scholarly journals Evolution of supernovae-driven superbubbles with conduction and cooling

2019 ◽  
Vol 490 (2) ◽  
pp. 1961-1990 ◽  
Author(s):  
Kareem El-Badry ◽  
Eve C Ostriker ◽  
Chang-Goo Kim ◽  
Eliot Quataert ◽  
Daniel R Weisz
Keyword(s):  
Cooling Rate ◽  
Evaporation Rate ◽  
Mass Density ◽  
Dynamical Evolution ◽  
Effective Diffusivity ◽  
Blast Waves ◽  
Conductive Heat ◽  
Hydrodynamic Simulations ◽  
Non Linear ◽  
Order Of Magnitude

ABSTRACT We use spherically symmetric hydrodynamic simulations to study the dynamical evolution and internal structure of superbubbles (SBs) driven by clustered supernovae (SNe), focusing on the effects of thermal conduction and cooling in the interface between the hot bubble interior and cooled shell. Our simulations employ an effective diffusivity to account for turbulent mixing from non-linear instabilities that are not captured in 1D. The conductive heat flux into the shell is balanced by a combination of cooling in the interface and evaporation of shell gas into the bubble interior. This evaporation increases the density, and decreases the temperature, of the SB interior by more than an order of magnitude relative to simulations without conduction. However, most of the energy conducted into the interface is immediately lost to cooling, reducing the evaporative mass flux required to balance conduction. As a result, the evaporation rate is typically a factor of ∼3–30 lower than predicted by the classical similarity solution of (Weaver et al. 1977), which neglects cooling. Blast waves from the first ∼30 SNe remain supersonic in the SB interior because reduced evaporation from the interface lowers the mass they sweep up in the hot interior. Updating the Weaver solution to include cooling, we construct a new analytic model to predict the cooling rate, evaporation rate, and temporal evolution of SBs. The cooling rate, and hence the hot gas mass, momentum, and energy delivered by SBs, is set by the ambient interstellar mass density and the efficiency of non-linear mixing at the bubble–shell interface.

scholarly journals Dynamical evolution of Oort cloud comets to near-Earth space

2006 ◽  
Vol 2 (S236) ◽  
pp. 43-54 ◽  
Author(s):  
Olga A. Mazeeva
Keyword(s):  
Dynamical Evolution ◽  
Absolute Magnitude ◽  
Oort Cloud ◽  
Outer Solar System ◽  
Earth Space ◽  
Near Earth Space ◽  
Long Period ◽  
Order Of Magnitude ◽  
Orbital Periods ◽  
Stellar Perturbations

AbstractThe dynamical evolution of 2⋅105 hypothetical Oort cloud comets by the action of planetary, galactic and stellar perturbations during 2⋅109 years is studied numerically. The evolution of comet orbits from the outer (104 AU <a<5⋅104 AU, a is semimajor axes) and the inner Oort cloud (5⋅103 AU <a<104 AU) to near-Earth space is investigated separately. The distribution of the perihelion (q) passage frequency in the planetary region is obtained calculating the numbers of comets in every interval of Δ q per year. The flux of long-period (LP) comets (orbital periods P>200 yr) with perihelion distances q<1.5 AU brighter than visual absolute magnitude H10=7 is ∼ 1.5 comets per year, and ∼18 comets with H10<10.9. The ratio of all LP comets with q<1.5 AU to ‘new’ comets is ∼5. The frequency of passages of LP comets from the inner Oort cloud through region q<1.5 AU is ∼3.5⋅10−13 yr−1, that is roughly one order of magnitude less than frequency of passages of LP comets from the outer cloud (∼5.28⋅10−12 yr−1). We show that the flux of ‘new’ comets with 15<q<31 AU is higher than with q<15 AU, by a factor ∼1.7 for comets from the outer Oort cloud and, by a factor ∼7 for comets from the inner cloud. The perihelia of comets from the outer cloud previously passed through the planetary region are predominated in the Saturn-Uranus region. The majority of inner cloud comets come in the outer solar system (q>15 AU), and a small fraction (∼0.01) of them can reach orbits with q<1.5 AU. The frequency of transfer of comets from the inner cloud (a<104 AU) to the outer Oort cloud (a>104 AU), from where they are injected to the region q<1.5 AU, is ∼6⋅10−14 yr−1.

