Gravitational Instability Research Articles

FU Orionis disk outburst: Evidence for a gravitational instability scenario triggered in a magnetically dead zone

Context. FUors outbursts are a crucial stage of accretion in young stars. However, a complete mechanism at the origin of the outburst still remains missing. Aims. We aim to constrain the instability mechanism in the star FU Orionis itself by directly probing the size and evolution in time of the outburst region with near-infrared (NIR) interferometry, and to confront it with physical models of this region. Methods. As the prototype of the FUors class of objects, FU Orionis has been a regular target of NIR interferometry. In this paper, we analyze more than 20 years of NIR interferometric observations to perform a temporal monitoring of the region of the outburst, and compare it to the spatial structure deduced from 1D magneto-hydrodynamic (MHD) simulations. Results. We measure from the interferometric observations that the size variation of the outburst region is compatible with a constant or slightly decreasing size over time: -0.56-0.36+0.14 AU/100 yr and -0.30-0.19+0.19 AU/100 yr in the H and K bands, respectively. The temporal variation and the mean size probed by NIR interferometry are consistently reproduced by our 1D MHD simulations. We find that the most compatible scenario is a model of an outburst occurring in a magnetically layered disk, where a magneto-rotational instability (MRI) is triggered by a gravitational instability (GI) at the outer edge of a dead zone. The scenario of a pure thermal instability (TI) fails to reproduce our interferometric sizes because it can only be sustained in a very compact zone of the disk <0.1 AU. The comparison between the data and the MRI-GI models favors MHD parameters of αMRI = 10−2, TMRI = 800 K, and Σcrit = 10 g cm−2, with more work needed in terms of observations and modeling in order to improve the precision of these values. Locally, in the very inner part of the disk, TI can be triggered in addition to MRI-GI, which qualitatively better matches our observation but is not strongly constrained by the currently available data. The scenario of MRI-GI could be compatible with an external perturbation that enhances the GI, such as tidal interaction with a stellar companion, or a planet at the outer edge of the dead zone. Conclusions. We favor a layered-disk model driven by MRI turbulence in order to explain the spatial structure and temporal evolution of the outburst region on FU Orionis. Understanding this phase will provide a crucial link between the early phase of disk evolution and the process of planet formation in the first inner astronomical units.

On Secular Gravitational Instability in Vertically Stratified Disks

Secular gravitational instability (GI) is one promising mechanism for explaining planetesimal formation. Previous studies of secular GI utilized a razor-thin disk model and derived the growth condition in terms of vertically integrated physical values such as dust-to-gas surface density ratio. However, in weakly turbulent disks where secular GI can operate, a dust disk can be orders of magnitude thinner than a gas disk, and analyses treating the vertical structures are necessary to clarify the interplay of the midplane dust motion and the upper gas motion. In this work, we perform vertically global linear analyses of secular GI with a vertical domain size of a few gas scale heights. We find that dust grains accumulate radially around the midplane while gas circulates over the whole vertical region. We obtain well-converged growth rates when the outer gas boundary is above two gas scale heights. The growth rates are underestimated if we assume the upper gas to be steady and regard it just as the source of external pressure to the dusty lower layer. Therefore, treating the upper gas motion is important even when the dust disk is much thinner than the gas disk. Conducting a parameter survey, we represent the growth condition in terms of the Toomre Q value for dust and dust-to-gas surface density ratio. The critical dust disk mass for secular GI is ∼10−4 M * for a dust-to-gas surface density ratio of 0.01, a Stokes number of 0.1, and a radial dust diffusivity of 10−4 c s H, where c s is the gas sound speed, and H is the gas scale height.

Continental Tip With Thinned Lithosphere and Thickened Crust Is a Favorable Location for Subduction Initiation

AbstractThe collapse of passive margins and subsequent subduction initiation (SI) are key steps in the Wilson Cycle. However, the occurrence and mechanism of SI at passive margins have long been questioned due to the lack of Cenozoic observations. In this study, we propose that the continental tip, where arc/plateau blocks with thinned lithosphere and thickened crust accrete beside the passive margin, is a favorable location for SI. Our three‐dimensional numerical model and force analysis demonstrate that the continental tip, with its reduced frictional resistance and increased gravitational instability, is better suited for SI than other parts of the passive margin. Upon completion of SI, the retreat of self‐sustained subduction can create a transform plate boundary by tearing the passive margin. Our model explains why SI can occur at continental tips such as the Scotia and the Caribbean, as well as locations with similar tectonic settings, while most parts of the Atlantic margin remain stable over long geological periods.

