Natsuki Funakoshi, Daisuke Kawata, Jason L. Sanders+5 more
AstronomerThe authors place Mira-based nuclear stellar disc (NSD) star-formation ages on the same scale as red-giant ages used to date Gaia-Sausage-Enceladus (GSE). They fit Gaia DR3 proper motions of 2394 O-rich disc Miras with a period-dependent, action-based quasi-isothermal distribution function, then match their vertical velocity dispersion–period relation to the APOGEE red-giant dispersion–age relation. The red-giant ages come from a Bayesian neural network trained on Kepler asteroseismic ages. The recalibration places the NSD star-formation rise and peak 8.5–10.5 Gyr ago, overlapping the final stage of the GSE-induced starburst, the thick-to-thin disc transition, and contraction of the star-forming gas disc. If NSD star formation traces bar formation, this temporal agreement supports a possible—not established—scenario in which GSE seeded the bar, while merger-supplied gas and tidally driven inflow increased the inner Galaxy's baryonic dominance.
PublicDid the Milky Way's last significant galaxy merger help create its central bar? Previous estimates used different kinds of stars to date the merger and the bar's possible formation, so their clocks could not be compared directly. This study uses stellar motions to recalibrate the ages inferred from Mira variable stars onto the age scale used for red giants. On that shared scale, star formation in the Milky Way's nuclear stellar disc rose and peaked 8.5–10.5 billion years ago, overlapping the final stage of a burst of star formation induced by the Gaia-Sausage-Enceladus merger and other changes in the Galactic disc. If the nuclear disc's star formation marks the bar's birth, the timing suggests that the merger may have helped start the bar's formation. The authors also propose that gas brought in or pushed inward by the merger made ordinary matter more dominant in the inner Galaxy. The timing does not establish that the merger caused the bar.
Young explorerOur Milky Way has a big group of stars shaped like a bar in its middle. Long ago, it joined with another galaxy. Did that help the bar begin? Scientists used stars as clocks, but first they had to make the different clocks agree. They found that many stars near the middle formed around the time of the galaxy joining. If those stars tell us when the bar began, the joining might have helped make it. That is a possible story, not something we know for sure.
Parth Mehrotra, Aaron Smith, Yuan Bian+13 more
AstronomerThis simulation study examines the timing of ionizing-photon production and Lyman-continuum (LyC) escape in thirteen z > 3 haloes from THESAN-ZOOM, post-processed with COLT radiative transfer at approximately 10 Myr intervals. The clearest delayed association is between SFR10/SFR100 and LyC escape fraction. Selecting the nearest positive cross-correlation peak yields typical lags of about 16 Myr and peak correlations of 0.4–0.6 in massive haloes; lower-mass systems show longer, less coherent delays. Fitted delays scale approximately as stellar mass to the power −0.19 and halo mass to the power −0.27, but the shortest lags approach the snapshot spacing. Recurrent variability spans multiple amplitude-dependent timescales, consistent with repeated star-formation and feedback episodes. Recent star formation closely tracks intrinsic and escaping photon rates, whereas escape fraction reflects evolving gas transparency. The simulated Hα-to-UV luminosity ratio retains a delayed association with escape, offering a potential observable link between burst phase and leakage. High transparency during a fading phase can still produce little escaping radiation: the overlap between photon production and transmission, rather than escape fraction alone, shapes the ionizing output relevant to interpreting observed leakers and cosmic reionization.
PublicComputer simulations suggest that a galaxy’s ability to let ionizing light escape depends on timing, not just on how transparent its gas becomes. The researchers studied thirteen simulated galaxies in the early universe. In the more massive systems, changes in a measure of recent star formation were most clearly linked to changes in the escaping fraction of ionizing light after a typical delay of about 16 million years. Smaller systems showed longer and less consistent delays, and the shortest delays were close to the simulations’ time resolution. The findings are consistent with young stars helping clear escape routes through surrounding gas as the stars’ light output fades. Open routes therefore do not necessarily mean much light escapes. A simulated relationship involving hydrogen-line and ultraviolet brightness offers a possible way to connect observations to this timing. These results may help interpret galaxies’ contributions to cosmic reionization.
Young explorerIn computer-made galaxies, scientists explored how light gets past gas around stars. Stars can help open paths through the gas, but by then they may be making less light. So even a wide-open path might let only a little light out. The study suggests that both things must happen together: stars need to make lots of light while the paths are open.
M. Gliozzi, L. Spinoglio, J. A. Fernandez-Ontiveros+4 more
AstronomerThis study tests whether the inactive-galaxy M-sigma relation applies to local AGN, with implications for reverberation-mapping calibration and indirect black hole mass estimates. Using the representative, largely unbiased 12 micron AGN sample, spanning Seyfert 1, Seyfert 2, and hidden broad-line region galaxies (HBLRs), the authors estimate black hole masses with the X-ray scaling method using available good-quality NuSTAR data. This method applies to AGN accreting at moderate or high levels. They find an AGN M-sigma relation that differs from the inactive-galaxy relation and exhibits substantial scatter, limiting its predictive power for black hole mass estimation. The sample's MBH-Mgal relation is consistent with that of a large nearby type 1 AGN sample but inconsistent with the inactive-galaxy relation. Evidence that Seyfert 1 galaxies and HBLRs have similar, systematically higher Eddington ratios than Seyfert 2 galaxies is suggestive rather than conclusive.
PublicAstronomers often estimate the masses of black holes in active galaxies using a relationship established in inactive galaxies. This study tests whether that approach is reliable. The researchers used a local sample selected at a wavelength of 12 microns and estimated black hole masses from X-ray data with a method suited to moderately or highly accreting black holes. They found that the active galaxies follow a different mass relationship, with considerable scatter, making it a fairly limited mass predictor. A second relationship, between black hole mass and galaxy mass, also differs from that in inactive galaxies but agrees with another active-galaxy sample. There are tentative signs that two categories of active galaxies feed their black holes at higher rates relative to their Eddington limits than a third category.
Young explorerScientists use clues from galaxies to guess how heavy their black holes are. They checked whether a rule made from quiet galaxies also works for galaxies with black holes that are feeding. Using X-ray clues, they found that the feeding galaxies did not follow the same rule very well. So that rule may not give very good guesses for these black holes.
Noah S. J. Rogers, Evan D. Skillman, Richard W. Pogge+7 more
AstronomerUsing optical spectra from the Large Binocular Telescope Primordial He Abundance Project, the authors derive gas-phase N, O, Ne, S, Cl, Ar, K, and Fe abundance patterns in 62 low-metallicity nebulae. They assess ionization correction factors and select those that reproduce the observed ionic abundance trends. Ne/O, S/O, and Ar/O show no metallicity dependence and agree with solar ratios. Given Type Ia enrichment of S and Ar, the authors interpret the solar S/O and Ar/O as evidence for more extended star formation histories in local galaxies than in high-redshift galaxies at fixed O/H. They report the first ISM K abundances in low-metallicity extragalactic nebulae; constant Cl/O and K/O suggest production that tracks alpha elements. Gas-phase Fe/O decreases with O/H, attributed to dust depletion. Correcting for depletion gives an average [Fe/O] of -0.80, which the authors interpret as implying Fe-deficient stars capable of hard ionizing spectra. For 50 nebulae, the metallicity-insensitive log(N/O) plateau is -1.43 ± 0.10, consistent with previous work. Five galaxies show significantly enhanced N/O; possible measurement biases and nucleosynthetic sources are discussed rather than uniquely established.
PublicAstronomers analyzed light from 62 glowing gas clouds with low abundances of elements heavier than helium, using observations from a project designed to measure primordial helium. They measured several elements and found that neon, sulfur, and argon maintain roughly constant proportions relative to oxygen, matching the Sun’s ratios. The authors interpret the sulfur and argon results as suggesting that nearby galaxies formed stars over more extended periods than distant, high-redshift galaxies with the same oxygen abundance. They also report the first interstellar potassium abundance measurements in this class of gas cloud. Potassium and chlorine track oxygen, suggesting linked production histories. Iron in the gas becomes relatively scarcer as oxygen abundance rises, which the authors attribute to iron being locked into dust. After correction, the low iron abundance suggests stars capable of producing strongly ionizing light. Nitrogen generally follows a common pattern, but five galaxies have unusually high nitrogen-to-oxygen ratios. The authors discuss both possible sources of extra nitrogen and ways measurements could be biased.
