Three-dimensional Hydrodynamic Simulations Research Articles

Destruction of the central black hole gas reservoir through head-on galaxy collisions

A massive black hole exists in almost every galaxy. Black holes occasionally radiate a vast amount of light by releasing gravitational energy of accreting gas with a cumulative active period of only a few 108 yr, the so-called duty cycle of the active galactic nuclei. Many galaxies today host a starving massive black hole. Although galaxy collisions have been thought to enhance nucleus activity1,2, the origin of the duty cycle, especially the shutdown process, is still a critical issue3. Here, we show that galaxy collisions are also capable of suppressing black hole fuelling, by using an analytic model and three-dimensional hydrodynamic simulations and by applying the well-determined parameter sets for the galactic collision in the Andromeda galaxy4,5. Our models demonstrate that a central collision of galaxies can strip the torus-shaped gas surrounding the massive black hole, the putative fuelling source. The derived condition for switching off the black hole fuelling indicates that a notable fraction of currently bright nuclei can become inactive, which is reminiscent of the fading or dying active nucleus phenomena6,7,8,9 that are associated with galaxy merging events. Galaxy collisions may therefore be responsible for both switching off and turning on the nucleus activity, depending on the collision orbit (head-on or far-off-centre).

Sustained Kozai–Lidov Oscillations in Misaligned Circumstellar Gas Disks

Abstract A disk around one component of a binary star system with sufficiently high inclination can undergo Kozai–Lidov (KL) oscillations during which the disk inclination and disk eccentricity are exchanged. Previous studies show that without a source of accretion, KL unstable disks exhibit damped oscillations, due to viscous dissipation, that leave the disk stable near or below the critical inclination for KL oscillations. With three-dimensional hydrodynamical simulations we show that a highly misaligned circumbinary disk that flows onto the binary components forms highly inclined circumstellar disks around each component. We show that a continuous infall of highly inclined material allows the KL oscillations to continue. The KL disk oscillations produce shocks and eccentricity growth in the circumstellar disks that affect the conditions for planet formation.

Supernova Explosions in Accretion Disks in Active Galactic Nuclei: Three-dimensional Models

Abstract Supernova (SN) explosions can potentially affect the structure and evolution of circumnuclear disks in active galactic nuclei (AGN). Some previous studies have suggested that a relatively low rate of SN explosions can provide an effective value of alpha viscosity between 0.1 and 1 in AGN accretion disks within a 1 pc scale. In order to test this possibility, we provide some analytic scalings of the evolution of an SN remnant embedded in a differentially rotating smooth disk. We calibrate our estimates using three-dimensional hydrodynamical simulations where the gas is modeled as adiabatic with index γ. Our simulations are suited to include the fact that a fraction of the momentum injected by the SN escapes from the disk into the corona. Based on these results, we calculate the contribution of SN explosions to the effective alpha viscosity, denoted by α SNe, in a model AGN accretion disk, where accretion is driven by the local viscosity α. We find that for AGN galaxies with a central black hole of and a disk with viscosity α = 0.1, the contribution of SN explosions may be as large as , provided that . On the other hand, in the momentum conservation limit, which is valid when the push by the internal pressure of the SN remnant is negligible, we find .

Acoustic-gravity wave propagation characteristics in three-dimensional radiation hydrodynamic simulations of the solar atmosphere.

There has been tremendous progress in the degree of realism of three-dimensional radiation magneto-hydrodynamic simulations of the solar atmosphere in the past decades. Four of the most frequently used numerical codes are Bifrost, CO5BOLD, MANCHA3D and MURaM. Here we test and compare the wave propagation characteristics in model runs from these four codes by measuring the dispersion relation of acoustic-gravity waves at various heights. We find considerable differences between the various models. The height dependence of wave power, in particular of high-frequency waves, varies by up to two orders of magnitude between the models, and the phase difference spectra of several models show unexpected features, including ±180° phase jumps. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

Whole-beam self-focusing in fusion-relevant plasma.

