How The Universe Acquired Its Magnetic Fields
When we look into space, all of the astrophysical objects seen are enclosed in magnetic fields. This holds not only in the neighborhood of stars and planets but likewise in the deep space between galaxies and galactic clusters.
These fields are weak– generally much weaker than those of a refrigerator magnet– yet they are dynamically substantial because they have extensive effects on the dynamics of the universe. Regardless of decades of extreme interest and research, the origin of these cosmic magnetic fields is one of the most profound mysteries in cosmology.
Previous studies have provided insight into how turbulence, the swirling motion common to all types of fluids, could intensify pre-existing magnetic fields via the so-called dynamo process. However, this remarkable revelation has presented a new mystery: if a turbulent dynamo can only amplify an existing field, where does the initial “seed” magnetic field originate?
A complete and internally consistent solution to the origin of astrophysical magnetic fields hinges on our understanding of how the seed fields emerge. A recent study by MIT graduate student Muni Zhou, her supervisor Nuno Loureiro, a professor of nuclear science and engineering at MIT, and collaborators from Princeton University and the University of Colorado at Boulder has provided an answer that reveals the underlying mechanisms that generate a field from a completely non-magnetic state until it is strong enough for the dynamo process to take hold and amplify the field to the magnitudes observed.
Magnetic fields are everywhere
Magnetic fields occur naturally throughout the universe and were first observed on Earth thousands of years ago when they interacted with magnetized minerals like lodestone.
Despite their use in navigation, the origin and nature of these fields remained a mystery for a long time. It wasn’t until the early 20th century that scientists discovered magnetism on the sun through its impact on the sun’s light spectrum. With the aid of more powerful telescopes, researchers have since discovered that magnetic fields are widespread throughout the universe.
Despite decades of research, the origins of magnetic fields in the universe remain shrouded in mystery. While recent advancements have brought us closer to understanding some aspects of this question, many fundamental questions about the natural origins of magnetic fields in the universe are yet to be answered. Despite the practical applications of electromagnets and permanent magnets, the origins of the magnetic fields that we encounter in the universe remain one of the most intriguing and elusive mysteries of modern astrophysics.
Amplifying magnetic fields– the dynamo effect
The origin of magnetic fields in the universe has long been a puzzling mystery for scientists, who initially approached the problem by studying how electric and magnetic fields are generated in the laboratory. While electric fields are created by the movement of conductors, like copper wire, in magnetic fields, this induction process is not applicable to the vast expanse of space where there are no apparent wires or large steel structures.
Research into the Earth’s magnetic field source approximately a century ago revealed that the Earth’s core is made up of liquified nickel and iron, which led scientists to theorize that the convective motion of this hot, electrically conductive liquid and the rotation of the Earth combine to produce the Earth’s magnetic field.
Scientists have since developed models that demonstrate how convective motion can intensify an existing field through self-organization, a feature often observed in complex dynamical systems. This process, similar to that seen in a power station, requires a magnetic field to make a magnetic field.
Similarly, in stars and galaxies, the electrically conducting fluid is plasma, a state of matter that exists at incredibly high temperatures where electrons are torn away from their atoms. The dynamo effect can magnify an existing magnetic field in such a medium, provided it begins at some marginal level. While recent progress has been made in understanding the natural origins of magnetic fields in the universe, several aspects of this question remain unresolved.
Making the first magnetic fields
The puzzle of how magnetic fields are generated in the universe has been a long-standing mystery, but recent research has shed new light on this complex issue. In a groundbreaking study published in PNAS on May 5, Zhou and her team explored the underlying theory and conducted numerical simulations to demonstrate how a seed field can be created and what fundamental processes are at work.
What makes this research unique is the focus on the extremely low particle density in the plasma between stars and galaxies. The team’s calculations took into account the dynamics of this unique plasma and demonstrated that the first magnetic fields could be spontaneously generated through large-scale motions, similar to the mechanisms observed in terrestrial examples.
The researchers were able to determine the amplitude of the expected spontaneously produced magnetic field, which can rise from zero to a level where the plasma is “magnetized”. This allows the traditional dynamo mechanism to take control and raise the fields to the levels observed in the universe.
Presentation of the magnetic field generation model
The team’s work represents a self-consistent model for the generation of magnetic fields at a cosmological scale, providing a significant breakthrough in understanding magnetogenesis in the universe. Further refinements of the model and examinations of the handoff from the seed field generation to the amplification stage of the dynamo will be the focus of the team’s future studies.
The study’s groundbreaking approach to the fundamental challenge of understanding the origins of magnetic fields in the universe has garnered high praise from experts in the field. Professor Ellen Zweibel of the University of Wisconsin at Madison hailed the research as a remarkable achievement, commending the team’s innovative use of state-of-the-art plasma physics theory and numerical simulations to shed light on this long-standing mystery.
The research was supported by prestigious grants from the National Science Foundation CAREER Award and the Future Investigators of NASA Earth and Space Science Technology (FINESST) program, reflecting the significance and potential impact of the team’s findings.
Read the original article on MIT News.
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