James McLellan Stone - US grants

STONE, James 95-28299 Dr. Stone will conduct a theoretical study of magnetohydrodynamic instabilities in accretion disks and the nature of magnetosphere- disk interactions using 2- and 3-dimensional model codes developed by Stone and his collaborators. Angular momentum transport and the evolution of magnetic instabilities in protostars, cataclysmic variable stars and X-ray sources are the focuses of the numerical models to be produced. ***

AST-0113571
J. Stone

The product of this research will be an improved general purpose solver for astrophysical gas dynamics, including magnetohydrodynamics, self-gravity, and radiative cooling effects. It will be a successor to the PI's widely used ZEUS code and will be a new generation code exploiting new hardware and software capabilities. Solvers optimized for scalar processors able to run on distributed memory parallel machines will greatly enhance the range of astrophysical problems addressable with direct numerical simulation. The project is interfaced to the graduate program of the Center for Scientific Computation and Applied Mathematical Modeling, which will allow hands on graduate training in numerical simulations for astrophysics and in use of numerical algorithms for parallel architectures.

AST 0098625
Stone
A wide variety of objects, ranging from new stars in formation (protostars), to objects which are the cinders of burned out stars (white dwarfs, neutron stars, and black holes), to active galactic nuclei (AGN, such as quasars) are thought to have accretion disks surrounding them. Inflows of gas from these disks onto the central object seem to account for some of the most dramatic components of the Universe. They emit prodigious amounts of power and radiate it over a tremendous swath of the electromagnetic spectrum (from the mid-infrared to hard X-rays and gamma rays). Our theoretical understanding of these accretion flows, however, is still limited by the complexities involved in developing the necessary magnetohydrodynamics (MHD) and radiation hydrodynam-ics computer models. Our understanding of the local physics that control such flows has progressed rapidly in the last few years. It is now important to examine how local processes such as the magnetorotational instability (MRI) determine global disk structure and evolution, especially since only global disk models can be directly compared to high spatial-, spectral-, and time-resolution observations of accretion flows around protostars, white dwarfs, neutron stars, and black holes.
Using computational methods, this project will develop the first time-dependent, three-dimensional MHD models of the interaction of an accretion disk with a magnetized and rotating central star. These calculations will allow quantitative measurement of the mixing rate of the stellar field into the disk, the size of the interaction region, the time-averaged torque exerted on the star, and the geometry and kinematics of any polar cap accretion flows that might form. Such quantities are fundamental to the theory of how magnetized stars interact with accretion disks, yet to date they have yet to be calculated from first principles. Direct comparison of the simulations to a large and varied set of observations will be undertaken, including spectroscopic observations of magnetospheric funnel flows and accretion shocks in T Tauri stars, and the observed distribution of the rotation rates in T Tauri stars. Synthetic spectra of the models will be compared to that observed for accreting black holes at the center of early type galaxies and the galactic center, while fluctuations in the mass accretion rate can be compared to X-ray variabil-ity observed by RXTE in X-ray binaries. These global calculations are the first step towards star-disk interaction models which span many decades in radius.
The calculations will all be performed with a variety of 2D and 3D MHD computer codes, using large allocations of supercomputer time on massively parallel machines at the national supercomputer centers. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC).
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AST-0205972
Ostriker

Several lines of observational and theoretical evidence suggest that giant molecular clouds (GMCs) have short lifetimes, forming and dissociating within a few tens of millions of years. Prevailing theoretical arguments favor instability mechanisms in spiral arms to form GMCs, but existing work has suffered from technical limitations, and has not previously directly demonstrated that condensations with the properties of GMCs indeed form. Dr. Eve Ostriker, at the University of Maryland, will lead an investigation of a series of linear stability analyses, nonlinear numerical simulations, and supporting diagnostics to address outstanding questions concerning GMC formation in spiral galaxies. The modeling will include several important technical innovations. These researchers will, for the first time:
o Use direct numerical simulations to study development of the Parker instability in 3D with realistic rotational shear self-consistent with large-scale density gradients through arm and interarm regions of galaxies, also incorporating self-gravity to study linear and nonlinear coupling of Parker and Jeans modes;
o Comprehensively survey, using spectral methods, shearing-wavelet integrations, and magneto-hydrodynamic (MHD) simulations, the potential effects of the magnetorotational instability in galactic disks, focusing on coupling to self-gravitating modes in both secular-growth and saturated-state regimes;
o Incorporate a realistic multi-phase gaseous medium for the initial conditions in two and three- dimensional simulations of self-gravitating and magnetically-driven galactic disk instabilities;
o Directly confront stochastic coagulation vs. collective instability mechanisms for forming GMC-scale condensations by performing controlled experiments of multiphase evolution with and without self-gravity and magnetic effects.

