**Black Hole Jets Influence Gas Beyond Galaxies, Shaping Their Evolution** Black hole jets, powerful streams of heated plasma emitted from the centers of galaxies, extend far beyond the visible edges of galaxies. These jets may play a crucial role in determining the future of galaxies by influencing the gas that surrounds them. Galaxies, which contain hundreds of billions of stars, are surrounded by a vast envelope of gas called the circumgalactic medium (CGM). This gas eventually cools and forms stars, but astronomers have long wondered why galaxies do not contain even more stars, given the large amount of star-forming gas available. A study led by Sanchayeeta Borthakur of Arizona State University and Namrata Roy, now at the Raman Research Institute, suggests that jets from supermassive black holes may regulate the formation of new stars by affecting the CGM. Their findings were published in the Astrophysical Journal Letters. The study focused on active black holes that emit strong jets—narrow streams of hot, fast-moving plasma that extend beyond a galaxy's visible edge. The researchers looked for a distinct imprint left by these jets in the ionization state of the gaseous reservoir. The ionized gas, or "glow" from hydrogen, they were searching for in the CGM is extremely faint, so no single galaxy would show it clearly. To detect this signal, they combined observations of hundreds of galaxies with active jets using data from the Dark Energy Spectroscopic Instrument (DESI) survey and radio jet measurements from the LOFAR Two-meter Sky Survey (LoTSS). They analyzed measurements taken along the jet axes and searched for a telltale sign of ionized hydrogen gas along the jet paths, known as H-alpha. The results showed that the H-alpha signal was weak when averaged over all directions around the galaxies but became clear and strong along the radio jets. This indicates that the gas does not glow uniformly everywhere but is particularly bright 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 provides a clear signature of how jets can illuminate or disrupt surrounding gas at great distances, all the way to the CGM. As a check, the team also used the absorption signature of magnesium to trace cooler gas. Unlike the directional glow in H-alpha, magnesium was more isotropically distributed and showed no connection to the jet direction. This implies that the cool gas component might already exist as a reservoir surrounding the galaxy uniformly on all sides. The jet, meanwhile, brightens, heats, and ionizes gas along its own path, causing it to glow in H-alpha. 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. This means 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.