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An international team of astronomers, spearheaded by researchers from Tsinghua University in China, has achieved groundbreaking results in mapping the magnetic environment of the Milky Way. In collaboration with scientists from Italy, Australia, Germany, and other countries, the team used two of the world's most advanced radio telescopes, China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST) and South Africa's MeerKAT array, to conduct unprecedented observations of globular clusters, some of the galaxy's oldest and most mysterious star systems. Their findings, reported by China Central Television (CCTV), provide the most detailed measurements yet of magnetic fields and gas within these clusters, reshaping our understanding of how they evolve and how our galaxy's magnetism operates.

An aerial drone photo taken on Feb. 18, 2025 shows China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST) under maintenance in southwest China's Guizhou Province. (Xinhua/Ou Dongqu)

Globular clusters are densely packed, spherical collections of millions of stars, many of which are as old as the universe itself. These clusters often host pulsars, which are rapidly spinning neutron stars that emit steady beams of radio waves, like cosmic lighthouses. As these pulsar signals travel through space, they are subtly altered by the magnetic fields and ionized gas they pass through, providing astronomers with a natural probe of the conditions between stars. By studying these changes in remarkable detail, the researchers have gained new insights into both the internal environment of the clusters and the larger magnetic structure of the Milky Way.

FAST, the world's largest single-dish radio telescope, is uniquely capable of detecting the faint radio signals emitted by pulsars, thanks to its immense 500-meter-wide dish. MeerKAT, on the other hand, consists of 64 dishes working together as an array, excelling at measuring tiny variations in the polarization of radio waves over large areas of the sky. Combined, the two observatories form a powerful observational system that enabled the team to conduct high-precision measurements of 43 pulsars located in eight different globular clusters. The results are featured in the ScienceDirect Bulletin study titled "Probing globular cluster with MeerKAT and FAST: a pulsar polarization census."

One of the most surprising discoveries was that seven of the eight globular clusters studied contained almost no measurable ionized gas. This finding contradicts longstanding theories that predicted such gas would accumulate within these ancient star systems over time. "We expected these clusters to be filled with gas, but they're surprisingly 'clean,'" said Dr Zhang Lei, the lead data analyst on the project, in an interview with CCTV. "This means something, possibly radiation from white dwarfs and young stars, is efficiently clearing out the gas, which challenges our current theories on how these clusters evolve." These internal processes likely involving stellar winds or other energetic emissions may be far more effective at expelling gas than previously assumed.

In addition to revealing the surprising absence of gas, the study doubled the known measurements of magnetic field rotations in globular clusters and improved the accuracy of gas density readings by a factor of eight compared to previous efforts. These new observations provide critical data for building more accurate models of the Milky Way's magnetic field. As pulsar signals are distorted by magnetic fields and ionized particles during their journey, astronomers can analyze these effects such as Faraday rotation and signal dispersion—to map the structure and fluctuations of the galaxy's magnetic environment in three dimensions. This understanding is essential for exploring cosmic processes like star formation, supernova feedback, and the movement of cosmic rays through space.

According to CCTV, the FAST–MeerKAT collaboration is only just beginning. Future work will include monitoring "glitches" in pulsars, sudden and unexplained changes in their spin rate—as well as studying turbulent interstellar gas and continuing the search for potential extraterrestrial signals. These objectives are part of broader efforts to explore the formation and evolution of galaxies and to expand our knowledge of the high-energy universe.

The significance of these discoveries goes beyond globular clusters. Understanding the behavior of these ancient star systems helps scientists reconstruct the early history of the Milky Way, offering clues about how galaxies form and evolve. The revelation that these clusters may be actively clearing out gas challenges conventional models and opens new avenues for research into stellar and galactic dynamics. Moreover, this study highlights the value of global scientific cooperation, demonstrating how international partnerships can harness advanced technologies to make major strides in our understanding of the cosmos.