The Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia's national science agency, and the Square Kilometer Array International Observatory (SKAO) jointly released the most detailed and largest map of the cosmic magnetic field to date, presenting the originally "invisible" cosmic magnetic field structure in unprecedented detail. The new map, called SPICE-RACS, covers five times more area than all previous studies of its kind combined and is considered an important milestone in understanding how energy is distributed and transported in the universe.
The new results rely on the ASKAP radio telescope at Inyarrimanha Ilgari Bundara (ASKAP operating base) in Western Australia. This facility is part of CSIRO and is responsible for scanning large areas of the sky for radio signals in the ASKAP Rapid Continuous Survey (RACS). As early as 2020, ASKAP completed the largest and fastest radio survey at the time, laying the foundation for this magnetic field mapping.
According to the research team, the SPICE-RACS map is based on a physical principle: when light passes through a magnetic field, its polarization is reversed. By measuring the degree of rotation of radio signals from all directions in the universe during their propagation, and combining it with data recorded by ASKAP, scientists can infer the location and strength of these magnetic fields. Dr. Alec Thomson, one of the project leaders and currently a commissioning scientist at SKAO, said that this is the first time that researchers have been able to analyze the structure of the nearby interstellar medium in detail on such a large scale, while systematically studying a huge number of distant galaxies.
To construct the map, the team reprocessed data from nearly all galaxies detected in the RACS survey. "We extracted rotation measurements from every galaxy detected by RACS, which totals nearly four million objects, and reprocessed the raw data from ASKAP to obtain a more complete picture of the cosmic magnetic field," Thomson said. In his view, this provides an unprecedented sample size for exploring magnetic structures from the local environment of the Milky Way to the distant universe.
The scientific community has long recognized that magnetic fields play a key role in shaping the environment on Earth and in space, but it has been difficult to observe directly. For example, without the protection of the earth's outer geomagnetic field, the flow of high-energy particles from the sun (solar wind) would greatly reduce the habitability of the earth. However, compared to gravity or electromagnetic radiation, humans still know very little about the origin and evolution of cosmic-scale magnetic fields, which is mainly limited by observational methods.
Professor Naomi McClure-Griffiths, SKAO's chief scientist, pointed out that for the past two decades, the astronomical community has basically relied on the same limited data set to study the cosmic magnetic field, and these data do not even cover the entire southern sky. "Now, we can finally answer some of the 'big questions' about the magnetic structure of the universe with a more complete view of the sky," she said. SPICE-RACS allows scientists to study the interactions of the Milky Way with neighboring galaxies such as the Magellanic Clouds on a galactic scale and analyze the role that magnetic fields play.
More importantly, the new map is expected to help answer the fundamental question of "when did the cosmic magnetic field appear?" McClure-Griffiths said that in the past, researchers once believed that such problems were almost impossible to solve through observational methods, but now with the emergence of high-sensitivity large-scale polarization surveys, "this view is no longer true." By counting the magnetic field characteristics of galaxies at different times and at different distances, researchers have the opportunity to reconstruct the generation and evolution trajectory of the magnetic field in the history of the universe.
Along with the data release, CSIRO will also make relevant data sets available to scientific researchers around the world in an open format. Tim Galvin, a CSIRO astronomer involved in the project, said that these resources will be freely accessible to any team, whether for independent research or to replicate existing results. He emphasized that open data not only facilitates more research teams to explore new scientific problems, but also helps strengthen the core principle of "reproducibility" in scientific research.
CSIRO's data portal platform is therefore regarded as an important scientific research infrastructure, not only for professional researchers, but also welcomes in-depth exploration by the public who are curious about astronomical and scientific data. Galvin pointed out that multiple research teams are currently working on the data of this project and continue to produce new results, which further proves the scientific value of this resource library.
The international cooperation team participating in this work is called the "Cosmic Magnetic Polarization Survey (POSSUM)" cooperation group, which is composed of multinational research institutions. Although SPICE-RACS is considered one of the most comprehensive maps of the cosmic magnetic field currently available, the team emphasizes that this is only the starting point for future plans for larger-scale, higher-precision observations. With the new generation of radio facilities such as the Square Kilometer Array telescope fully put into operation, mankind's "map" of the hidden magnetic structure of the universe is expected to continue to expand and update.
According to reports, the results of this research have been accepted by the Publications of the Astronomical Society of Australia, but the peer review process has not yet been completed. The research team and CSIRO stated in a press release that they will continue to improve the data and methods in the future, and look forward to the global scientific research community raising more questions and explanations on this basis to deepen human understanding of the cosmic magnetic field and its role in the evolution of the universe.