The Fermi Bubbles: Supersonic AGN Jets with Anisotropic Cosmic Ray Diffusion

Understand

The Fermi Gamma-ray Space Telescope reveals two large bubbles in the Galaxy, which extend nearly symmetrically ~50 degrees above and below the Galactic center (GC).

• Using three-dimensional (3D) magnetohydrodynamic (MHD) simulations that self-consistently include the dynamical interaction between cosmic rays (CR) and thermal gas, and anisotropic CR diffusion along the magnetic field lines, we show that the key characteristics of the observed gamma-ray bubbles and the spatially-correlated X-ray features in ROSAT 1.5 keV map can be successfully reproduced by a recent jet activity from the central active galactic nucleus (AGN).
• We find that after taking into account the projection of the 3D bubbles onto the sky, the physical heights of the bubbles can be much smaller than previously thought, greatly reducing the formation time of the bubbles to about a Myr.
• This relatively small bubble age is needed to reconcile the simulations with the upper limit of bubbles ages estimated from the cooling time of high-energy electrons.