3D Hydrodynamical Simulations Research Articles

Alpha Centauri: Disc Dynamics, Planet Stability, Detectability

Alpha Centauri is a triple stellar system, and it contains the closest star to Earth (Proxima Centauri). Over the last decades, the stars in Alpha Cen and their orbits have been investigated in great detail. However, the possible scenarios for planet formation and evolution in this triple stellar system remain to be explored further. First, we present a 3D hydrodynamical simulation of the circumstellar discs in the binary Alpha Cen AB. Then, we compute stability maps for the planets within Alpha Cen obtained through N-body integrations. Last, we estimate the radial velocity (RV) signals of such planets. We find that the circumstellar discs within the binary cannot exceed 3 au in radius and that the available dust mass to form planets is about 30 M⊕. Planets around A and B are stable if their semimajor axes are below 3 au, while those around C are stable and remain unperturbed by the binary AB. For rocky planets, the planetary mass has only a mild effect on the stability. Therefore, Alpha Cen could have formed and hosted rocky planets around each star, which may be detected with RV methods in the future. The exoplanetary hunt in this triple stellar system must continue.

The density of the Milky Way’s corona atz≈ 1.6 through ram pressure stripping of the Draco dSph galaxy

ABSTRACTSatellite galaxies within the Milky Way’s (MW's) virial radius Rvir are typically devoid of cold gas due to ram pressure stripping by the MW’s corona. The density of this corona is poorly constrained today and essentially unconstrained in the past, but can be estimated using ram pressure stripping. In this paper, we probe the MW's corona at z ≈ 1.6 using the Draco dwarf spheroidal galaxy. We assume that (i) Draco’s orbit is determined by its interaction with the MW, whose dark matter halo we evolve in time following cosmologically motivated prescriptions, (ii) Draco’s star formation was quenched by ram pressure stripping and (iii) the MW’s corona is approximately smooth, spherical, and in hydrostatic equilibrium. We used Gaia proper motions to set the initial conditions and Draco’s star formation history to estimate its past gas content. We found indications that Draco was stripped of its gas during the first pericentric passage. Using 3D hydrodynamical simulations at a resolution that enables us to resolve individual supernovae and assuming no tidal stripping, which we estimate to be a minor effect, we find a density of the MW corona ≥8 × 10−4 cm−3 at a radius ≈0.72Rvir. This provides evidence that the MW’s corona was already in place at z ≈ 1.6 and with a higher density than today. If isothermal, this corona would have contained all the baryons expected by the cosmological baryon fraction. Extrapolating to today shows good agreement with literature constraints if feedback has removed ≲30 per cent of baryons accreted on to the halo.

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

ABSTRACT We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\, \mathrm{M_\odot }$ red giant branch primary and a $1\, \mathrm{M_\odot }$ companion modelled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, ∼15 per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of ${\sim}2\, {\rm yr}$, after which the envelope would be unbound.

3D multi-system Bayesian calibration with energy conservation to study rapidity-dependent dynamics of nuclear collisions

Considerable information about the early-stage dynamics of heavyion collisions is encoded in the rapidity dependence of measurements. To leverage the large amount of experimental data, we perform a systematic analysis using three-dimensional hydrodynamic simulations of multiple collision systems — large and small, symmetric and asymmetric. Specifically, we perform fully 3D multi-stage hydrodynamic simulations initialized by a parameterized model for rapidity-dependent energy deposition, which we calibrate on the hadron multiplicity and anisotropic flow coefficients. We utilize Bayesian inference to constrain properties of the early- and late-time dynamics of the system, and highlight the impact of enforcing global energy conservation in our 3D model.