Young explorerScientists studied light from 62 glowing clouds in space to learn what they are made of. Some ingredients stayed in similar proportions, but five galaxies had more nitrogen compared with oxygen than the usual pattern. The scientists also measured potassium in this kind of cloud for the first time. They think dust hides some iron, and they are exploring why some galaxies look different.
F. Duplancic, M. Siudek, D. Navarro-Gironés+21 more
AstronomerUsing PAUS photometric redshifts, the study examines the association between galaxy interactions and AGN activity to z ≈ 1. The authors identify 16,824 galaxy pairs with projected separations below 100 kpc and radial-velocity differences below 3,500 km/s. Cross-matching with multi-wavelength AGN catalogues yields 270 AGNs in pairs from a parent sample of 8,880 AGNs. Controls are matched in redshift, absolute magnitude, and environment. AGNs in pairs exhibit progressively redder rest-frame colours with increasing redshift, especially at z ≳ 0.5; isolated AGNs and non-AGNs in pairs show no significant colour evolution, remaining near Mg − Mr ≈ 0.65. AGN-hosting pairs preferentially show disturbed morphologies, smaller projected separations, and smaller velocity offsets, consistent with more dynamically advanced interactions. These observational associations suggest an increasingly important role for interactions in triggering nuclear activity at intermediate redshifts, but do not establish a causal connection.
PublicResearchers used the Physics of the Accelerating Universe Survey to investigate whether close galaxy encounters are linked to active galactic nuclei, unusually active central regions of galaxies. They identified 16,824 galaxy pairs, including 270 active nuclei, and compared them with carefully matched control groups. Galaxies with active nuclei in pairs had progressively redder intrinsic colours at higher redshifts, unlike isolated active galaxies and paired galaxies without active nuclei. Pairs containing active nuclei also tended to look disturbed and have smaller separations and velocity differences. These findings suggest that galaxy interactions may become more important in triggering central activity at intermediate redshifts. They show an association, not proof that encounters cause the activity.
Young explorerSome galaxies have very busy centers. Scientists studied galaxies that are close together and found that pairs with busy centers often looked jumbled. Their colours were also redder in the more distant groups they studied. The scientists think galaxy encounters might help wake up those centers, but they have not proved it.
Marshall Hobson-Ritz, Sarv Parteek Singh, Eddie Schlafly+2 more
AstronomerThe study measures the extinction-curve shape parameter R(V) in nine nearby dense molecular clouds using APOGEE spectroscopy and ten-band PS1, 2MASS, and WISE photometry. Most clouds exhibit a positive R(V)–E(B-V) correlation, with substantial cloud-to-cloud variation in its strength. Clouds with the strongest correlations tend to show large R(V) dispersion at fixed E(B-V); this dispersion decreases dramatically when the clouds are divided into separate regions. The authors interpret this regional dependence as evidence that local environmental conditions beyond density influence the R(V)–E(B-V) relation, rather than identifying a specific physical driver.
PublicDust blocks some colors of starlight more strongly than others, and this pattern offers clues about the sizes of dust grains. Researchers measured how that pattern varies in nine nearby dense clouds of molecular gas. In most clouds, the pattern's shape parameter increases as the dust-induced reddening increases, but the strength of this relationship differs considerably between clouds. Clouds with the strongest relationships also tend to show a wide range of shape values at the same reddening. That spread shrinks dramatically when individual regions are considered separately. The findings suggest that local conditions beyond density help shape dust's effect on starlight, but do not establish which conditions are responsible.
Young explorerSpace has dusty clouds that change the colors of light shining through them. Scientists studied nine nearby clouds. In most, the way dust changed the light was linked to how much redder the light looked, but each cloud behaved differently. Some clouds seemed especially mixed up until the scientists looked at smaller parts separately. Those parts behaved more alike. This suggests that what happens in each part of a cloud matters, not just how crowded it is.
Andrés E. Piatti
AstronomerA direct cross-match of optical Gaia-ESO DR5 and near-infrared SDSS-V/MWM DR19 measurements finds close one-to-one agreement in atmospheric parameters and Ce abundances, but an X-shaped stretching of the Nd abundance scale. The authors infer that the SDSS-V pipeline amplifies intrinsic Nd variations by a factor of 5.54 relative to the optical baseline. They attribute this to continuum depression by CN and CO molecular line blanketing in the APOGEE H-band at high metallicity, which drives the chi-squared fitting procedure toward inflated abundances. Their empirical calibration removes the previously reported negative radial [Nd/Fe] gradient of -0.052 dex/kpc in NIR surveys and brings it into agreement with rising optical trends. The study interprets the Nd scale expansion as a spectroscopic artefact rather than a physical Galactic trend.
PublicTwo surveys measuring the chemical makeup of stars agree well on stellar properties and cerium, but disagree on neodymium. Comparing stars observed by both surveys, the researchers find that the near-infrared analysis exaggerates neodymium differences by a factor of 5.54 relative to the optical measurements. They attribute the mismatch to crowded molecular absorption features that lower the apparent background light level in stars richer in heavy elements, misleading the abundance-fitting software. The team provides an empirical correction that removes a previously reported decrease in neodymium relative to iron with Galactic radius, bringing the infrared results into agreement with the increasing trends found in optical data. They conclude that the conflicting trend comes from the measurement analysis, not the Galaxy itself.
Young explorerScientists used two kinds of starlight to work out what stars are made of. For one ingredient, called neodymium, one method made the differences between stars look too big. The scientists say crowded marks in the light confused the computer. Their correction made the two methods agree better about how this ingredient changes across our galaxy.
Nicholas Clark, Els Peeters, Jan Cami+29 more
AstronomerJWST MIRI IFU spectroscopy pointed at the central source of the oxygen-rich planetary nebula NGC 6302 yields four template spectra representing spatial variations in PAH emission. Major bands at 6.2, 7.7, 8.6, 11.2, and 12.7 micrometres, along with several minor features, vary in width, peak wavelength, and relative intensity. The 11.2-micrometre band is class B, typical of planetary nebulae, whereas the 6–9-micrometre bands are class A, less common in these objects. The 7.7/11.2 band ratio implies an estimated mean cation fraction of 75%, and the 11–15-micrometre features indicate diverse PAH edge structures. To explain the spectral variations, the authors propose spatial differences in PAH size, ranging from large and non-compact to small and compact, and suggest differences in shielding. They conclude that PAHs formed in situ during the current planetary-nebula phase, likely from small hydrocarbons produced through CO photodissociation; this formation pathway is an interpretation of the observations rather than a directly observed process.
PublicCarbon-based molecules called polycyclic aromatic hydrocarbons, or PAHs, occur in oxygen-rich planetary nebulae, but how they form and change there remains uncertain. Using infrared spectra from JWST, researchers mapped differences in PAH emission in the planetary nebula NGC 6302. They detected several characteristic molecular signatures whose shapes, wavelengths, and relative strengths vary across the observed region. From these signatures, they estimate that about 75% of the PAHs carry a positive electric charge, on average. They propose that differences in molecular size, shape, and protection from radiation help explain the changing signatures. The authors conclude that the PAHs formed within the nebula during its current phase, probably from smaller hydrocarbons originating when light broke apart carbon monoxide. This chemical pathway is inferred, not directly witnessed.
Young explorerScientists used the Webb telescope to study a cloud in space called NGC 6302. They found signs of tiny molecules made with carbon. The molecules give off different patterns of light in different parts of the cloud. The scientists think some molecules are bigger than others, and some may be better protected from strong light. They also think these molecules were made inside the cloud from smaller pieces, but they did not watch that happen.
