New observations and simulations show that high-energy particle jets emitted by the massive central black hole of the brightest galaxy cluster of galaxies can be used to map the structure of invisible inter-cluster magnetic fields. These discoveries provide astronomers with a new tool to study previously unexplored aspects of galaxy clusters.
As galaxy clusters grow in collisions with surrounding matter, they create arc shocks and awakenings in their diluted plasma. The movement of plasma induced by these activities can drape intra-cluster magnetic layers, forming virtual walls of magnetic force. These magnetic layers, however, can only be observed indirectly when something interacts with them. Because it is simply difficult to identify such interactions, the nature of intra-cluster magnetic fields remains poorly understood. A new approach to map / characterize magnetic layers is strongly desired.
An international team of astronomers, including Kyushu University graduate student Haruka Sakemi (now a researcher at the National Astronomical Observatory of Japan – NAOJ), used the MeerKAT radio telescope located in the North Karoo Desert in South Africa to observe a galaxy in the Abell 3376 merging galaxy cluster known as MRC 0600-399. Located over 600 million light-years away from the constellation Columba, MRC 0600-399 is known to have unusual jet structures bent at 90-degree angles. Previous x-ray observations have revealed that MRC 0600-399 is the nucleus of a sub-cluster penetrating the main cluster of galaxies, indicating the presence of strong magnetic layers at the boundary between the main and sub-clusters. These characteristics make the MRC 0600-399 an ideal laboratory for studying the interactions between jets and strong magnetic layers.
MeerKAT’s observations revealed unprecedented detail of the jets, most strikingly, a weak “double false” structure extending in the opposite direction of the bend points and creating a “T” shape. These new details show that, like a jet of water hitting a window, this is a very chaotic collision. Dedicated computer simulations are needed to explain the morphology of the observed jet and the possible configurations of the magnetic field.
Takumi Ohmura, a graduate student from Kyushu University (now a researcher at the University of Tokyo Cosmic Ray Research Institute – ICRR), of the team performed simulations on NAOJ’s ATERUI II supercomputer, the most powerful computer in the world dedicated to astronomical calculations. The simulations assumed a strong magnetic field in the form of an arc, neglecting messy details like turbulence and the movement of the galaxy. This simple model provides a good match with the observations, indicating that the magnetic pattern used in the simulation reflects the actual magnetic field strength and structure around MRC 0600-399. More importantly, it demonstrates that simulations can successfully represent the underlying physics so that they can be used on other objects to characterize more complex magnetic field structures in galaxy clusters. This offers astronomers a new way of understanding the magnetized Universe and a tool to analyze better quality data from future radio observatories like the SKA (the Square Kilometer Array).
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