Galaxy bubbles are more complex than imagined


May 09, 2023

(Nanowerk News) Astronomers have uncovered new evidence of the nature of the giant high-energy gas bubbles stretching far above and below the center of the Milky Way galaxy.

In a study recently published in Natural Astronomy (“Thermal and chemical properties of eROSITA bubbles from Suzaku observations”), a team led by scientists at The Ohio State University were able to show that the shells of these structures – nicknamed “eRosita bubbles” after being discovered by the eRosita X-ray telescope – are more complex than previously thought.

Despite being very similar in shape to a Fermi bubble, the eRosita bubble is larger and more energetic than its counterpart. Known collectively as “galactic bubbles” for their size and location, they provide an exciting opportunity to study the history of star formation as well as reveal new clues about how the Milky Way came to be, said Anjali Gupta, lead author of the study and a former Ohio State postdoctoral researcher who is now a co-author of the study. professor of astronomy at Columbus State Community College.

These bubbles are in the gas that surrounds the galaxy, an area called the circumgalactic medium.

“Our goal is really to learn more about the circumgalactic medium, a place that is very important for understanding how our galaxy formed and evolved,” said Gupta. “A lot of the areas we study just happen to be in bubble regions, so we wanted to see how different those bubbles would be compared to areas far from the bubbles.”

Previous studies assumed that these bubbles were heated by gas shocks as they blew out of the galaxy, but the main findings of this paper indicate that the temperature of the gas inside the bubbles is not that different from that of the area outside.

“We were surprised to find that the temperatures in the bubble region and outside the bubble region were the same,” said Gupta. Additionally, studies have shown that these bubbles are so bright because they are filled with a very dense gas, not because they are hotter than their surroundings.

Gupta and Smita Mathur, a co-author of the study and a professor of astronomy at Ohio State, conducted their analysis using observations made by the Suzaku satellite, a collaborative mission between NASA and the Japan Aerospace Exploration Agency.

By analyzing 230 archival observations made between 2005 and 2014, the researchers were able to characterize the diffuse emission – electromagnetic radiation from very low-density gas – from the galactic bubble, as well as the other hot gas that surrounds it.

While the origin of these bubbles has been debated in the scientific literature, this research is the first to start solving them, said Mathur. When the team found numerous non-solar neon-oxygen and magnesium-oxygen ratios in the shell, the results strongly suggest that bubble galaxies were originally formed by nuclear star-forming activity, or injection of energy by massive stars and other types. astrophysical phenomena, not through supermassive black hole activity.

“Our data support the theory that these bubbles most likely formed due to intense star formation activity at the center of the galaxy, in contrast to black hole activity occurring at the center of the galaxy,” said Mathur. To further investigate the implications of their discovery for other aspects of astronomy, the team hopes to use new data from other upcoming space missions to continue to characterize the properties of these bubbles, as well as work on new ways to analyze the data they already have. .

“Scientists really need to understand the formation of bubble structures, so by using different techniques to refine our models, we will be able to better constrain the temperature and emission size we are looking for,” said Gupta.


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