Reace H. J. Willis, Vincent J. Esposito, Thomas H. Speak+2 more
AstronomerQuantum chemical calculations identify a thermodynamically viable, barrierless, low-temperature gas-phase pathway from cyclopropenylidene (c-C3H2) and the CP radical to phosphaethynyl cyclopropenylidene (c-C3HCP). Both reactants have been detected toward circumstellar shells, motivating searches for the proposed product in phosphorus-rich environments; the abstract reports no detection of the product. Calculations also explore CP + benzene formation of C6H5CP, but a tentative transition state appears with some methods and not others, leaving barrierless synthesis and broader CP substitution of benzoid PAHs uncertain. The study provides coupled-cluster quartic-force-field and second-order vibrational-perturbation rovibrational predictions for c-C3HCP, plus density-functional predictions for CP-benzene and both CP-naphthalene isomers. Predicted weak infrared intensities and overlap with PAH features disfavor IR searches, whereas large dipole moments suggest possible radio detectability.
PublicComputer calculations suggest that two molecules already detected in shells around stars—cyclopropenylidene and the phosphorus-containing CP radical—could react in cold gas to make a molecule called phosphaethynyl cyclopropenylidene. The calculations indicate that this reaction needs no energy barrier to be crossed, but the new molecule has not been reported as detected here. A related reaction involving benzene is less certain: different calculation methods disagree about whether a small barrier exists. The researchers also predict spectral signatures for several related molecules. Their infrared signals would probably be weak and hard to distinguish from other aromatic molecules, while their electrical properties may make radio searches more promising.
Young explorerScientists used computers to work out how tiny bits of matter might join together in cold space to make a new molecule. The starting pieces have been found around stars, but this study does not say the new molecule has been found. Another way of making a related molecule is still uncertain because the computer methods did not all agree. The scientists think looking for radio signals from these molecules might work better than looking for their infrared light.
Jiaqi Lin, Zhenya Zheng, Bin Ma+2 more
AstronomerThe study compares rest-frame ultraviolet variability in 11 type 1 quasars in the Cosmic Himalayas overdensity at z=2.16–2.20 with controls matched in black hole mass and Eddington ratio, drawn from 1,138 Stripe 82 quasars at 2.11≤z≤2.25. Combined SDSS, PS1, and ZTF g- and r-band light curves span up to 27 observer-frame years. The overdensity quasars tend toward shorter damped random walk (DRW) damping timescales, with median offsets of −0.32 dex in g and −0.13 dex in r, and slightly larger asymptotic amplitudes. None of the four DRW comparisons is statistically significant; the largest timescale offset has p=0.16. Ensemble structure functions generally exceed control medians, but 18 of 19 lag bins in each band remain within the 95% pointwise envelopes. Injection–recovery simulations predict an 80% probability of nominal 3σ detection with approximately 60 quasars, conditional on a true uniform −0.32 dex g-band timescale offset and comparable variability scatter and data. Environmental effects on accretion-flow variability remain tentative and require larger samples and higher-precision light curves, such as those expected from LSST.
PublicDoes living in a crowded cosmic neighborhood change how a quasar flickers? Researchers studied 11 quasars—bright sources powered by gas accreting onto supermassive black holes—in an extreme concentration called the Cosmic Himalayas. Using brightness records spanning up to 27 years, they compared these objects with quasars of similar redshift, black hole mass, and relative accretion rate. The crowded-region quasars showed hints of faster and slightly stronger brightness variations, but the evidence was not statistically convincing. Simulations suggest that roughly 60 quasars with comparable data could offer a strong test if the assumed difference is real; they do not establish that such a difference exists. Larger, more precise studies are needed to determine whether cosmic environment affects quasar flickering.
Young explorerGas near giant black holes can shine very brightly and change how bright it looks. Scientists watched 11 of these bright lights in a crowded part of space and compared them with similar ones. The crowded lights seemed to flicker a little differently, but the scientists cannot yet tell whether that is a real difference or just chance. They need to watch more of them more carefully to find out.
Tiancheng Sun, Maosheng Xiang, Jifeng Liu+2 more
AstronomerThe study reconstructs the high-alpha disk’s age–metallicity distribution using approximately 145,000 Gaia DR3 subgiants with [Fe/H] > -1, galactocentric radii of approximately 6.5–9.5 kpc, and absolute vertical distances from the disk plane of approximately 1.5 kpc or less. Forward modelling accounts for individual age and metallicity uncertainties and corrects for sample selection. The reconstructed distribution contains a broad, dominant component peaking near 10.6 Gyr and [Fe/H] = -0.38, and an older, more metal-poor component peaking near 12.4 Gyr and [Fe/H] = -0.79. These findings favour episodic star formation and enrichment over a single temporally smooth phase within the sampled regime. This interpretation is qualitatively consistent with cosmological simulations in which recurrent gas accretion modulates star formation, but does not establish that mechanism. The older component’s age is close to the approximately 12.3 Gyr epoch inferred for the proposed Low-energy–Kraken–Heracles accretion event, suggesting only a possible connection. Evidence that the dominant component splits into populations peaking near 11.1 and 10.0 Gyr is tentative.
PublicDid the Milky Way’s high-alpha disk form stars steadily, or in repeated episodes? Researchers examined approximately 145,000 subgiant stars from Gaia DR3, accounting for uncertainties in their ages and iron abundances and correcting for how stars entered the sample. The sample covers distances of approximately 6.5–9.5 kiloparsecs from the Galactic center, heights of approximately 1.5 kiloparsecs or less from the disk plane, and iron abundances above [Fe/H] = -1. The reconstructed distribution shows a broad, dominant group whose ages peak near 10.6 billion years and whose iron abundances peak near [Fe/H] = -0.38, plus an older, more iron-poor group peaking near 12.4 billion years and [Fe/H] = -0.79. This supports repeated episodes of stronger star formation rather than one smooth phase. Simulations offer a possible explanation: repeated arrivals of gas can change the rate of star formation. The older group also falls close in age to a proposed galactic accretion event, Low-energy–Kraken–Heracles, dated to about 12.3 billion years ago, but a connection is not established. There are tentative hints that the dominant group contains two smaller groups with age peaks near 11.1 and 10.0 billion years.
Young explorerScientists studied about 145,000 stars in a part of our galaxy to ask whether stars were made steadily or in several busy times. After allowing for uncertainty in the stars’ ages and iron content, they found signs of two groups. The bigger group’s ages bunch up around 10.6 billion years, and an older group with less iron bunches up around 12.4 billion years. This suggests there were several busy times of making stars, but it does not prove exactly what caused them. Computer models show that gas arriving again and again could help. A proposed event in which the galaxy took in material about 12.3 billion years ago might be connected to the older group, but scientists are not sure. There are also uncertain hints that the bigger group has two parts, with ages bunching up around 11.1 and 10.0 billion years.
Zack Freeman, Maximilian Häberle, Anil Seth+11 more
AstronomerThe authors search for stellar-mass black holes in Omega Centauri through microlensing of cluster stars, using nearly 200 single-band Hubble Space Telescope images spanning 13 years. They target events expected to last roughly one year, develop a new lensing-fit cost function, and assess detection completeness with synthetic events based on a recent Monte Carlo simulation of the cluster. These synthetic events also train a neural network for candidate selection. Application to the observations, followed by visual inspection, yields no convincing black hole microlensing candidates. Unlike earlier expectations, the simulation-based event analysis and measured completeness indicate that no detectable events would be expected in this dataset. The null result therefore does not establish an absence of black holes. The photometric dataset is released for future use.
PublicResearchers searched for black holes left behind by massive stars in Omega Centauri, the Milky Way’s most massive star cluster. They looked for microlensing: a black hole’s gravity temporarily magnifying the light of a cluster star. Using nearly 200 Hubble Space Telescope images collected over 13 years, they searched for signals expected to last about a year. They tested their search method and trained a neural network with artificial events based on a computer simulation of the cluster. The observations and follow-up visual checks revealed no convincing black hole lensing events. Importantly, their simulation-based analysis suggests that this dataset was not expected to yield any detectable events, contrary to earlier expectations. Finding none therefore does not mean the cluster has no black holes. The team has made its brightness measurements available for future research.
