Black hole jets reach far beyond galaxies' visible edges, potentially deciding their fate

The study found that black hole jets can reach far beyond the visible edges of galaxies and may influence the gas reservoir that regulates star formation. The research team used optical data from the DESI survey and radio observations from the LOFAR Two-meter Sky Survey (LoTss) to detect a distinct glow in the ionized hydrogen gas along the jet paths. This glow is strongest along the direction of the jets, indicating that the jets affect the gas in a directional manner. The findings suggest that the jets can disrupt the gas that galaxies need to keep growing, potentially shaping their future.

• The jets are narrow streams of hot, fast-moving plasma emitted by supermassive black holes.
• The study focused on active black holes that emit strong jets and looked for a distinct imprint left by these jets in the ionization state of the gaseous reservoir.
• The ionized gas, or "glow" from hydrogen gas, is so faint that no single galaxy would show it clearly. The team combined observations of hundreds of galaxies with active jets using DESI and LoTss data.
• The signal was weak when averaged over all directions around the galaxies but became clear and strong along the jet paths.
• The glow from ionized hydrogen is brightest in two places: close to the galaxy, where the jet first hits the CGM, and much farther out near the CGM's outer edge, where the jet releases most of its energy.

This mechanism helps shape the galaxy's environment, influencing its growth and evolution—and determining whether it continues to form stars or becomes quiescent. The findings offer some of the clearest evidence yet of how a black hole can affect a galaxy far beyond its central region. By heating, stirring and disturbing gas throughout the CGM, jets can prevent that gas from cooling down and falling inward to fuel new stars. This acts as a brake on the galaxy's growth, changes its fate and makes it much less active in star formation. The black hole is not just "feeding" at the center of the galaxy, as some might think. It also reaches out and changes the galaxy's environment, which can eventually change its fate.

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