Wave modes and instabilities in gravitating magnetized polytropic quantum plasmas including viscosity tensor and FLR corrections

ABSTRACT The present analytical study extends the problems of pressure anisotropy-driven instabilities and gravitational instability in space plasmas to mixed quantum polytropic gas in the interior of dense stars accounting for the effects of viscosity, finite Larmor radius (FLR) and self-gravitational effects. The generalized polytrope pressure laws are considered as adiabatic equations in which the pressure components depend upon the plasma density, magnitude of the magnetic field, and the polytrope indices. The modified properties of waves and instabilities in gravitating quantum plasmas have been analysed using the quantum magnetohydrodynamic (QMHD) fluid description in the magnetohydrodynamic (MHD) and Chew–Goldberger–Low (CGL) limits. In the parallel propagation, the Jeans instability modified by quantum diffraction parameters and firehose mode modified by FLR parameter is obtained separately. The Jeans instability condition depends upon the quantum diffraction term and polytrope index β, and it remains unaffected due to viscosity and ion Larmor frequency. The growth rate of the Jeans instability decreases due to viscosity and quantum diffraction parameters, while the growth rate of the firehose instability increases due to FLR corrections. In the transverse mode, a similar nature is observed in the growth rates; however, the instability region decreases significantly due to polytrope indices and different dispersion properties of MHD and CGL viscous quantum plasmas. The analytical results have been applied in dense degenerate stars to measure the characteristic parameters and understand the MHD wave propagation, pressure anisotropy-driven, and gravitationally driven instabilities.

Gravitational Waves from Rapid Structure Formation on Microscopic Scales before Matter-Radiation Equality.

The existence of scalar fields can be probed by observations of stochastic gravitational waves. Scalar fields mediate attractive forces, usually stronger than gravity, on the length scales shorter than their Compton wavelengths, which can be non-negligible in the early Universe, when the horizon size is small. These attractive forces exhibit an instability similar to the gravitational instability, only stronger. They can, therefore, lead to the growth of structures in some species. We identify a gravitational waves signature of such processes and show that it can be detected by future gravitational waves experiments.

Spirals and Clumps in V960 Mon: Signs of Planet Formation via Gravitational Instability around an FU Ori Star?

The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due to the scarcity of observations of fragmented protoplanetary disks around young stars and the low occurrence rate of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered light with several spiral arms. This finding motivated a reanalysis of archival Atacama Large Millimeter/submillimeter Array 1.3 mm data acquired just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of gravitational instability occurring on planetary scales. This study discusses the significance of this finding for planet formation and its potential connection with the outbursting state of V960 Mon.

Insights of Active Extension Within a Collisional Orogen From GNSS (Central Betic Cordillera, S Spain)

AbstractThe coexistence of shortening and extensional tectonic regimes is a common feature in orogenic belts. The westernmost end of the Western Mediterranean is an area undergoing shortening related to the 5 mm/yr NNW‒SSE convergence of the Nubia and Eurasia Plates. In this region, the Central Betic Cordillera shows a regional ENE‒WSW extension. Here, we present GNSS‐derived geodetic data along a 170 km‐long transect orthogonal to the main active normal faults of the Central Betic Cordillera. Our data indicate that the total extension rate along the Central Betic Cordillera is 2.0 ± 0.3 mm/yr. Extension is accommodated in the eastern (0.8 ± 0.3 mm/yr in the Guadix‐Baza Basin) and western (1.3 ± 0.3 mm/yr in the Granada Basin) parts of the Central Betic Cordillera, while no extension is recorded in the central part of the study area. Moreover, our data permit us to quantify, for the first time, short‐term fault slip rates of the Granada Fault System, which is one of the main seismogenic sources of the Iberian Peninsula. We deduce a fault slip rate of ∼1.3 ± 0.3 mm/yr for the whole Granada Basin, with 0.9 ± 0.3 mm/yr being accommodated in the Granada Fault System and 0.4 ± 0.3 mm/yr being accommodated in the southwestern sector of the Granada Basin, where no active faults have been previously described at the surface. The heterogeneous extension in the Central Betic Cordillera could be accommodated by shallow high‐angle normal faults that merge with a detachment at depth. Part of the active extension could be derived from gravitational instability because of underlying over‐thickened crust.

