scholarly journals Is multiphase gas cloudy or misty?

2020 ◽  
Vol 494 (1) ◽  
pp. L27-L31 ◽  
Author(s):  
Max Gronke ◽  
S Peng Oh
Keyword(s):  
Radiative Transfer ◽  
Thermal Instability ◽  
Weak Dependence ◽  
Multistage Process ◽  
Pressure Balance ◽  
Hydrodynamic Simulations ◽  
Contraction Phase ◽  
Gas Cloud ◽  
Resolution Requirements ◽  
Cold Gas

ABSTRACT Cold T ∼ 104 K gas morphology could span a spectrum ranging from large discrete clouds to a fine ‘mist’ in a hot medium. This has myriad implications, including dynamics and survival, radiative transfer, and resolution requirements for cosmological simulations. Here, we use 3D hydrodynamic simulations to study the pressure-driven fragmentation of cooling gas. This is a complex, multistage process, with an initial Rayleigh–Taylor unstable contraction phase that seeds perturbations, followed by a rapid, violent expansion leading to the dispersion of small cold gas ‘droplets’ in the vicinity of the gas cloud. Finally, due to turbulent motions, and cooling, these droplets may coagulate. Our results show that a gas cloud ‘shatters’ if it is sufficiently perturbed out of pressure balance (δP/P ∼ 1) and has a large final overdensity χf ≳ 300, with only a weak dependence on the cloud size. Otherwise, the droplets reassemble back into larger pieces. We discuss our results in the context of thermal instability and clouds embedded in a shock-heated environment.

scholarly journals Hydrodynamic simulations of an isolated star-forming gas cloud in the Virgo cluster

2020 ◽  
Vol 499 (4) ◽  
pp. 5873-5890
Author(s):  
Francesco Calura ◽  
Michele Bellazzini ◽  
Annibale D’Ercole
Keyword(s):  
Star Formation ◽  
Three Dimensional ◽  
Virgo Cluster ◽  
General Interest ◽  
Hydrodynamic Simulations ◽  
Star Forming ◽  
Neutral Gas ◽  
Asymmetric Shape ◽  
Gas Cloud ◽  
Cold Gas

ABSTRACT We present a suite of three-dimensional, high-resolution hydrodynamic simulations that follow the evolution of a massive (107 M⊙) pressure-confined, star-forming neutral gas cloud moving through a hot intracluster medium (ICM). The main goal of the analysis is to get theoretical insight into the lifetimes and evolution of stellar systems like the recently discovered star-forming cloud SECCO 1 in the Virgo cluster of galaxies, but it may be of general interest for the study of the star-forming gas clumps that are observed in the tails of ram pressure stripped galaxies. Building up on a previous, simple simulation, we explored the effect of different relative velocity of the cloud and larger temperature of the ICM, as well as the effect of the cloud self-gravity. Moreover, we performed a simulation including star formation and stellar feedback, allowing for a first time a direct comparison with the observed properties of the stars in the system. The survivability of the cold gas in the simulated clouds is granted on time-scales of the order of 1 Gyr, with final cold gas fractions generally >0.75. In all cases, the simulated systems end up, after 1 Gyr of evolution, as symmetric clouds in pressure equilibrium with the external hot gas. We also confirm that gravity played a negligible role at the largest scales on the evolution of the clouds. In our simulation with star formation, star formation begins immediately, it peaks at the earliest times, and decreases monotonically with time. Inhomogeneous supernova explosions are the cause of an asymmetric shape of the gas cloud, facilitating the development of instabilities and the decrease of the cold gas fraction.

scholarly journals Atmospheric Escape and the Evolution of Close-In Exoplanets

2019 ◽  
Vol 47 (1) ◽  
pp. 67-90 ◽  
Author(s):  
James E. Owen
Keyword(s):  
Radiative Transfer ◽  
Lower Mass ◽  
Hydrodynamic Simulations ◽  
One Dimensional ◽  
Hot Jupiters ◽  
Atmospheric Escape ◽  
Hydrodynamic Calculations ◽  
Ionization Chemistry ◽  
Exoplanet Systems ◽  
Over Time