Young explorerScientists looked for black holes in a big group of stars called Omega Centauri. A black hole’s gravity can make a star look brighter for a while, like a hidden magnifying glass. The scientists searched through pictures taken by the Hubble Space Telescope over 13 years, but found no clear signs of this happening. They also used a computer to make pretend events and test their search. Those tests suggested they should not expect to spot any in these pictures, so finding none does not mean there are no black holes there.
Karan Akbari, Sayantan Bhattacharya
AstronomerThis signal-injection study tests Lomb–Scargle recovery efficiencies for periodic supermassive black hole binary searches over four decades in mass, using mergers from TNG100-1 and sinusoidal or sawtooth signals. Quasar magnitudes are assigned from mass-matched DR7 objects, with extrapolation at low mass. The authors apply the earlier study’s frequency-bin thresholds, calibrated with 100,000 noise-only light curves per binary, using observed PTF cadences, one Stripe 82 cadence, and an LSST-like cadence. Brightness assignment reverses the inferred mass trend: sinusoid recovery declines toward high mass at fixed absolute magnitude Mi = −23, but rises above approximately 100 million solar masses with DR7-based magnitudes. Above that mass, PTF sinusoid recovery is 39.8%, versus the earlier 44.7%; LSST-like recovery is 76.9%, versus 22.6%, with the discrepancy mostly unexplained. Denser sampling over unchanged PTF baselines never reduced recovery in the tests. Most high-mass sawtooth signals remain undetected even with LSST-like sampling. These are simulated recovery fractions, not binary detections; tabulated low-mass efficiencies are likely too high for a deeper survey.
PublicHow often would a search recognize the repeating brightness changes that might signal a pair of supermassive black holes? The researchers tested this by adding artificial repeating signals to light curves based on simulated mergers, then checking whether a search method recovered them. The assumed quasar brightness strongly changed how recovery depended on black hole mass. For smooth signals above about 100 million solar masses, recovery with PTF observing times was 39.8%, close to an earlier estimate of 44.7%. With LSST-like observing times, recovery reached 76.9%, much higher than the earlier 22.6%, for mostly unexplained reasons. Most high-mass sawtooth-shaped signals were still missed. These tests do not establish actual binary discoveries, and their low-mass recovery estimates are probably too optimistic for a deeper survey.
Young explorerScientists put pretend repeating flickers into computer-made stories of bright objects in space. Then they checked whether a computer could spot them. It found many smooth flickers but missed most jagged ones in some tests. How bright they made the objects mattered a lot. This was practice, not a discovery of real black hole pairs.
Scott M. Croom, Rebecca McElroy, Dougal Dobie+6 more
AstronomerSDSS and SAMI data establish at least one full changing-look cycle in the AGN of J085337.26+014303.6 at z=0.0582: type 1.9 in 2001, type 1 in 2015 and 2021, and type 1.9 again in 2022. Although the broad lines show dust obscuration, spectral analysis and WISE photometry indicate that the transitions reflect a physical state change rather than variable obscuration. The WISE light curve suggests, but does not establish, a brief return to type 1.9 in 2020. Host light dominates the optical even in the high state, with the AGN contributing only about 10% at 4000 angstroms within a central aperture; the brightest W2 measurements instead place the AGN at a luminosity similar to that of the entire host. Broad Balmer profiles show evidence for a weak, very broad component with FWHM 5000–6000 km/s in the low state and a stronger component with FWHM about 2000 km/s dominating the high state. Two spatially distinct broad-line regions are proposed to explain these components, rather than established by the observations.
PublicThe active center of galaxy J085337.26+014303.6 has changed its spectral appearance and then changed back. Observations show one state in 2001, a different state in 2015 and 2021, and a return to the earlier state in 2022. Infrared measurements hint at another brief return in 2020, but that episode is uncertain. Although dust obscures some of the emitted light, the analysis points to a real change in the active center’s physical state, not simply more or less dust blocking our view. The surrounding galaxy dominates the visible light even when the center is in its high state, whereas at its brightest in the measured infrared band the active center rivals the whole galaxy. The researchers also find evidence for two components in broad hydrogen emission lines. They propose that these arise in two separate regions of the line-emitting gas, but this explanation is not yet established.
Young explorerA galaxy has a busy center whose light changed and then changed back. Scientists found that this really happened at least once, and they think it may have happened briefly another time too. Dust hides some light, but the changes seem to come from the center itself, not from dust moving in front of it. The light also has clues that glowing gas may be in two separate places near the center. That is an idea the scientists suggest, not something they know for sure.
Jozsef Vinko, Eniko Regos, Krisztian Sarneczky
AstronomerThe study estimates the expected numbers of very young supernovae in different substructures and galaxy types of the Virgo cluster, at a distance of approximately 16.5 Mpc, over the proposed roughly 10-year lifetime of the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST). It anticipates that wide, deep, high-cadence surveys will substantially increase opportunities to discover nearby cluster transients within hours of explosion. These are predictions, not reported detections; the abstract gives no numerical supernova yields. Observational tests are planned through the ongoing University of Arizona-led Shadow-LSST discovery and follow-up program.
PublicThe researchers estimate how many newly exploded stars could be found in different parts of the Virgo galaxy cluster and in different types of galaxies during the proposed roughly 10-year LSST sky survey at the Vera Rubin Observatory. Virgo is about 16.5 million parsecs away. Surveys that cover large areas, detect faint objects, and revisit the sky frequently are expected to make it easier to catch stellar explosions within hours of their onset. The abstract does not report discoveries or give the predicted totals. The team plans to test its predictions with observations from the ongoing University of Arizona-led Shadow-LSST program.
Young explorerStars sometimes explode. The scientists are working out how many very new star explosions a planned sky survey might find in a big group of galaxies called Virgo. Looking at lots of sky again and again could help catch some explosions just hours after they happen. These are guesses about what scientists might find, not explosions they say they have already found. They plan to check their guesses by watching the sky.
Daniel Giovanni Vargas, Darío Barreiro-Lage, Carlos Cabezas+2 more
AstronomerThe authors develop a natural-language-processing pipeline linking chemical-string representations of molecules to column densities in TMC-1. Astrochemically informed embeddings feed a neural-network regressor applied to inventory molecules and out-of-distribution species. Reported mean squared errors are 0.17/0.58, mean absolute errors 0.29/0.59, and coefficients of determination 0.88/0.51 for the train+validation and validation datasets, respectively; the abstract does not specify the numerical scale of the regression targets. The authors interpret the latent vectors as encoding chemical relationships and potential interstellar detectability. Applying them to systematic permutations of the TMC-1 inventory identifies candidates for future detection, alongside many apolar species, not new observational detections. Models trained on inventories representing different historical epochs suggest that recent detections have transformed, rather than incrementally refined, the inferred picture of interstellar chemistry. The representations are proposed as a foundation for further data-driven astrochemical exploration.
PublicThis study uses machine learning to explore which molecules might be found in the interstellar cloud TMC-1. The model learns connections between molecular structures and column densities, a measure of how much of a molecule lies along a line of sight. It then predicts abundance trends for molecules within and beyond its training inventory and suggests candidates for future searches. These suggestions are predictions, not newly detected molecules. By comparing models trained on molecular inventories from different historical periods, the researchers conclude that recent discoveries have substantially changed the picture of chemistry in this cloud. They propose that the model's mathematical representations could help guide future exploration.
Young explorerScientists taught a computer to look for patterns in the molecules already found in a cloud in space. Molecules are tiny groups of atoms. The computer suggested other molecules scientists could look for next. Those are guesses to check, not new things scientists have found yet.
Naira R. Arakelyan, Sergey V. Pilipenko, Stefan Gottlöber+3 more
AstronomerIn the HESTIA simulations, approximately one-quarter of Milky Way or M31 analogues show a change greater than 45° in their gaseous disk rotation-axis orientation over the last 6 Gyr. Satellite accretion is the likely cause in six of seven cases; the connection is unclear in the remaining case. All galaxies with such reorientations had angular momentum amplitudes below the sample median 6 Gyr ago. The authors interpret these simulation findings as supporting a quiet evolutionary phase for the Local Group over the last 6 Gyr. They also suggest that satellite-driven reorientation could explain difficulties in identifying correlations between galaxy rotation axes and the orientation of large-scale structure.
