Large-scale phenomena in spiral galaxies such as shear, supernovae, and magnetic fields all contribute to the formation and subsequent evolution of filamentary structure and star formation within them. In this paper, we analyze the properties and dynamics of filaments in a simulated Milky Way-like galaxy from B. Zhao et al. Using filament and superbubble structure analysis codes, we investigate the roles of Galactic shear, supernovae, superbubbles, and magnetic fields on the stability and fragmentation of filaments. We find that local shear has little effect on filament stability and the largest structures at outer radii of the disk may be more likely to be dissipated by shear than supernovae. Filaments are largely parallel to the magnetic field, which plays a significant role in filament stability. By measuring the ratio of surface pressure on a filament to that on its central spine, chi(f) = P-surf/P-central, we find that filaments with chi(f) <= 1 are dominated by their own self-gravity and have a strong tendency to be gravitationally supercritical, whereas those with chi(f) > 1 are either transitory or in the act of being formed. Finally, we investigate the role of interstellar medium pressure on filament dynamics and stability as a function of Galactic radius, finding considerable changes in filament stability and the accompanying star formation rates in the inner versus outer regions of the disk.

There is abundant observational evidence for the hierarchical, interconnected nature of filaments in the interstellar medium extending from galactic down to subparsec scales. New JWST images of NGC 628, in particular, show clusters forming along the two spiral arms of this galaxy. In this paper, we investigate filament and cluster properties in an NGC 628-like multiscale high-resolution magnetohydrodynamic simulation. We use a filament finding tool to identify filaments and derive the probability density functions (PDFs) for the filament lengths and masses. Using a clustering algorithm, we identify star clusters formed between 268 and 278 Myr and follow this population as the galaxy evolves for 60 Myr, calculating their mass PDFs, average radius growth rate, and average mass loss rate. We find a power-law index of α _m = −1.35 for the filament masses. Calculating the power-law index from our cluster mass PDF, we find a value of α _c _, _m = −1.35 when the clusters first form, exactly our filament mass power-law index. This shows that properties of young clusters arise from the gravitational fragmentation of their host filaments. We track the postformation evolution of the clusters as they become unbound, increase in radius, and decrease in mass, yielding an ever steeper mass power-law index. After 60 Myr, the mass power-law index is α _c _, _m = −1.55, matching other simulations and observations.

We hypothesize that dust rings in protoplanetary disks formed by an embedded planet should have properties that reflect the planet's mass. We use 2D hydrodynamical simulations of planet-disk interactions to investigate this, focusing on planets ranging from 0.5-2.0 & times; the pebble-isolation mass, for three different aspect ratios. We find the ring's dust mass, peak location, and width to correlate with planet mass. We confirm a positive linear relationship between a planet's Hill radius and the location of a ring's density peak and demonstrate how this relationship can be used to constrain planet masses in observed systems by applying it to PDS 70. The dust ring width and mass change with planet mass for planet masses up to the pebble-isolation mass, beyond which they become constant. The steepness of the gas pressure radial profile is asymmetric, with the direction of the asymmetry being determined by whether the planet mass is above or below the pebble-isolation mass. We therefore propose a new way to define the pebble-isolation mass: the minimum planet mass that perturbs the gas enough for the pressure gradient interior to the pressure maximum to exceed the pressure gradient exterior to it. We discuss how our findings could be used to constrain or estimate planet masses from gas or dust observations of disks with measurable substructures and apply our results to five disks in the exoALMA sample to estimate planet masses and constrain disk aspect ratios. We also discuss how the potential for planetesimal formation in a ring varies with planet mass.

