Misaligned Jets from Sgr A* and the Origin of Fermi/eROSITA Bubbles

Abstract

One of the leading explanations for the origin of Fermi Bubbles is past jet activity in the Galactic center supermassive black hole Sgr A ^* . The claimed jets are often assumed to be perpendicular to the Galactic plane. Motivated by the orientation of pc-scale nuclear stellar disk and gas streams, as well as a low inclination of the accretion disk around Sgr A ^* inferred by the Event Horizon Telescope, we perform hydrodynamical simulations of nuclear jets significantly tilted relative to the Galactic rotation axis. The observed axisymmetry and hemisymmetry (north–south symmetry) of Fermi/eROSITA bubbles (FEBs) due to quasi-steady jets in Sgr A ^* could be produced if the jet had a super-Eddington power (≳5 × 10 ^44 erg s ^−1 ) for a short time (jet active period ≲6 kyr) for a reasonable jet opening angle (≲10°). Such powerful explosions are, however, incompatible with the observed O viii /O vii line ratio toward the bubbles, even after considering electron–proton temperature nonequilibrium. We argue that the only remaining options for producing FEBs are (i) a low-luminosity (≈10 ^40.5−41 erg s ^−1 ) magnetically dominated jet or accretion wind from the Sgr A ^* , or (ii) a supernovae or tidal disruption event driven wind of a similar luminosity from the Galactic center.

Keywords

• Jets
• Milky Way Galaxy
• Galactic center
• Circumgalactic medium
• Diffuse x-ray background
• Hydrodynamical simulations