On the Potential for Cumulate Mantle Overturn in Mercury

AbstractMercury has a compositionally diverse surface exhibiting geochemical terranes that represent different periods of igneous activity, suggesting diverse mantle source compositions. Mercury's juvenile mantle likely formed after fractional solidification of a magma ocean, which produced distinct mineralogical horizons with depth. To produce the diversity of observed volcanic terranes, dynamic mixing of materials from distinct mantle horizons is required. One process that could dynamically mix the juvenile cumulate pile is cumulate mantle overturn, where dense layers in shallow planetary mantles sink into deeper, less dense layers as Rayleigh‐Taylor instabilities. Gravitationally unstable density stratification is a requisite starting condition for overturn; solidification of the Mercurian magma ocean is likely to have produced such a density inversion, with a relatively dense clinopyroxene‐bearing pyroxenite layer atop lower density dunite and harzburgite layers. Sulfides are present in abundance on Mercury's surface and would be additional mantle phase(s) if they are indigenous to the planet's interior. Sulfides have variable densities; they could potentially enhance the formation of gravitational instabilities or prevent them from developing. Exploring physically reasonable mantle density and viscosity structures, we evaluate the potential for cumulate mantle overturn in Mercury and predict the possible timing, scale, and rate of overturn for plausible physical parameter combinations. Our analysis suggests that overturn is possible in Mercury's mantle within 100 Myr of magma ocean solidification, providing a mechanism for producing the mantle sources that would melt to form surface compositions on Mercury, and overturn may control the spatial scale of volcanic provinces observed on the surface today.

A multiscale study of the coupling effects of H[formula omitted]S impurity and dissolution reactions on convective mixing in CO[formula omitted] geological storage

In the present work, a multi-scale study of density-driven flow in CO2 geological storage coupled with H2S impurity and solid–liquid chemical reactions is conducted. Linear stability analysis is first performed to predict the initial interfacial instability at Darcy scale. The nonlinear simulations based on the lattice Boltzmann method (LBM) are further conducted to capture more information of the long term mixing behaviors at pore scale. The results of theoretical analysis and numerical simulations demonstrate that the miscible interface stability and convective mixing processes are determined by the competition among the gravitational instability and the reaction-infiltration instability. As the chemical reaction intensifies, the system gradually becomes dominated by reaction-infiltration instability from gravitational instability. The presence of H2S could suppress the gravitational instability but enhance the infiltration instability, thus, it has completely different effects under slow and fast reaction conditions. This investigation could improve our understand for the coupling effects of CO2 and H2S on the miscible interface stability and density-driven convective mixing process, which is significative for engineering of geological storage of CO2.

Fully nonlinear gravitational instabilities for expanding Newtonian universes with inhomogeneous pressure and entropy: Beyond the Tolman’s solution

Fully nonlinear gravitational instabilities for expanding Newtonian universes with inhomogeneous pressure and entropy: Beyond the Tolman’s solution

Luminosity Outburst Energized by the Collision between the Infalling Streamer and Disk in W51 North

We report the detection of the disk/torus, outflow, and inflow structures traced by H2O masers toward a high-mass young stellar object W51 North during its H2O maser outburst stage using the Karl G. Jansky Very Large Array (VLA). It is found that the disk has a radius of ∼4000 au and an inclination angle with respect to the sky plane of ∼60° by combining the VLA and the Atacama Large Millimeter/submillimeter Array data. Additionally, a peculiar flow perpendicular to the SiO bipolar outflow is detected in the H2O maser, SiO, and HC3N lines, which is newly-identified as an infalling streamer rather than an old outflow from this source, as reported in previous studies. Combining the VLA map and the Tianma radio telescope monitoring of the H2O masers suggests that the origin of the luminosity outburst of H2O masers during 2020 January–April is likely related to the energy release from the collision between the infalling streamer and the disk. This may provide an additional mechanism to account for the luminosity outburst or episodic accretion beyond disk fragmentation caused by gravitational instability.