PublicComputer simulations of galaxies resembling the Milky Way or Andromeda suggest that a galaxy’s gas disk can substantially change the direction of its spin. About one-quarter of the simulated galaxies shifted their spin axes by more than 45 degrees during the past 6 billion years. In six of seven cases, taking in a smaller satellite galaxy was the likely cause, though the link was unclear in one case. Every galaxy with a large shift had started that period with less angular momentum than the sample’s middle value. The authors interpret the findings as supporting a relatively quiet recent history for our Local Group of galaxies. They also suggest that these shifts could help explain why links between galaxy spin directions and surrounding large-scale structures are difficult to identify. These are simulation findings, not direct observations of such changes.
Young explorerScientists used computers to make pretend galaxies like our Milky Way and its neighbor Andromeda. About one in four had a big change in the direction its gas disk was spinning over billions of years. In most of those cases, the scientists think taking in a smaller galaxy caused the change, but they are not sure about every case. These computer galaxies may help explain why real galaxies do not always spin in directions that clearly match the huge patterns around them.
Lin-Na Xu, Ning Jiang, Tinggui Wang+15 more
AstronomerEP J062132.0+623837 was discovered in 14-day-binned Einstein Probe Wide-field X-ray Telescope survey data and localized by EP/FXT to the central region of 2MASX J06213207+6238390 at z=0.084. During FXT and Swift/XRT follow-up, its observed X-ray luminosity was (3–9) × 10^43 erg s^-1, with power-law spectra having photon indices Γ ≈ 1.5. Relative to an archival spectrum obtained four years earlier, enhanced broad Balmer emission marks a changing-look transition from Type 1.8 to Type 1.5. Optical and mid-infrared light curves show dramatic nuclear brightening around 2010 and substantial subsequent variability. The authors identify the source as a changing-look AGN on the basis of its spatial coincidence and multi-wavelength behavior, and highlight wide-field time-domain X-ray surveys as a promising complement to optical searches.
PublicAstronomers have identified a changing-look active galactic nucleus—a galaxy’s active central region whose spectral appearance has changed. Einstein Probe first detected the X-ray source EP J062132.0+623837, and follow-up observations placed it near the center of its host galaxy. An optical spectrum showed much stronger broad hydrogen emission lines than a spectrum taken four years earlier, establishing a change in its classification. Longer-term visible-light and infrared records also show strong brightening around 2010 followed by substantial variability. Together, these observations led the researchers to identify the X-ray source as a changing-look active nucleus. The study highlights the promise of repeated wide-field X-ray surveys for finding more such objects alongside optical surveys.
Young explorerScientists found a source of X-rays in the middle of a galaxy. They also looked at its light and compared it with an older observation. Some marks in the light had grown much stronger, showing that the galaxy’s busy center had changed its appearance. Older records showed that the center had become much brighter and kept changing in brightness. The scientists think watching large areas of the sky in X-rays could help them find more changing galaxy centers.
Yang Cheng, Morgan Fouesneau, Ivelina G. Momcheva+2 more
AstronomerThe authors report stellar-mass inference from sparse JWST observations using a self-supervised multimodal model trained on single-band F150W images paired with observed-frame 1–2 μm PRISM spectra. For galaxies at 1 < z ≤ 3, the joint image-spectrum representation achieves R² ≈ 0.9 and σ_NMAD = 0.24 dex, without the multi-band coverage required by traditional SED fitting. Cross-modal CLIP alignment improves single-modality performance by ΔR² = +0.04 for imaging and +0.09 for spectroscopy, narrowing but not eliminating the gap to joint-modality inference. Code and documentation are available on GitHub.
PublicResearchers report an AI method for estimating the total mass of stars in distant galaxies from limited JWST observations. Instead of requiring images in many wavelength bands, as traditional methods do, it learns from a single-band image paired with a spectrum, which separates the galaxy’s light by wavelength. Using both types of observation gives better estimates than using either alone, though the estimates still have scatter. A training technique that links images and spectra also improves performance when only one type of observation is used. The reported results apply to galaxies in the study’s redshift range of 1 < z ≤ 3.
Young explorerHow much do all the stars in a faraway galaxy weigh together? Researchers taught a computer to make a guess using a galaxy picture and its light sorted into different colors. Together, these clues helped it make better guesses than either clue alone. The guesses are not perfect, but the method can help when only a little information about a galaxy is available.
Qiaoya Wu, Yue Shen
AstronomerThis DESI DR1 value-added catalog characterizes 1,717,774 unique quasars across 1,774,723 spectra. Uniform spectral decomposition separates the continuum, host-galaxy emission at z<1, and Fe II emission, with measurements of major broad and narrow lines from Lyα to Hα where covered. Derived quantities include single-epoch black hole mass estimates from Hβ, Mg II, and C IV, bolometric luminosities, and Eddington ratios. Systemic redshifts account for intrinsic line-velocity shifts and agree with pipeline redshifts within 500 km s−1 for 88.6% of the sample; they are especially useful at z>1, where blueshifted high-ionization lines strongly constrain pipeline redshifts. Local fits also characterize several optical coronal lines. The authors find systematic variation of several emission-line ratios, including coronal-line ratios, with Eddington ratio. The catalog is intended to support studies of quasar populations, accretion, emission-line physics, and connections among broad-, coronal-, and narrow-line regions.
PublicResearchers have assembled a catalog describing the light from more than 1.7 million quasars in the first data release of the Dark Energy Spectroscopic Instrument. They separate components of each spectrum and measure emission lines, providing estimates of black hole masses, total light output, and Eddington ratios, which characterize accretion relative to the black hole's Eddington limit. They also calculate redshifts that account for shifts intrinsic to individual emission lines. These agree with the survey pipeline's redshifts within a velocity difference of 500 kilometers per second for 88.6% of the sample and are particularly useful above redshift 1. The team finds that several ratios of emission-line strengths vary systematically with Eddington ratio, including ratios involving coronal lines. The catalog is a resource for investigating quasar populations and the physics of gas around black holes; its black hole masses are estimates rather than direct measurements.
Young explorerScientists made a huge list of more than a million bright objects in space called quasars. They studied the light from each one, looking at patterns that help them estimate things about its black hole. They found that some parts of the light pattern change together with an estimate of how the black hole is feeding. These estimates are not exact. Other scientists can use the list to learn more about quasars and the gas around their black holes.
Uzay Aydin, Mehmet Tanriver
AstronomerSpecLess is an open-source Python package using survey-specific XGBoost models to classify galaxies from broadband photometry, without spectroscopy at inference time. Its targets are high-confidence Galaxy Zoo 1 elliptical/spiral morphologies and four SDSS spectroscopic activity reference classes: starforming, starburst, Seyfert, and LINER. Held-out macro F1 scores reach 0.9332 for SDSS and 0.9237 for KiDS morphology, and 0.7637 for SDSS and 0.7398 for DESI activity. Starforming and starburst references are recovered more effectively than Seyfert and LINER; feature ablations indicate complementary optical and mid-infrared contributions. Tests on matched galaxies with identical labels and partitions isolate catalogue dependence: cross-survey macro F1 deficits relative to target-trained models are 0.0153–0.0354 for morphology and 0.0406–0.0660 for activity, depending on transfer direction. Colour-only refits, additive corrections, and optical–infrared substitutions do not consistently restore target-trained performance. Version 0.3.0 provides four pretrained survey-specific classifiers as a reproducible baseline, not a survey-independent solution.
PublicSpecLess is a free, open-source software package that sorts galaxies using brightness measurements in different wavelength bands, without needing a spectrum when classifying a new galaxy. It estimates whether galaxies are elliptical or spiral and assigns them to four activity categories defined using spectra. Tests show strong performance for galaxy shape, with more mixed success for activity categories. Crucially, models perform worse when transferred to another survey, even when tested on the same galaxies. The adjustments explored did not consistently remove this gap, so the released package provides separate models for different surveys rather than one universally transferable classifier.