Fast ignition inertial confinement fusion requires the production of a low-density channel in plasma with density scale-lengths of several hundred microns. The channel assists in the propagation of an ultra-intense laser pulse used to generate fast electrons which form a hot spot on the side of pre-compressed fusion fuel. We present a systematic characterization of an expanding laser-produced plasma using optical interferometry, benchmarked against three-dimensional hydrodynamic simulations. Magnetic fields associated with channel formation are probed using proton radiography, and compared to magnetic field structures generated in full-scale particle-in-cell simulations. We present observations of long-lived, straight channels produced by the Habara–Kodama–Tanaka whole-beam self-focusing mechanism, overcoming a critical barrier on the path to realizing fast ignition.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Common-envelope evolution with an asymptotic giant branch star

Common-envelope phases are decisive for the evolution of many binary systems. Cases with asymptotic giant branch (AGB) primary stars are of particular interest because they are thought to be progenitors of various astrophysical transients. In three-dimensional hydrodynamic simulations with the moving-mesh code AREPO, we study the common-envelope evolution of a 1.0 M⊙ early-AGB star with companions of different masses. Although the stellar envelope of an AGB star is less tightly bound than that of a red giant, we find that the release of orbital energy of the core binary is insufficient to eject more than about twenty percent of the envelope mass. Ionization energy that is released in the expanding envelope, however, can lead to complete envelope ejection. Because recombination proceeds largely at high optical depths in our simulations, it is likely that this effect indeed plays a significant role in the considered systems. The efficiency of mass loss and the final orbital separation of the core binary system depend on the mass ratio between the companion and the primary star. Our results suggest a linear relation between the ratio of final to initial orbital separation and this parameter.

Numerical study of coorbital thermal torques on cold or hot satellites

ABSTRACT We evaluate the thermal torques exerted on low-mass planets embedded in gaseous protoplanetary discs with thermal diffusion, by means of high-resolution three-dimensional hydrodynamics simulations. We confirm that thermal torques essentially depend on the offset between the planet and its corotation, and find a good agreement with analytic estimates when this offset is small compared to the size of the thermal disturbance. For larger offsets that may be attained in discs with a large pressure gradient or a small thermal diffusivity, thermal torques tend towards an asymptotic value broadly compatible with results from a dynamical friction calculation in an unsheared medium. We perform a convergence study and find that the thermal disturbance must be resolved over typically 10 zones for a decent agreement with analytic predictions. We find that the luminosity at which the net thermal torque changes sign matches that predicted by linear theory within a few percents. Our study confirms that thermal torques usually supersede Lindblad and corotation torques by almost an order of magnitude for low-mass planets. As we increase the planetary mass, we find that the ratio of thermal torques to Lindblad and corotation torques is progressively reduced, and that the thermal disturbance is increasingly distorted by the horseshoe flow. Overall, we find that thermal torques are dominant for masses up to an order of magnitude larger than implemented in recent models of planetary population synthesis. We finally briefly discuss the case of stellar or intermediate-mass objects embedded in discs around active galactic nuclei.

Atmospheric structure and dynamics of evolved massive stars. Thanks to 3D radiative hydrodynamical simulations of stellar convection

AbstractEvolved massive stars are major cosmic engines, providing strong mechanical and radiative feedback on their host environment. They contribute to the enrichment of their environment through a strong stellar winds, still poorly understood. Wind physics across the life cycle of these stars is the key ingredient to accomplish a complete understanding of their evolution in the near and distant Universe. Nowadays, the development of the observational instruments is so advanced that the observations became very sensitive to the details of the stellar surface making possible to quantitatively study what happens on their surfaces and above where the stellar winds become dominant. Three-dimensional radiative hydrodynamics simulations of evolved stars are essential to a proper and quantitative analysis of these observations. This work presents how these simulations have been (and will be) crucial to prepare and interpret a multitude of observations and how they are important to achieve the knowledge of the mass-loss mechanism.

