Single-event origin of the Fermi Bubbles' X-ray shells and gamma-ray emission

Determine whether the expanding soft X-ray shells and the volume-filling gamma-ray emission associated with the Milky Way’s Fermi Bubbles originate from the same single outburst event from the Galactic Center black hole Sgr A* or whether they arise from multiple distinct outbursts separated in time.

Background

The Fermi Bubbles comprise large, bipolar structures observed above and below the Galactic plane in X-rays (ROSAT/eROSITA) and gamma rays (Fermi-LAT). Competing scenarios attribute their origin either to starburst-driven outflows or to past activity of Sgr A*, each implying different energetics and timescales. Establishing whether the X-ray shells and the gamma-ray emission trace a single event or multiple episodes is central to constraining the history of Galactic Center activity and the mechanisms powering these structures.

Accretion onto supermassive black holes can be highly episodic, potentially producing recurrent outbursts over ~10^5-year timescales. This stochasticity complicates efforts to link distinct observational components to a single causal event, motivating a clear determination of the event multiplicity for the Fermi Bubbles.