Scientists use synchrotron intensity gradients to map maximum magnetic fields within galaxy clusters

In a new study, scientists map magnetic fields within galaxy clusters, reveal the effects of galaxy mergers on magnetic field structure, and question previous assumptions about the efficiency of turbulent dynamo processes in amplifying these fields. I threw it.

A galaxy cluster is a large, gravitationally bound system containing many galaxies, hot gas, and dark matter. They represent some of the most massive structures in the universe. These clusters are made up of hundreds to thousands of galaxies held together by gravity and embedded in vast halos of hot gas called the intracluster medium (ICM).

The ICM is primarily composed of ionized hydrogen and helium, held together by the gravity of the cluster itself. Magnetic fields within large-scale structures like galaxy clusters play a crucial role in shaping astrophysical processes. They influence the ICM, influence the formation and evolution of galaxies, contribute to the transport of cosmic rays, participate in the magnetization of the Universe, and act as tracers of large-scale structural evolution.

Previous studies and simulations suggest that the magnetic field within the cluster evolves and is sensitive to cluster dynamics, indicating that amplification occurs during coalescence events.

This research nature communicationsuses a method called synchrotron intensity gradients (SIGs) to map magnetic fields within clusters, especially during galaxy mergers. This method provides a unique perspective on the structure of the magnetic field and provides a tool to compare numerical predictions from simulations with observed data.

The study’s lead author, Professor Alex Lasallian of the University of Wisconsin-Madison, told Phys.org about his motivation for studying magnetic fields in galaxy clusters, saying, “The focus of my research is to understand the role of magnetic fields in astrophysical environments. “It’s about doing it,” he said. Especially in magnetized turbulent media. ”

“Over the past 20 years, I have worked extensively with my students to study magnetic turbulence and reconnection processes. The techniques used to map magnetic fields within galaxy clusters are derived from years of research. It is based on theoretical and numerical insights.”

synchrotron radiation intensity gradient

Synchrotron intensity refers to the radiation emitted when charged particles (usually electrons) spiral along magnetic field lines at relativistic speeds. This phenomenon is known as synchrotron radiation.

The SIG method introduces a unique perspective by mapping magnetic fields through processes rooted in synchrotron intensity gradients. The basic principle behind the applied technology involves exploiting the interaction between a magnetic field and a conductive fluid, especially an ionized gas or plasma.

The key idea is that the magnetic field affects the movement of these fluids, and the fluid’s resistance to bending helps discern its direction. Professor Lasallian explained: “These movements create velocity gradients, and the fluctuations in the magnetic field are perpendicular to the magnetic field. By measuring these gradients, we can determine the direction of the magnetic field.”

This approach represents a new method of measuring magnetic fields, developed by Professor Lasallian’s group based on basic research in magnetohydrodynamics.

“We are leveraging data that was initially thought to be irrelevant to magnetic field research, and are able to derive important results from diverse archival datasets collected for purposes unrelated to magnetic field research,” Lasallian said. said.

Mapping the magnetic field

The researchers obtained the largest scale map of magnetic fields ever studied, particularly in the halos of galaxies within galaxy clusters.

“We confirmed the accuracy of our technique by comparing the direction of the magnetic field obtained with our technique with the direction of a conventional magnetic field based on polarization measurements. We also measured the accuracy of SIG in numerical simulations. “We did,” Professor Lasallian said.

This study demonstrated that SIG opens new avenues for mapping unprecedented large-scale magnetic fields. The complexity of plasma motion within merging galaxy clusters is revealed through the structure of the magnetic fields.

This discovery has implications for our understanding of galaxy cluster dynamics and evolution and provides unique insight into the role of magnetic fields in key processes within galaxy clusters.

Overcoming depolarization

In traditional synchrotron polarization measurements, depolarization is a challenge when mapping the magnetic field in the galaxy cluster region, excluding debris. Unlike other methods, SIG is not affected by depolarization. This study aimed to verify whether SIG and polarization exhibit the same magnetic field direction in which polarization resides.

Lead author Ph.D. student Yue Hu, together with Italian scientists Dr. Annalisa Bonafede and Dr. Chiara Stuardi, successfully tested magnetic field measurements inside the artifact, confirming the reliability of the SIG magnetic field map. Hydrodynamic simulations by Professor Lasallian’s PhD student Ka Wai Ho further confirmed the accuracy of the map.

SIG provides a unique way to address long-standing questions about the origin, evolution, and influence of magnetic fields within galaxy clusters without facing the challenges that traditional measurements pose.

ICM heat conduction

SIG also allows researchers to test and validate existing theories about heat transfer within ICMs and the generation of cooling flow, a poorly understood process.

“The heat transfer of the intracluster plasma (fully ionized gas) in the ICM is significantly reduced in the direction perpendicular to the magnetic field. Therefore, the ability of heat to be transported in different directions depends on the structure of the magnetic field. “The thermal conductivity changes control the formation of a cold gas flow surrounded by hot gas, the so-called cooling flow,” Professor Lasallian explained.

cosmic ray acceleration

Cosmic rays are high-energy charged particles that interact strongly with the magnetic fields within the halo of a galaxy cluster. Dr. Gianfranco Brunetti, a co-author of this paper, is a leading expert on the acceleration process of cosmic rays in galaxy clusters. He is excited to unravel the previously mysterious structure of the magnetic field.

“Galaxy clusters are known to accelerate cosmic rays through the interaction of moving magnetic fields and cosmic rays. The full extent of this acceleration is still unknown and depends on the dynamics of the magnetic field,” Professor Lasallian said. Stated.

Furthermore, cosmic rays follow the path of magnetic field lines. This means that the escape of cosmic rays from the cluster is influenced by the specific structure of these magnetic fields.

The dynamics of magnetic fields within clusters can now be mapped using SIG technology, helping to understand the operation of the largest particle accelerators in the universe.

summary

SIG has the ability to map magnetic fields in regions where polarization information is lost, providing valuable insight into galaxy cluster halos and even larger recently discovered synchrotron structures, megahalos.

The future of magnetic field mapping in galaxy clusters looks promising as the astrophysics community looks forward to commissioning the Square Kilometer Array (SKA) telescope in 2027. SKA provides the synchrotron intensity of the SIG technique as well as polarization that can be used with other techniques developed by Prof. Lasallian’s group to study the detailed 3D structure of astrophysical magnetic fields.

Professor Lasallian said: “Gradient techniques are a practical result of our improved understanding of fundamental magnetohydrodynamic processes and encourage us to dig deeper into these important processes. The benefits of basic research are not always immediately obvious. “Although it’s not going to happen, we’re making progress in our understanding of important physical processes.” The process causes tectonic movements and affects many aspects of science and engineering. ”