Frederic Rasio - US grants

Supercomputer simulations of the final coalescence and merger of compact binary stars will be performed using a new 3D relativistic hydrodynamic computer code developed by the PI and his students. In particular, the first 3D relativistic calculations of the tidal disruption of a neutron star by a black hole in a close binary system will be performed using this code. The gravitational wave signals emitted during these compact binary merger events will be computed self-consistently as part of the simulations. The dependence of the signals on the properties of the nuclear fluid will be studied systematically.

Coalescing binary systems containing compact stars are among the most important sources of gravitational radiation for current laser interferometer detectors such as LIGO. The theoretical study of gravitational wave sources is crucial for the interpretation of data to be collected by the interferometers, and for the planning of future, more advanced detectors. The new hydrodynamic calculations for binaries containing a neutron star in orbit around a black hole will represent a
significant improvement over previous, more approximate treatments. The study of coalescing compact binaries is important for many other problems of great current interest in astrophysics, such as the origin of gamma-ray bursts, and the production of heavy elements in galaxies. The 3D
relativistic hydrodynamics code developed by the PI is a general tool, which will be useful for studying many other problems involving relativistic stars and fluids. Public outreach activities are planned that will take advantage of the resources of the nearby Adler Planetarium and Astronomy Museum in Chicago and will educate the public about Einstein's theory of General Relativity and the great discovery potential of gravitational wave astronomy.

AST 0206276

PI Rasio

Close interactions happen frequently in dense stellar systems, such as the cores of globular star clusters, where the density of stars can be so high that even physical collisions between stars can occur. They can also happen during the evolution of close binary stars, where they often lead to
mergers of the two components. Close stellar interactions play a crucial role in determining the long-term dynamical evolution and final fate of dense star clusters. In addition, dynamical interactions in these clusters are thought to be responsible for the production of large numbers of exotic objects such as X-ray sources, binary radio pulsars, and blue stragglers. Understanding the long-term dynamical evolution of dense stellar systems and the formation mechanisms for the peculiar sources they contain are two long-standing problems in theoretical astrophysics.

This project will focus on a number of theoretical and computational studies dealing with various aspects of these hydrodynamic stellar interactions in dense star clusters and in binary star systems. Large-scale numerical simulations of the hydrodynamic and stellar evolution processes will be performed on parallel supercomputers, providing quantitatively accurate theoretical predictions that can be compared directly to observations. Much of the work will be carried out by undergraduate students.
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AST 0507727
Frederic Rasio
Northwestern University
Dynamics of Extrasolar Planetary Systems
ABSTRACT
A theoretical study of the dynamics and stability of extrasolar planetary systems will be conducted.
The overall goal is a better understanding of the formation and evolution of planetary systems
around other stars, particularly those in extreme environments. Special emphasis will be placed on
multiple planet systems, systems during stellar interactions, pulsar planet systems, and interactions
between planetary dynamics and the central star. Central to this work is the combination of orbital
dynamics and hydrodynamic methods in the simulations, as well as stellar evolution where
appropriate. Planned improvements include removing approximations in gravitational scattering and
better treatments of tides and tidal heating (among others). The dynamics simulation tools
developed here will also have application to many broader areas of astrophysics.
The work here is part of a student-oriented research program in computational astrophysics which
will be continued. A postdoctoral fellow will be supported and trained in numerical modeling as
well. The resulting animations will also be incorporated into public exhibitions and activities at the
nearby Adler Planetarium.