3D hydrodynamical survey of the impact of a companion on the morphology and dynamics of AGB outflows

AbstractWith the use of high-resolution ALMA observations, complex structures that resemble those observed in post-AGB stars and planetary nebulae are detected in the circumstellar envelopes of low-mass evolved stars. These deviations from spherical symmetry are believed to be caused primarily by the interaction with a companion star or planet. With the use of three-dimensional hydrodynamic simulations, we study the impact of a binary companion on the wind morphology and dynamics of an AGB outflow. We classifiy the wind structures and morphology that form in these simulations with the use of a classification parameter, constructed with characteristic parameters of the binary configuration. Finally we conclude that the companion alters the wind expansion velocity through the slingshot mechanism, if it is massive enough.

Long-term evolution of surviving companion stars of Type Iax supernovae

ABSTRACT The nature of the progenitors and explosion mechanism of Type Iax supernovae (SNe Iax) remain a mystery. The single-degenerate (SD) systems that involve the incomplete pure deflagration explosions of near-Chandrasekhar-mass white dwarfs (WDs) have recently been proposed for producing SNe Iax in which non-degenerate companions are expected to survive from SN explosions. In this work, we concentrate on the main-sequence (MS) donor SD progenitor systems. By mapping the computed companion models from three-dimensional hydrodynamical simulations of ejecta-companion interaction into a one-dimensional stellar evolution code mesa, we investigate the long-term appearance and observational signatures of surviving MS companions of SNe Iax by tracing their post-impact evolution. Depending on different MS companion models, it is found that the shocked surviving companion stars can significantly expand and evolve to be more luminous (5–$500\, L_{\odot }$) for a time-scale of 10–104 yr. Comparing with the late-time light curve of an observed SN Iax (SN 2005hk), it is suggested that surviving MS companions of SNe Iax would expect to be visible about 1000 d after the explosion when SN itself has been faded.

Suppression of H2-cooling in protogalaxies aided by trapped Lyα cooling radiation

ABSTRACT We study the thermal evolution of UV-irradiated atomic cooling haloes using high-resolution three-dimensional hydrodynamic simulations. We consider the effect of H− photodetachment by Lyα cooling radiation trapped in the optically-thick cores of three such haloes, a process that has not been included in previous simulations. Because H− is a precursor of molecular hydrogen, its destruction can diminish the H2 abundance and cooling. We find that the critical UV flux for suppressing H2-cooling is decreased by ∼15–50 per cent in our fiducial models. Previous one-zone modelling found a larger effect, with Jcrit reduced by a factor of a few; we show that adopting a constant halo mass to determine the trapped Lyα energy density, as is done in the one-zone models, yields a larger reduction in Jcrit, consistent with their findings. Our results nevertheless suggest that Lyα radiation may have an important effect on the thermal evolution of UV-irradiated haloes, and therefore on the potential for massive black hole formation.

Convectively Driven 3D Turbulence in Massive Star Envelopes. I. A 1D Implementation of Diffusive Radiative Transport

Abstract Massive (M > 30 M ⊙) stars exhibit luminosities that are near the Eddington limit for electron scattering, causing the increase in opacity associated with iron at T ≈ 180 , 000 K to trigger supersonic convection in their outer envelopes. Three-dimensional radiative hydrodynamics simulations by Jiang and collaborators with the Athena++ computational tool have found order-of-magnitude density and radiative flux fluctuations in these convective regions, even at optical depths ≫ 100 . We show here that radiation can diffuse out of a parcel during the timescale of convection in these optically thick parts of the star, motivating our use of a “pseudo” Mach number to characterize both the fluctuation amplitudes and their correlations. In this first paper, we derive the impact of these fluctuations on the radiative pressure gradient needed to carry a given radiative luminosity. This implementation leads to a remarkable improvement between 1D and 3D radiative pressure gradients, and builds confidence in our path to an eventual 1D implementation of these intrinsically 3D envelopes. However, simply reducing the radiation pressure gradient is not enough to implement a new 1D model. Rather, we must also account for the impact of two other aspects of turbulent convection: the substantial pressure and the ability to transport an appreciable fraction of the luminosity, which will be addressed in upcoming works. This turbulent convection also arises in other instances where the stellar luminosity approaches the Eddington luminosity. Hence, our effort should apply to other astrophysical situations where an opacity peak arises in a near Eddington-limited, radiation pressure-dominated plasma.