Young explorerScientists made a computer tool that uses measurements of a galaxy’s light to help sort it into groups, such as spiral or oval-shaped galaxies. It does not always get the answer right. When the light measurements come from a different sky survey, the tool makes more mistakes than a version trained for that survey. The fixes scientists tried did not always solve this problem.
L. Bruno, B. Koribalski, R. P. Norris+7 more
AstronomerLOFAR, uGMRT, and MeerKAT observations of ORC J1555+2726 (ORC4) at 50–1284 MHz reveal frequency- and resolution-dependent morphology, with decreasing ring-to-interior brightness contrast toward lower frequencies. The measured integrated spectral slope is α = 1.06 ± 0.03, the 150 MHz radio power is (5.4 ± 0.5) × 10^25 W Hz−1, and the radial spectrum flattens to α ≈ 0.5 at the ring. Negative (convex) spectral curvature and the radio colour-colour behaviour imply flattening toward high frequencies, inconsistent with shock acceleration of thermal particles followed by standard ageing. The authors interpret these features as evidence for mixed electron spectra, likely produced by shock re-acceleration of a fossil relativistic population. Higher-energy re-accelerated electrons may dominate the ring, while lower-energy electrons may be distributed more uniformly throughout a possibly ellipsoidal volume; this physical picture remains an interpretation rather than an established formation mechanism.
PublicOdd radio circles are enormous sources beyond our galaxy, with bright radio rings, fainter interiors, and massive elliptical galaxies at their centres. Researchers studied one of them, ORC4, using three radio observatories. They found that the ring stands out less clearly at lower radio frequencies and that the radio spectrum flattens toward higher frequencies. These spectral features cannot be explained by a shock accelerating thermal particles followed by standard ageing. The researchers instead suggest that a shock has re-energized an old population of energetic electrons. In this interpretation, higher-energy electrons mainly produce the bright ring, while lower-energy electrons are spread more evenly through the source. The explanation is plausible, but the origin of ORC4 is not settled.
Young explorerScientists used radio telescopes to study a huge ring far beyond our galaxy. The ring has a faint glow inside, and it looks less different from its middle when they look at lower radio frequencies. They think a powerful shock might have given old, tiny particles called electrons a new boost, helping make the bright ring and the glow inside. That is a possible explanation, not something they know for sure.
Jia-Yuan Fang, Jian-Ming Yan, Zong-Kuan Guo
AstronomerThis simulation-based study forecasts constraints on Lorentz violation in the minimal pure-gravity Standard-Model Extension (SME) from Galactic-center stars S2 and S55. Simulated astrometry and spectroscopy use fiducial parameters based on the GRAVITY Collaboration’s multi-star solution, with trajectories incorporating leading Lorentz-violating two-body dynamics and the Schwarzschild 1PN correction. Separate Fisher analyses resolve seven of eight independent SME directions for each star; combining the differently oriented orbits resolves all eight by breaking geometrical degeneracies. MCMC confirms the Fisher forecasts, yielding characteristic 95% credible-level sensitivities of approximately 10^(-3)–10^(-2) for time-space components and 10^(-5)–10^(-4) for spatial components. These are forecast sensitivities from simulated data, not observational constraints or a detection of Lorentz violation.
PublicThe researchers used simulated observations of two stars, S2 and S55, near the center of our Galaxy to explore how their orbits could test possible departures from Lorentz symmetry in gravity. Their model allows gravitational effects that depend on direction. Each star alone leaves one combination of the model’s eight independent parameters unresolved, but analyzing both together distinguishes all eight because their orbits have different orientations. A second statistical analysis supports the predicted sensitivity. The study shows how combining differently oriented stellar orbits could improve such tests; it does not report evidence that Lorentz symmetry is violated.
Young explorerScientists made computer versions of two stars moving around the middle of our galaxy. They asked whether watching those stars could help test if gravity works differently in different directions. One pretend star alone could not untangle every clue, but using both stars’ differently tilted paths helped untangle them all. This was a computer test, not a discovery that gravity really behaves that way.
Igor Pavlov
AstronomerThis theoretical study applies nonlinear programming to constrained minima and local extrema of selected characteristics of a classical interacting N-body system in phase space. For nonzero total angular momentum, the authors prove that these extrema can occur only on planar trajectories, which need not be bounded. They then derive restrictions on angular momentum and total energy for bounded planar trajectories, described as circular or elliptical, that preserve the system’s planar structure over time, and determine key system characteristics on those trajectories. An appendix treats related results for a more general model. These are mathematical results, not observational findings.
PublicThis mathematical study examines how a system of interacting particles can move when certain system properties reach constrained minimum or other locally extreme values. The authors prove that, if the system has nonzero angular momentum, these special motions must stay in a single plane, although they need not remain within a limited region. They also work out conditions involving total energy and angular momentum that allow bounded, circular or elliptical planar motion while preserving the flat arrangement. The results concern a theoretical model, not observations of a particular astronomical system.
Young explorerImagine little dots moving and pulling on one another. The researchers used math to show that, under special rules, certain special ways of moving must fit on a flat sheet, even though the dots might travel very far. They also worked out rules for when the dots can stay in a limited space and keep their flat arrangement. This is a math result, not something they watched in the sky, and it does not mean all moving dots must stay flat.
Koti Joy, Unnikrishnan Sureshkumar, Anand Narayanan+4 more
AstronomerUsing two-point and marked correlation functions, this observational study examines environmental trends in galaxy properties in GAMA’s southern G02 and G23 regions, not previously studied in this context. Among the properties tested, u−r and g−r colors correlate most strongly with local overdensity, followed by stellar mass. Specific star formation rate decreases with environmental density, consistent with the trend in u-band luminosity, which traces young stellar populations. Galaxies brighter in g, J, and K preferentially occupy denser environments. Comparison with GAMA’s equatorial regions indicates that cosmic variance does not significantly alter these conclusions, whereas comparisons of G02 subsets show that redshift incompleteness affects clustering measurements. The correlations constrain galaxy assembly models; the authors propose environmental trends in color and near-infrared luminosity as tracers of stellar mass growth and quenching with redshift.
PublicGalaxies have different properties depending on how crowded their surroundings are. Using observations from two southern areas of the Galaxy and Mass Assembly survey, researchers found that galaxy color has the strongest connection to local crowding among the properties examined, followed by the mass in stars. In denser surroundings, galaxies tend to form fewer new stars relative to their existing stellar mass. Galaxies brighter in certain visible and near-infrared bands also tend to occupy denser regions. Comparisons with other survey areas suggest that differences between the sampled regions do not significantly change the conclusions. However, missing redshift measurements do affect the measured clustering. These findings can help test models of how galaxies build up their stars, and the authors suggest that some of the trends could help trace stellar growth and the shutting down of star formation over cosmic time.
Young explorerGalaxies are huge groups of stars. Scientists looked at galaxies in busy places with lots of neighbors and in quieter places. They found that a galaxy’s color is especially closely linked to how crowded its neighborhood is. Galaxies in crowded places also tend to make fewer new stars for the amount of stars they already have. Some missing measurements affect how the scientists measure the crowding, so they need to be careful. These clues can help scientists study how galaxies grow.
Yan-Kun Zhang, Tie Liu, Wenyu Jiao+35 more
AstronomerALMA-QUARKS 1.3-mm continuum observations identify more than 320 superfine dusty fibrils within 121 massive star-forming clumps spanning Galactocentric distances of approximately 1.2–12.9 kpc. The survey achieves a linear resolution of about 900 AU at 3 kpc. Typical fibril widths are approximately 0.01 pc, roughly ten times narrower than dusty filaments identified by Herschel in nearby clouds. Their mass–length relation follows M ∝ l², resembling that of larger Galactic filaments in space-based and ground-based single-dish surveys. However, their H₂ column densities, 10²³–10²⁴ cm⁻², exceed the 10²⁰–10²³ cm⁻² range reported for Herschel filaments. The authors interpret this expanded sample as further evidence for the importance of filamentary structure in star formation across physical scales; the abstract does not establish a causal mechanism.