This award supports the acquisition of high-performance computing equipment that will enable research on the theory of gravitational-wave (GW) sources. The work will involve both research and technology training of undergraduate and graduate students. The equipment consists of a large computer cluster (56 nodes, each with two dual-core CPUs) with gigabit networking, designed for high computational efficiency-to-cost ratio for GW source simulations. In addition, 16 of the nodes will be equipped with specialized hardware (GRAPE boards) for direct N-body simulations in stellar dynamics. A major storage component is also part of the proposed system. Visualizations from the simulation results will be developed for use in both research analysis and training as well as for public outreach presentations at the nearby Adler Planetarium. For this development effort will be enabled by the acquisition of a Tiled Wall Display (almost 25 million pixels) operated by a small cluster of 7 nodes with high-level graphics capabilities. All the acquired instrumentation will be used in a wide range of computational astrophysics projects on binary star evolution and compact object formation, stellar dynamics, and hydrodynamics. The results will greatly improve the understanding of the most important GW sources for current laser interferometer detectors, and they will also allow for better physical interpretation of future GW observations. Examples of specific projects include: (i) modeling populations of binary compact objects driven to inspiral by GW emission; the primary goal is the application of empirical constraints to theoretical models and the derivation of reliable predictions for binary inspiral detection rates and for measurements of source properties. (ii) dynamical simulations of black holes in dense star clusters; frequent dynamical interactions in these systems can lead to the formation of large numbers of merging black hole binaries and may be the dominant source of detectable black hole mergers for ground-based interferometers such as LIGO. (iii) hydrodynamic calculations of the final mergers of compact binaries containing a black hole and a neutron star; these will be performed using a sophisticated 3-D relativistic hydrodynamics code and will represent a significant improvement over previous, more approximate treatments based on Newtonian gravity. The study of GW sources is also important in many other areas of astrophysics. For example, coalescing compact binaries may also be sources of gamma-ray bursts, and they may play a key role for the production of many heavy elements in galaxies. The research activities enabled by this instrumentation will involve the training of several undergraduate and graduate students, including students from under-represented minorities. A graduate student studying high performance computing and a team of up to about ten undergraduates will also be trained in all phases of the instrument acquisition, set-up, and commissioning.

Relativistic binary systems, in which two compact stars orbit each other in a very tight orbit, are among the most important sources of gravitational radiation for current laser interferometer detectors such as LIGO. The theoretical study of gravitational wave sources is crucial for the interpretation of data to be collected by the interferometers, and for the planning of future, more advanced detectors. This project consists of two closely related studies: (1) Numerical calculations of the final mergers of compact binary systems containing a black hole and a neutron star. These are to be performed using a sophisticated 3-D relativistic hydrodynamic code and as part of a new collaboratione between Northwestern and Penn State University. The new hydrodynamic calculations represent a significant improvement over previous, more approximate treatments based on Newtonian gravity. (2) Stellar dynamical simulations of black holes in dense star clusters. Frequent dynamical interactions in these systems can lead to the formation of large numbers of coalescing black hole binaries and may represent a dominant source of detectable stellar black hole mergers for gravitational wave detectors.
The study of coalescing compact binaries is important in many other areas of astrophysics, such as gamma-ray bursts, and the production of heavy elements in galaxies. The stellar dynamics and relativistic hydrodynamics computer codes to be developed are general tools, which are useful for studying many other problems involving relativistic stars and fluids. This research involves the training of several undergraduate students, including students from under-represented minorities, and one graduate student. Outreach activities will take advantage of the resources of the nearby Adler Planetarium and Astronomy Museum in Chicago, allowing the results and methodology to be presented to a large and diverse public.

Abstract
AST - 0607498
Rasio

This project is about the black holes at the center of dense star clusters. The Principal Investigator and his team will carry out detailed supercomputer simulations of the processes that lead to the formation and collapse of such black holes. The two main classes of dynamical evolution paths that will be studied are: (i) the rapid contraction of young star clusters, leading to runaway collisions and mergers of ordinary stars and the production of a very massive remnant that could undergo direct gravitational collapse to a black hole; and (ii) the dynamical evolution of dense systems of stellar black holes, which can also merge together and grow rapidly in mass, as they form tight black hole binaries driven to complete coalescence by the energy loss to gravitational radiation. The computational methods will make it possible to study these problems for a wide range of systems, from small star clusters all the way to large proto-galactic nuclei, with a unified and realistic treatment of all-important astrophysical processes.

