The baryon cycle is the engine of galactic evolution. Stars forge heavy elements such as carbon, oxygen and silicon, and stellar feedback in the form of supernova explosions and intense radiation drives those metals out of galaxies into the circumgalactic medium, from which the gas can eventually cool and fall back to fuel new generations of stars. Models have long predicted that this redistribution should begin almost as soon as star formation does, but direct observational constraints at the earliest cosmic epochs have been extraordinarily hard to obtain. Previous measurements of metal enrichment during reionization relied mostly on absorption lines imprinted on the light of distant quasars, which probe random sightlines through the intergalactic medium and are only indirectly connected to individual galaxies.

The new work takes a fundamentally different approach: measuring absorption directly against the ultraviolet glow of the galaxies themselves. The team exploited ultra-deep, medium-resolution near-infrared spectroscopy from JWST’s NIRSpec instrument, obtained as part of the Cycle 4 programme SPURS, the SPectroscopic Ultra-deep Reionization-era Survey, in the Abell 2744 field. Only three galaxies in the survey met the demanding selection criterion: their rest-frame ultraviolet continuum near 1,450 angstroms had to be detected at a signal-to-noise ratio above 10, allowing faint absorption lines to be measured against the stellar light. Crucially, the galaxies were chosen purely on continuum brightness, with no prior knowledge of whether metal absorption would be present.

The three targets span a remarkable range of cosmic time. Galaxy A sits at a systemic redshift of 9.31, corresponding to roughly 530 million years after the Big Bang, while Galaxies B and C lie at redshifts 7.88 and 7.29, near the midpoint of reionization at around 650 to 750 million years. In all three systems, the team identified a suite of absorption transitions spanning more than two orders of magnitude in ionization potential: neutral oxygen (O I), low-ionization silicon and carbon (Si II and C II), and highly ionized species (Si IV and C IV). The absorption features appear strikingly similar to those seen in the well-studied spectra of star-forming galaxies at redshift around 3, when the universe was more than three times older.

The kinematics tell the most compelling story. By anchoring each galaxy’s rest frame to the centroid of the strong nebular emission line [O III] 5008, the researchers found that the metal absorption is consistently blueshifted by roughly 50 to 250 kilometres per second relative to the systemic velocity. Because Hubble expansion cannot produce a velocity offset relative to a galaxy’s own rest frame, these blueshifts indicate gas that is physically moving, most plausibly in outflows driven by stellar feedback, although turbulent interstellar motions or more complex internal kinematics may also contribute. The neutral, low-ionization and high-ionization lines all share broadly overlapping velocity structure, typically extending to about minus 200 kilometres per second, pointing to a common reservoir of disturbed, metal-enriched gas.

The coexistence of ions spanning such a wide range of ionization energies within the same blueshifted complex is difficult to reconcile with a single quiescent component of cold interstellar gas. Instead, it points to a multiphase structure, the signature expected when feedback-driven winds shred and accelerate material across cold, warm and hot phases. The data even hint at ionization-dependent stratification: the high-ionization absorption appears more blueshifted than the neutral and low-ionization lines by roughly 60 to 210 kilometres per second depending on the system, a pattern consistent with simulations such as FIRE-2, in which more highly ionized gas traces a faster or more extended component of a multiphase outflow. Higher-resolution spectra would be needed to confirm this ordering in detail.

Independent lines of evidence reinforce the picture. Interpreting the measured line widths as purely thermal broadening yields upper limits on the gas temperature of order ten million kelvin, far above the temperatures at which the detected ions can survive, meaning non-thermal motions such as turbulence and unresolved velocity substructure must dominate the profiles. Equivalent-width ratios between high- and low-ionization species, and between neutral and low-ionization species, place the three galaxies in the same parameter space occupied by lower-redshift star-forming galaxies, with Galaxy A, the most distant, showing somewhat stronger high-ionization absorption relative to its low-ionization lines. The spectra show no broad emission lines or other definitive signatures of an active galactic nucleus, so the feedback is most naturally attributed to intense star formation.

The host galaxies themselves are extreme objects. Spectral energy distribution modelling of Hubble and JWST photometry yields stellar masses between about one and six billion solar masses, strikingly blue ultraviolet slopes between minus 2.12 and minus 2.26, and gas-phase metallicities of roughly one-third to one-tenth of the solar value, subsolar but far from pristine. The youngest stellar populations are forming stars at rates of 19 to 39 solar masses per year. That chemically enriched, outflowing gas could coexist with such blue, dust-poor ultraviolet continua connects these systems to the so-called blue monster galaxies recently identified at even higher redshifts, in which efficient star formation and feedback-driven redistribution of gas and dust shape the observed light.

