Magnetic halo challenges galaxy formation models

September 23 () –

X-ray observations from space have identified several magnetized structures that extend far above and below the plane of the Milky Way, about 16,000 light years.

This discovery challenges previous models of the structure and evolution of our galaxy, revealing one of the origins of the so-called eROSITA bubbles, which are fed on a large scale. by intense flows of gas and energy that are also generated by the explosive death of stars in supernovas.

Remarkably, these bubbles, observed by the eROSITA satellite (an X-ray telescope aboard the Russian-German Spectr-Roentgen-Gamma SRG space mission), stretch across the sky from horizon to horizon, providing the first detailed measurements of the Milky Way’s magnetic halo. These results have been published in Nature Astronomy.

The study reveals that the magnetic fields within these bubbles are highly organized, forming thin filamentous structures. These filaments extend up to about 150 times the diameter of the full moon, showing their immense scale. The filaments are related to hot winds with a temperature of 3.5 million Kelvin, expelled from the Galactic Disk and fed by star-forming regions.

He-Shou Zhang, the first author of the article and a researcher at INAF (National Institute for Astrophysics of Italy), highlights that “our results find that intense star formation at the edge of the galactic bar contributes significantly to these expansive and multiphase flows.”

“This work provides the first detailed measurements of magnetic fields in the Milky Way’s X-ray-emitting halo and uncovers new connections between star formation activities and galactic outflows. Our findings show that the magnetic ridges we observe are not simply random structures, but are closely related to star-forming regions in our galaxy,” he adds. in a statement from Radboud University, which participated in the study.

The research team used an exhaustive multi-wavelength study, spanning frequencies from radio to gamma rays, to analyze these structures. This detailed approach allowed them to confirm the extended nature of these magnetic features and their association with galactic feedback processes. Notably, the study represents the first observational evidence linking the Milky Way’s star-forming ring at the end of the galactic bar with the formation of large-scale galactic outflows.

“This study marks a significant advance in our understanding of the Milky Way,” says Gabriele Ponti of INAF. “It is well established that a small fraction of ‘active’ galaxies can launch outflows, driven by accretion onto supermassive black holes or star formation events, that deeply impact their host galaxy.

“Such outflows are thought to be key ingredients in regulating the growth of galaxies and the black holes at their centers. What I find fascinating here is that we see that the Milky Way, a quiescent galaxy like many others, can also expel powerful outflows, and in particular that the star-forming ring at the end of the galactic bar contributes significantly to galactic outflow.

“Perhaps the Milky Way reveals a common phenomenon in galaxies similar to the Milky Waythus helping us to shed light on the growth of these objects.

This work was made possible using more than 10 different all-sky surveys, spanning frequencies from radio waves to gamma raysHe-Shou Zhang concludes: “Our work is a timely result. It is the first comprehensive multi-wavelength study of eROSITA bubbles since their discovery in 2020.

“The study opens new frontiers in our understanding of the galactic halo and will contribute to our knowledge of the complex and impetuous star formation ecosystem of the Milky Way.”