Tidal disruption events as the origin of the eROSITA and Fermi bubbles

¹ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
² Sterrenkundig Observatorium, Ghent University, Krijgslaan 281-S9, 9000 Ghent, Belgium

^★ Corresponding author; tassilo.scheffler@ugent.be

Received: 23 August 2024
Accepted: 29 January 2025

Abstract

Context. The recently discovered spherical eROSITA bubbles extend up to a latitude of ±80°−85° in the X-ray regime of the Milky Way halo. Similar to the γ-ray Fermi bubbles, they evolve around the Galactic center, making a common origin plausible. However, the driving mechanism and evolution of both bubbles are still under debate.

Aims. We investigate whether hydrodynamic energy injections at the Galactic center, such as tidal disruption events, could have inflated both bubbles. The supermassive black hole Sagittarius A* is expected to tidally disrupt a star every 10–100 kyr, potentially leading to an outflow from the central region that drives a shock propagating into the Galactic halo due to its vertically declining density distribution, ultimately forming a superbubble that extends out of the disk similar to the eROSITA and Fermi bubbles.

Methods. We model tidal disruption events in the Galaxy using three-dimensional hydrodynamical simulations, considering different Milky Way mass models and tidal disruption event rates. We then generate synthetic X-ray maps and compare them with observations.

Results. Our simulation results of a β-model Milky Way halo show that superbubbles, blown for 16 Myr by regular energy injections at the Galactic center that occur every 100 kyr, can have a shape, shell stability, size, and evolution time similar to estimates for the eROSITA bubbles, and an overall structure reminiscent of the Fermi bubbles. The γ-rays in our model would stem from cosmic ray interactions at the contact discontinuity, where they were previously accelerated by first-order Fermi acceleration at in situ shocks.

Conclusions. Regular tidal disruption events in the past 10–20 million years near the Galactic center could have driven an outflow resulting in both, the X-ray emission of the eROSITA bubbles and the γ-ray emission of the Fermi bubbles.