Magnetically activated accretion outbursts of pre-main-sequence discs

ABSTRACT We investigate whether triggering of the magnetorotational instability (MRI) in protoplanetary discs can account for the wide diversity of observed accretion outbursts. We show that short-lived, relatively low accretion rate events probably result from triggering in the inner disc and can occur at low surface densities, comparable to or smaller than the minimum mass solar nebula, and thus are very unlikely to result from MRI triggering by gravitational instability. We develop time-dependent accretion disc models using an α-viscosity approach and calculate light curves to compare with observations. Our modelling indicates that the lag time between infrared and optical bursts seen in Gaia 17bpi can be explained with an outside-in propagation with an α ∼ 0.1 in the MRI-active region, consistent with other estimates. While outbursts in inner discs can show time delays of a few yr between infrared and optical light curves, our models indicate that large, FU Ori-like bursts can exhibit infrared precursors decades before optical bursts. Detecting such precursors could enable analysis of the central star before it is overwhelmed by the rapid accreting material, as well as constraining outburst physics. Our results emphasize the importance of near-infrared monitoring of young stellar objects in addition to optical surveys. In addition, our findings emphasize the need for more sophisticated, three-dimensional, non-ideal magnetohydrodynamic simulations to fully exploit observational results.

Soft-sediment deformation structures in the Mesoproterozoic Kaimur Sandstone, Vindhyan Supergroup (Central India), and their seismotectonic implications

The unequivocal identification of soft-sediment deformation structures (SSDS) is a significant attribute to constrain the effect of transient geological events in the spatio-temporal evolution of ancient sedimentary basins. This paper reports and discusses, for the first time, the occurrence of several cm- to dm-scale SSDS within sandstone successions of the Mesoproterozoic Kaimur Group (Vindhyan Supergroup), exposed at the Hanumandhara Hill of Chitrakoot-Satna border region, Madhya Pradesh State, India. The SSDS are confined to a deformed interval comprising seven individual sedimentary units of variable composition and texture, which are sandwiched between nearly horizontally undeformed sandstone beds. The SSDS consist of load structures (load casts, flame structures, pseudonodules and ball-and-pillow structures), contorted lamination, convolute lamination, boudins and pinch-and-swell structures, deformed cross-stratification, slump structures, clastic injections, fluid escape structures, and syn-sedimentary fractures/faults. The present study suggests that the formation of these SSDS is essentially related to a combination of processes (gravitational instability, liquefaction, fluidization, and fluid escape) predominantly induced by seismic shocks. In addition, the restricted occurrence of fractures/faults in these deformed layers emphasizes the passage of seismically-induced Rayleigh waves. Considering the observed types of SSDS, their lateral homogeneity and geographic distribution along with the geodynamic framework of the Vindhyan Basin, the whole area can be tentatively attributed to having experienced moderate- to high-magnitude (M ≥ 5) seismicity. The present study combined with earlier reports of seismically-induced SSDS, from other regionally disposed formations belonging to the Lower (e.g., Kajrahat Limestone, Chopan Porcellanite, Koldaha Shale, Rohtas Limestone, and Glauconitic Sandstone of the Semri Group) and Upper (e.g., Bhander Limestone of the Bhander Group) Vindhyan Supergroup, respectively, provides evidence for the constant regional-scale seismo–tectonic activity within the Paleo-Mesoproterozoic Vindhyan Basin. Importantly, this observation further suggests that the intracratonic basins can be active tectonically contrary to the earlier propositions.