Assessing the Observability of Deep Meridional Flow Cells in the Solar Interior

Meridional circulation regulates the Sun’s interior dynamics and magnetism. While it is well accepted that meridional flows are poleward at the Sun’s surface, helioseismic observations have yet to provide a definitive answer for the depth at which those flows return to the equator, or the number of circulation cells in depth. Here, we explore the observability of multiple circulation cells stacked in radius. Specifically, we examine the seismic signature of several meridional flow profiles by convolving time–distance averaging kernels with mean flows obtained from a suite of 3D hydrodynamic simulations. At mid and high latitudes, we find that weak flow structures in the deep convection zone can be obscured by signals from the much stronger surface flows. This contamination of 1–2 m s−1 is caused by extended side lobes in the averaging kernels, which produce a spurious equatorward signal with flow speeds that are 1 order of magnitude stronger than the original flow speeds in the simulations. At low latitudes, the flows in the deep layers of the simulations are stronger (>2 m s−1) and multiple cells across the convection zone can produce a sufficiently strong signal to survive the convolution process. Now that meridional flows can be measured over two decades of data, the uncertainties arising from convective noise have fallen to a level where they are comparable in magnitude to the systematic biases caused by nonlocal features in the averaging kernels. Hence, these systematic errors are beginning to influence current helioseismic deductions and need broader consideration.

Towards a holistic view of the origin of multiple stellar populations in globular clusters

The presence of multiple stellar populations in globular clusters is now well accepted, however, very little is known regarding how they formed. Answering this question is one of the major challenges of stellar astrophysics, yet of great interest, given the importance of globular clusters in different fields, from stellar evolution to gravitational wave emission and galaxy assembly. We present a series of 3D hydrodynamic simulations both of isolated clusters and at a cosmological scale aimed at probing the formation of globular clusters and their multiple stellar populations. We focus first on the effects of both rotation and Type Ia supernovae on the formation of the second population with particular attention on the chemical composition of the newborn stars. Then, we present the first simulations of the SImulating the Environment where Globular clusters Emerged project aimed at probing the formation of globular clusters through sub-parsec cosmological zoom-in simulations.

Collisionless shock acceleration of protons in a plasma slab produced in a gas jet by the collision of two laser-driven hydrodynamic shockwaves

We have recently proposed a new technique of plasma tailoring by laser-driven hydrodynamic shockwaves generated on both sides of a gas jet [Marquès et al., Phys. Plasmas 28, 023103 (2021)]. In a continuation of this numerical work, we study experimentally the influence of the tailoring on proton acceleration driven by a high-intensity picosecond laser in three cases: without tailoring, by tailoring only the entrance side of the picosecond laser, and by tailoring both sides of the gas jet. Without tailoring, the acceleration is transverse to the laser axis, with a low-energy exponential spectrum, produced by Coulomb explosion. When the front side of the gas jet is tailored, a forward acceleration appears, which is significantly enhanced when both the front and back sides of the plasma are tailored. This forward acceleration produces higher-energy protons, with a peaked spectrum, and is in good agreement with the mechanism of collisionless shock acceleration (CSA). The spatiotemporal evolution of the plasma profile is characterized by optical shadowgraphy of a probe beam. The refraction and absorption of this beam are simulated by post-processing 3D hydrodynamic simulations of the plasma tailoring. Comparison with the experimental results allows estimation of the thickness and near-critical density of the plasma slab produced by tailoring both sides of the gas jet. These parameters are in good agreement with those required for CSA.

Dust evolution in a supernova interacting with the ISM

ABSTRACT Supernovae (SNe) explosions are thought to be an important source of dust in galaxies. At the same time strong shocks from SNe are known as an efficient mechanism of dust destruction via thermal and kinetic sputtering. A critically important question of how these two hypotheses of SNe activity control the dust budget in galaxies is still not quite clearly understood. In this paper, we address this question within 3D multifluid hydrodynamical simulations, treating separately the SNe injected dust and the dust pre-existed in ambient interstellar gas. We focus primarily on how the injected and the pre-existing dust is destroyed by shock waves and hot gas in the SN bubble depending on the density of ambient gas. Within our model, we estimate an upper limit of the SN-produced dust mass which can be supplied into interstellar medium. For an SN progenitor mass of 30 M⊙ and the ejected dust mass Md = 1 M⊙, we constrain the dust mass that can be delivered into the ISM as ≥0.13 M⊙, provided that the SN has injected large dust particles with a ≥ 0.1 µm.

