Black hole plasma jets reach beyond visible galaxies to shut down star formation

Galaxies should, by all rights, be making far more stars than they do. They sit inside vast reservoirs of cold gas — raw material stretching 10 to 20 times the width of the visible galaxy — and yet something keeps that fuel from cooling, collapsing, and igniting into new suns. A new study points squarely at the supermassive black holes sitting at galaxies' cores, and at the narrow jets of superheated plasma they fire outward at extraordinary range.

The research, led by astronomers Sanchayeeta Borthakur of Arizona State University and Namrata Roy, now at the Raman Research Institute in India, and published in the Astrophysical Journal Letters, offers some of the clearest evidence yet that these jets do not merely churn gas near the galactic center — they reach hundreds of thousands of light-years outward, heating and disrupting the very reservoir a galaxy depends on to keep forming stars.

This is a pathbreaking result that solves the long-standing mystery of how black holes influence galaxies, their stars, and life as we know it!— Sanchayeeta Borthakur, Associate Professor, ASU School of Earth and Space Exploration

The central puzzle the study addresses is one of scale. A supermassive black hole is roughly the size of our solar system. Its host galaxy can hold about 100 billion such solar systems. How does something so comparatively tiny exert enough energy to shape the fate of something so vast?

The surprising question is: how can something so small energetically impact something so enormous?— Namrata Roy, Assistant Professor, Raman Research Institute; former ASU Exploration Prize Postdoctoral Fellow

The answer the team found lies in the jets themselves — narrow, fast-moving streams of hot plasma that active black holes blast outward when feeding on surrounding gas. Rather than spreading energy evenly in all directions like a lamp, the jets act more like a focused beam, ionizing and heating gas specifically along their paths.

To detect this effect, the researchers had to be clever. The faint glow of ionized hydrogen gas in the circumgalactic medium — the technical name for a galaxy's surrounding gas envelope, abbreviated CGM — is too dim to observe clearly around any single galaxy. So the team stacked observations of hundreds of galaxies with active jets, drawing on data from two major surveys: the Dark Energy Spectroscopic Instrument (DESI) and the LOFAR Two-meter Sky Survey (LoTSS). They then searched for a specific chemical fingerprint of ionized hydrogen, known as H-alpha, aligned with the jet axes.

When they averaged the signal across all directions around the galaxies, it was weak. But along the radio jet paths, the H-alpha signal became clear and strong — the gas was glowing brightest precisely where the jets were passing through. The effect was not uniform but sharply directional, concentrated along the jet axes.

What excites me most is the scale of the connection. 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.— Namrata Roy, Assistant Professor, Raman Research Institute

The glow was brightest at two specific locations: close to the galaxy, where the jet first strikes the CGM, and much farther out near the CGM's outer edge, where the jet deposits most of its energy. This two-peak pattern gives researchers a map of how the jet's influence travels and where it does its most significant work.

To confirm the jets were the cause rather than some pre-existing property of the gas, the team also tracked cooler gas using the absorption signature of magnesium. Unlike the H-alpha glow, magnesium was distributed roughly equally in all directions around the galaxies, with no alignment to the jet axes. This suggests the cool gas already exists as a uniform reservoir on all sides — and that it is the jet, specifically, that heats and ionizes gas along its own path.

The CGM is the gas envelope surrounding every large galaxy, including the Milky Way, extending 10 to 20 times the size of the galaxy's visible disk. It is the primary reservoir from which galaxies draw the cold, dense gas needed to form new stars. When jets heat this gas, it can no longer cool and fall inward to fuel star formation — effectively acting as a brake on the galaxy's growth and pushing it toward a quiescent, star-forming-dead state.

The implication is that supermassive black holes are not passive objects sitting at galactic centers while stars form around them. They actively regulate — and can ultimately shut down — their host galaxy's ability to grow, through jets that reach far beyond anything visible to conventional observation.

This work opens a new direction to explore further the intricacies of the connection between the supermassive black holes trillions of miles from where we are to how we came to be here.— Sanchayeeta Borthakur, Associate Professor, ASU School of Earth and Space Exploration

The researchers note that scientists still do not fully understand how energy from active black holes travels such distances or how it changes along the way — this study provides evidence of the mechanism but does not close every question. Further observations will be needed to quantify the overall impact across different galaxy populations.

Why it matters — This research helps explain why galaxies — including potentially our own Milky Way's future — stop forming stars, tracing the mechanism to supermassive black holes whose jets can reshape a galaxy's fate from its very core to its outermost gas envelope.

Reported by phys.org, eurekalert.org, mid-day.com, bioscience.com.pk