Fundamental investigation of reactive-convective transport: Implications for long-term carbon dioxide (CO2) sequestration

The density-driven convection coupled with chemical reaction is the preferred mechanism for permanently storing CO2 in saline aquifers. This study uses a 2D visual Hele-Shaw cell to evaluate and visualize the density-driven convection formed due to gravitational instabilities. The primary goal of the experiments is to understand the various mechanisms for the mass transfer of gaseous CO2 into brine with different initial ionic concentrations and flow permeability. Moreover, the impact of CO2 injection locations, reservoir dipping angle, and permeability heterogeneity is also investigated. We observed that the presence of salts resulted in earlier onset of convection and a larger convective finger wavelength than the case with no dissolved salts. Additionally, a higher lateral mixing between CO2 fingers is observed when dipping is involved. The CO2 dissolution, indicated by the area of the pH-depressed region, depends on the type and concentration of the ions present in the brine and is observed to be 0.38–0.77 times compared to when no salt is present. Although convective flow is slowed in the presence of salts, the diffusive flux is enhanced, as observed from both qualitative and quantitative results. Moreover, the reduced formation permeability, introduced by using a flow barrier, resulted in numerous regions not being swept by the dissolved CO2, indicating an inefficient dissolution. We also investigated the effect of discrete high-conductivity fractures within the flow barriers, which showed an uneven vertical sweep and enhanced flow channeling. Lastly, the parameters regarding CO2 leakage risk during storage are identified and discussed.

Evaporation-driven gravitational instability in the liquid layer of a polymer solution: Theoretical and numerical studies

The drying of the thin liquid film of polymer solution is a complex process accompanying instabilities induced by concentration gradients that develop during the evaporation. This study investigates evaporation-driven gravitational instabilities (Rayleigh–Taylor instability) in the thin liquid film of a polymer solution based on theoretical and numerical analyses, specifically focusing on the onset of instability at the early stage of the drying process. Evaporation-driven convection is taken into account by employing a dynamic moving boundary condition and concentration-dependent material functions (dynamic viscosity and diffusivity). A theoretical analysis predicts the onset of gravitational instability (τc), showing good agreement with the results of a numerical simulation analysis (τd), suggesting scaling relationships between the onset of instability and the initial concentration (Ci), τc∼Ci−1/2, for a slow evaporation rate and dilute concentration range, which rapidly increases with an increase in the concentration due to an instability-retardation effect. A nonlinear two-dimensional numerical simulation visualizes the development of a polymer-dense layer, pluming, and a convection–diffusion flow throughout the liquid film under transient evaporation. The concentration-gradient-driven convection–diffusion flow enhances the gravitational instability and pluming further at higher frequencies. Meanwhile, for a polymer solution with high viscosity, viscosity thickening delays the onset of instability, retarding the development of instability. This study provides a fundamental understanding of the mechanism behind how convective instability develops in a drying polymer solution during evaporation and information on how to develop pluming of a polymer-dense skin layer at early stages of drying of a polymer solution film. The findings suggest that the proper control of hydrodynamic instability induced by a concentration gradient in a thin polymer solution film is important to prevent or enhance the formation of a convection pattern in the thin polymer film.

Breaking of Internal Waves Parametrically Excited by Ageostrophic Anticyclonic Instability

Abstract A gradient-wind balanced flow with an elliptic streamline parametrically excites internal inertia-gravity waves through ageostrophic anticyclonic instability (AAI). This study numerically investigates the breaking of internal waves and the following turbulence generation resulting from the AAI. In our simulation, we periodically distort the calculation domain following the streamlines of an elliptic vortex and integrate the equations of motion using a Fourier spectral method. This technique enables us to exclude the overall structure of the large-scale vortex from the computation and concentrate on resolving the small-scale waves and turbulence. From a series of experiments, we identify two different scenarios of wave breaking conditioned on the magnitude of the instability growth rate scaled by the buoyancy frequency λ/N. First, when , the primary wave amplitude excited by AAI quickly goes far beyond the overturning threshold and directly breaks. The resulting state is thus strongly nonlinear turbulence. Second, if , weak wave–wave interactions begin to redistribute energy across frequency space before the primary wave reaches a breaking limit. Then, after a sufficiently long time, the system approaches a Garrett–Munk-like stationary spectrum, in which wave breaking occurs at finer vertical scales. Throughout the experimental conditions, the growth and decay time scales of the primary wave energy are well correlated. However, since the primary wave amplitude reaches a prescribed limit in one scenario but not in the other, the energy dissipation rates exhibit two types of scaling properties. This scaling classification has similarities and differences with D’Asaro and Lien’s wave–turbulence transition model. Significance Statement Due to the gradients in buoyancy and pressure, density-stratified seawater supports oscillatory vertical motion called internal waves. When waves significantly skew a density isosurface, dense water lifts over lighter water resulting in gravitational instability and high energy dissipation. In this wave-breaking process, seawater is vertically mixed, transporting heat and nutrients essential to maintain Earth’s climate and ecosystems. This study investigates the generation and breaking of ocean internal waves in a novel numerical simulation setup; we temporally distort the model shape to emulate the wave excitation forced by a larger-size horizontal eddy, a ubiquitous situation at O(1–10) km scales in the upper ocean. The simulation results exhibit two unique wave-breaking scenarios with distinct scaling features in turbulence energy dissipation rates.