Perhaps the most profound implication concerns the speed of chemical enrichment. Detecting carbon and oxygen absorption in a galaxy at redshift 9.3, barely half a billion years after the Big Bang, requires extremely rapid metal production, consistent with highly efficient early star formation. Recent theoretical work shows that such rapid enrichment does not demand a dominant contribution from the hypothetical first generation of Population III stars: ordinary Population II star formation with a high upper-mass cutoff of roughly 200 to 300 solar masses can produce sufficient metal yields on short timescales, in line with expectations that the maximum stellar mass rises at low metallicity. The relative abundance patterns of the three galaxies overlap those of previously studied high-redshift absorbers, without extreme offsets that would signal exotic nucleosynthetic channels.

The observations do not directly constrain which sources drove reionization, and the broader population of high-redshift absorbers remains diverse, ranging from enriched systems to extremely metal-poor gas, indicating that early enrichment proceeded in a patchy, inhomogeneous fashion. But they decisively rule out a picture in which galaxy environments stayed chemically pristine until late times. Within the first several hundred million years of cosmic history, at least a subset of luminous galaxies had already built the full toolkit of the baryon cycle: metals in multiple ionization phases, feedback-driven kinematics, and gas circulating between the interstellar and circumgalactic media. The same processes that today regulate star formation across the universe were evidently at work almost from the beginning.

Subject of Research: Multiphase metal-enriched gas outflows around galaxies during the epoch of reionization

Article Title: Early metal-enriched baryon cycling before the midpoint of cosmic reionization

Article References: Zhu, Y., Ji, Z., Becker, G. D., Ding, J., Egami, E., Fan, X., Jin, X., Liu, W., Lyu, J., Ma, Z., Narisetty, S., Rieke, G. H., Wu, Y., Yue, M., Zhang, J., & Rieke, M. J. (2026). Early metal-enriched baryon cycling before the midpoint of cosmic reionization. Nature Astronomy. https://doi.org/10.1038/s41550-026-02988-2

Image Credits: AI Generated

DOI: 10.1038/s41550-026-02988-2

Keywords: JWST, early universe, cosmic reionization, baryon cycle, galactic outflows, metal enrichment, circumgalactic medium, NIRSpec, high-redshift galaxies, stellar feedback, absorption spectroscopy, Population II stars

A team led by Sanchayeeta Borthakur of Arizona State University and Namrata Roy, now an assistant professor at the Raman Research Institute and a former ASU Exploration Prize Postdoctoral Fellow, has found evidence that narrow jets of heated plasma, blasted out by supermassive black holes, can reach far beyond the visible boundaries of their host galaxies and disrupt the gas those galaxies need to keep growing. The research, published in The Astrophysical Journal Letters, offers some of the clearest evidence yet that black holes can influence galactic environments on scales hundreds of thousands of light-years across, far beyond the compact region where the black hole itself resides.

The scale mismatch at the heart of this problem is staggering. A supermassive black hole, even an actively feeding one, occupies a region roughly the size of our solar system. Its host galaxy, by contrast, can contain around one hundred billion solar systems worth of stars and gas. When such a black hole feeds on infalling matter, it releases enormous amounts of energy that heat the surrounding gas, but how that energy travels outward and affects structures millions of times larger has remained one of the most persistent puzzles in astrophysics. Roy has compared the challenge to imagining an ant leaving its impression hundreds or thousands of kilometers away, a vivid illustration of just how disproportionate the influence appears to be.

The answer, according to the new work, lies in the jets themselves. Active black holes that emit strong jets launch narrow streams of hot, fast-moving plasma that shoot out far beyond a galaxy’s visible edge. Rather than spreading their energy equally in all directions, these jets act less like a lamp illuminating a room and more like a powerful beam that leaves a glowing trail wherever it passes. The team hypothesized that if jets truly penetrate the circumgalactic medium, they should leave a distinct imprint in the ionization state of the surrounding gas, a chemical and physical fingerprint written along the jet’s path.

Detecting that fingerprint was far from straightforward. The glow of ionized hydrogen in the CGM, observed through a specific emission feature known as H-alpha, is so faint that no single galaxy could reveal it clearly. To overcome this limitation, the researchers combined observations of hundreds of galaxies with active jets, drawing optical data from the Dark Energy Spectroscopic Instrument, or DESI, survey and radio jet measurements from the LOFAR Two-meter Sky Survey, known as LoTSS. By stacking the signals from many galaxies and aligning them along the directions of their radio jets, the team could search for a coherent H-alpha signal that would otherwise remain buried in noise.