The relationship between magnetic field strength and gas density is essential to understand the interstellar medium and star formation. Zeeman measurements in dense atomic and molecular gas phases have traditionally been used to directly probe magnetic field strengths in the Milky Way. This allowed derivation of a relationship between magnetic field strength B and gas number density n. We recently generalized this relation as a two-part power-law with non-zero slopes and a transition density given as B/B_0 ∝ (n/n_0)^α_1 for n ≤ n_0 and (n/n_0)^α_2 for n > n_0. Here, we extend our previous hierarchical Bayesian framework by incorporating a large body of pulsar observations that probe the diffuse interstellar medium and explicitly modelling density uncertainties through a global log-density correction parameter R applied to all densities. We also account for magnetic field geometry and measurement uncertainties through a magnetic hyperparameter to estimate B. This results in a stronger constraint on the diffuse gas part of the B–n relation. Our results confirm a non-zero exponent in the diffuse gas and a broad transition density with our best model and data set yielding maximum a posteriori results of α_1 = 0.18^+0.02_-0.02, α_2 = 0.63^+0.08_-0.05, n_0 = 1630^+2560_-1430 cm^-3, and B_0 = 7.60^+2.00_-3.47 μG.

The increasing precision of planetary mass and radius observations is bringing major questions about the structure and formation of planets–such as the nature of the radius valley and origin of super-Mercuries–within reach, demanding the development of interior structure models with more physics to more accurately determine planetary radii for a given composition. Here, we present a new model that includes state-of-the-art equations of state following the latest experimental and computational results, a physically-motivated mineralogy allowing multiple species to coexist within planetary layers, a non-adiabatic temperature profile, melting, and other features. This model replicates Earth's radius and moment of inertia coefficient to within 0.2%, Mars and the Moon's to within 0.5%, and Mercury, Venus, and Europa's to within 1% or 3σ. We use this model to calculate mass-radius relationships for H/He-enveloped, water-rich, Earth-like, and iron-rich bodies with masses between 0.01-100 M_⊕. We calculate mass-radius tables and fit piece-wise power-laws to them for <8M_⊕ planets, finding that the exponent in M=aR^b increases with mass and core mass fraction. We find radii generally smaller than in literature mass-radius relations at low instellations and larger at high instellations, with our improvement on the literature comparable to observational uncertainties. State-of-the-art interior structure models are thus required to interpret observational data. Our mass-radius curves comprising 32,971 model planets are publicly available.

Understanding what environmental conditions prevailed on early Earth during the Hadean eon, and how this set the stage for the origins of life, remains a challenge. Geologic processes such as serpentinization and bombardment by chondritic material during the late veneer might have been very active, shaping an atmospheric composition reducing enough to allow efficient photochemical synthesis of HCN, one of the key precursors of prebiotic molecules. HCN can rain out and accumulate in warm little ponds (WLPs), forming prebiotic molecules such as nucleobases and the sugar ribose. These molecules could condense to nucleotides, the building blocks of RNA molecules, one of the ingredients of life. Here, we perform a systematic study of potential sources of reducing gases on Hadean Earth and calculate the concentrations of prebiotic molecules in WLPs based on a comprehensive geophysical and atmospheric model. We find that in a reduced H _2 -dominated atmosphere, carbonaceous bombardment can produce enough HCN to reach maximum WLP concentrations of ∼1–10 mM for nucleobases and, in the absence of seepage, ∼10–100 μ M for ribose. If the Hadean atmosphere was initially oxidized and CO _2 -rich (90%), we find serpentinization alone can reduce the atmosphere, resulting in WLP concentrations of an order of magnitude lower than the reducing carbonaceous bombardment case. In both cases, concentrations are sufficient for nucleotide synthesis, as shown in experimental studies. RNA could have appeared on Earth immediately after it became habitable (about 100 Myr after the Moon-forming impact), or it could have (re)appeared later at any time up to the beginning of the Archean.

We use global MHD galaxy simulations to investigate the effects of spiral arms on the evolution of magnetic fields and star formation within a self-regulated interstellar medium. The same galaxy is simulated twice: once with self-consistent stellar spiral arms and once more with the stellar spirals suppressed via a novel numerical approach, using the Ramses adaptive mesh refinement code. Spiral arms continually promote star formation, with 2.6 times higher rates in the spiral galaxy. The higher rate is due to high gas columns gathered along the spiral arms, rather than increasing the star formation efficiency at a given gas column. In both cases, the magnetic field is initially amplified via a small-scale dynamo driven by turbulence due to supernova feedback. Only the spiral galaxy exhibits late-time, consistent field growth due to a large-scale dynamo ( e -folding time ∼600 Myr). This results in volume-averaged field strengths of ∼1 μ G after 1 Gyr of evolution. The mean fields tend to align themselves with the spiral arms and are coherent up to 10 kpc scales. We demonstrate a novel large-scale dynamo mechanism, whereby spiral-driven radial flows enable the mean-field amplification.

