The Fermi Bubbles and the Galactic Center

Two giant lobes of gamma-ray emitting plasma, known as the Fermi Bubbles, extend 12 kpc above and below the Galactic Center. They are thought to be created by a past episode of AGN activity at the Galactic Center and/or nuclear star formation. Our team has led three approved HST programs (13448 in Cycle 21, 15339 in Cycle 25, and 17746 in Cycle 32) totalling 96 orbits to study the Bubbles in ultraviolet absorption using COS and STIS. This dataset has opened a new UV window on the Galactic Center and allowed us to study the kinematics, spatial extent, chemical abundances, and physical conditions of the clouds embedded in the nuclear outflow. Our latest work is studying stellar sightlines near the Galactic Center, and probing the three-dimensional locations of the outflowing clouds.

Our Fermi Bubble research has led to the following series of papers:

Paper 1: Fox et al. 2015 (discovery of Fermi Bubble absorbers)
Paper 2: Bordoloi et al. 2017 (survey of northern bubble)
Paper 3: Savage et al. 2017 (pair of stellar sightlines through the southern bubble)
Paper 4: Karim et al. 2018 (survey of southern bubble)
Paper 5: Ashley et al. 2020 (joint (N+S) bubble kinematic analysis)
Paper 6: Fox et al. 2021 (non-detection of H2 emission in bubbles)
Paper 7: Cashman et al. 2021 (detection of H2 absorption in bubbles)
Paper 8: Ashley et al. 2022 (metallicity of Fermi Bubble clouds)
Paper 9: Cashman et al. 2023 (abundance analysis in Inner Galaxy cloud)
Paper 10: Bordoloi et al. 2025 (high-latitude H I clouds in the northern bubble)
Paper 11: Cashman et al. 2025 (kinematic analysis of foreground UV absorption)