Using helium 10 830 Å transits to constrain planetary magnetic fields

ABSTRACT Planetary magnetic fields can affect the predicted mass-loss rate for close-in planets that experience large amounts of ultraviolet irradiation. In this work, we present a method to detect the magnetic fields of close-in exoplanets undergoing atmospheric escape using transit spectroscopy at the 10 830 Å line of helium. Motivated by previous work on hydrodynamic and magnetohydrodynamic photoevaporation, we suggest that planets with magnetic fields that are too weak to control the outflow’s topology lead to blueshifted transits due to dayside-to-nightside flows. In contrast, strong magnetic fields prevent this day-to-night flow, as the gas is forced to follow the magnetic field’s roughly dipolar topology. We post-process existing 2D photoevaporation simulations, computing synthetic transit profiles in helium to test this concept. As expected, we find that hydrodynamically dominated outflows lead to blueshifted transits of the order of the sound speed of the gas. Strong surface magnetic fields lead to unshifted or slightly redshifted transit profiles. High-resolution observations can distinguish between these profiles; however, eccentricity uncertainties generally mean that we cannot conclusively say that velocity shifts are due to the outflow for individual planets. The majority of helium observations are blueshifted, which could be a tentative indication that close-in planets generally have surface dipole magnetic field strengths $\lesssim \!\! 0.3$ G. More 3D hydrodynamic and magnetohydrodynamic simulations are needed to confirm this conclusion robustly.

3D hydrodynamics simulations of a 3 M⊙ core helium burning star

ABSTRACT The inner structure of core helium burning (CHeB) stars remains uncertain due to the yet unknown nature of mixing at the boundary of their cores. Large convective cores beyond a bare Schwarzschild model are favoured both from theoretical arguments and from asteroseismological constraints. However, the exact nature of this extra mixing, and in particular the possible presence of semiconvective layers, is still debated. In this work, we approach this problem through a new avenue by performing the first full-sphere 3D hydrodynamics simulations of the interiors of CHeB stars. We use the ppmstar explicit gas dynamics code to simulate the inner 0.45$\, {\rm M}_{\odot }$ of a 3 M⊙ CHeB star. Simulations are performed using different Cartesian grid resolutions (7683, 11523, and 17283) and heating rates. We use two different initial states, one based on mesas's predictive mixing scheme (which significantly extends the core beyond the Schwarzschild boundary) and one based on the convective premixing approach (which exhibits a semiconvective interface). The general behaviour of the flow in the convective core and in the stable envelope (where internal gravity waves are observed) is consistent with our recent simulations of core convection in massive main-sequence stars, and so are the various luminosity scaling relations. The semiconvective layers are dominated by strong internal gravity waves that do not produce measurable species mixing, but overshooting motions from the convective core gradually homogenize the semiconvective interface. This process can possibly completely erase the semiconvective layers, which would imply that CHeB stars do not harbour a semiconvection zone.

Marine Macro-Litter (Plastic) Pollution of German and North African Marina and City-Port Sea Floors

The macro-litter (plastic) sea-bottom pollution of 14 city harbors and marinas in North Africa and in the western Baltic Sea was investigated using a new simple mobile underwater camera system. The study was complemented by a harbor-manager survey and 3D hydrodynamic transport simulations. The average pollution in German marinas was 0.1 particles/m2 sea floor (0.04–1.75). The pollution in North African marinas on average was seven times higher (0.7 particles/m2) and exceeded 3 particles/m2 in city-center harbors. The resulting > 100,000 litter particles per harbor indicate the existence of a problem. At 73–74%, plastic particles are dominating. Existing legal and management frameworks explain the lack of plastic bottles and bags on sea floors in Germany and are one reason for the lower pollution levels. Items that indicate the role of untreated sewage water were not found. Harbor festivals seem to be quantitatively irrelevant for open sea-bottom pollution. Our method tends to underestimate the pollution level. Model simulations indicate that storms can cause litter reallocations and sediment cleanings. However, marina sea-floor monitoring is recommendable because it addresses pollution hotspots, is cost-effective and takes place close to emission sources. Further, the effectiveness of land-based pollution-reduction measures can easily be assessed.