Extensive ground and space based surveys have now characterized the properties of thousands of exoplanets; their radii, masses, orbits around their host stars, and the beginnings of accurate measurements of the chemical compositions of their atmospheres and cores. How are these properties linked to their formation in physically and chemically evolving protoplanetary disks wherein they accrete pebbles, planetesimals, and gas as they undergo migration? To address this challenge, our review assembles a large and varied body of exoplanet observations as well as recent Atacama Large Millimeter Array (ALMA) and James Webb Space Telescope (JWST) observations of disk structure, chemistry, kinematics, and winds. The latest advances in theory and MHD simulations that bear on these issues are also reviewed and compared with the observations. Taken together, this review argues that a new dynamic paradigm for planet formation is emerging wherein MHD disk winds and not disk turbulence play a central role in disk evolution and planet formation including: angular momentum transport, gap and ring formation. disk astrochemistry, and planet formation and migration. These processes leave their mark on the resulting atmospheric composition, radii, and orbital characteristics of exoplanet populations, offering the possibility of future observational tests.

Stellar multiple systems play a pivotal role in cluster dynamics and stellar evolution, producing intense astronomical phenomena like X-ray binaries, gamma-ray bursts, type Ia supernova and stellar mergers, which are prime sources of gravitational waves. However, their origin remains poorly understood. Here we report the discovery of a septuple protostellar system embedded in a Keplerian disk within the high-mass star-forming region NGC 6334IN, with close separations of 181-461 au. A stability analysis reveals that the disk surrounding the septuple system is dynamically unstable, indicating that the septuple system formed through disk fragmentation. Previous studies have typically found only two or three members forming through disk fragmentation in both low- and high-mass star-forming regions. Our findings provide compelling observational evidence that the fragmentation of a gravitationally unstable disk is a viable mechanism for the formation of extreme high-order multiplicity, confirming what was previously only a theoretical concept. The results shed new light on the formation of extreme high-order multiplicity in cluster environments.

High-resolution surveys reveal that the interstellar medium in the Milky Way and nearby galaxies consists of interlinked hierarchies of filamentary structure and superbubbles extending from galactic to subparsec scales. The characterization of filament properties across this hierarchy is of fundamental importance for the origin of giant molecular clouds and their star clusters. In this paper, we characterize the properties of filaments greater than 25 pc in length that are produced in the multiscale galactic MHD simulations of B. Zhao et al. By adapting the FilFinder algorithm of E. W. Koch & E. W. Rosolowsky, we extract over 500 filaments ranging up to 10 kpc in scale, to derive the probability distribution functions for filament masses and lengths, magnetic field orientations, and the gravitational stability and fragmentation patterns of filaments. We find power-law distributions for filament masses and lengths. The former has a power-law index α m = 1.85 that is nearly identical to that of observed giant molecular cloud (GMC) mass functions in extragalactic and Galactic surveys, suggesting that GMC properties are inherited from their host filaments. The fragmentation of magnetized filaments on 200 pc scales or less occurs when they exceed an average critical line mass, as predicted by theory. On larger scales, however, kiloparsec filaments form out of the cold neutral medium, and fragmentation follows local variations in the critical line mass along spiral arms or at the boundaries of superbubbles.

