204 research outputs found

    Dust dynamics and distribution in protoplanetary disks

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    Feinkörniger Staub ist der grundlegende Baustein von terrestrischen Planeten wie der Erde, die um junge Sterne entstehen. Gleichzeitig beeinflusst der Staub astronomische Beobachtungen, da er den Hauptbeitrag zur OpazitĂ€t in den Gasscheiben leistet, die entstehende Sterne umgeben (sog. protoplanetare Scheiben). Daher sind genaue Modelle der Verteilung und Bewegung von Staub in protoplanetaren Scheiben von entscheidender Bedeutung fĂŒr das VerstĂ€ndnis der Anfangsbedingungen der Planetenentstehung und fĂŒr die Interpretation astronomischer Beobachtungen von jungen Planeten- und Sternensystemen. Dieses Thema ist besonders relevant, da neueste astronomischen Beobachtungen protoplanetarer Scheiben neue MaßstĂ€be in Bezug auf Auflösung und Empfindlichkeit setzen und dadurch unser derzeitiges VerstĂ€ndnis und unsere Modelle infrage stellen. In dieser Arbeit prĂ€sentiere ich ein neuartiges und in sich konsistentes Modell der turbulenten Durchmischung von Staub. Das Modell bestĂ€tigt detaillierte Vorhersagen, wobei Nachteile frĂŒherer Modelle hinsichtlich der Drehimpulserhaltung, der uneindeutigen Definition der durchmischten GrĂ¶ĂŸe und Auswirkungen der Bahndynamik wegfallen. Somit verbessern wir die Beschreibung der Bewegung von Staub in turbulenten protoplanetaren Scheiben maßgeblich. Anschließend zeige ich auf, wie turbulente Durchmischung von Staub und andere TransportphĂ€nomene im frĂŒhen Sonnensystem, den Mangel an bestĂ€ndigen Kohlenstoffverbindungen, im inneren Bereich des heutigen Sonnensystems erklĂ€ren kann. Im Folgenden konzentriert sich die Arbeit auf die dreidimensionale Verteilung des Staubs in protoplanetaren Scheiben in Gegenwart eines Riesenplaneten. Mithilfe von hydrodynamischen Zwei-Fluid-Simulationen (Gas + Staub) finden wir, dass ein Planet die Staubverteilung in protoplanetaren Scheiben stark beeinflusst. Wir beschreiben beobachtbare Merkmale in synthetischen Radiowellenbeobachtungen, die es erlauben, auf die Anwesenheit eines unentdeckten Riesenplaneten in einer protoplanetaren Scheibe zu schließen. Schließlich untersuchen wir die Verwirbelung von Staub durch einen Riesenplaneten, zusĂ€tzlich zur Durchmischung durch turbulentes Gas. Wir konzentrieren uns dabei auf deren kombinierte Wirkung auf die dreidimensionale Verteilung des Staubs und untersuchen Merkmale, die mit Radiowellenbeobachtungen einer protoplanetarer Scheibe beobachtbar sind und RĂŒckschlĂŒsse auf die Anwesenheit eines noch unentdeckten Planeten erlauben. Diese Arbeit bietet neue Einblicke in die Dynamik von Staub in turbulenten protoplanetaren Scheiben und liefert eine ErklĂ€rung fĂŒr den Mangel an bestĂ€ndigen Kohlenstoffverbindungen im inneren Sonnensystem. Außerdem beschreiben wir mögliche beobachtbare Merkmale von noch unentdeckten Riesenplaneten in Radiowellenbeobachtungen von protoplanetaren Scheiben.Fine-grained dust is the fundamental building block of terrestrial planets, like Earth, that form around young stars. At the same time, the dust distribution in the gaseous disks around forming stars, so-called protoplanetary disks, influences astronomical observations, because dust is the main contributor to the opacity in protoplanetary disks. Therefore, accurate models of the distribution and dynamics of dust are critical to understanding the initial stages of planet formation and interpreting astronomical observations of forming planetary and stellar systems. This is particularly relevant because recent astronomical observations of protoplanetary disks have reached new heights in terms of resolution and sensitivity, challenging our current understanding and models. In this thesis, I introduce a novel and self-consistent turbulent dust transport model based on a density-weighted mean-field theory that also captures non-local transport effects. The model improves upon the limitations of earlier models related to the conservation of angular momentum, the ambiguous nature of the transported quantity, and the transport effects of orbital dynamics. We therefore provide an improved description of dust dynamics in turbulent protoplanetary disks. Subsequently, I present how turbulent dust dynamics and transport in the early Solar System can explain the lack of refractory carbon in the inner Solar System today. The thesis then focuses on the three-dimensional dust distribution in protoplanetary disks in the presence of an embedded giant planet. With the help of radiative two-fluid (gas+dust) hydrodynamic simulations, we find that a planet significantly influences the dust distribution in protoplanetary disks. We identify observational signatures in synthetic radio continuum observations that hint at the potential presence of a yet undetected giant planet in a protoplanetary disk. Finally, we investigate dust stirring by a giant planet in addition to dust mixing caused by turbulent gas. We focus on the combined effects on the three-dimensional dust morphology and study observable effects of turbulent and planetary dust stirring in radio continuum observations of protoplanetary disks with an embedded planet. Our work provides novel insights into turbulent dust dynamics in protoplanetary disks and offers an explanation for the lack of refractory carbon in the inner Solar System. We also describe observational signatures of giant planets in protoplanetary disks that help with the interpretation of continuum observations. These results help guide astronomers toward the detection of forming and yet unobserved planets in protoplanetary disks