Simulation of blast waves with tailored explosive charges

1985 ◽  
Vol 158 ◽  
pp. 137-152
Author(s):  
M. Sanai ◽  
H. E. Lindberg ◽  
J. D. Colton
Keyword(s):  
Shock Tube ◽  
Charge Density ◽  
Cost Effective ◽  
Development Programme ◽  
Blast Waves ◽  
Charge Density Distribution ◽  
Test Conditions ◽  
Order Of Magnitude ◽  
Explosive Charges ◽  
Simulation Time

We have developed a compact and cost-effective shock tube to simulate the static and dynamic pressures of blast waves. The shock tube is open at both ends and is driven by high explosives distributed over a finite length of the tube near one end. The overall charge length is determined by the simulation time of interest, and the charge-density distribution is tailored to produce the pressure-waveform shape desired. For the shock tube to simulate a typical blast wave, the charge density must be highest at the charge front (closest to the test section) and gradually reduced towards the back. The resulting shock tube is an order of magnitude shorter than a conventional dynamic airblast simulator (DABS) in which concentrated explosives are used to drive the shock.Tailored charges designed using this method were built and tested in a simulation development programme sponsored by the U.S. Defense Nuclear Agency (DNA). The pressures measured for several charge distributions agreed very well with SRI's PUFF hydrocode computations and demonstrated the feasibility of the compact simulator under realistic test conditions.

scholarly journals A new distance to the Brick, the dense molecular cloud G0.253+0.016

2021 ◽  
Vol 502 (1) ◽  
pp. 1246-1252
Author(s):  
M Zoccali ◽  
E Valenti ◽  
F Surot ◽  
O A Gonzalez ◽  
A Renzini ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Formation Rate ◽  
Dynamical Evolution ◽  
Galactic Centre ◽  
The Galaxy ◽  
Centre Region ◽  
Order Of Magnitude ◽  
Red Clump

ABSTRACT We analyse the near-infrared colour–magnitude diagram of a field including the giant molecular cloud G0.253+0.016 (a.k.a. The Brick) observed at high spatial resolution, with HAWK-I@VLT. The distribution of red clump stars in a line of sight crossing the cloud, compared with that in a direction just beside it, and not crossing it, allow us to measure the distance of the cloud from the Sun to be 7.20, with a statistical uncertainty of ±0.16 and a systematic error of ±0.20 kpc. This is significantly closer than what is generally assumed, i.e. that the cloud belongs to the near side of the central molecular zone, at 60 pc from the Galactic centre. This assumption was based on dynamical models of the central molecular zone, observationally constrained uniquely by the radial velocity of this and other clouds. Determining the true position of the Brick cloud is relevant because this is the densest cloud of the Galaxy not showing any ongoing star formation. This puts the cloud off by one order of magnitude from the Kennicutt–Schmidt relation between the density of the dense gas and the star formation rate. Several explanations have been proposed for this absence of star formation, most of them based on the dynamical evolution of this and other clouds, within the Galactic centre region. Our result emphasizes the need to include constraints coming from stellar observations in the interpretation of our Galaxy’s central molecular zone.

scholarly journals Global torques and stochasticity as the drivers of massive black hole pairing in the young Universe

2020 ◽  
Vol 498 (3) ◽  
pp. 3601-3615 ◽  
Author(s):  
Elisa Bortolas ◽  
Pedro R Capelo ◽  
Tommaso Zana ◽  
Lucio Mayer ◽  
Matteo Bonetti ◽  
...  
Keyword(s):  
Black Hole ◽  
Large Scale ◽  
High Redshift ◽  
Dynamical Evolution ◽  
Dynamical Friction ◽  
Massive Black Hole ◽  
Orbital Decay ◽  
Orbital Phase ◽  
Order Of Magnitude ◽  
Statistical Sample