Context. The fragmentation of high-mass star-forming regions depends on a variety of physical parameters, including density, the magnetic field, and turbulent gas properties. Aims. We evaluate the importance of the density and magnetic field structures in relation to the fragmentation properties during high-mass star formation. Methods. Observing the large parsec-scale Stokes I millimeter dust continuum emission with the IRAM 30 m telescope and the intermediate-scale (<0.1 pc) polarized submillimeter dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behavior of these regions on the density and magnetic field structures. Results. Based on the IRAM 30 m data, we infer density distributions n ∝ r−p of the regions with typical power-law slopes p around ~1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (~1 pc) and the number of fragments on smaller core scales (<0.1 pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around ~2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. The magnetic fields of several regions appear to be aligned with filamentary structures that lead toward the densest central cores. Furthermore, we find different polarization structures; some regions exhibit central polarization holes, whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes I intensities, following roughly a power-law slope of ∝ SI−0.62. We estimate magnetic field strengths between ~0.2 and ~4.5 mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. A comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between ~2 and ~7, consistent with collapsing star-forming regions. Conclusions. Finding no clear correlations between the present-day large-scale density structure, the magnetic field strength, and the smaller-scale fragmentation properties of the regions, indicates that the fragmentation of high-mass star-forming regions may not be affected strongly by the initial density profiles and magnetic field properties. However, considering the limited evolutionary range and spatial scales of the presented CORE analysis, future research directions should include density structure analysis of younger regions that better resemble the initial conditions, as well as connecting the observed intermediate-scale magnetic field structure with the larger-scale magnetic fields of the parental molecular clouds.

Star formation takes place in filamentary molecular clouds which arise by physical processes that take place in the cold, neutral medium (CNM). We address the necessary conditions for this diffuse ($n \approx 30$ cm$^{-3}$), cold (T $\approx$ 60 K), magnetized gas undergoing shock waves and supersonic turbulence, to produce filamentary structures capable of fragmenting into cluster forming regions. Using RAMSES and a magnetized CNM environment as our initial conditions, we simulate a 0.5 kpc turbulent box to model a uniform gas with magnetic field strength of 7 $\mu G$, varying the 3D velocity dispersion via decaying turbulence. We use a surface density of $320 M_{\odot} pc^{-2}$, representative of the inner 4.0 kpc CMZ of the Milky Way and typical luminous galaxies. Filamentary molecular clouds are formed dynamically via shocks within a narrow range of velocity dispersions in the CNM of 5 - 10 km/s with a preferred value at 8 km/s. Cluster sink particles appear in filaments which exceed their critical line mass, occurring optimally for velocity dispersions of 8 km/s. Tracking the evolution of magnetic fields, we find that they lead to double the dense star forming gas than in purely hydro runs. Perpendicular orientations between magnetic field and filaments can increase the accretion rates onto filaments and hence their line masses. Because magnetic fields help support gas, MHD runs result in average temperatures an order of magnitude higher than unmagnetized counterparts. Finally, we find magnetic fields delay the onset of cluster formation by $\propto 0.4$ Myr.

There is now abundant observational evidence that star formation is a highly dynamical process that connects filament hierarchies and supernova feedback from galaxy-scale kiloparsec filaments and superbubbles to giant molecular clouds (GMCs) on 100 pc scales and star clusters (1 pc). Here we present galactic multiscale MHD simulations that track the formation of structure from galactic down to subparsec scales in a magnetized, Milky Way-like galaxy undergoing supernova-driven feedback processes. We do this by adopting a novel zoom-in technique that follows the evolution of typical 3 kpc subregions without cutting out the surrounding galactic environment, allowing us to reach 0.28 pc resolution in the individual zoom-in regions. We find a wide range of morphologies and hierarchical structures, including superbubbles, turbulence, and kiloparsec atomic gas filaments hosting multiple GMC condensations that are often associated with superbubble compression, down to smaller-scale filamentary GMCs and star cluster regions within them. Gas accretion and compression ultimately drive filaments over a critical, scale-dependent line mass leading to gravitational instabilities that produce GMCs and clusters. In quieter regions, galactic shear can produce filamentary GMCs within flattened, rotating disklike structures on 100 pc scales. Strikingly, our simulations demonstrate the formation of helical magnetic fields associated with the formation of these disklike structures.