Shock–multicloud interactions in galactic outflows – I. Cloud layers with lognormal density distributions

ABSTRACT We report three-dimensional hydrodynamical simulations of shocks (${\cal M_{\rm shock}}\ge 4$) interacting with fractal multicloud layers. The evolution of shock–multicloud systems consists of four stages: a shock-splitting phase in which reflected and refracted shocks are generated, a compression phase in which the forward shock compresses cloud material, an expansion phase triggered by internal heating and shock re-acceleration, and a mixing phase in which shear instabilities generate turbulence. We compare multicloud layers with narrow ($\sigma _{\rho }=1.9\bar{\rho }$) and wide ($\sigma _{\rho }=5.9\bar{\rho }$) lognormal density distributions characteristic of Mach ≈ 5 supersonic turbulence driven by solenoidal and compressive modes. Our simulations show that outflowing cloud material contains imprints of the density structure of their native environments. The dynamics and disruption of multicloud systems depend on the porosity and the number of cloudlets in the layers. ‘Solenoidal’ layers mix less, generate less turbulence, accelerate faster, and form a more coherent mixed-gas shell than the more porous ‘compressive’ layers. Similarly, multicloud systems with more cloudlets quench mixing via a shielding effect and enhance momentum transfer. Mass loading of diffuse mixed gas is efficient in all models, but direct dense gas entrainment is highly inefficient. Dense gas only survives in compressive clouds, but has low speeds. If normalized with respect to the shock-passage time, the evolution shows invariance for shock Mach numbers ≥10 and different cloud-generating seeds, and slightly weaker scaling for lower Mach numbers and thinner cloud layers. Multicloud systems also have better convergence properties than single-cloud systems, with a resolution of eight cells per cloud radius being sufficient to capture their overall dynamics.

Rotational manipulation of a microscopic object inside a microfluidic channel.

Observations and analyses of a microscopic object are essential processes in various fields such as chemical engineering and life science. Microfluidic techniques with various functions and extensions have often been used for such purposes to investigate the mechanical properties of microscopic objects such as biological cells. One of such extensions proposed in this context is a real-time visual feedback manipulation system, which is composed of a high-speed camera and a piezoelectric actuator with a single-line microfluidic channel. Although the on-chip manipulation system enables us to control the 1 degree-of-freedom position of a target object by the real-time pressure control, it has suffered from unintended changes in the object orientation, which is out of control in the previous system. In this study, we propose and demonstrate a novel shear-flow-based mechanism for the control of the orientation of a target object in addition to the position control in a microchannel to overcome the problem of the unintended rotation. We designed a tributary channel using a three-dimensional hydrodynamic simulation with boundary conditions appropriate for the particle manipulation to apply shear stress to the target particle placed at the junction and succeeded in rotating the particle at an angular velocity of 0.2 rad/s even under the position control in the experiment. The proposed mechanism would be applied to feedback controls of a target object in a microchannel to be in a desired orientation and at a desired position, which could be a universally useful function for various microfluidic platforms.