The Disc Miner

Detecting planets in the early stages of formation is key to reconstructing the history and diversity of fully developed planetary systems. The aim of this work is to identify potential signatures from planet-disc interaction in the circumstellar discs around MWC 480, HD 163296, AS 209, IM Lup, and GM Aur, through the study of molecular lines observed as part of the ALMA large program MAPS. Extended and localised perturbations in velocity, line width, and intensity have been analysed jointly using the DISCMINER modelling framework, in three bright CO isotopologues, 12CO, 13CO, and C18O J = 2−1, to provide a comprehensive summary of the kinematic and column density substructures that planets might be actively sculpting in these discs. We find convincing evidence for the presence of four giant planets located at wide orbits in three of the discs in the sample: two around HD 163296, one in MWC 480, and one in AS 209. One of the planet candidates in HD 163296, P94, previously associated with velocity signatures detected in lower velocity resolution 12CO data, is confirmed and linked to localised velocity and line width perturbations in 13CO and C18O too. We highlight that line widths are also powerful tracers of planet-forming sites as they are sensitive to turbulent motions triggered by planet-disc interactions. In MWC 480, we identified non-axisymmetric line width enhancements around the radial separation of candidate planet-driven buoyancy spirals, which we used to narrow the location of the possible planet to an orbital radius of R = 245 au and PA = 193°, at a projected distance of 1.33″ from the star. In the disc of AS 209, we found excess 12CO line widths centred at R = 210 au, PA = 151°, at a projected distance of 1.44″, spanning around the immediate vicinity of a circumplanetary disc candidate proposed previously, which further supports its presence. We report no clear localised or extended kinematic signatures in the discs of IM Lup or GM Aur that could be associated with the presence of planets or gravitational instabilities. On the other hand, we demonstrate that pressure minima exhibit line width minima counterparts in optically thick emission, making them robust tracers of gaps in the gas surface density when analysed together with azimuthal velocity flows. Finally, we show that nine out of eleven millimetre dust continuum rings in the sample are co-located with pressure bumps traced by kinematic modulations, indicating that aerodynamic confinement via pressure traps is a common mechanism for the formation of dust substructures in these discs. Overall, our analysis reveals that all discs in the sample present a remarkable level of substructure in all the line profile observables considered, regardless of the CO isotopologue. However, the magnitude and morphology of the substructures vary between discs and tracers, indicating that the kinematics and thermodynamic properties are likely shaped by different physical mechanisms in each object. We propose that the main kinematic signatures identified in the discs of MWC 480, HD 163296, and AS 209 have a planetary origin, although they do not always manifest as highly localised perturbations, while the discs of IM Lup and GM Aur do not yield clear signatures pointing to the presence of massive planets. Our simultaneous analysis of multiple tracers and observables aims to lay the groundwork for robust studies of molecular line properties focused on the search for young planets in discs.

