Black Hole Jets May Control a Galaxy’s Fate

Supermassive black holes sit at the center of galaxies, but a new study suggests their influence doesn’t stop anywhere close to the center. It may reach all the way to a galaxy’s outer edges, and decide whether that galaxy keeps making stars at all.

A Giant Envelope of Gas

Every large galaxy, including the Milky Way, is surrounded by a vast envelope of gas called the circumgalactic medium, or CGM. This gas reservoir stretches 10 to 20 times the size of a galaxy’s visible portion and serves as the raw material for new stars. Over time, CGM gas cools, drifts inward, and clumps together, eventually forming the stars, planets, and everything else that makes up a galaxy’s visible structure. For years, astronomers have puzzled over a basic mismatch: given how much star-forming gas surrounds typical galaxies, why don’t they end up with even more stars than they actually have? Something appears to be keeping a significant portion of that fuel from ever cooling down.

A Small Object With an Outsized Question

A new study, published in The Astrophysical Journal Letters and led by astronomers Sanchayeeta Borthakur of Arizona State University and Namrata Roy of the Raman Research Institute, points to an answer: narrow jets of heated plasma blasted out by the supermassive black holes at galaxy centers. Despite releasing enormous amounts of energy, these black holes are physically small, roughly comparable in size to our own solar system. Their host galaxies, by contrast, can contain the equivalent of around 100 billion similarly sized solar systems. Namrata Roy, an assistant professor at RRI and former ASU Exploration Prize Postdoctoral Fellow, put the puzzle directly: “The surprising question is: How can something so small energetically impact something so enormous?”

Looking in the Right Direction

To find an answer, the research team searched for a specific signature within the CGM: a faint glow from ionized hydrogen gas known as H-alpha, produced when the gas becomes energized. That glow is so faint that no single galaxy would show it clearly on its own, so the team combined observations from hundreds of galaxies with active jets, drawing on optical data from the Dark Energy Spectroscopic Instrument and radio jet measurements from the LOFAR Two-meter Sky Survey. When the team averaged signals from every direction around these galaxies, the result was weak and largely undetectable. But when they specifically looked along the direction of each galaxy’s radio jets, a clear, strong H-alpha signal appeared. Borthakur and Roy describe the effect less like a lamp illuminating a room evenly in all directions, and more like a focused beam that makes gas glow specifically where it passes through.

Bright Near the Source, Bright Again Far Away

The ionized gas glowed most intensely in two distinct locations: close to the galaxy, where a jet first collides with the surrounding CGM, and again much farther out, near the CGM’s outer boundary, where researchers believe the jet deposits most of its remaining energy. Roy said the sheer scale involved is what makes the finding so striking: “A black hole is incredibly small compared to a galaxy, but its impact can reach hundreds of thousands of light-years, far into the galaxy’s outer reaches. The jet carries the energy outward, and the gas lights up along its path.” As an additional check, the researchers also examined a separate tracer, the absorption signature of magnesium, associated with cooler gas. Unlike the directional H-alpha glow, magnesium showed up more evenly distributed in all directions and displayed no clear connection to jet direction, suggesting this cooler gas component already surrounds galaxies in a relatively uniform layer, largely undisturbed by the jets passing through it.

A Brake on Galaxy Growth

By heating, stirring, and generally disturbing the gas throughout the CGM, these jets appear capable of preventing that gas from cooling and falling inward to fuel new star formation. In effect, this acts as a brake on a galaxy’s overall growth, potentially shifting how a galaxy evolves over cosmic time. The findings indicate a supermassive black hole isn’t simply feeding quietly at a galaxy’s center; its jets can reach outward and directly reshape the galaxy’s surrounding environment, ultimately influencing whether that galaxy continues forming stars or gradually becomes quiescent. Borthakur called the result a pathbreaking one that “solves the long-standing mystery of how black holes influence galaxies, their stars and life as we know it,” adding that the work opens a new direction for exploring the connection between supermassive black holes and the conditions that ultimately made life possible.

Why Earlier Searches Came Up Empty

Previous studies had searched for H-alpha emission connected to black-hole jets without success, and this new study helps explain why those earlier attempts failed: the signal only becomes clear once astronomers specifically look along the direction of the jets themselves. Had this team instead assumed the CGM looked uniform in every direction and simply averaged observations across all directions around each galaxy, as earlier research effectively did, the distinct H-alpha glow tracing the jet paths would have been washed out and remained hidden. The approach highlights the value of combining large optical and radio survey datasets like DESI and LoTSS: by pooling together many individually weak signals and accounting carefully for jet direction, astronomers can detect genuine patterns that would otherwise stay buried in the noise. The study gives both observers and theorists a new, concrete way to test exactly how black-hole jets shape the galaxies that host them.

Sources

This report draws on Arizona State University’s own announcement of the study by Sanchayeeta Borthakur, Namrata Roy, and colleagues, published in The Astrophysical Journal Letters (2026).