found everywhere in the universe, from planets and stars to galaxies and galaxy clusters. The magnetisation of cosmic systems is often explained by a process called a dynamo, where turbulent motion in hot, ionised conducting fluids (plasma) converts kinetic energy into magnetic energy. In this picture, weak magnetic fields grow exponentially until they become strong enough to back-react on the flow itself, at which point the growth slows and eventually saturates. 

However, the standard dynamo models usually assume a stationary environment, one where stars or galaxies have already formed. Galaxies require 5 – 10 billion years, a significant fraction of the age of the universe, to generate strong, coherent fields. But this fails to explain the similar magnetisation found in galaxies that existed when the universe was ten times younger. To alleviate this, Prof. Subramanian and his co-researchers ask a key question: how do dynamos operate while these objects are still forming?

Finding the Answers

To answer this question, the team of researchers comprising Muhammed Irshad P, Pallavi Bhat, Kandaswamy Subramanian, and Anvar Shukurov, therefore, focused their work on magnetic field amplification during gravitational collapse, when gas clouds contract due to gravity, to form stars and galaxies. To study dynamos in this evolving environment, the team adopted a framework that followed the collapse itself, using a coordinate system called `supercomoving coordinates’ developed in cosmology that simplifies the equations by factoring out the overall contraction. This allowed the team to apply well-understood dynamo theory, originally developed for stationary systems, to a dynamically evolving setting.

The study revealed that collapse dramatically accelerates the dynamo process. Instead of growing at a steady exponential rate, the fields grow even faster—what the researchers call super-exponential growth. As the gas collapses, turbulent motions become more intense and operate on smaller scales, boosting the efficiency of the dynamo. As a result, strong magnetic fields can form well within a galactic free-fall time of about a hundred million years. The team also found that the final field strength increases more steeply with density than that predicted from simple compression alone. These features help to explain observations of strong magnetic fields even in young galaxies.

Implications and Significance:

In summary, the results suggest that stars and galaxies may be born already magnetised, rather than acquiring their fields over billions of years. This magnetic field can later be maintained by random motions, via the standard dynamo, in protostellar or protogalactic discs. Such early magnetic fields could influence how gas collapses, shaping the masses of forming stars and the evolution of galaxies. The team’s proposed model also offers a path forward to correctly model magnetic field evolution in large-scale computer simulations of cosmic structure formation. 

The work has been published in Physical Review Letters and was also featured in American Physical Society Physics news (https://physics.aps.org/articles/v19/s26).

Edited by Ramyani Kundu and Priyanka (Research and Development Office)

This blog has been adapted from the original research article,

M. Irshad P. et al., Phys. Rev. Lett. 136, 091201 (2026), available here: https://doi.org/10.1103/fp1v-xrr5