ABSTRACT The forthcoming Laser Interferometer Space Antenna (LISA) will probe the population of coalescing massive black hole (MBH) binaries up to the onset of structure formation. Here, we simulate the galactic-scale pairing of ∼106 M⊙ MBHs in a typical, non-clumpy main-sequence galaxy embedded in a cosmological environment at z = 7–6. In order to increase our statistical sample, we adopt a strategy that allows us to follow the evolution of six secondary MBHs concomitantly. We find that the magnitude of the dynamical-friction-induced torques is significantly smaller than that of the large-scale, stochastic gravitational torques arising from the perturbed and morphologically evolving galactic disc, suggesting that the standard dynamical friction treatment is inadequate for realistic galaxies at high redshift. The dynamical evolution of MBHs is very stochastic, and a variation in the initial orbital phase can lead to a drastically different time-scale for the inspiral. Most remarkably, the development of a galactic bar in the host system either significantly accelerates the inspiral by dragging a secondary MBH into the centre, or ultimately hinders the orbital decay by scattering the MBH in the galaxy outskirts. The latter occurs more rarely, suggesting that galactic bars overall promote MBH inspiral and binary coalescence. The orbital decay time can be an order of magnitude shorter than what would be predicted relying on dynamical friction alone. The stochasticity and the important role of global torques have crucial implications for the rates of MBH coalescences in the early Universe: both have to be accounted for when making predictions for the upcoming LISA observatory.

Mass Transfer in Mira-Type Binaries

2012 ◽  
Vol 21 (1-2) ◽  
Author(s):  
S. Mohamed ◽  
Ph. Podsiadlowski
Keyword(s):  
Mass Transfer ◽  
Orbital Plane ◽  
Planetary Nebulae ◽  
Transfer Rates ◽  
Hydrodynamic Simulations ◽  
Transfer Mode ◽  
Mass Transfer Mechanism ◽  
Accretion Rates ◽  
Order Of Magnitude ◽  
Symbiotic Binaries

AbstractDetached, symbiotic binaries are generally assumed to interact via Bondi-Hoyle-Littleton (BHL) wind accretion. However, the accretion rates and outflow geometries that result from this mass-transfer mechanism cannot adequately explain the observations of the nearest and best studied symbiotic binary, Mira, or the formation of some post-AGB binaries, e.g. barium stars. We propose a new mass-transfer mode for Mira-type binaries, which we call ‘wind Roche-lobe overflow’ (WRLOF), and which we demonstrate with 3D hydrodynamic simulations. Importantly, we show that the circumstellar outflows which result from WRLOF tend to be highly aspherical and strongly focused towards the binary orbital plane. Furthermore, the subsequent mass-transfer rates are at least an order of magnitude greater than the analogous BHL values. We discuss the implications of these results for the shaping of bipolar (proto)-planetary nebulae and other related systems.

scholarly journals Approaching the Black Hole by Numerical Simulations

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 99 ◽  
Author(s):  
Christian Fendt
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Direct Evidence ◽  
Dynamical Evolution ◽  
Numerical Code ◽  
Physical Processes ◽  
Hydrodynamic Simulations ◽  
Environmental Material ◽  
Physical Laws ◽  
Radiative Interaction

Black holes represent extreme conditions of physical laws. Predicted about a century ago, they are now accepted as astrophysical reality by most of the scientific community. Only recently has more direct evidence of their existence been found—the detection of gravitational waves from black hole mergers and of the shadow of a supermassive black hole in the center of a galaxy. Astrophysical black holes are typically embedded in an active environment which is affected by the strong gravity. When the environmental material emits radiation, this radiation may carry imprints of the black hole that is hosting the radiation source. In order to understand the physical processes that take place in the close neighborhood of astrophysical black holes, numerical methods and simulations play an essential role. This is simply because the dynamical evolution and the radiative interaction are far too complex in order to allow for an analytic solution of the physical equations. A huge progress has been made over the last decade(s) in the numerical code development, as well as in the computer power that is needed to run these codes. This review tries to summarize the basic questions and methods that are involved in the undertaking of investigating the astrophysics of black holes by numerical means. It is intended for a non-expert audience interested in an overview over this broad field. The review comes along without equations and thus without a detailed expert discussion of the underlying physical processes or numerical specifics. Instead, it intends to illustrate the richness of the field and to motivate further reading. The review puts some emphasis on magneto-hydrodynamic simulations but also touches radiation transfer and merger simulations, in particular pointing out differences in these approaches.

scholarly journals Intensity mapping as a probe of axion dark matter

2020 ◽  
Vol 500 (3) ◽  
pp. 3162-3177
Author(s):  
Jurek B Bauer ◽  
David J E Marsh ◽  
Renée Hložek ◽  
Hamsa Padmanabhan ◽  
Alex Laguë
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Neutral Hydrogen ◽  
Matrix Formalism ◽  
Intensity Mapping ◽  
Matter Power Spectrum ◽  
Wide Range ◽  
Non Linear ◽  
Order Of Magnitude ◽  
Magnitude Improvement

