Fermi Bubbles and Galactic Center Dynamics

The Fermi Bubbles are two enormous lobes of gamma‐ray emission extending roughly 8–10 kiloparsecs above and below the Milky Way’s centre. First revealed by the Fermi Gamma‐ray Space Telescope, these structures appear remarkably uniform in spectrum and sharply bounded in outline. Their origin is widely attributed to a past episode of energy release in the Galactic Centre, such as a phase of intense accretion onto the central supermassive black hole or a nuclear starburst. In both scenarios, fast outflows of cosmic rays and hot plasma inflate bipolar cavities, which in turn drive shocks into the surrounding halo. Multiwavelength observations—from microwave haze to X-ray arcs—trace the interplay between relativistic particles, magnetised plasma and the circumgalactic medium. Hydrodynamic and magnetohydrodynamic simulations have been employed to reproduce their morphology, spectral uniformity and edge sharpness, while analyses of kinematic tracers (atomic and molecular gas) probe the impact of the wind on the Galaxy’s interstellar medium. Collectively, studies of the Fermi Bubbles offer a unique window onto feedback processes in a normal spiral galaxy, bridging our understanding of black-hole activity, galactic winds and the assembly of baryons in galaxy halos.

Research from Nature Portfolio

Recent hydrodynamic simulations indicate that the large‐scale asymmetry observed in soft X-ray counterparts of the Fermi Bubbles can be explained by a persistent wind in the circumgalactic medium. A flow impinging on the northern halo at a few hundred kilometres per second generates density and metallicity gradients that distort one bubble more strongly than the other, while also redistributing halo gas. This model naturally accounts for brightness variations and morphological skews in both lobes, suggesting that the Galaxy is simultaneously accreting low-metallicity gas and expelling hot, enriched plasma. The results underscore the dynamic coupling between inflow and feedback in the Milky Way’s environment.

Fermi Bubbles and Galactic Center Dynamics publication trend

The graph below shows the total number of articles in fermi bubbles and galactic center dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Fermi Bubbles: Giant gamma-ray lobes above and below the Galactic Centre, inflated by past energetic events.

eROSITA bubbles: Soft X-ray counterparts to the Fermi Bubbles, detected by the eROSITA telescope.

Circumgalactic medium: The diffuse gas surrounding a galaxy, extending into its halo.

Galactic chimney: A channel of hot gas and magnetic fields linking the disc to the halo, carved by outflows.

Active Galactic Nucleus (AGN): A compact, highly luminous region around a supermassive black hole driven by accretion.

Inverse Compton emission: Photons gaining energy by scattering off high-speed electrons, producing X-rays or gamma rays.

References

1. GIANT GAMMA-RAY BUBBLES FROM FERMI-LAT: ACTIVE GALACTIC NUCLEUS ACTIVITY OR BIPOLAR GALACTIC WIND?. The Astrophysical Journal (2010).
2. The Spatially Uniform Spectrum of the Fermi Bubbles: The Leptonic Active Galactic Nucleus Jet Scenario. The Astrophysical Journal (2017).
3. Microwave Interstellar Medium Emission Observed by the Wilkinson Microwave Anisotropy Probe. The Astrophysical Journal (2004).
4. Direct observations of the atomic-molecular phase transition in the Milky Way’s nuclear wind. Monthly Notices of the Royal Astronomical Society (2023).
5. Asymmetric eROSITA bubbles as the evidence of a circumgalactic medium wind. Nature Communications (2023).
6. Morphological Evidence for the eROSITA Bubbles Being Giant and Distant Structures. The Astrophysical Journal Letters (2024).
7. Misaligned Jets from Sgr A* and the Origin of Fermi/eROSITA Bubbles. The Astrophysical Journal (2023).