Simulating Jets from a Neutron Star Companion Hours after a Core-collapse Supernova

Abstract We conduct three-dimensional hydrodynamical simulations to explore the interaction of the jets that a neutron star (NS) companion to a type Ic or type Ib core-collapse supernova (CCSN) launches a few hours after explosion with the ejecta of the CCSN. We assume that an NS companion at 5 R ⊙ from the exploding star accretes mass from the slower inner ejecta through an accretion disk, and that the disk launches two opposite jets. Although the energy of the jets is only about one percent of the total energy of the ejecta, it is comparable to the energy of the slower inner part of the ejecta. We find that the jets inflate one low-density hot bubble to one side of the ejecta, and that this bubble expands to influence ejecta gas up to expansion velocities of . The postshock jets’ material develops a large meridional flow and small vortexes. The boundary between the ejecta and jets’ postshock gases is unstable. The instabilities and vortexes mix jets’ gas with the ejecta. We expect such a hot bubble to contribute to the light curve of CCSNe that are progenitors of binary NS systems, in particular to observers on the side of the bubble.

Are the spiral arms in the MWC 758 protoplanetary disc driven by a companion inside the cavity?

ABSTRACT Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an ≈10MJup companion on an eccentric orbit internal to the spiral arms. Previous studies on MWC 758 have assumed an external companion. We compare simulated observations from three-dimensional hydrodynamics simulations of disc–companion interaction to scattered light, infrared and CO molecular line observations, taking into account observational biases. The inner companion hypothesis is found to explain the double spiral arms, as well as several additional features seen in MWC 758 – the arc in the north-west, substructures inside the spiral arms, the cavity in CO isotopologues, and the twist in the kinematics. Testable predictions include detection of fainter spiral structure, detection of a point source south-southeast of the primary, and proper motion of the spiral arms.

Disc formation and jet inclination effects in common envelopes

ABSTRACT The evolution and physics of the common envelope (CE) phase are still not well understood. Jets launched from a compact object during this stage may define the evolutionary outcome of the binary system. We focus on the case in which jets are launched from a neutron star (NS) engulfed in the outer layers of a red giant (RG). We run a set of three-dimensional hydrodynamical simulations of jets with different luminosities and inclinations. The luminosity of the jet is self-regulated by the mass accretion rate and an efficiency η. Depending on the value of η the jet can break out of the previously formed bulge (‘successful jet’) and aligns against the incoming wind, in turn, it will realign in favour of the direction of the wind. The jet varies in size and orientation and may present quiescent and active epochs. The inclination of the jet and the Coriolis and centrifugal forces, only slightly affect the global evolution. As the accretion is hypercritical, and the specific angular momentum is above the critical value for the formation of a disc, we infer the formation of a disc and launching of jets. The discs’ mass and size would be ∼10−2 M⊙ and ≳1010 cm, and it may have rings with different rotation directions. In order to have a successful jet from a white dwarf, the ejection process needs to be very efficient (η ∼ 0.5). For main-sequence stars, there is not enough energy reservoir to launch a successful jet.

Simulating coliform transport and decay from 3D hydrodynamics model and in situ observation in Nice area

In coastal area, raw wastewater can be directly discharged in the sea during extreme rain events or failure of the sewage network. The highly urbanized and touristic area of Nice is directly exposed to this risk. In order to protect the bathing population and to apply the European regulation (DCE, 2000), Nice municipality has decided to work on a forecasting tool of transport and fate of fecal bacterial indicators such as Escherichia coli. This paper deals with the first step of this approach which consists in developing a three-dimensional hydrodynamic simulation coupled with water quality parameters. The model used is based on Reynolds-Averaged Navier–Stokes’s equations for the calculation of the velocities and water depth (TELEMAC3D), and wave energy balance equation to account for the wave induced current (TOMAWAC). Two field measurements were conducted on a real wastewater pollution coming from a sewage pipe located at −38 m depth. The first campaign has validated the vertical diffusion of the effluent through the water column by the means of variable depth samples and has stressed the hourly variability of sewage bacterial quality. Due to the lack of data regarding this last point, the model could not be fully validated. The second campaign has been designed to overcome this issue and to gather all the data needed to proceed to the validation of our hydro-ecological simulation. The comparison of the field measurements and the simulations has successfully demonstrated the accuracy of the model. But the uncertainty associated with the laboratory analysis (MPN) are high, making the calibration and validation processes a complex task. Nevertheless, further research needs to be done regarding the variability of microbial quality in order to develop an operational tool allowing the forecast of bacterial pollution. The next step of this study will be to establish the hourly variation of microbial quality in the wastewater during dry and raining periods.