The result was striking. When the stacked signal was averaged over all directions around the galaxies, it was weak and inconclusive. But when the astronomers looked specifically along the axes of the radio jets, the H-alpha signal became clear and strong. This directional pattern demonstrates that the gas does not glow uniformly around these galaxies; instead, it shines most brightly precisely where the jets pass through it. The jet ionizes hydrogen gas along its trajectory, lighting up a trail that extends deep into the circumgalactic medium and providing direct evidence that black hole energy reaches and transforms gas at enormous distances from the galactic center.

The study also mapped where the glow was strongest, and the answer revealed two distinct hotspots. The ionized hydrogen emission peaked close to the galaxy, where the jet first slams into the circumgalactic medium, and again much farther out near the CGM’s outer edge, where the jet deposits most of its remaining energy. This double-peaked structure offers a clear physical signature of how jets interact with their surroundings as they bore outward, illuminating and disrupting gas all the way from the inner boundary of the CGM to its farthest reaches.

As a crucial check on their interpretation, the team examined a completely different tracer: the absorption signature of magnesium, which traces cooler gas in the same regions. Unlike the strongly directional H-alpha glow, the magnesium signal was distributed isotropically, appearing equally in all directions with no connection to the jet orientation. This contrast suggests that the cool gas reservoir already surrounds the galaxy uniformly on all sides, while the jet selectively brightens, heats, and ionizes gas only along its own path. In other words, the jets are not creating the reservoir, but they are actively transforming it, carving an energized channel through an otherwise symmetric halo of fuel.

These findings carry profound implications for how galaxies live and die. By heating, stirring, and disturbing gas throughout the circumgalactic medium, jets can prevent that gas from cooling down and falling inward to fuel new stars. The mechanism acts as a brake on galactic growth, throttling star formation and potentially pushing a galaxy from an active, star-forming state into quiescence. The black hole, in this picture, is not merely a passive engine feeding at the center of its galaxy; it reaches outward and reshapes the galaxy’s entire environment, and in doing so it helps determine whether the galaxy continues to build stars or fades into quiet retirement. This feedback loop may finally explain why galaxies have not converted their abundant surrounding gas into far more stars than observations show.

The directional nature of the discovery is itself a methodological breakthrough. Previous searches for this signal failed to detect it, and the new study suggests why: the signal only appears when observations are aligned with the jet direction. Had the team assumed the circumgalactic medium was identical in every direction, the effect would have been averaged away and lost forever. The work also underscores the growing power of large optical and radio surveys such as DESI and LoTSS, which allow astronomers to combine many weak signals into detections of galactic behavior that would otherwise remain hidden. For theorists and observers alike, the result opens a new way to test how black hole jets affect galaxies, and, as Borthakur noted, a new direction for exploring the intricate connection between supermassive black holes trillions of miles away and the conditions that made life on Earth possible. Co-authors on the study include Timothy Heckman of Johns Hopkins University and Tanmay Singh of Arizona State University, with support from NASA, the Space Telescope Science Institute, and the National Science Foundation.

Subject of Research: The directional impact of supermassive black hole jets on the circumgalactic medium and galaxy evolution

Article Title: ASU astronomers uncover black hole jets reaching far beyond their galaxies and deciding their fate

Article References: ASU astronomers uncover black hole jets reaching far beyond their galaxies and deciding their fate. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: supermassive black holes, black hole jets, circumgalactic medium, galaxy evolution, H-alpha emission, ionized gas, DESI survey, LOFAR, star formation, radio galaxies, astrophysics, galactic feedback

The scale of the computational challenge is staggering. Temperature contrasts in astrophysical multiphase systems span roughly ten orders of magnitude, and the cold gas, while dense, can be scattered in tiny structures across enormous volumes. Observations suggest cold clouds in the circumgalactic medium may be as small as tens of parsecs. To fully resolve such structures across a Milky Way-sized halo would require more than a quadrillion resolution elements, a number so vast that no supercomputer on Earth comes close. As a result, cold gas quantities in typical cosmological simulations remain unconverged, and researchers have had to resort to a hierarchy of idealized experiments, from turbulent mixing layers to cloud-crushing simulations, each isolating one piece of the physics.

One of the central results the review highlights concerns the survival of cold clouds blasted by hot winds, the classic ‘cloud crushing’ problem. In the absence of cooling, a cold cloud embedded in a supersonic wind is shredded by Kelvin-Helmholtz and Rayleigh-Taylor instabilities on a characteristic crushing time. Worse, the drag time needed to accelerate the cloud is far longer than the destruction time, giving rise to the long-standing ‘entrainment problem’: how can cold gas be flung to hundreds or even thousands of kilometers per second in galactic winds if it should be destroyed before it can accelerate? The answer, it turns out, lies in radiative cooling. When mixed gas at the interface cools faster than the cloud is disrupted, hot gas condenses onto the cold phase, allowing clouds not only to survive but to grow in mass as they are carried along.