Assessing the compound flood risk in coastal areas: Framework formulation and demonstration

Storm surge and river runoff can result in compound flooding in coastal areas. The impact of these events can be more significant than that generated by each component individually. This paper describes a framework for characterizing flooding during compound events and quantifying the relative importance of surge and river flows in controlling inundation depth (ID). For the analysis, we considered 1051 simulations of historical flood events covering about 40 years in Connecticut (CT), USA, and several simulated storms associated with synthetic climate scenarios. We simulated river discharge time series for each event using a physically based distributed hydrological model and retrieved the storm surge from tidal stations. These time series are used as upstream and downstream boundary conditions in 2D hydrodynamic simulation. We focused the analysis on seven locations along the coast of Connecticut covered by LiDAR-derived 1 m DEM. To capture the variability of inundation characteristics over the full-scale gradient from river to coast, we introduced a new topographic index, D-Index, that distinguishes topologic variabilities. Results from this study highlight that there is a correlation of ID to different drivers in distinct categories of the D-Index, which can correctly label the main source of hazard, either coast, river, or compound. We identified thresholds of standard deviation (σ) of the D-Index to identify areas where ID strongly correlates with either flow peak and volume, surge peak, or a combination of both. The study also shows that it is possible to use the results obtained from the 1 m analysis to generalize the findings for the entire CT coast to derive zones dominated by surge, river flow, or the compound effect of the two. This study can help coastal communities better understand the risk of the compound impacts of coastal storms, which is essential for increasing climate resilience.

Self-consistent dust and non-LTE line radiative transfer with SKIRT

We introduce Monte-Carlo-based non-local thermodynamic equilibrium (non-LTE) line radiative transfer calculations in the three-dimensional (3D) dust radiative transfer code SKIRT, which was originally set up as a dust radiative transfer code. By doing so, we developed a generic and powerful 3D radiative transfer code that can self-consistently generate spectra with molecular and atomic lines against the underlying continuum. We tested the accuracy of the non-LTE line radiative transfer module in the extended SKIRT code using standard benchmarks. We find excellent agreement between the S KIRT results, the published benchmark results, and the results obtained using the ray-tracing non-LTE line radiative transfer code MAGRITTE, which validates our implementation. We applied the extended SKIRT code on a 3D hydrodynamic simulation of a dusty active galactic nucleus (AGN) torus model and generated multiwavelength images with CO rotational-line spectra against the underlying dust continuum. We find that the low-J CO emission traces the geometrically thick molecular torus, whereas the higher-J CO lines originate from the gas with high kinetic temperature located in the innermost regions of the torus. Comparing the calculations with and without dust radiative transfer, we find that higher-J CO lines are slightly attenuated by the surrounding cold dust when seen edge-on. This shows that atomic and molecular lines can experience attenuation, an effect that is particularly important for transitions at mid- and near-infrared wavelengths. Therefore, our self-consistent dust and non-LTE line radiative transfer calculations can help the observational data from Herschel, ALMA, and JWST be interpreted.

Sensitivity of He Flames in X-Ray Bursts to Nuclear Physics

Through the use of axisymmetric 2D hydrodynamic simulations, we further investigate laterally propagating flames in X-ray bursts (XRBs). Our aim is to understand the sensitivity of a propagating helium flame to different nuclear physics. Using the Castro simulation code, we confirm the phenomenon of enhanced energy generation shortly after a flame is established by adding 12C(p, γ)13N(α, p)16O to the network, in agreement with the past literature. This sudden outburst of energy leads to a short accelerating phase, causing a drastic alteration in the overall dynamics of the flame in XRBs. Furthermore, we investigate the influence of different plasma screening routines on the propagation of the XRB flame. We finally examine the performance of simplified spectral deferred correction, a novel approach to hydrodynamics and reaction coupling incorporated in Castro, as an alternative to operator splitting.

