The cosmos is full of loud, spectacular things: supernovae, exploding stars, giant black holes gobbling gas in galaxies far away. Yet some of the most decisive work happens quietly, in the spaces where galaxies and their invisible engines meet. A new study maps how the jets blasted out by supermassive black holes—jets that carry energy across thousands of light-years—work like a hidden hand in the story of galaxy evolution. They heat, stir, and sometimes compress the gas around them, and in doing so they help decide which galaxies light up with stars and which stay dark.
This story comes from a collaboration led by Zuzanna Igo and Annamaria Merloni at the Max-Planck-Institut für Extraterrestrische Physik (MPE) in Germany, with support from the ORIGINS Excellence Cluster. Using a complete sample of radio-loud active galactic nuclei from the LOFAR-eFEDS field, the team stitched together a new, empirical picture of how jet power depends on host galaxy mass and environment. In other words: they’re building a time-averaged, universe-wide budget for jet energy, and then asking what that budget does to galaxies and their larger cosmic homes.
The Energetic Story of Radio Jets
The scientists pulled from a catalog of 682 radio-loud AGN in the nearby universe (redshift z < 0.4) detected by LOFAR at 144 MHz, and they split the sources into two broad flavors: compact jets, which stay tight and bright near the galaxy’s center, and complex jets, which flare into extended, sometimes multi-lobed structures that stretch far beyond the galaxy. They then translated the observed radio power into a jet kinetic power, Q, using empirical relations tied to how jets inflate cavities in hot gas around galaxies and clusters. To compare “how strong” the jets are across galaxies, they defined a specific jet power, λJet, as Q divided by the Eddington luminosity (the theoretical cap for how fast a black hole can eat). The mass of the central black hole was tied to the galaxy’s stellar mass, so λJet became a way to normalize jet power against the scale of its host.
Lead author Zuzanna Igo and co-author Annamaria Merloni have helped show that the incidence of radio AGN—the fraction of galaxies that host a jet at a given λJet—depends on the stellar mass of the host in a nontrivial way. Compact jets favor lower λJet, while complex jets become more common as galaxies get more massive and as jet power rises. The team fitted these incidence distributions with clean mathematical forms and then used them to reconstruct the radio luminosity function (RLF) broken down by host mass and morphology. In effect, they asked: if you know how often a galaxy of a given mass lights up with a compact jet versus a complex jet, how many jets should we expect at different radio powers, and what does that imply about the energy being dumped into the surrounding gas?
One striking result is a robust energy budget: when you integrate over the population, the kinetic energy carried by jets—EJet—outstrips the energy that could be delivered by radiative winds from accreting black holes, for most galaxies above a certain mass threshold. In the local universe, the kinetic channel wins hands down for galaxies with stellar masses above about 10^10.6 solar masses. And the split between compact and complex jets matters: compact jets dominate the average jet power for most galaxies, except the truly massive ones where complex jets take over the energy budget. The numbers are not abstract: the study pins down the total kinetic energy density of jets, a quantity the authors call Ωkin, to a precise band that aligns with earlier measurements, but now backed by a mass- and morphology-resolved census.
From Compact Cores to Cosmic Giants
The authors then asked a deeper, more physical question: how does this jet power compare to the gravitational anchors that keep gas bound to galaxies and halos? They compared EJet to the binding energy of the host galaxy (the energy required to unbind the galaxy’s stars and gas) and to the binding energy of the host dark matter halo (the energy needed to unbind the halo’s baryons). They find a nuanced picture. On galactic scales, compact jets have enough power to disrupt gas motion and disturb the central regions for many galaxies, but they typically do not completely unbind the galaxy’s gas. In the most massive galaxies, complex jets can approach or exceed the galaxy’s binding energy, but a lot of that energy stretches beyond the stellar body and into the halo itself, diluting the direct galaxy-wide disruption signal.
When you scale up to halos—the vast, dark matter–enshrouded environments galaxies inhabit—the math looks less friendly. Even the most powerful jets fall short of unbinding gas from an entire halo. Yet they aren’t powerless: the energy budget is enough to heat the halo’s gas and counteract cooling in groups of galaxies. The authors quantify a preventative effect, FP, which is the ratio of jet energy to the halo’s cooling energy. In smaller halos and groups, FP can exceed unity, suggesting jets can keep halos hot enough to slow down new star formation. In the largest clusters, FP remains modest, a reminder that cluster-scale cooling is stubborn and requires a chorus of heating processes to stay in balance.
