Fermi and eRosita bubbles as relics of the past activity of the Galactic black hole

Abstract

The newly launched X-ray satellite, eRosita, has recently revealed two gigantic bubbles extending to ∼ 80 • above and below the Galactic center. The morphology of these "eRosita bubbles" bears a remarkable resemblance to the Fermi bubbles previously discovered by the Fermi Gamma-ray Space Telescope and its counterpart, the microwave haze. The physical origin of these striking structures has been intensely debated; however, because of their symmetry about the Galactic center, they likely originate from some energetic outbursts from the Galactic center in the past. Here we propose a theoretical model in which the eRosita bubbles, Fermi bubbles, and the microwave haze could be simultaneously explained by a single event of jet activity from the central supermassive black hole a few million years ago. Using numerical simulations, we show that this model could successfully reproduce the morphology and multi-wavelength spectra of the observed bubbles and haze, which allows us to derive critical constraints on the energetics and timescales of the outburst. This study serves as an important step forward in our understanding of the past Galactic center activity of our Milky Way Galaxy, and may bring valuable insights into the broader picture of supermassive black hole-galaxy co-evolution in the context of galaxy formation.Recent data taken by the eRosita satellite has revealed striking images of two giant X-ray bubbles extending ∼ 80 • (which corresponds to ∼ 15 kpc assuming a distance to the Galactic Center (GC) of 8.5kpc) above and below the GC 1 . Despite the larger extent, the morphology of the "eRosita bubbles" is remarkably similar to the Fermi bubbles, the two gamma-ray bubbles detected by the Fermi Gamma-ray Space Telescope in 2010 2 . It was also shown previously that the gamma-ray bubbles have counterparts in the microwave band, known as the microwave/WMAP/Planck haze 3,4 , as well as polarized lobes in radio 5 . The