    Self-generated turbulent reconnection

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    Gravitational Waves and the Galactic Potential

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    Over the next decade, third-generation interferometers and the space-based LISA mission will observe binaries in galactic centers involving supermassive black holes with millions of solar masses. More precise measurements of more extreme events that probe stronger gravitational fields can have a tremendous impact on fundamental physics, astrophysics, and cosmology. However, at the galactic scale, accretion disks, dark matter halos, and dense populations of compact objects can interact gravitationally with coalescing bodies. The role these astrophysical structures play in the evolution and gravitational-wave signature of binary systems remains largely unexplored and previous studies have often relied on ad-hoc Newtonian approximations. In this thesis, we aim to improve this picture. We study how tidal deformations of matter surrounding black holes can mask off deviations from General Relativity. We also explore the deep connection between light rings -- closed orbits of massless particles -- and the proper oscillation modes of compact objects. We show that independently of the presence of an environment, the light ring controls the late-time appearance of infalling matter to distant observers and how the final black hole formed in a collision relaxes to stationarity. Finally, we develop the first fully-relativistic framework capable of studying gravitational wave emission in non-vacuum environments. We apply it to galactic black-hole binaries surrounded by a dark matter halo and observe the conversion between matter and gravitational waves. This coupling results in significant changes in the energy flux emitted, which could help constrain the properties of galactic matter distributions.Comment: PhD thesi

    The interplay of gas, dust, and magnetorotational instability in magnetized protoplanetary disks

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    The rich diversity of exoplanets discovered in various physical environments clearly shows that planet formation is an efficient process with multiple outcomes. To un- derstand the emergence of newborn planets, one can rewind the clock of planetary systems by investigating the formation and evolution of their natal environment, the so-called protoplanetary disks. In the core accretion scenario, rocky planets such as the Earth are thought to be formed from cosmic dust particles that grow into pebbles and planetesimals, the building blocks of planets, later assembling to- gether. An intricate puzzle in this theory is how exactly these building blocks are formed and kept long enough in the natal protoplanetary disk. Protoplanetary disks are weakly magnetized accretion disks that are subject to the magnetorotational instability (MRI). It is to date one of the main candidates for explaining their turbulence and angular momentum transport. The nonideal magnetohydrodynamic effects prevent the MRI from operating everywhere in the protoplanetary disk, leading to MRI active regions with high turbulence and non- MRI regions with low turbulence. It has been hypothesized that these variations in the disk turbulence can lead to pressure maxima where dust particles can be trapped. In these so-called dust traps, dust particles can grow efficiently into peb- bles and potentially planetesimals. Yet, it is still an open question how this MRI- powered mechanism shapes the secular evolution of protoplanetary disks, and how it is involved in the first steps of planet formation. It is because the interplay of gas evolution, dust evolution (dynamics and grain growth processes combined) and MRI-driven turbulence over millions of years has never been investigated. The central goal of this thesis is to bridge the gap in the core accretion scenario of planet formation by building the very first unified disk evolution framework that captures self-consistently this interplay. The unique approach adopted in this thesis leads to an exciting new pathway for the generation of spontaneous dust traps everywhere in the protoplanetary disk, which can be potential birth-sites for planets by forming and keeping their necessary building blocks

    The Fifteenth Marcel Grossmann Meeting

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    The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity

    Discontinuous Galerkin Spectral Element Methods for Astrophysical Flows in Multi-physics Applications

