The bright X-ray bubbles in the galactic center provide an opportunity to understand the effects of feedback on the evolution of galaxies. The shells of the eROSITA bubbles show enhanced X-rays over the sky background. It was previously believed that these shells had a single temperature component and followed the lower temperature shock-heated halogen gas.
Recently, Ohio State University scientists showed that the shells of eRosita bubbles are more complex than previously thought. Despite largely resembling Fermi bubbles, eRosita bubbles are larger and more energetic than their counterparts.
Astronomers revealed the properties of these giant bubbles of high-energy gas that extend far above and below the center of the Milky Way.
Anjali Gupta, lead author of the study and a former Ohio State postdoctoral researcher, said: “Our goal was to learn more about the circumgalactic medium, a place very important for understanding how our galaxy formed and evolved. Many of the regions we were studying happened to be in the region of the bubbles, so we wanted to see how different the bubbles are compared to the regions away from the bubble.
The main results of this study imply that the gas temperature inside the bubbles does not differ much from the area outside. Previous studies hypothesized that the gas shock heated these bubbles as they pushed outward from the Milky Way.
Scientists were surprised to find that the temperature inside the bubble region and outside the bubble region was the same. They also found that these bubbles are so bright because they are filled with extremely dense gas, not because they have a higher temperature than the surrounding environment.
The analysis was performed using Suzaku observations. The observations also showed that the X-rays from the garnets are more complex and best described by a two-temperature thermal model: one component close to the Milky Way’s virial temperature and the other at superficial temperatures.
Smita Mathur, co-author of the study and a professor of astronomy at Ohio State, said: “While the origin of these bubbles has been debated in the scientific literature, this study is the first to begin to settle it. Since the team found an abundance of non-solar neon-oxygen and magnesium-oxygen ratios in the shells, suggest their results strongly suggest that galactic bubbles were originally formed by nuclear star-forming activity or the injection of energy from massive stars and other types of astrophysical phenomena rather than by the activities of a supermassive black hole.”
“Our data support the theory that these bubbles are most likely formed as a result of intense star-forming activity at the galactic center, as opposed to black hole activity at the galactic center.”
The team aims to leverage new data from future satellite missions to continue characterizing the qualities of these bubbles and work on unique techniques to analyze the data they already have to further study the implications of their discovery for other areas of astronomy. .
Gupta said, “Scientists need to understand the formation of the bubble structure, so by using different techniques to improve our models, we can better constrain the temperature and emission measures we’re looking for.”
- Gupta, A., Mathur, S., Kingsbury, J. et al. Thermal and chemical properties of the eROSITA bubbles from Suzaku observations. Wet Astron (2023). DOI: 10.1038/s41550-023-01963-5