PublicAstronomers using the ALMA-QUARKS survey have discovered more than 320 very thin threads of dust inside 121 large clumps where stars form, across widely different parts of our Galaxy. These threads typically measure about 0.01 parsec across—roughly one-tenth the width of dusty filaments previously identified by Herschel in nearby clouds. They also contain more molecular gas along the line of sight. Despite these differences, their masses increase with the square of their lengths, a pattern also seen in larger filaments. The researchers interpret the findings as strengthening the case that threadlike structures matter to star formation on many scales.
Young explorerAstronomers found more than 320 tiny-looking threads of dust inside big clouds where stars are being born. These threads are much thinner than other dusty threads found before. The discovery gives scientists more clues that long, thin shapes in space may be important when stars form.
Giordano Felicioni, Maruša Bradač, Yoshihisa Asada+20 more
AstronomerUsing NIRCam and NIRSpec data across seven strong-lensing fields, the authors measure UV continuum slopes through forward modelling for 378 galaxies at 7.5<z<12.5, including 45 with spectra, reaching M_UV≈−16. The sample has mean β=−2.3±0.4, z=8.5±1.0, and M_UV=−18±1. They find no significant β evolution across this redshift range, supporting a flattening of the β–z relation above z≈7.5, and a weak negative β–M_UV trend. They interpret these findings as suggesting similar galaxy properties 300–600 Myr after the Big Bang and similar ISM composition across galaxy masses, possibly reflecting limited time for dust buildup. For 14 galaxies, a low-redshift-calibrated relation involving β, size, and Hβ equivalent width yields an estimated mean ionizing escape fraction of 0.26±0.22. Although this exceeds the average escape fraction needed to ionize the IGM by z≈6, extrapolating the low-redshift calibration may overestimate it.
PublicMassive galaxy clusters act as natural magnifying lenses, allowing researchers to study faint galaxies in the early universe. Using JWST imaging and spectroscopy, this study measures ultraviolet colors for 378 galaxies at redshifts between 7.5 and 12.5. The colors show no significant change over that interval and only a weak relationship with galaxy brightness. The authors suggest that these galaxies had broadly similar properties and that limited time for dust to accumulate may help explain the weak brightness dependence. For 14 galaxies, they also estimate that an average of about a quarter of the radiation capable of ionizing hydrogen escapes into surrounding space, though the uncertainty is large. Such radiation could contribute to cosmic reionization, but this estimate relies on a relationship calibrated using nearby galaxies and may be too high.
Young explorerBig groups of galaxies can work like magnifying glasses in space. Scientists used them to look at 378 galaxies from when the universe was very young. They checked a kind of light our eyes cannot see and found that its color did not change much across the times they studied. They also tried to work out how much special light could get out of some galaxies and change the gas around them. That part is uncertain because they used a rule learned from nearby galaxies, and it might give an answer that is too big.
Jorge Sarrato-Alós, José María Arroyo-Polonio
AstronomerThis study reassesses the cusp-core problem by comparing dynamically inferred dark matter profiles for 16 Milky Way satellites, using four modelling methods, with NIHAO and FIRE-2 CDM hydrodynamical simulations. Comparisons respect methodological reliability limits, match stellar mass, and evaluate simulated slopes at observationally accessible physical radii. Both inferred and simulated profiles show slopes becoming shallower with increasing stellar mass: approximately −1.5 at 10^5 solar masses, versus approximately 0 to −0.4 at 10^8 solar masses. Efficient core formation begins above roughly 10^6 solar masses for central galaxies; satellites show greater scatter, consistent with tidal disruption. Simulated profiles agree with dynamical inferences within about one standard deviation for most systems and outperform an NFW profile. Scatter among observational modelling methods is comparable to simulation–observation offsets. The authors find no clear tension at matched stellar mass when slopes are compared at fixed physical radii, suggesting that inconsistent comparison radii account for some apparent discrepancies. Willman 1 remains an unresolved outlier.
PublicDo small galaxies have sharply concentrated dark matter at their centers, or flatter central regions? Comparing models with observations has been complicated by studies measuring central concentration at different distances from a galaxy’s center. This study compares dark matter profiles inferred for 16 Milky Way satellite galaxies with computer simulations, matching galaxies by stellar mass and comparing the same physical distances wherever the methods are reliable. Most simulated profiles agree with the observational inferences within their uncertainties. Both show a trend toward flatter central dark matter distributions in galaxies with greater stellar mass. Different methods of interpreting the observations also produce appreciable differences. The findings suggest that inconsistent comparisons have contributed to the apparent conflict with cold dark matter simulations, rather than revealing a clear physical contradiction. They do not resolve every case: Willman 1 remains an unexplained exception.
Young explorerScientists compared ideas about dark matter inside small galaxies with computer-made galaxies. They made the comparison fairer by checking the same distances from the middle and matching galaxies with similar amounts of stars. Most of the computer galaxies then matched what scientists worked out from observations fairly well. That suggests some earlier disagreements came from comparing different places. But one galaxy, called Willman 1, is still a puzzle.
Yinbo Huang, David Benisty
AstronomerThe authors correct the Projected Mass Estimator (PME) with residual neural networks trained on thousands of IllustrisTNG galaxy groups, using separate networks for satellite samples of 5–50 members. The approach addresses orbital-geometry assumptions and small-sample noise. In simulated-halo tests, the classical PME gives mass ratios M_proj/M_true of 1.30 (+0.72/−0.62) using 2D distances and 1.46 (+0.97/−0.72) using 3D distances, with RMSEs of 0.29 and 0.32 dex. The corrected estimator yields 1.02 (+0.30/−0.26) and an RMSE of 0.13 dex. Applied to the Milky Way, it estimates a total mass of 1.144 (+0.399/−0.296) × 10^12 solar masses; the brightest 5–10 satellites favor lower estimates of (0.8–0.95) × 10^12 solar masses. The demonstrated accuracy improvement is simulation-based, while the Milky Way result is an application of that calibrated method. The authors describe the modified PME as providing tighter constraints on virial masses and inferred dark matter content in groups and clusters.
PublicEstimating a galaxy’s total mass from the motions of its satellite galaxies is difficult, especially when only a few satellites are available. The researchers trained a neural network on simulated galaxy groups to correct a conventional mass-estimation method. In tests on simulated systems, the correction substantially reduced both the tendency to overestimate mass and the overall estimation error. Applied to the Milky Way, the method gives about 1.14 trillion times the Sun’s mass, with a reported uncertainty of roughly 0.30 trillion below and 0.40 trillion above that estimate. Using only the brightest 5–10 satellites favors a lower value, about 0.8–0.95 trillion solar masses. The improved accuracy was demonstrated in simulations, and the Milky Way estimate still carries uncertainty.
Young explorerHow heavy is our galaxy? Scientists look at how little galaxies move around it to help work that out. But having only a few little galaxies to watch makes the answer tricky. Researchers used pretend galaxies in a computer to teach a program how to improve their guesses. It worked better in those computer tests. They then used it to estimate our galaxy’s weight, but the answer is still not exact.
Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya+3 more
AstronomerThe authors revisit 46,061 galaxies flagged but rejected by GOTHIC as dual active galactic nucleus (DAGN) candidates, using a supervised YOLOv11 oriented-bounding-box model trained on annotated SDSS imaging to distinguish dual nuclei from stellar contaminants and spurious alignments. Validation precision, recall, and F1 are 0.919, 0.905, and 0.912, respectively. After removing star-dominated and blended detections, the model yields 29,605 dual-nucleus candidates; structured visual inspection suggests 54.5–62% are consistent with genuine dual nuclei, implying roughly 14,000–18,000 plausible systems. Cross-calibration with GOTHIC centroid separations and a cut at d ≤ 6.87 arcseconds produce a conservative subset of approximately 13,672 candidates, with calibrated separations reaching about 0.56 arcseconds. Spectra of the most compact systems, with separations ≤ 1 kpc, are dominated by stellar absorption and show no resolved double-peaked emission. The catalogue refines the candidate population but does not establish confirmed DAGN; higher-resolution follow-up is required.