As GMC formation is intimately coupled to star formation, and the cold ISM is the most dynamically-responsive component of a disk galaxy, the results of this project will have broad impacts on both Galactic and extragalactic astronomical research, with implications for understanding the global regulation of star formation and the structure and evolution of spiral galaxies across the Hubble sequence.
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AST-0607472
Goodman

It has long been assumed that turbulent angular momentum transport is a driving force explaining why accretion disks accrete, simply because such disks have very large Reynolds numbers (Re). Theoretical and numerical studies have shown that magneto-rotational instabilities (MRI) can support vigorous turbulence, so that MRI is now the favored mechanism for accretion in disks ranging from quasars to cataclysmic variables. However, MRI requires sufficient ionization to provide good electrical conductivity, which cool disks may not provide, so hydrodynamic turbulence is sometimes invoked. This project is an experimental laboratory study of high-Re MRI in liquid metal, to demonstrate MRI and study its nonlinear behavior, to investigate the stability of hydrodynamic flows at large Re, and to compare the laboratory results quantitatively with simulated astrophysical disks. These comparisons will help to validate theoretical tools applicable to nonlinear saturation of resistive MRI in astrophysical systems, especially proto-stellar disks.

Success will require the combined efforts of experimental physicists, computational fluid-dynamicists, and theoretical astrophysicists, who have much to learn from one another. Student training will be particularly valuable, since the field of experimental astrophysics is still rather small.

This work is for the acquisition of a high-performance computer cluster for computational astrophysics and for the analysis of data from the Sloan Digital Sky Survey, Wilkinson Microwave Anisotropy Probe, the Atacama Cosmology Telescope, and the Southern Cosmology Survey. The cluster will be available to researchers from several institutions and will be available for the training of students in high-performance computing.

AST-0908269
Stone

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

This project will investigate the gas dynamics of protoplanetary disks, and the interaction of disks with planets. The work includes (1) studies of angular momentum transport by the magnetorotational instability (MRI) in protoplanetary disks, (2) studies of the propagation and damping of, and gap opening by, density waves excited by disk-planet interaction, and (3) fully global models of protoplanetary disks that can investigate the structure and evolution of disks over a wide range of radii. Realistic models of protoplanetary disks are challenging because of the diverse range of physics that must be included, and these calculations will be the most sophisticated yet attempted. These simulations will follow the turbulent mixing and settling of dust grains in the disk self-consistently with the gas dynamics by integrating the motion of millions of particles drawn from a realistic size distribution. Effects to be added are recombination on grains, as part of a twelve-species non-equilibrium ionization and recombination network, all of the relevant non-ideal magnetohydrodynamic (MHD) processes, and radiative diffusion and optically thin cooling to follow the thermodynamics of the gas. All of the necessary code elements have been implemented and tested within Athena, a new and powerful grid-based code for astrophysical MHD. The result should be the most realistic and accurate models of the non-ideal MHD of protoplanetary disks possible, and a deep understanding of the environment of planet formation and the interaction of planets with the disk.

The project includes training of graduate students, and animations and visualizations for dissemination of the results to the wider public. The team is vigorously engaged in involving women and under-represented groups in theoretical and computational astrophysics through a Princeton summer undergraduate research program. The work continues to foster interdepartmental and international collaboration by providing access to the Athena code to the astrophysics community through an open-source software philosophy.

This is an Institutional Infrastructure proposal to build a GPU cluster to support research in data-parallel code development and optimization, as well as research applications, in three scientific domains, namely, seismology, biology and astrophysics. These goals build on a close collaboration with an expert team in GPU computing from computer science. The proposed cluster will serve not only as an invaluable resource for computation, but will also aid cross-fostering of techniques and concepts between disciplines and will be used to stimulate collaboration and synergistic research activity in a wide range of areas.

Even though domain scientists are increasingly dependent on computation to achieve their research goals, most are not experts in parallel programming or GPU architectures. The difficulty of parallel programming for GPU clusters is an impediment to scientific progress. In order to relieve scientists of the burdens of parallel programming, computer scientists at Princeton have developed systems for automatically parallelizing programs for GPU. Building on this success, the PIs plan to extend these techniques to GPU clusters and work closely with the seismologists, biologists and astrophysicists to accelerate the pace of science.

This project will establish a joint research center in fusion and astro-plasma physics involving two units within Princeton University (the Princeton Plasma Physics Laboratory, PPPL, and the Department of Astrophysical Sciences) and three institutes within the Max Planck Society (MPS) (the Institute of Plasma Physics at Garching and Greifswald, the Institute for Astrophysics at Garching, and the Institute for Solar System Research at Lindau).