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    In engineering applications, discontinuous Galerkin methods (DG) have been proven to be a powerful and flexible class of high order methods for problems in computational fluid dynamics. However, the potential benefits of DG for applications in astrophysical contexts is still relatively unexplored in its entirety. To this day, a decent number of studies surveying DG for astrophysical flows have been conducted. But the adoption of DG by the astrophysics community is just beginning to gain traction and integration of DG into established, multi-physics simulation frameworks for comprehensive astrophysical modeling is still lacking. It is our firm believe, that the full potential of novel approaches for numerically solving the fluid equations only shows under the pressure of real-world simulations with all aspects of multi-physics, challenging flow configurations, resolution and runtime constraints, and efficiency metrics on high-performance systems involved. Thus, we see the pressing need to propel DG from the well-trodden path of cataloguing test results under "optimal" laboratory conditions towards the harsh and unforgiving environment of large-scale astrophysics simulations. Consequently, the core of this work is the development and deployment of a robust DG scheme solving the ideal magneto-hydrodynamics equations with multiple species on three-dimensional Cartesian grids with adaptive mesh refinement. We chose to implement DG within the venerable simulation framework FLASH, with a specific focus on multi-physics problems in astrophysics. This entails modifications of the vanilla DG scheme to make it fit seamlessly within FLASH in such a way that all other physics modules can be naturally coupled without additional implementation overhead. A key ingredient is that our DG scheme uses mean value data organized into blocks - the central data structure in FLASH. Having the opportunity to work on mean values, allows us to rely on a rock-solid, monotone Finite Volume (FV) scheme as "backup" whenever the high order DG method fails in cases when the flow gets too harsh. Finding ways to combine the two schemes in a fail-safe manner without loosing primary conservation while still maintaining high order accuracy for smooth, well-resolved flows involves a series of careful considerations, which we document in this thesis. The result of our work is a novel shock capturing scheme - a hybrid between FV and DG - with smooth transitions between low and high order fluxes according to solution smoothness estimators. We present extensive validations and test cases, specifically its interaction with multi-physics modules in FLASH such as (self-)gravity and radiative transfer. We also investigate the benefits and pitfalls of integrating end-to-end entropy stability into our numerical scheme, with special focus on highly compressible turbulent flows and shocks. Our implementation of DG in FLASH allows us to conduct preliminary yet comprehensive astrophysics simulations proving that our new solver is ready for assessments and investigations by the astrophysics community

    Advances in Fundamental Physics

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    This Special Issue celebrates the opening of a new section of the journal Foundation: Physical Sciences. Theoretical and experimental studies related to various areas of fundamental physics are presented in this Special Issue. The published papers are related to the following topics: dark matter, electron impact excitation, second flavor of hydrogen atoms, quantum antenna, molecular hydrogen, molecular hydrogen ion, wave pulses, Brans-Dicke theory, hydrogen Rydberg atom, high-frequency laser field, relativistic mean field formalism, nonlocal continuum field theories, parallel universe, charge exchange, van der Waals broadening, greenhouse effect, strange and unipolar electromagnetic pulses, quasicrystals, Wilhelm-Weber’s electromagnetic force law, axions, photoluminescence, neutron stars, gravitational waves, diatomic molecular spectroscopy, information geometric measures of complexity. Among 21 papers published in this Special Issue, there are 5 reviews and 16 original research papers

    The Role of Nonideal Magnetohydrodynamic Effects, Gravitational Instability, and Episodic Accretion in Star-Formation

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    My dissertation focuses on the effect of magnetic fields on disk and core evolution during star-formation. We investigate the fragmentation scales of gravitational instability of a rotationally-supported self-gravitating protostellar disk using linear perturbation analysis in the presence of two nonideal magnetohydrodynamic (MHD) effects: Ohmic dissipation and ambipolar diffusion. Our results show that molecular clouds exhibit a preferred lengthscale for collapse that depends on mass-to-flux ratio, magnetic diffusivities, and the Toomre-Q parameter. In addition, the influence of the magnetic field on the preferred mass for collapse leads to a modified threshold for the fragmentation mass, as opposed to a Jeans mass, that might lead to giant planet formation in the early embedded phase. Furthermore, we apply the nonideal MHD threshold for fragmentation scales to fit the data of prestellar core lifetimes and as well as the number of enclosed cores formed in a clump, as found with the observations of Herschel and Submillimeter Array (SMA), respectively. Our results show that the trend found in the observed lifetime and fragmentation mass cannot be explained in a purely hydrodynamic scenario. Our best-fit model exhibits B∝n0.43B\propto n^{0.43}, which signifies a means to indirectly infer the effect of the ambipolar diffusion on mildly supercritical dense regions of molecular clouds. We also develop a semi-analytic formalism of episodic mass accretion (therefore episodic luminosity) from a disk to star, which provides a good match to the observed luminosity distribution of protostars. In contrast, neither a constant nor a time-dependent but smoothly varying mass accretion rate is able to do so. Our analytic work provides insight into global MHD simulations of protoplanetary disks that we carry out using the FEOSAD code. Our numerical results demonstrate the long-term evolution of disks, including the formation and evolution of clumps, and especially the episodic nature of accretion, which might explain the origin of observed knots in the molecular jet outflows
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