An evolution of hyperbolic magneto-hydrodynamic (HMHD) wave propagating through radiative quantum plasma including cosmic ray pressure

The gravitational (Jeans) instability of radiative quantum plasma including cosmic ray (CR) pressure and diffusion is theoretically investigated using a generalized hyperbolic magneto-hydrodynamic model. It concurrently includes the impacts of the finite electrical resistivity, the Hall parameter, and the Coriolis force. The application of normal mode technique yields a unique form of a generalized dispersion relation. This dispersion relation is further discussed in the different modes of propagation with the different axis of rotation along the direction of the magnetic field. It has been noted that all the considered parameters affect the system's growth rate in both directions, but the Hall parameter does not affect it in the transverse direction. We also explored that together with the CRs, the Hall parameter, resistivity, rotation, and quantum parameter suppressed the Jeans instability's growth rate. Thus, these parameters act as stabilizing agents to the instability. The study identified radiative instability and analyzed the impact of an arbitrary heat-loss function on the system. The current findings provide new theoretical support to the existing various astronomic observations on the cosmic plasma and in the development of unique galactic formations of distinct scale lengths.

Lack of Correlations between Cold Molecular Gas and AGN Properties in Type 1 AGNs at z ≲ 0.5

We present new NOrthern Extended Millimeter Array (NOEMA) observations of the CO(2–1) emission in eight of the brightest Palomar-Green quasars at z ≲ 0.5 to investigate the role of active galactic nucleus (AGN) feedback in luminous quasars detected at low redshifts. We detect CO(2–1) emission in three objects, from which we derive CO luminosities, molecular gas masses and fractions, and gas depletion times. In combination with data available in the literature, we build a total sample of 138 local type 1 AGNs with CO(2–1) measurements. We compare the AGN properties with the host galaxy molecular gas properties, considering systems nondetected in CO emission. We find that the CO luminosity does not correlate with AGN luminosity and Eddington ratio, while the molecular gas fraction is weakly correlated with Eddington ratio. The type 1 AGNs can be roughly separated into two populations in terms of infrared-to-CO luminosity ratio, with one population presenting values typically found in normal star-forming systems, while the other having lower ratio values, comparable to those measured for starbursts. We find no evidence that AGN feedback rapidly quenches star formation in type 1 AGNs. Our results may imply an underlying the role of host galaxy gravitational instabilities or the fast inflow of cold gas in triggering AGN activity.

The Generation of Eocene Mafic Dike Swarms During the Exhumation of a Core Complex, Biarjmand Area, NE Iran

Abstract Several swarms of parallel E–W dikes cuts late Neoproterozoic- to early Paleozoic (540 Ma) basement in the Biarjmand area, NE Iran. The microgabbroic to doleritic dike are several hundred meters long and 0.5 to 3 meters wide. U–Pb dating of their zircon grains yields a crystallization age of 46.0 ± 7.1 Ma for the dike swarms. The dikes have SiO2 contents of 46.0–49.3 wt%, and Fe2O3 contents of 9.80–14.8 wt% with variable MgO (4.92–9.16 wt%), TiO2 (1.47–2.65 wt%), and K2O contents (0.33–1.13 wt%). The dikes have low contents of high field strength elements (HFSEs), and have some similarities to transitional mid-ocean ridge basalts (T-MORB) based on their chemical composition. Positive ${\varepsilon}_{Nd}(t)$ values of +5.2 to +6.0 for the dike samples imply that the basaltic magma was generated from depleted lithospheric mantle. After the closure of the Sabzevar ocean and obduction of the large mantle peridotite body over the continental crust in the late Cretaceous-Paleocene, the gravitational instability in the central Iran/Eurasia plate collision zone triggered exhumation of old basement coeval with injection of the mafic magma. During exhumation, mylonitic deformation with brittle-ductile structures affected the basement metagranite and the host rocks. The metagranite and dike swarms cut the Cretaceous Sabzevar ophiolite, and the disparting of ophiolite members probably occurred during basement exhumation in the Cenozoic. The similar ages of the mafic dike swarms and other Eocene magmatic rocks of the Urumiah (Urmia) Dokhtar magmatic arc (UDMA), western Iran, is consistent with a rapid extensional regime over the Sabzevar suture zone on an earlier collision zone in NE Iran. This process provided a suitable setting for the exhumation of the old basement, the emplacement of the parallel dike swarm, and the development of shallow basins in this area.