The major research goal of the center is to harness the expertise and resources of both the fusion and astrophysical plasma communities to tackle fundamental problems that impede progress in both communities. Such problems include understanding the process of magnetic reconnection, the generation and transport of energetic (superthermal) particles in collisionless shocks, and the generation and dissipation of turbulence in magnetized plasmas. Research conducted at the center will advance our understanding in many areas of theoretical plasma astrophysics, fusion physics, basic plasma experiments, and tokamaks.

More broadly, the joint center will foster interdisciplinary collaboration between the plasma and astrophysics communities, both nationally and internationally. It will forge new collaborations between Universities, the national fusion labs, and international partners. It will leverage the tools and expertise developed independently in both communities (for example, laboratory experiments and sophisticated computer codes) in order to address fundamental research questions. It will provide international research collaboration opportunities for postdocs, graduate, and undergraduate students, and provide opportunities for students and teachers at high-schools, local, and regional institutions to engage in scientific inquiry in ways that enhance their understanding of science concepts and scientific ways of thinking through a well established outreach program at PPPL.

This award has been designated as a Science Across Virtual Institutes (SAVI) award and is being co-funded by NSF's Office of International Science and Engineering.

This project will create a Theoretical and Computational Astrophysics Network with major nodes at the University of Illinois at Urbana-Champaign, the University of California at Berkeley, and Princeton University, to advance the theory of black hole accretion and outflows. Accretion of matter onto black holes is central to many astrophysical and gravitational phenomena, but current theory lacks self-consistent models both for high accretion rate flows where radiation forces are important, and for low accretion rate flows where collisionless plasma effects are important. The network team brings together expertise in high performance computing techniques, astrophysics, and plasma physics in order to address this need. The team will develop a general relativistic, radiation magnetohydrodynamics code to study luminous accreting black holes, and a multi-fluid relativistic magnetohydrodynamics code with anisotropic electron and ion pressures, conduction, viscosity, and radiative heating and cooling to study slowly accreting systems. These new codes will be used to address fundamental questions about the structure and observational appearance of the inner accretion disk as well as the origin and maintenance of the large-scale magnetic fields believed to power relativistic jets, and then will be made publicly available to the research community. The network will contribute to scientific workforce development by supporting the work of undergraduate students, graduate students, and postdocs; and a program of visualizations, released on the internet, will help communicate the excitement of black hole astrophysics to the scientific community and to the broader public.

The goal of this proposal is to apply magnetohydrodynamic (MHD) modeling tools to the study of interacting close binary systems such as cataclysmic variables (CVs), with the complementary goal of improving the understanding of magneto-rotational instability in accretion disks. While observations of CVs have provided a wealth of constraints on physical models of accretion, advanced MHD models have yet to be applied to the study of the disks in these systems.

The project will compare results from the numerical simulations of the disks around close binary star systems to observational data in order to further constrain disk parameters such as physical disk size, angular momentum transport, and global disk features (i.e. spiral shocks, hot spots, etc.). The project will also contribute to scientific workforce development through the involvement of undergraduate and graduate students. The project will communicate results to the public through the development of animations and visualizations of the close binary disk models made available via the web.

Over 99% of the visible matter in the Universe is a plasma, that is a dilute gas of ions, electrons, and neutral particles. Despite their ubiquity, many fundamental and important physical processes which control the dynamics of plasmas remain poorly understood. In turn, this limits our ability to intepret diverse phenomena in space such as accretion onto black holes at the centers of galaxies or the interaction of the solar wind with the upper layers of the Earth?s atmosphere, and it also impacts our ability to engineer and operate experiments on Earth such as magnetically confined fusion devices. The Max-Panck/Princeton Center for Plasma Physics (MPPC) was established as a joint venture of the Max Planck Society (MPS) in Germany and Princeton University in order to forge new collaborations between Universities, the national plasma labs, and international partners in order to tackle some of the most pressing problems in plasma dynamics. The center fosters interdisciplinary collaboration between the plasma and astrophysics communities, as well as international collaboration between these communities in the US, Germany, and elsewhere. It serves to train the next generation of plasma scientists in experimental science, computation, and theory, and its international scope provides unique training for early career scientists, particularly valuable as plasma and fusion science become increasingly international. Finally, the center provides opportunities for the public, as well as students and teachers at public schools, local, and regional institutions to engage in scientific inquiry in ways that enhance their understanding of science concepts and scientific ways of thinking through a well established outreach program at the Princeton Plasma Physics Lab.

