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The Milky Way is home to gas, dust, billions of stars, and a supermassive black hole at its center. Living in this galactic home gives us exclusive insight into its components, but it also hinders our ability to get a zoomed out view of its structure. A recent discovery has the potential to redefine our understanding of the structure of the Milky Way and how it evolved over time.
A team of researchers from the National Institute for Astrophysics (INAF) in Italy have identified massive structures that make up the galactic halo that surrounds the Milky Way, which may be powered by intense outflows of gas and energy generated by the explosive death of stars. The findings are detailed in a study published Monday in Nature Astronomy.
Using more than 10 different all-sky surveys in different wavelengths, the team behind the new study scoured the galaxy using frequencies ranging from radio to gamma-rays. The astronomers were able to confirm the large scale of several magnetized structures in the galaxy, extending to heights of over 16,000 light-years far above and below the galactic plane. The magnetic fields within these bubbles are also highly organized, forming thin filaments that stretch up to around 150 times the width of the Moon.
The study suggests that these structures share a common origin story with the eROSITA bubbles, giant structures made of hot gas that were detected in the first all-sky survey map produced by the eROSITA X-ray telescope in 2020. “The new study adds to a body of evidence that there are hot bubbles of gas and plasma above and below the Milky Way, and if the Milky Way is representative of spiral galaxies, then those might exist in other galaxies,” Martijn Oei, a researcher on radio astronomy and cosmology at Caltech who was not involved in the study, told Gizmodo.
The Fermi Gamma-Ray Space Telescope first revealed theses hot bubbles in 2020; the telescope observed mysterious structures emitting higher-energy gamma rays than the rest of the Milky Way’s disk. These structures could be the result of massive amounts of energy being emitted by the supermassive black hole at the center of the Milky Way, in addition to jets of hot gas triggered by the death and subsequent collapse of a star in an explosive supernova.
“This work provides the first detailed measurements of the magnetic fields in the Milky Way’s X-ray emitting halo and uncovers new connections between star-forming activities and galactic outflows,” He-Shou Zhang, a researcher at INAF and lead author of the study, said in an emailed statement. “Our findings show that the magnetic ridges we observed are not just coincidental structures but are closely related to the star-forming regions in our galaxy.”
These galactic outflows also contribute to stellar formation regions, helping fuel the birth of stars and playing a vital role in the evolution of galaxies. When a star dies, new stars are formed from the collapsing cloud of material left behind. The new findings suggest that there’s a link between galactic outflows and the Milky Way’s star-forming ring at the end of its Galactic Bar, a straight bar feature that extends across the center of the galaxy where most of the stars, gas, and dust reside.
“This study marks a significant step forward in our understanding of the Milky Way,” Gabriele Ponti, a researcher at INAF, and one of the authors of the new paper, said in a statement. “What is fascinating to me here is that we see that also the Milky Way, a quiescent galaxy like many others, can eject powerful outflows and, in particular, that the star-forming ring at the end of the Galactic bar contributes significantly to the Galactic outflow.”
Galactic outflows are largely responsible for the growth and evolution of galaxies over time. Observing these powerful accretions in the Milky Way can help scientists better understand how galaxies like our own developed over time, and where our galactic home fits into the larger universe. “What we’re now learning is that the halos of galaxies, or the large scale surroundings of galaxies, are magnetic, and magnetic fields play an important role in how galaxies evolve,” Oei said. “The Milky Way is one of our most exciting laboratories because it is the only spiral galaxy that we can study up close.”