The stellar dynamics computer codes developed for this project are general tools, which will be useful for studying many other problems involving dense star clusters with or without massive black holes. Some of the novel algorithms and numerical techniques are of wide applicability. The planned research activities will involve the training of several undergraduate students at Northwestern University, and will likely include students from under-represented minorities. Outreach activities are also planned, taking advantage of the resources of the nearby Adler Planetarium and Astronomy Museum in Chicago.

AWARD NO: AST-0732444
PI: Frederic Rasio
INSTITUTION: Northwestern University
TITLE: Conference on ""Extreme Solar Systems"", Santorini, Greece

This award will provide funding for partial travel support to attendees from US institutions to attend the conference Extreme Solar Systems to be held in Santorini, Greece, 25-29 June 2007. The meeting is expected to bring together about 150 researchers from the US, Europe, and Asia, and will focus on the ""extreme"" aspects of current research on extrasolar planets, such as developments toward the detection and characterization of terrestrial-mass planets, planets and ""hot Jupiters"" around evolved stars, including giants, white dwarfs and neutron stars, and on a number of other currently debated important topics.

In the short history of planet detection around other stars, this is the first meeting that has been devised to address a broad range of topics with specific emphasis on the extreme character of extrasolar planets. The topics covered by this conference address key problems in a frontier research field of highly interdisciplinary character. Most of the presentations by leaders in the field will be related to issues at or beyond the current limits of our knowledge of the extrasolar planetary systems. The meeting will provide common grounds for a large number of experts to exchange ideas and advance understanding of the formation and evolution of planetary systems around other stars. This knowledge is necessary to obtain a consistent integrated picture of the physics of planetary systems and to better constrain our understanding of the origins of life on Earth and elsewhere in the Universe.

This award will enable more students, junior researchers, scientists and smaller institutions, and members of underrepresented groups to participate.

This award supports the acquisition of high-performance computing (HPC) equipment that will enable research in the area of gravitational-wave physics relevant to ground-based GW detectors, such as the NSF-funded Laser Interferometer Gravitational-wave Observatory (LIGO). The research enabled by this equipment focuses on both modeling the astrophysical sources of gravitational waves, as well as the development of computational tools for the analysis of gravitational-wave signals obtained by LIGO, bringing together a collaboration of physicists with computer scientists and applied mathematicians. The hybrid character of the equipment originates from the incorporation of cutting-edge Graphics Programming Units (GPUs appropriate for scientific computing) used as accelerators for massively parallel computations in additional to regular computing units.

The study of gravitational wave sources is important in many other areas of physics and the enabled research work has a strong interdisciplinary character. The equipment will further enable the multi-faceted training of students in HPC technology and computational research, including algorithmic development for GPUs most desirable for a technically sophisticated workforce, competitive in the 21st century. A small fraction of the computing time resources will also be coupled to another NSF-funded project at Northwestern, a GK-12 program; these resources will bring computational thinking and simulation tools to K-12 classroom through activities and modules tied to the science curriculum thus engaging teachers and students in inquiry-based learning, understanding of the research process, and advancing communication and outreach skills of the graduate students.

Many stars form in large clusters containing anywhere from thousands to many millions of objects. Stars in these clusters are born with a broad range of masses. Furthermore, the most massive stars evolve quickly, ending their lives in just a few million years and leaving behind black holes as remnants. The star clusters themselves, however, can continue to live for many billions of years, and indeed the globular clusters seen in many galaxies are thought to contain some of the oldest stars in the Universe. Therefore, many of the star clusters we see today should contain large numbers of black holes formed a long time ago. This research will use state-of-the-art supercomputer simulations to study the formation and evolution of these black holes in a variety of star cluster environments. It will also leverage innovative hybrid computational techniques, including General-Purpose computing on Graphics Processing Units (GPGPU).