The MPPC focuses its effort studying four key topics: magnetic reconnection, acceleration and propagation of non-thermal particles, the properties of plasma turbulence, and magnetohydrodynamic processes in astrophysical plasmas such as the magneto-rotational instability. Uniquely, it leverages international expertise and resources such as experimental facilities and computational methods to lead new studies in theoretical, experimental, and computational plasma physics. The US program concentrates strongly on postdoctoral researchers, who work with senior researchers supported by existing funds. While the postdoc program is the engine that drives research in the center, there are a number of ways in which each participating organization has fused together as a center, for example (1) joint mentoring of postdocs, (2) exchange visits of senior members, (3) joint experiments, (4) joint code development and validation, (5) fostering collaborations across the entire US and German plasma and astrophysics communities, and (6) annual meetings of the center as a whole, and more frequent topical workshops for the community. For example, the MPPC will host a summer school in computational plasma physics at Princeton University within the current period of funding.

This project is jointly funded by NSF's Divisions of Physics and Astronomy (Mathematical & Physicsal Sciences Directorate), and the Office of International Science and Engineering.

Since black holes (BH) are by definition invisible, the only way that astronomers can detect them is by observing material accreting onto (or falling into) the black hole. Given the strong gravity, intense radiation and powerful magnetic fields near black holes, it is not surprising that such accretion is complex and can only be understood by running sophisticated numerical models on supercomputers. A research collaboration between the University of Illinois, Princeton University and the University of California-Berkeley will model the behavior of BH accretion in the realm intermediate between strong and weak accretion, when interesting effects such as jets of outflowing material and unusual oscillations in the accretion are known to take place. This work will help to unravel mysteries related to black holes, such as how the jets form and how the structure of the accretion flow changes over time. The team will communicate the excitement of black-hole astrophysics to the public through lectures and visualizations, and to future generations of students through a black hole summer school.

The theory of black-hole (BH) accretion and outflows is central to many areas of modern astrophysics and gravitational physics. The collaboration team has developed numerical techniques that permit nearly ab initio modeling of black-hole accretion in both the high- and low-accretion-rate limits. The team plans to develop new numerical techniques and codes suitable for studying the difficult, intermediate-accretion-rate regime, which is associated with jets, quasi-periodic oscillations, and state transitions around stellar-mass black holes. Additions to the models include radiation forces, pair production and transport, nonthermal particle production and transport, and collisionless plasma effects, all of which are critical for making progress on long-standing problems in black-hole astrophysics, such as the structure and observational appearance (spectrum, time variability, polarization) of accretion at intermediate accretion rates, as well as questions about the origin and maintenance of large-scale magnetic fields believed to power relativistic jets from such systems. The group will make their new codes available for others to use through public releases.

Most of the visible matter in the Universe is a plasma, that is a dilute gas of ions, electrons, and neutral particles. Many fundamental and important physical processes that occur in plasmas remain poorly understood. This, in turn, limits our ability to understand diverse phenomena in space such as how stars form or how the particles flowing from the Sun affect the upper layers of the Earth's atmosphere. It also impacts our ability to engineer and operate experiments on Earth such as magnetically confined fusion devices. The Max-Panck Princeton Center for Plasma Physics (MPPC) was established as a joint venture of the Max Planck Society in Germany, Princeton University, and the Department of Energy's Princeton Plasma Physics Laboratory (PPPL) in order to forge new collaborations between Universities, the national plasma labs, and international partners in order to investigate some of the most pressing problems in plasma physics. By supporting students and early career scientists, the MPPC serves to train the next generation of experimental, computational, and theoretical plasma physicists, and its international scope provides unique training for early career scientists. The center provides unique opportunities for the public, as well as students and teachers at public and regional schools, to engage in scientific inquiry in ways that enhance their understanding of science concepts and scientific ways of thinking through a well established outreach program at PPPL.

The MPPC effort at Princeton University is focused on three cross-cutting problems in plasma astrophysics: cosmic ray transport and feedback, the interplay between turbulence and reconnection, and dynamo action in accretion disks, stellar convection, and galaxies. New fluid closure models for cosmic rays will be developed and applied to models of the interstellar medium in galaxies to understand the role of cosmic-ray feedback on galaxy formation. New theoretical and computational studies of magnetic field amplification by dynamo action driven by the magneto-rotational instability in accretion disks, and convection in rotating stars, will be undertaken. Using new computational tools developed by members of the MPPC, new studies of plasma turbulence in the kinetic regime, relevant to conditions in the solar wind, will be developed. The Center fosters interdisciplinary collaboration between the plasma and astrophysics communities, as well as international collaboration between these communities in the US, Germany, and elsewhere. Its international scope provides unique training for graduate students and postdocs. This award provides renewed support for Princeton University's participation in MPPC, with support for PPPL's participation provided by the Department of Energy.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.