Exoplanets with substantial hydrogen/helium atmospheres have been discovered in abundance, many residing extremely close to their parent stars. The extreme irradiation levels that these atmospheres experience cause them to undergo hydrodynamic atmospheric escape. Ongoing atmospheric escape has been observed to be occurring in a few nearby exoplanet systems through transit spectroscopy both for hot Jupiters and for lower-mass super-Earths and mini-Neptunes. Detailed hydrodynamic calculations that incorporate radiative transfer and ionization chemistry are now common in one-dimensional models, and multidimensional calculations that incorporate magnetic fields and interactions with the interstellar environment are cutting edge. However, comparison between simulations and observations remains very limited. While hot Jupiters experience atmospheric escape, the mass-loss rates are not high enough to affect their evolution. However, for lower-mass planets, atmospheric escape drives and controls their evolution, sculpting the exoplanet population that we observe today. ▪ Observations of some exoplanets have detected atmospheric escape driven by hydrodynamic outflows, causing the exoplanets to lose mass over time. ▪ Hydrodynamic simulations of atmospheric escape are approaching the sophistication required to compare them directly to observations. ▪ Atmospheric escape sculpts sharp features into the exoplanet population that we can observe today; these features have recently been detected.

Simulations of the W50-SS433 system

2018 ◽  
Vol 14 (S342) ◽  
pp. 257-259
Author(s):  
Dimitrios Millas ◽  
Oliver Porth ◽  
Rony Keppens
Keyword(s):  
Radiative Transfer ◽  
Supernova Remnant ◽  
Relativistic Hydrodynamic ◽  
Astrophysical Jets ◽  
Hydrodynamic Simulations ◽  
X Ray ◽  
System A ◽  
The Universe

AbstractSupernovae and astrophysical jets are two of the most energetic and intriguing objects in the universe. We examine an interesting scenario that involves the interaction of these two extreme phenomena, motivated by observations of the W50-SS433 system: a jet launched from the microquasar SS433 (an X-ray binary) located inside a supernova remnant, W50. These observations revealed a unique morphology of the remnant, attributed to the presence of the jet. We performed full 3D relativistic hydrodynamic simulations to better capture the interaction between the remnant and the jet and post-processed the data with a radiative transfer code to create emission maps.

scholarly journals Observational signatures of outbursting protostars - I: From hydrodynamic simulations to observations

2019 ◽  
Vol 487 (4) ◽  
pp. 5106-5117 ◽  
Author(s):  
Benjamin MacFarlane ◽  
Dimitris Stamatellos ◽  
Doug Johnstone ◽  
Gregory Herczeg ◽  
Giseon Baek ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Radiation Field ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Hydrodynamic Simulations ◽  
Long Wavelength ◽  
Fu Ori ◽  
Flux Increase

Abstract Accretion onto protostars may occur in sharp bursts. Accretion bursts during the embedded phase of young protostars are probably most intense, but can only be inferred indirectly through long-wavelength observations. We perform radiative transfer calculations for young stellar objects (YSOs) formed in hydrodynamic simulations to predict the long wavelength, sub-mm and mm, flux responses to episodic accretion events, taking into account heating from the young protostar and from the interstellar radiation field. We find that the flux increase due to episodic accretion events is more prominent at sub-mm wavelengths than at mm wavelengths; e.g. a factor of ∼570 increase in the luminosity of the young protostar leads to a flux increase of a factor of 47 at 250 $\mu$m but only a factor of 10 at 1.3 mm. Heating from the interstellar radiation field may reduce further the flux increase observed at longer wavelengths. We find that during FU Ori-type outbursts the bolometric temperature and luminosity may incorrectly classify a source as a more evolved YSO due to a larger fraction of the radiation of the object being emitted at shorter wavelengths.

scholarly journals High-resolution three-dimensional simulations of gas removal from ultrafaint dwarf galaxies

2019 ◽  
Vol 630 ◽  
pp. A140 ◽  
Author(s):  
Donatella Romano ◽  
Francesco Calura ◽  
Annibale D’Ercole ◽  
C. Gareth Few
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Three Dimensional ◽  
Energy Output ◽  
Potential Well ◽  
Hydrodynamic Simulations ◽  
Stellar Feedback ◽  
Gas Removal ◽  
Cold Gas