This insight has been crystallized into a simple survival criterion: clouds endure if the cooling time of the mixed gas is shorter than their destruction time, which can be recast as a minimum cloud size of roughly a few parsecs under typical wind conditions. Simulations show that surviving clouds grow continuously through cooling-driven mass transfer in their turbulent wakes, and that this same mixing efficiently transfers momentum, accelerating even dense molecular clouds entrained in galactic outflows. Magnetic fields, once heralded as a potential savior of the entrainment problem, help but are not sufficient on their own for the high density contrasts typical of real astrophysical clouds; combined with cooling, however, they shift the survival threshold by orders of magnitude.

The review also delves into thermal instability, the classic mechanism by which a hot medium can spontaneously fragment into a cold, clumpy phase. When radiative cooling increases as temperature drops, small density perturbations run away into dense clumps. In stratified halo atmospheres, precipitation occurs when the ratio of cooling time to free-fall time falls below a critical value of order ten, a criterion modified by turbulence, halo rotation, magnetic fields and cosmic rays. A related and still contentious question is whether cooling clouds ‘shatter’ into a characteristic scale of tiny fragments or instead undergo a violent pulsation dubbed ‘splattering’ before fragmenting, with recent three-dimensional simulations tending to favor the latter picture.

Scaling up, the review surveys supernova-driven bubbles, stratified ‘tall box’ simulations of galaxy disks, and fully global models of dwarf and Milky Way-mass galaxies. A consistent picture emerges: most outflowing mass travels in the warm phase at around 10,000 Kelvin, while most of the energy is carried by the hot, million-degree gas. Hot gas mass loading factors hover near 0.1 across a wide range of star formation rates, and warm outflows in massive galaxies tend to fall back as fountain flows rather than escaping. Including cosmic rays transforms these results, converting fountains into steady, cooler, denser winds that can double the outflowing mass and substantially reshape the circumgalactic medium.

At the largest scales, the review examines how simulations handle the circumgalactic and intracluster media. In cluster cores, jets from supermassive black holes stir turbulence that triggers local thermal instability, producing ‘chaotic cold accretion’ in which cold filaments rain onto the central galaxy and feed the black hole in a self-regulating cycle. In cosmological zoom-in simulations, a recent revolution has come from ‘super-Lagrangian’ refinement schemes that boost resolution specifically in the halo, reaching below 100 parsecs in the circumgalactic medium. These enhanced-resolution models consistently show more and smaller cool clouds, higher covering fractions of cool gas, and non-converged cloud mass functions, confirming that cold gas structure in halo simulations is far from fully resolved.

What emerges most clearly from this comprehensive synthesis is that the diverse simulation approaches, from idealized mixing layers to full cosmological models, are not competitors but complementary layers of a single framework. Small-scale experiments provide the physical intuition, survival criteria and subgrid prescriptions that large-scale simulations need; large-scale simulations in turn supply the realistic boundary conditions, pressures and turbulence levels under which the small-scale physics operates. The ultimate arbiter, the authors stress, is observation, and connecting simulations to real spectra, emission maps and absorption measurements through radiative transfer remains one of the field’s most demanding tasks.

The challenges ahead are formidable: achieving numerical convergence in multiphase diagnostics, capturing the interplay of magnetic fields, conduction, viscosity and cosmic rays, and resolving the critical scales that govern whether cold gas survives, grows or shatters. But the trajectory is clear. GPU-accelerated codes, adaptive refinement targeted at cooling lengths, and a maturing theoretical framework are converging on a unified picture of the multiphase Universe, one simulation at a time.

Subject of Research: Numerical simulations of multiphase gas dynamics in the interstellar, circumgalactic and intracluster media

Article Title: Simulations of multi-phase gas in and around galaxies

Article References: Gronke, M., & Schneider, E. E. (2026). Simulations of multi-phase gas in and around galaxies. Living Reviews in Computational Astrophysics, 12(1), Article 2. https://doi.org/10.1007/s41115-026-00025-7

Image Credits: AI Generated

DOI: 10.1007/s41115-026-00025-7

Keywords: multiphase gas, galaxy simulations, circumgalactic medium, thermal instability, galactic winds, cloud crushing, turbulent mixing layers, computational astrophysics, radiative cooling, cosmic rays, supernova feedback, Kelvin-Helmholtz instability