Common Envelope Wind Tunnel: The Effects of Binary Mass Ratio and Implications for the Accretion-driven Growth of LIGO Binary Black Holes

Abstract We present three-dimensional local hydrodynamic simulations of flows around objects embedded within stellar envelopes using a “wind tunnel” formalism. Our simulations model the common envelope dynamical inspiral phase in binary star systems in terms of dimensionless flow characteristics. We present suites of simulations that study the effects of varying the binary mass ratio, stellar structure, equation of state, relative Mach number of the object’s motion through the gas, and density gradients across the gravitational focusing scale. For each model, we measure coefficients of accretion and drag experienced by the embedded object. These coefficients regulate the coupled evolution of the object’s masses and orbital tightening during the dynamical inspiral phase of the common envelope. We extrapolate our simulation results to accreting black holes with masses comparable to that of the population of LIGO black holes. We demonstrate that the mass and spin accrued by these black holes per unit orbital tightening are directly related to the ratio of accretion to drag coefficients. We thus infer that the mass and dimensionless spin of initially nonrotating black holes change by of order 1% and 0.05, respectively, in a typical example scenario. Our prediction that the masses and spins of black holes remain largely unmodified by a common envelope phase aids in the interpretation of the properties of the growing observed population of merging binary black holes. Even if these black holes passed through a common envelope phase during their assembly, features of mass and spin imparted by previous evolutionary epochs should be preserved.

Three-dimensional hydrodynamic simulations of the upper atmosphere of π Men c: Comparison with Lyα transit observations

Context. π Men c is the first planet to have been discovered by the Transiting Exoplanet Survey Satellite. It orbits a bright, nearby star and has a relatively low average density, making it an excellent target for atmospheric characterisation. The existing planetary upper atmosphere models of π Men c predict significant atmospheric escape, but Lyα transit observations indicate the non-detection of hydrogen escaping from the planet. Aims. Our study is aimed at constraining the conditions of the wind and high-energy emission of the host star and reproducing the non-detection of Lyα planetary absorption. Methods. We modelled the escaping planetary atmosphere, the stellar wind, and their interaction employing a multi-fluid, three-dimensional hydrodynamic code. We assumed a planetary atmosphere composed of hydrogen and helium. We ran models varying the stellar high-energy emission and stellar mass-loss rate, and, for each case, we further computed the Lyα synthetic planetary atmospheric absorption and compared it with the observations. Results. We find that a non-detection of Lyα in absorption employing the stellar high-energy emission estimated from far-ultraviolet and X-ray data requires a stellar wind with a stellar mass-loss rate about six times lower than solar. This result is a consequence of the fact that, for π Men c, detectable Lyα absorption can be caused exclusively by energetic neutral atoms, which become more abundant with increasing velocity or density of the stellar wind. By considering, instead, that the star has a solar-like wind, the non-detection requires a stellar ionising radiation about four times higher than estimated. The reason for this is that despite the fact that a stronger stellar high-energy emission ionises hydrogen more rapidly, it also increases the upper atmosphere heating and expansion, pushing the interaction region with the stellar wind farther away from the planet, where the planet atmospheric density that remains neutral becomes smaller and the production of energetic neutral atoms less efficient. Conclusions. Comparing the results of our grid of models with what is expected and estimated for the stellar wind and high-energy emission, respectively, we support the idea that it is likely that the atmosphere of π Men c is not hydrogen-dominated. Therefore, future observations should focus on the search for planetary atmospheric absorption at the position of lines of heavier elements, such as He, C, and O.