The dominant mechanism forming multiple stellar systems in the high-mass regime (M$_\ast \gtrsim $ 8 $M_{\odot}$) remained unknown because direct imaging of multiple protostellar systems at early phases of high-mass star formation is very challenging. High-mass stars are expected to form in clustered environments containing binaries and higher-order multiplicity systems. So far only a few high-mass protobinary systems, and no definitive higher-order multiples, have been detected. Here we report the discovery of one quintuple, one quadruple, one triple and four binary protostellar systems simultaneously forming in a single high-mass protocluster, G333.23--0.06, using Atacama Large Millimeter/submillimeter Array high-resolution observations. We present a new example of a group of gravitationally bound binary and higher-order multiples during their early formation phases in a protocluster. This provides the clearest direct measurement of the initial configuration of primordial high-order multiple systems, with implications for the in situ multiplicity and its origin. We find that the binary and higher-order multiple systems, and their parent cores, show no obvious sign of disk-like kinematic structure. We conclude that the observed fragmentation into binary and higher-order multiple systems can be explained by core fragmentation, indicating its crucial role in establishing the multiplicity during high-mass star cluster formation.

There is now abundant observational evidence that star formation is a highly dynamical process that connects filament hierarchies and supernova feedback from galaxy scale kpc filaments and superbubbles, to giant molecular clouds (GMCs) on 100 pc scales and star clusters (1 pc). Here we present galactic multi-scale MHD simulations that track the formation of structure from galactic down to sub pc scales in a magnetized, Milky Way like galaxy undergoing supernova driven feedback processes. We do this by adopting a novel zoom-in technique that follows the evolution of typical 3-kpc sub regions without cutting out the surrounding galactic environment, allowing us to reach 0.28 pc resolution in the individual zoom-in regions. We find a wide range of morphologies and hierarchical structure including superbubbles, turbulence, kpc atomic gas filaments hosting multiple GMC condensations that are often associated with superbubble compression; down to smaller scale filamentary GMCs and star cluster regions within them. Gas accretion and compression ultimately drive filaments over a critical, scale - dependent, line mass leading to gravitational instabilities that produce GMCs and clusters. In quieter regions, galactic shear can produce filamentary GMCs within flattened, rotating disk-like structures on 100 pc scales. Strikingly, our simulations demonstrate the formation of helical magnetic fields associated with the formation of these disk like structures.

Prebiotic molecules, fundamental building blocks for the origin of life, have been found in carbonaceous chondrites. The exogenous delivery of these organic molecules onto the Hadean Earth could have sparked the polymerization of the first RNA molecules in Darwinian ponds during wet-dry cycles. Here, we investigate the formation of the RNA and DNA nucleobases adenine, uracil, cytosine, guanine, and thymine inside parent body planetesimals of carbonaceous chondrites. An up-to-date thermochemical equilibrium model coupled with a 1D thermodynamic planetesimal model is used to calculate the nucleobase concentrations. Different from previous studies, we assume the initial volatile concentrations more appropriate for the formation zone of carbonaceous chondrite parent bodies. This represents more accurately cosmochemical findings that these bodies have formed inside the inner, ∼2–5 au, warm region of the solar system. Due to these improvements, our model represents the concentrations of adenine and guanine measured in carbonaceous chondrites. Our model did not reproduce per se the measurements of uracil, cytosine, and thymine in these meteorites. This can be explained by transformation reactions between nucleobases and the potential decomposition of thymine. The synthesis of prebiotic organic matter in carbonaceous asteroids could be well explained by a combination of (i) radiogenic heating, (ii) aqueous chemistry involving a few key processes at a specific range of radii inside planetesimals where water can exist in the liquid phase, and (iii) a reduced initial volatile content (H 2 , CO, HCN , and CH 2 O) of the protoplanetary disk material in the parent body region compared to the outer region of comets.