Context. The faintest Local Group galaxies found lurking in and around the Milky Way halo provide a unique test bed for theories of structure formation and evolution on small scales. Deep Subaru and Hubble Space Telescope photometry demonstrates that the stellar populations of these galaxies are old and that the star formation activity did not last longer than 2 Gyr in these systems. A few mechanisms that may lead to such a rapid quenching have been investigated by means of hydrodynamic simulations, but these have not provided any final assessment so far. Aims. This is the first in a series of papers aimed at analyzing the roles of stellar feedback, ram pressure stripping, host-satellite tidal interactions, and reionization in cleaning the lowest mass Milky Way companions of their cold gas using high-resolution, three-dimensional hydrodynamic simulations. Methods. We simulated an isolated ultrafaint dwarf galaxy loosely modeled after Boötes I, and examined whether or not stellar feedback alone could drive a substantial fraction of the ambient gas out from the shallow potential well. Results. In contrast to simple analytical estimates, but in agreement with previous hydrodynamical studies, we find that most of the cold gas reservoir is retained. Conversely, a significant amount of the metal-enriched stellar ejecta crosses the boundaries of the computational box with velocities exceeding the local escape velocity and is, thus, likely lost from the system. Conclusions. Although the total energy output from multiple supernova explosions exceeds the binding energy of the gas, no galactic-scale outflow develops in our simulations and as such, most of the ambient medium remains trapped within the weak potential well of the model galaxy. It seems thus unavoidable that to explain the dearth of gas in ultrafaint dwarf galaxies, we will have to resort to environmental effects. This will be the subject of a forthcoming paper.

Thermal Instability with Radiative Transfer

1970 ◽  
Vol 13 (2) ◽  
pp. 222 ◽  
Author(s):  
C. Christophorides
Keyword(s):  
Radiative Transfer ◽  
Thermal Instability

Thermal instability induced by buoyancy and surface tension with radiative transfer

1974 ◽  
Vol 30 (2) ◽  
pp. 144-154
Author(s):  
C. V. Gopalakrishnan Nair ◽  
M. G. Palekar
Keyword(s):  
Surface Tension ◽  
Radiative Transfer ◽  
Thermal Instability

scholarly journals Cooling and instabilities in colliding flows

2021 ◽  
Author(s):  
R N Markwick ◽  
A Frank ◽  
J Carroll-Nellenback ◽  
B Liu ◽  
E G Blackman ◽  
...  
Keyword(s):  
Thermal Instability ◽  
Three Dimensional ◽  
Oscillation Period ◽  
Three Dimensions ◽  
Temperature Dependent ◽  
Radiative Shock ◽  
Hydrodynamic Simulations ◽  
Protostellar Jets ◽  
The One ◽  
Cooling Function

Abstract Collisional self-interactions occurring in protostellar jets give rise to strong shocks, the structure of which can be affected by radiative cooling within the flow. To study such colliding flows, we use the AstroBEAR AMR code to conduct hydrodynamic simulations in both one and three dimensions with a power law cooling function. The characteristic length and time scales for cooling are temperature dependent and thus may vary as shocked gas cools. When the cooling length decreases sufficiently rapidly the system becomes unstable to the radiative shock instability, which produces oscillations in the position of the shock front; these oscillations can be seen in both the one and three dimensional cases. Our simulations show no evidence of the density clumping characteristic of a thermal instability, even when the cooling function meets the expected criteria. In the three-dimensional case, the nonlinear thin shell instability (NTSI) is found to dominate when the cooling length is sufficiently small. When the flows are subjected to the radiative shock instability, oscillations in the size of the cooling region allow NTSI to occur at larger cooling lengths, though larger cooling lengths delay the onset of NTSI by increasing the oscillation period.

scholarly journals Simulating the outer layers of rapidly rotating stars

2020 ◽  
Vol 495 (4) ◽  
pp. 5052-5059
Author(s):  
F J Robinson ◽  
J Tanner ◽  
S Basu
Keyword(s):  
Radiative Transfer ◽  
Velocity Profile ◽  
The Other ◽  
Radiative Cooling ◽  
Rotating Stars ◽  
Near Surface ◽  
Hydrodynamic Simulations ◽  
Zonal Velocity ◽  
Rotating Star ◽  
Rapidly Rotating Stars

ABSTRACT This paper presents the results of a set of radiative hydrodynamic simulations of convection in the near-surface regions of a rapidly rotating star. The simulations use microphysics consistent with stellar models, and include the effects of realistic convection and radiative transfer. We find that the overall effect of rotation is to reduce the strength of turbulence. The combination of rotation and radiative cooling creates a zonal velocity profile in which the motion of fluid parcels near the surface is independent of rotation. Their motion is controlled by the strong up and down flows generated by radiative cooling. The fluid parcels in the deeper layers, on the other hand, are controlled by rotation.

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