By studying hot gas glowing in circumgalactic space, astrophysicists have found evidence of the existence of enormous magnetic fields winding through and around our galaxy’s dark matter halo.
Our little piece of the Universe is contained in a sort of shell made of dark matter. Although the space between the few stars scattered in this largely invisible sphere seems empty, a lot is happening in the outer reaches of the Milky Way. By studying hot gas glowing in circumgalactic space, astrophysicists have found evidence of the existence of enormous magnetic fields winding through and around the dark matter halo. “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,” explained He-Shou Zhang, an astrophysicist at INAF.
The results of the study
“Our results demonstrate that the magnetic ridges we observed are not simply random structures, but are closely related to star-forming regions in our galaxy,” he added. The study was conducted on X-rays emitted by two enormous structures that extend above and beyond the Milky Way. Discovered in 2020, these “eROSITA bubbles” extend over 45,000 light-years to either side of the galactic center. They are powered by huge outflows of gas and plasma. When the bubbles were discovered, scientists thought there were two main contenders for pinpointing their source. One was the activity of the supermassive black hole at the center of the Milky Way. If it had gone through a period of jet activity, the heat and energy created could have caused the bubbles to explode.
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Star formation
The second explanation was star formation activity. The galaxy is rather quiet now, but it may have undergone a period of intense star formation. This, too, may have produced enough heat and energy to create the eROSITA bubbles that expand in the galactic halo. When the researchers studied the polarization of the light spectrum emitted by the eROSITA bubbles, they found huge, long magnetic filaments. If we could see these filaments with our eyes, they would stretch into the sky up to 150 times longer than they are wide.
These filaments suggest that the origin of the eROSITA bubbles was star formation. At a distance of about 10,000 to 16,000 light-years from the galactic center, a star-forming ring may have produced the heat and winds that caused hot gas and plasma to escape into the galactic halo for a distance of tens of thousands of years light and beyond.
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