Multidimensional Radiation Hydrodynamics Simulations of Pulsational Pair-instability Supernovae

Stars with masses of 80–130 M ⊙ can encounter pulsational pair-instability at the end of their lives, which triggers consecutive episodes of explosive burning that eject multiple massive shells. Collisions between these shells produce bright transients known as pulsational pair-instability supernovae (PPI SNe) that may explain some extreme supernovae. In this paper, we present the first 2D and 3D radiation hydrodynamics simulations of PPI SNe with the CASTRO code. Radiative cooling causes the collided shells to evolve into thin, dense structures with hot spots that can enhance the peak luminosity of the SN by factors of 2–3. The light curve peaks at 1.9–2.1 × 1043 erg s−1 for 50 days and then plateaus at 2–3 × 1042 erg s−1 for 200 days, depending on the viewing angle. The presence of 12C and 16O and the absence of 28Si and 56Fe in its spectra can uniquely identify this transient as a PPI SN in follow-up observations. Our models suggest that multidimensional radiation hydrodynamics is required to model the evolution and light curves of all shell-collision SNe, such as Type IIne, not just PPI SNe.

Numerical simulations of the random angular momentum in convection – II. Delayed explosions of red supergiants following ‘failed’ supernovae

ABSTRACT When collapse of the iron core in a massive red or yellow supergiant does not lead to an energetic supernova, a significant fraction of the convective hydrogen envelope will fall in towards the black hole formed from the collapsing core. The random velocity field in the convective envelope results in finite specific angular momentum in each infalling shell. Using 3D hydrodynamical simulations, we follow the infall of this material to small radii, resolving the circularization radii of the flow. We show that infall of the convective envelope leads to nearly complete envelope ejection in a ≳1048 erg explosion with outflow speeds of ≳200 km s−1. The light curve of such an explosion would show a characteristic, red plateau as the ejecta cools and a hydrogen recombination front recedes through the expanding ejecta. Adopting supernova IIp scalings, the event would have a plateau luminosity of ≳1040 erg s−1 and a duration of several hundreds of days. These events would appear quite similar to luminous red novae with red or yellow supergiant progenitors; some luminous red novae may, in fact, be signposts of black hole formation. The mechanism studied here produces more energetic explosions than the weak shock generated from radiation of neutrino energy during the protoneutron star phase. Because we cannot simulate all the way to the horizon, our results are likely lower limits on the energy and luminosity of transients produced during the collapse of a red or yellow supergiant to form a black hole.

Exploration of cross-beam energy transfer mitigation constraints for designing an ignition-scale direct-drive inertial confinement fusion driver

The compression of direct-drive inertial confinement fusion (ICF) targets is strongly impacted by cross-beam energy transfer (CBET), a laser-plasma instability that limits ablation pressure by redirecting laser energy outward and that is projected to be mitigated by laser bandwidth. Here, we explore various CBET mitigation constraints to guide the design of future ICF facilities. First, we find that the flat, Gaussian, and Lorentzian spectral shapes have similar CBET mitigation properties, and a flat shape with nine spectral lines is a good surrogate for what can be obtained with other spectral shapes. Then, we conduct a comprehensive study across energy scales and ignition designs. 3D hydrodynamic simulations are used to derive an analytical model for the expected CBET mitigation as a function of laser and plasma parameters. From this model, we study the bandwidth requirements of conventional and shock ignition designs across four different energy scales and find that they require between 0.5 and 3±0.2% relative bandwidth. Best mitigation is achieved when the beam radius over critical radius Rb/Rc is kept low during the drive while the plasma temperature is kept high. In a steady state, we find that the bandwidth required to mitigate 85% of CBET scales as (Rb/Rc)2.15Ln−0.58I0.7, where Ln is the density scale length, and I the laser intensity. Finally, we find that the chamber beam port layout does not influence CBET mitigation. In the case of a driver using many monochromatic beamlets, we find that ∼10 beamlets per port is required, with diminishing returns above ∼20.

