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

TL;DR

This study explores whether tidal disruption events at the Galactic center can explain the origin and properties of the eROSITA and Fermi bubbles through hydrodynamical simulations, matching observed shapes and emissions.

Contribution

It demonstrates that regular TDEs can inflate superbubbles consistent with observed eROSITA and Fermi bubbles, providing a unified origin scenario.

Findings

Simulations produce bubbles similar in shape and size to observations.

Cosmic ray interactions at shocks explain gamma-ray emissions.

TDE-driven outflows can last for 16 million years.

Abstract

Context: The recently discovered spherical eROSITA bubbles arise up to a latitude of $\pm$80\deg-85\deg in the X-ray regime of the Milky Way halo. Similar to the $\gamma$-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 e.g. tidal disruption events (TDEs), 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 TDEs in the Galaxy using three-dimensional hydrodynamical simulations, considering different Milky Way mass models and TDE rates. We then generate synthetic X-ray maps and compare them with observations. Results: Our simulation results of a $\beta$-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 $\gamma$-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 TDEs in the past 10-20 Myr near the Galactic center could have driven an outflow resulting in both, the X-ray emission of the eROSITA bubbles and the $\gamma$-ray emission of the Fermi bubbles.