The universe without wires: scientists have revealed how the magnetic field could appear “out of nothing”

All astrophysical objects that humans observe are surrounded by magnetic fields. And not just in the vicinity

stars and planets, but also in deep space between galaxies and clusters. Yes, these fields are very faint – usually much weaker than those of a refrigerator magnet. However, their dynamic significance has a profound impact on the life of the universe. Despite decades of research, the origin of these cosmic magnetic fields remains one of the deepest mysteries in cosmology. 

Magnetic fields everywhere

Natural magnetic fields are observed everywhere in the universe, having been first detected on Earth thousands of years ago  They were used for navigation long before humans understood their nature or origin.Magnetism on the Sun was discovered in the early 20th century due to its effect on the   spectrum Since then, using more powerful deep-space telescopes, scientists have found that these fields are everywhere.

And, although scientists have long since learned how to make and use permanent magnets and  electromagnets, the natural origin of these fields in the universe has remained a mystery.A recent study has unraveled some of this puzzle, but many aspects of the puzzle are still debated.

In previous studies, scientists have understood how turbulence can amplify pre-existing magnetic fields through a so-called dynamo process. But this discovery only raised more questions.  If a turbulent dynamo could only amplify an existing one, then where did the primordial, "germ" magnetic field come from?

As part of the new work, scientists have shown the mainprocesses that generate a field from a completely unmagnetized state to a point where it is strong enough for the dynamo mechanism to amplify it to observable magnitudes.

Dynamo effect and the universe without wires

Scientists have been looking at a way to create electric and magnetic fields in the lab.When conductors, such as copper wire, move through them, electric fields appear.They can then manipulate electrical currents, which is how electricity is generated that people useThrough this induction process, large generators or dynamos convertA  key feature of dynamos is that they require magnetic fields to work.

But there are no wires or big steel structures in the universe, so how do they come into being?Progress in solving this problem began about a century ago, when scientists began to think about the source of the Earth's magnetic field.By that time, studies of the propagation of seismic waves had shown that most of the planetsScientists also realized that there was a core on Earth made up of molten nickel and iron.The researchers hypothesized that the convective motion of this hot, electrically conductive fluid and the planet's rotation somehow combine to create the Earth's field.

Eventually , models emerged that showed how convective motion couldThis is an example of self-organization —a property often observed in complex dynamical systems— where large-scale structures spontaneously growBut just like in a power plant, you need a magnetic field to create a magnetic field.

However , in stars and galaxies, as well as in the space between them, the electrically conductive fluid is not molten metal, but plasma.This state of matter occurs when electrons break away from their atoms.On Earth, plasma can be seen in the form of lightning.In such an environment, the dynamo effect can amplify the existing magnetic field if it starts at some minimal level.

Simulation of Primary Magnetic Fields

Where did this primary or minimal come from?a magnetic field? To find out, scientists conducted a study, the results of which are published by PNAS. Study author and MIT graduate student Moonee Zhou developed the basic theory and conducted numerical simulations on powerful supercomputers to understand what fundamental processes are responsible for the appearance of the minimum field.

Visualization of filamentary primary magnetic fields resulting from large-scale movements of unmagnetized plasma. 
Credit: Muni Zhou et al.

One of the important properties of plasma that existsbetween stars and galaxies - it is highly scattered, about one particle per cubic meter. Moreover, inside stars the density of particles is approximately 30 orders of magnitude higher. The low density indicates that particles in cosmological plasmas never collide, which has an important effect on their behavior.

Scientists tracked the dynamics in plasma, whichdeveloped from well-ordered waves, but became turbulent as the amplitude increased, and the interactions became highly nonlinear. By incorporating the detailed influence of small-scale plasma dynamics on macroscopic astrophysical processes, they demonstrated that primordial magnetic fields can be spontaneously generated due to general large-scale movements as simple as shear flows. As on Earth, mechanical energy was converted into magnetic energy.

An important result of their calculations wasamplitude of the expected spontaneously generated magnetic field. It turned out that it can grow from zero to the level at which the plasma becomes “magnetized,” that is, when the presence of the field strongly affects its dynamics. At this point, a traditional dynamo mechanism can raise the fields to observable levels. Thus, the new work presents a self-consistent model for the generation of magnetic fields on a cosmological scale and explains how they could appear “out of nothing.”

What's the bottom line?

Professor Ellen Zweibel of WisconsinUniversity of Madison, co-author of the study, notes: “Despite decades of progress in cosmology, the origin of magnetic fields in the universe remains unknown. It's nice to see modern plasma physics theory and numerical simulations that aim to solve this fundamental problem."

Zhou and her colleagues will continue to improvemodel and study the transition from the initial field generation to the dynamo amplification phase. The scientists also want to find out whether this process can operate on a time scale consistent with astronomical observations. To quote the researchers, “This work represents the first step in building a new paradigm for understanding magnetogenesis in the Universe."

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