PublicResearchers used deep learning to re-examine 46,061 galaxies previously rejected by an automated search for pairs of active galactic nuclei. Such pairs could help trace merging galaxies and the pairing of their central supermassive black holes, but foreground stars and overlapping features can imitate two galactic centres. The new image-analysis model selected 29,605 candidates after filtering out star-dominated and blended detections. Visual checks suggest that about 55–62% are consistent with genuine pairs of galactic nuclei, rather than misleading alignments. A more conservative selection contains about 13,672 candidates. These are not confirmed pairs of active black holes: spectra of the most closely spaced systems are dominated by starlight and do not show resolved double-peaked emission. Higher-resolution observations are needed to determine their nature.
Young explorerWhen galaxies come together, scientists look for two bright centres that might each have an active giant black hole. But a star in front of a galaxy can make it look like there are two centres when there are not. The researchers taught a computer to look through galaxy pictures and pick out promising pairs. It found many possibilities, but they are not sure discoveries yet. Scientists need a closer look to find out which ones really have two active black holes.
Alberto Manuel Martínez-García
AstronomerUsing published positional and kinematic data for 73 Milky Way dwarf galaxies, the authors identify 22 members of the Vast Polar Structure (VPOS) from their orbital poles, presenting their largest census to date. Most members co-rotate; Bootes III, Kim 1, and Sculptor are the three counter-rotating systems. The revised census increases the known membership by nearly 50%, adding Delve 4, Kim 1, Kim 3, Eridanus III, Pictor II, and YMCA-1. Updated structural parameters confirm a planar distribution almost perpendicular to the Galactic disc, with c/a = 0.27 and a thickness of 15 kpc.
PublicMany small galaxies near the Milky Way form a thin, flat arrangement called the Vast Polar Structure, oriented almost at right angles to our galaxy’s disc. By examining published positions and motions of 73 dwarf galaxies, the researchers identify 22 members of this structure, increasing its known membership by nearly 50%. Most orbit in the same direction, but three travel in the opposite direction. The updated analysis confirms that the arrangement is thin, measuring 15,000 parsecs in thickness.
Young explorerOur Milky Way has smaller galaxies nearby. Some move in a group shaped like a thin sheet standing almost upright compared with the Milky Way’s flat disc. Scientists studied where 73 little galaxies are and how they move. They picked out 22 that belong to this sheet-shaped group. Most go around the same way, but three go the other way.
Dani R. Lipman, Jakub Poznanski, Savannah R. Gramze+46 more
AstronomerUsing ACES ALMA CS (2–1) data, the authors catalog 235 high velocity dispersion compact cloud (HVCC) candidates in the Milky Way’s Central Molecular Zone: 163 identified visually and 72 additional candidates found with automated dendrogram methods. The sample includes structures with diameters below 5 pc and velocity extents between 20 and 140 km/s; most show thin, spiked position–velocity morphologies. The catalog characterizes physical and kinematic properties, line ratios, and position–position–velocity distributions. Elevated HNCO-to-C-shock-tracer ratios along known orbital-stream edges are interpreted as evidence for a buildup of bar-lane gas accreting onto the CMZ. Some candidates overlap the 50 km/s cloud and known circumnuclear disk features. The catalog supports future investigation of nuclear inflow and the dominant mechanisms disrupting CMZ gas flows; those mechanisms are not established here.
PublicAstronomers used ALMA observations to identify 235 candidate compact gas clouds near the center of the Milky Way, where gas displays unusually broad ranges of velocity. They found 163 candidates by visual inspection and another 72 with an automated method. Most appear as narrow spikes in diagrams that compare position with velocity. Measurements of molecular emission near the edges of known gas streams suggest that gas flowing along the galaxy’s bar may be accumulating as it enters the central region, but this is an interpretation rather than a confirmed explanation. Some candidates also overlap previously known central gas structures. The catalog will help researchers investigate how gas reaches the galaxy’s center and which processes most strongly disturb its motion.
Young explorerNear the middle of our galaxy, clouds of gas move at very different speeds. Astronomers made a list of 235 possible little gas clouds with especially big differences in speed. They also found clues that more gas may be piling up as it flows into this busy middle area. The list will help them study how the gas gets there and what makes it move in such a jumbled way.
Shuo Kong, Griselda Arroyo-Chávez, Volker Ossenkopf-Okada+4 more
AstronomerThe study develops observable kinematic predictions for collision-induced magnetic reconnection (CMR), a proposed filament-formation mechanism in which magnetic fields play an active role. It identifies two predicted position–velocity signatures: convergence near the filament with two diverging motions farther away, producing a blueshift–redshift–blueshift–redshift pattern when the collision midplane is inclined; and velocity oscillations along the filament spine, currently attributed to magnetic transport of gas clumps in the converging flow. The first signature arises mainly outside the filament and may be confused with environmental emission. The second originates mainly within the filament and is therefore considered a more robust observational test. Both the integral-shaped filament and the Stick filament in Orion A show longitudinal velocity oscillations, but their spatial oscillation frequencies and velocity spreads differ. These observations provide relevant tests, not confirmation of CMR as their formation mechanism.
PublicThe researchers describe ways to test a proposed explanation for how long filaments of gas form through collisions and magnetic reconnection. The model predicts two patterns in the gas motions: an alternating sequence of motion toward and away from us around an inclined collision region, and an oscillating velocity pattern along the filament itself. The first could be difficult to separate from surrounding gas. The second should be a more reliable test because it comes mainly from gas inside the filament. Two filaments in the Orion A cloud—the integral-shaped filament and the Stick filament—do show velocity oscillations, although the spacing of the oscillations and the range of velocities differ. The authors currently interpret the predicted oscillations as magnetic fields transporting gas clumps, but the observed patterns do not establish that this proposed mechanism formed the filaments.
Young explorerSpace has long strands of gas. Scientists have an idea that crashes and magnetic forces help make them. They predict that gas along a strand would move in a repeating pattern. Two real strands show a pattern like that, but the patterns are not exactly the same. This is a clue to test the idea, not proof that it is right.
G.A. Gontcharov, A.M. Kudashov, O.S. Ryutina+1 more
AstronomerThe study constrains non-standard stellar-core cooling using homogeneous TRGB estimates for 27 globular clusters from Stetson, Hubble Space Telescope, and Gaia photometry, paired with cluster-specific MESA calculations. The primary likelihood includes 24 clusters, excluding three hot-flasher systems, and accounts for stellar variability, finite upper-RGB sampling through its full conditional distribution, and correlated observational and stellar-physics uncertainties. The observed TRGB is 0.078 (+0.036, −0.037) mag fainter than the standard-cooling prediction, whereas additional energy losses would brighten it. To avoid an artificially stringent limit from this downward fluctuation, the authors apply a power-constrained profile likelihood and obtain an axion-electron coupling bound of g_ae < 6.4 × 10^-14 at 95% confidence. They also present sensitivity estimates for a neutrino magnetic dipole moment and millicharged particles, rather than detections.
PublicRed giants can help test whether hypothetical particles carry energy out of stellar cores: such extra cooling would make the brightest stage of these stars more luminous. The researchers combined brightness measurements for 27 globular clusters with stellar-evolution calculations, using 24 clusters in their main analysis. They accounted for variable stars, the limited number of very bright giants, and uncertainties shared across the measurements and models. The observed brightness limit was actually a little fainter than the standard model predicted, not brighter. To prevent that downward fluctuation from producing an artificially tight constraint, they used a statistical safeguard. Their result limits how strongly hypothetical axions could interact with electrons; it is not a detection of axions. They also estimated sensitivity to two other possible sources of extra cooling.
Young explorerScientists looked at big, old stars to check an idea: could tiny, unseen particles carry energy away from inside them? Their star calculations say this would make the stars shine brighter at one stage. But the stars looked a little dimmer than expected. The team carefully allowed for uncertainty and set a limit on the idea. They did not discover the tiny particles.