The fragmentation mode of high-mass molecular clumps and the accretion processes that form the most massive stars ($M\gtrsim 8M_\odot$) are still not well understood. To this end, we have undertaken a large observational program (CORE) making use of interferometric observations from the Northern Extended Millimetre Array (NOEMA) for a sample of 20 luminous ($L>10^4L_\odot$) protostellar objects in the 1.37 mm wavelength regime in both continuum and line emission, reaching $\sim$0.4" resolution (800 au at 2 kpc). Using the dense gas tracer CH$_3$CN, we find velocity gradients across 13 cores perpendicular to the directions of bipolar molecular outflows, making them excellent disk candidates. Specific angular momentum ($j$) radial profiles are on average $\sim10^{-3}$ km /s pc and follow $j \propto r^{1.7}$, consistent with a poorly resolved rotating and infalling envelope/disk model. Fitting the velocity profiles with a Keplerian model, we find protostellar masses in the range of $\sim 10-25$ $M_\odot$. Modelling the level population of CH$_3$CN lines, we present temperature maps and find median gas temperatures in the range $70-210$ K. We create Toomre $Q$ maps to study the stability of the disks and find almost all (11 of 13) disk candidates to be prone to fragmentation due to gravitational instabilities at the scales probed by our observations. In particular, disks with masses greater than $\sim10-20\%$ of the mass of their host (proto)stars are Toomre unstable, and more luminous protostellar objects tend to have disks that are more massive and hence more prone to fragmentation. Our finings show that most disks around high-mass protostars are prone to disk fragmentation early in their formation due to their high disk to stellar mass ratio. This impacts the accretion evolution of high-mass protostars which will have significant implications for the formation of the most massive stars.

Methods: Observing the large pc-scale Stokes I mm dust continuum emission with the IRAM 30m telescope and the intermediate-scale (<0.1pc) polarized submm dust emission with the Submillimeter Array toward a sample of 20 high-mass star-forming regions allows us to quantify the dependence of the fragmentation behaviour of these regions depending on the density and magnetic field structures. Results: We infer density distributions n~r^{-p} of the regions with typical power-law slopes p around ~1.5. There is no obvious correlation between the power-law slopes of the density structures on larger clump scales (~1pc) and the number of fragments on smaller core scales (<0.1pc). Comparing the large-scale single-dish density profiles to those derived earlier from interferometric observations at smaller spatial scales, we find that the smaller-scale power-law slopes are steeper, typically around ~2.0. The flattening toward larger scales is consistent with the star-forming regions being embedded in larger cloud structures that do not decrease in density away from a particular core. Regarding the magnetic field, for several regions it appears aligned with filamentary structures leading toward the densest central cores. Furthermore, we find different polarization structures with some regions exhibiting central polarization holes whereas other regions show polarized emission also toward the central peak positions. Nevertheless, the polarized intensities are inversely related to the Stokes I intensities. We estimate magnetic field strengths between ~0.2 and ~4.5mG, and we find no clear correlation between magnetic field strength and the fragmentation level of the regions. Comparison of the turbulent to magnetic energies shows that they are of roughly equal importance in this sample. The mass-to-flux ratios range between ~2 and ~7, consistent with collapsing star-forming regions.

We used all-atom Molecular Dynamics (MD) computer simulations to study the formation of pre-polymers between the four nucleotides in RNA (AMP, UMP, CMP, GMP) in the presence of different substrates that could have been present in a prebiotic environment. Pre-polymers are C3′–C5′ hydrogen-bonded nucleotides that have been suggested to be the precursors of phosphodiester-bonded RNA polymers. We simulated wet–dry cycles by successively removing water molecules from the simulations, from ~60 to 3 water molecules per nucleotide. The nine substrates in this study include three clay minerals, one mica, one phosphate mineral, one silica, and two metal oxides. The substrates differ in their surface charge and ability to form hydrogen bonds with the nucleotides. From the MD simulations, we quantify the interactions between different nucleotides, and between nucleotides and substrates. For comparison, we included graphite as an inert substrate, which is not charged and cannot form hydrogen bonds. We also simulated the dehydration of a nucleotide-only system, which mimics the drying of small droplets. The number of hydrogen bonds between nucleotides and nucleotides and substrates was found to increase significantly when water molecules were removed from the systems. The largest number of C3′–C5′ hydrogen bonds between nucleotides occurred in the graphite and nucleotide-only systems. While the surface of the substrates led to an organization and periodic arrangement of the nucleotides, none of the substrates was found to be a catalyst for pre-polymer formation, neither at full hydration, nor when dehydrated. While confinement and dehydration seem to be the main drivers for hydrogen bond formation, substrate interactions reduced the interactions between nucleotides in all cases. Our findings suggest that small supersaturated water droplets that could have been produced by geysers or springs on the primitive Earth may play an important role in non-enzymatic RNA polymerization.