ABSTRACT We consider intensity mapping (IM) of neutral hydrogen (H i) in the redshift range 0 ≲ z ≲ 3 employing a halo model approach where H i is assumed to follow the distribution of dark matter (DM) haloes. If a portion of the DM is composed of ultralight axions, then the abundance of haloes is changed compared to cold DM below the axion Jeans mass. With fixed total H i density, $\Omega _{\rm H\, \rm {\small I}}$, assumed to reside entirely in haloes, this effect introduces a scale-independent increase in the H i power spectrum on scales above the axion Jeans scale, which our model predicts consistent with N-body simulations. Lighter axions introduce a scale-dependent feature even on linear scales due to its suppression of the matter power spectrum near the Jeans scale. We use the Fisher matrix formalism to forecast the ability of future H i surveys to constrain the axion fraction of DM and marginalize over astrophysical and model uncertainties. We find that a HIRAX-like survey is a very reliable IM survey configuration, being affected minimally by uncertainties due to non-linear scales, while the SKA1MID configuration is the most constraining as it is sensitive to non-linear scales. Including non-linear scales and combining a SKA1MID-like IM survey with the Simons Observatory CMB, the benchmark ‘fuzzy DM’ model with ma = 10−22 eV can be constrained at few per cent. This is almost an order of magnitude improvement over current limits from the Ly α forest. For lighter ULAs, this limit improves below 1 per cent, and allows the possibility to test the connection between axion models and the grand unification scale across a wide range of masses.

scholarly journals Using large-scale structure data and a halo model to constrain generalized dark matter

2019 ◽  
Vol 490 (1) ◽  
pp. 813-831 ◽  
Author(s):  
Daniel B Thomas ◽  
Michael Kopp ◽  
Katarina Markovič
Keyword(s):  
Dark Matter ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Linear Structure ◽  
Microwave Background ◽  
Wavenumber Range ◽  
Significant Difference ◽  
Linear Modelling ◽  
Non Linear ◽  
Order Of Magnitude

ABSTRACT Constraints on the properties of the cosmological dark matter have previously been obtained in a model-independent fashion using the generalized dark matter (GDM) framework. Here we extend that work in several directions: We consider the inclusion of WiggleZ matter power spectrum data (MPS), and show that this improves the constraints on the two perturbative GDM parameters, $c^2_\mathrm{ s}$ and $c^2_\text{vis}$, by a factor of 3, for a conservative choice of wavenumber range. A less conservative choice can yield an improvement of up to an order of magnitude compared to previous constraints. In order to examine the robustness of this result we develop a GDM halo model (HM) to explore how non-linear structure formation could proceed in this framework, since currently GDM has only been defined perturbatively and only linear theory has been used when generating constraints. We then examine how the HM affects the constraints obtained from the MPS data. The less-conservative wavenumber range shows a significant difference between linear and non-linear modelling, with the latter favouring GDM parameters inconsistent with ΛCDM, underlining the importance of careful non-linear modelling when using this data. We also use this HM to establish the robustness of previously obtained constraints, particularly those that involve weak gravitational lensing of the cosmic microwave background. Additionally, we show how the inclusion of neutrino mass as a free parameter affects previous constraints on the GDM parameters.

scholarly journals The Glass Transition Within the Thermodynamics of Irreversible Processes

1998 ◽  
Vol 53 (3-4) ◽  
pp. 157-170
Author(s):  
H. Baur
Keyword(s):  
Glass Transition ◽  
Cooling Rate ◽  
Dissipative Process ◽  
Point Of View ◽  
Clear Distinction ◽  
Irreversible Processes ◽  
Free Enthalpy ◽  
Thermodynamics Of Irreversible Processes ◽  
Non Linear ◽  
Phenomenological Point

Abstract The glass transition caused by a finite cooling rate is a continuous non-linear dissipative process whose description requires a clear distinction between equilibrium and non-equilibrium quantities. The so-called Davies or Prigogine-Defay relations (in form of an equation as well as in form of an inequality) are not relevant in such a process. The determining quantities of the glass transition are -from a macroscopic phenomenological point of view -the fluidity of the melt and the partial free enthalpy of the microscopic vacancies in the melt. All of the characteristics of the dynamics of the glass transition are essentially due to these two quantities.

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