The Double-Episode Jet Genesis of the eROSITA and Fermi Bubbles

TL;DR

This study uses 3D magnetohydrodynamic simulations to propose that two episodic AGN jet events from the Galactic center created the Fermi and eROSITA bubbles, explaining their morphology and emissions across multiple wavelengths.

Contribution

It introduces a novel model where two separate AGN jet episodes produce the observed bubbles, aligning with multi-wavelength observations and revealing the bubbles as a record of episodic galactic activity.

Findings

Simulations reproduce the observed morphology and emissions of the bubbles.

The first jet forms the eROSITA bubbles, the second forms the Fermi bubbles.

Cosmic-ray acceleration at shock fronts explains gamma-ray features.

Abstract

The Fermi and eROSITA bubbles are giant gamma-ray and X-ray lobes in the Milky Way, extending up to $\sim$50{\deg} and ~$\sim$80{\deg} in galactic latitude, respectively, yet their origins remain debated. Using three-dimensional magnetohydrodynamic simulations, we investigate a scenario in which two temporally separated episodes of active galactic nucleus (AGN) jets launched from the Galactic center produce the bubbles, with each structure bounded by a forward shock. Our simulations reveal that the first jet pair, launched 15 Myr ago, forms the outer eROSITA bubbles (extending to $\sim$18 kpc), while the second, launched 5 Myr ago, creates the nested Fermi bubbles ($\sim$10 kpc height). This model broadly reproduces the observed elongated morphology, multi-band X-ray surface brightness distribution, O VIII/O VII line ratios, radio ridge structures, and gamma-ray emissions of the bubbles. Cosmic-ray electrons are accelerated \textit{in situ} at the shock fronts, explaining the sharp edges and nearly uniform gamma-ray surface brightness distribution of Fermi bubbles. The results suggest that the eROSITA and Fermi bubbles encode a time-resolved record of episodic AGN activity in the Galactic center, providing a physically motivated framework for interpreting their multi-wavelength properties.