To translate these ideas into something tangible, the team introduces the concept of an equivalence radius, Req. This is the radius within which the jet’s energy could balance the halo’s cooling luminosity if fully contained. With a simple, standard halo gas profile, Req tends to be a few percent of the halo’s radius for clusters and somewhat larger for groups. The practical upshot is provocative: many jets in the sample probably deposit their energy primarily in the central regions of groups and massive galaxies, where heating can directly offset cooling and influence how gas flows into the heart of the galaxy or halo.
All of this is grounded in a rigorous data pipeline, but the human side of the work is just as important. The team’s analysis demonstrates how to braid together an incidence distribution (how often jets appear at a given power), a census of host masses, and a physically motivated breakdown by radio morphology to produce a coherent, testable global energetics budget. In short, they’re not just cataloging how bright jets are; they’re mapping how a population of black holes, through their jets, stirs the cosmic soup that feeds galaxies.
What This Means for Galaxy Evolution
The headline takeaway is both simple and profound: kinetic feedback from jets is the dominant energy channel that regulates the gas in most massive galaxies today. Radiative feedback, the kind of wind or outflow powered by bright quasars, remains important—but its global energy budget trails the jets for the bulk of the mass range in the local universe. Put another way: in the modern cosmos, the quiet engines at galaxy centers are the principal gardeners who shape where stars grow and where gas sits hot and still.
That conclusion has immediate implications for how scientists simulate galaxies. Modern cosmological simulations and semi-analytic models embed “sub-grid” recipes for how black holes heat or displace gas. The Igo-Merloni result provides a mass- and morphology-resolved target for those recipes: jet power doesn’t just scale with black hole mass in a simple way, it scales with the mass of the host and with how the jet looks on the sky. This nuance matters, because different feedback prescriptions can sometimes produce similar observable outcomes, a phenomenon known as degeneracy. By offering a detailed, incidence-based mapping of jet energy across galaxy masses, the study helps disentangle which prescriptions are physically plausible and which ones are mere fit artifacts.
Beyond simulations, the findings illuminate how galaxies and their halos co-evolve. In smaller groups, where FP can approach or exceed unity, jets can heat gas enough to suppress fresh cooling and slow down star formation on cosmic timescales. In larger clusters, where FP drops, jets still contribute to a hot, buoyant core—creating cavities and bubbles visible in X-ray observations—but maintaining global balance likely requires a symphony of heating sources, with jets playing a leading, but not solitary, role. The upshot is a more nuanced view of feedback: jets sculpt the inner regions of halos, regulate gas flows into galaxies, and help keep the cosmic gas from freezing into new stars too quickly, all while leaving the outer most reaches of halos relatively unscathed.
The work also highlights the surprising role of jet morphology. Compact jets, which are easier to hide in plain sight, dominate the energy output for most galaxies. Complex jets, which spread their influence over many kiloparsecs, become energetically decisive only in the most massive systems. In other words, the way a jet looks on the sky is a clue to where its energy lands and how it shapes its surroundings. This linkage between morphology, energy, and environment offers a new lens for interpreting radio surveys and for connecting radio observations to the gas physics that govern star formation.
Finally, the study is a reminder of how much we still learn from combining big data with physical intuition. The authors build their conclusions from a careful synthesis: a complete incidence distribution, cross-matched with a robust stellar mass function, and anchored by simple, well-mill-tested models of halo gas. It’s a powerful recipe for turning noisy observations into physical insight about energy flows that move through galaxies as surely as gravity does.
For readers who like a mental image, think of a galaxy as a city with a central power plant (the black hole). The plant emits jets that act like a slow, pervasive heater in the city’s plumbing—warming the water supply, preventing it from cooling into new fuel, and shaping which neighborhoods thrive with new life (stars) and which stagnate. The Igo-Merloni results tell us where that heater shines brightest, how far its warmth can reach, and when it’s likely to warm the city’s outskirts rather than its core. It’s not a dramatic, single-blast scenario; it’s a quiet, persistent balancing act that tunes the cosmos on timescales we can barely imagine but can measure with precision and care.
Credit where it’s due: this project comes from the Max-Planck-Institut für Extraterrestrische Physik in Garching, Germany, with support from the ORIGINS cluster, and it’s led by Zuzanna Igo and Annamaria Merloni. Their work—bridging observations, statistics, and physical energetics—offers a concrete, testable frame for thinking about black holes not as isolated curiosities but as active agents in the grand, ongoing drama of galaxy evolution.
