An article published in the journal “Nature” reports the discovery of a gigantic structure formed by hot gas with a shape similar to that of an hourglass with lobes that extend from the center of the Milky Way. A team of researchers used observations conducted with eROSITA, one of the instruments of the Spektr-RG space telescope, which identified this structure at X-rays that is very similar to the so-called Fermi bubbles.
Launched on July 13, 2019, the Spektr-RG Space Telescope completed its first survey of the sky at energies between 0.2 and 8 keV, offering a much more detailed X-ray view of the sky than the ROSAT space telescope in 1990 did at energies between 0.1 and 1.4 keV.
ROSAT had already made it possible to identify a structure with a shape similar to that of Fermi bubbles, to the point that an article published in “The Astrophysical Journal” in June 2020 offered a common explanation for the origin of both. What were called eROSITA bubbles are somewhat different from those identified by ROSAT. This is normal considering the different energies of the X-rays detected by the two instruments. However, this is likely another observation of the same structure.
The mapping conducted by eROSITA offers new details, confirming the excellent results obtained in mapping the sky to X-rays. The top image (Courtesy MPE/IKI. All rights reserved) shows a false color map with the eROSITA bubbles. The bottom image (Courtesy MPE. All rights reserved) shows a schematic view of the eROSITA bubbles (yellow), the Fermi bubbles (purple), and the galactic disk in the spirals.
Gabriele Ponti of the Italian national instrutute of astrophysics in Brera, one of the authors of this study, stressed the fact that eROSITA is confirmed as a unique instrument for detecting and studying widespread structures. Regarding the connection with the Fermi bubbles, he stated that at the moment it’s not yet clear whether the two structures are associated with two distinct episodes of activity of the galactic nucleus or they’re two different manifestations of the same phenomenon.
According to the model described in the research published in June in “The Astrophysical Journal”, the two structures were generated by an ancient activity of the supermassive black hole at the center of the Milky Way, which in the past may have had an active galactic nucleus activity. The new research based on eROSITA data doesn’t rule out that the new bubbles were generated by intense star formation activity. The data collected can be used by other scientists to test various models.
The eROSITA bubbles support theories concerning large-scale interactions between the center of a galaxy and the halo surrounding it. These are interactions energetic enough to perturb the structure itself, its energy content and the chemical composition of the circumgalactic medium. Again, other scientists will be able to test their theories by including the eROSITA bubbles.
Meanwhile, eROSITA is conducting a second full X-ray sky mapping that is even more detailed than the first. This will also offer further information on the bubbles, their composition, the ionization of the chemical elements that compose them, the temperature and density of the gas that emits the X-rays inside them. The new map will also allow to estimate the position and motions of the shock waves, which could help to understand which is the correct model of their origin. eROSITA has already confirmed that it’s an excellent astronomical instrument, and we can expect even better results.