Three-dimensional SPH Simulations of FU Orionis Star Flares in the Clumpy Accretion Model

One of the early hypotheses about the origin of FU Orionis star (FUORs) outbursts explains them based on the fall of gas clumps from the remnants of protostellar clouds onto protoplanetary disks surrounding young stars. To calculate the consequences of such an event, we make 3D hydrodynamic simulations using the smoothed particle hydrodynamics method. It is shown that the fall of the clump on the disk in the vicinity of the star actually causes a burst of the star’s accretion activity, resembling in its characteristics the flares of known FUORs. In the region of incidence, an inhomogeneous gas ring is formed, which is inclined relative to the outer disk. During several revolutions around the star, this ring combines with the inner disk and forms a tilted disk. In the process of evolution, the inner disk expands, and its inclination relative to the outer disk decreases. After 100 revolutions, the angle of inclination is a few degrees. This result is of interest in connection with the discovery in recent years of protoplanetary disks, the inner region of which is inclined relative to the outer one. Such structures are usually associated with the existence in the vicinity of a star of a massive body (planet or brown dwarf), whose orbit is inclined relative to the plane of the disk. The results of our modeling indicate the possibility of an alternative explanation for this phenomenon.

How to form compact and other longer-lived planet-induced vortices: VSI, planet migration, or re-triggers, but not feedback

ABSTRACT Past computational studies of planet-induced vortices have shown that the dust asymmetries associated with these vortices can be long-lived enough that they should be much more common in mm/sub-mm observations of protoplanetary discs, even though they are quite rare. Observed asymmetries also have a range of azimuthal extents from compact to elongated even though computational studies have shown planet-induced vortices should be preferentially elongated. In this study, we use 2D and 3D hydrodynamic simulations to test whether those dust asymmetries should really be so long-lived or so elongated. With higher resolution (29 cells radially per scale height) than our previous work, we find that vortices can be more compact by developing compact cores when higher-mass planets cause them to re-form, or if they are seeded by tiny compact vortices from the vertical shear instability (VSI), but not through dust feedback in 3D as was previously expected in general. Any case with a compact vortex or core(s) also has a longer lifetime. Even elongated vortices can have longer lifetimes with higher-mass planets or if the associated planet is allowed to migrate, the latter of which can cause the dust asymmetry to stop decaying as the planet migrates away from the vortex. These longer dust asymmetry lifetimes are even more inconsistent with observations, perhaps suggesting that discs still have an intermediate amount of effective viscosity.

3D hydrodynamic simulations of massive main-sequence stars – I. Dynamics and mixing of convection and internal gravity waves

ABSTRACT We performed 3D hydrodynamic simulations of the inner $\approx 50{{\ \rm per\ cent}}$ radial extent of a $25\,\,\mathrm{\mathrm{M}_\odot }$ star in the early phase of the main sequence and investigate core convection and internal gravity waves in the core-envelope boundary region. Simulations for different grid resolutions and driving luminosities establish scaling relations to constrain models of mixing for 1D applications. As in previous works, the turbulent mass entrainment rate extrapolated to nominal heating is unrealistically high ($1.58\times 10^{-4}\,\,\mathrm{\mathrm{M}_\odot \, {\mathrm{yr}}^{-1}}$), which is discussed in terms of the non-equilibrium response of the simulations to the initial stratification. We measure quantitatively the effect of mixing due to internal gravity waves excited by core convection interacting with the boundary in our simulations. The wave power spectral density as a function of frequency and wavelength agrees well with the GYRE eigenmode predictions based on the 1D spherically averaged radial profile. A diffusion coefficient profile that reproduces the spherically averaged abundance distribution evolution is determined for each simulation. Through a combination of eigenmode analysis and scaling relations it is shown that in the N2-peak region, mixing is due to internal gravity waves and follows the scaling relation DIGW-hydro ∝ L4/3 over a $\gtrapprox 2\,\,\mathrm{\mathrm{dex}}$ range of heating factors. Different extrapolations of the mixing efficiency down to nominal heating are discussed. If internal gravity wave mixing is due to thermally enhanced shear mixing, an upper limit is $D_\mathrm{IGW}\lessapprox 2$ to $3\times 10^{4}\,\,\mathrm{cm^2\, s^{-1}}$ at nominal heating in the N2-peak region above the convective core.