The study of black hole formation and evolution is important in many areas of physics and
astronomy, including galaxy formation and cosmology, the study of quasars and other active
galactic nuclei, general relativity and gravitational wave astronomy. The stellar dynamics supercomputer codes to be developed for this project are general tools, which will be useful
for studying many other problems involving dense star clusters with or without massive black
holes. The planned research activities will involve the training of undergraduate students at Northwestern University, and will likely include students from under-represented minorities. Graduate students
will also receive training and mentoring. Outreach activities are also planned that will take
advantage of Dearborn Observatory on the Northwestern campus in Evanston, as well as the resources of the nearby Adler Planetarium and Astronomy Museum in Chicago.

This award provides support for junior speakers to attend the second "Future of Astronomy" conference in Evanston, IL. The conference follows on from a highly successful meeting held in 2011, and is designed to bring together a significant fraction of the top postdoctoral researchers in astronomy in North America. A key goal of the workshop is to create a venue where leading postdoctoral researchers from across the country, working in much different programs and in different areas, can come together to share their excitement and ideas on future key research areas. This is a significant opportunity for the attendees to speak about, and survey, the frontier of astrophysics, and the workshop will undoubtedly lead to numerous new collaborations being formed. Funding will additionally be targeted toward, although not limited to, women and under-represented minorities.

Most stars form in dense clusters, the largest of which contain many millions of stars. Since star clusters can exist for many billions of years, they are believed to contain large numbers of compact objects, such as black holes and neutron stars that formed a long time ago as the remnants of dead massive stars. This research program at Northwestern University will use state-of-the-art supercomputer simulations to study the formation and evolution of these compact objects in a variety of star cluster environments. The main focus will be on the production of close binaries containing two black holes, which can eventually merge and produce potentially detectable bursts of gravitational waves. The development of parallel computing techniques and new algorithms will have broad relevance and be of interest to scientists outside of physics and astronomy. The astrophysics research will be student-oriented and senior students will help train new team members, including undergraduate students. Education and public outreach activities are also planned that will take advantage of the facilities at the Adler Planetarium in Chicago, and at Dearborn Observatory on the Northwestern University campus in Evanston.

This project will address a number of key questions concerning the formation and dynamical evolution of compact objects (black holes and neutron stars) in dense star clusters. As they experience friction against the background of lighter stars, massive compact objects are expected to rapidly concentrate in the dense inner cores of clusters, where the rates of dynamical interactions are very high. These interactions can both produce binaries and tighten their orbits. In some cases, through successive mergers, perhaps helped by accretion of gas, an intermediate mass black hole could eventually be formed. Many of the objects formed by these processes are potential multi-messenger sources. The project will use a hybrid approach of combining Monte Carlo and N-body codes to optimize computing speed, accuracy and realism and overcome the dynamical range problem of simulating very large star clusters in which most of the interesting dynamics happens in a relatively small, high-density central region. A library of more than an thousand new cluster models will be made publicly available at the conclusion of the project.

This grant will allow the purchase of a high-performance-computing cluster, which is required by researchers at Northwestern University to investigate sources of gravitational-wave emission. Modeling and understanding of gravitational-wave sources is becoming extremely important as scientists are utilizing data from the Laser Interferometer Gravitational-wave Observatory to detect black holes and other exotic astrophysical objects (such as "neutron stars"). On one level, astronomers require large computers to develop programs that can help us understand the large amounts of data from gravitational-wave detectors, and pick out the real, astronomical sources from a wide variety of noise sources. But in addition, as detections of gravitational-wave sources occur more frequently, astronomers need to understand what those detections can tell us about the population of exotic objects throughout the universe. For instance, given the detections of gravitational-wave sources already, researchers ask how many black holes there might be, in our galaxy, and in other galaxies, and how massive are they? Also, researchers ask: how do those black holes form, and how do systems of pairs of black holes form? These are important questions in understanding objects at the extreme of the known laws of physics, and to answer these questions, astronomers need to understand not only the lives of individual stars and the formation of black holes and neutron stars, but they need to simulate populations of millions of stars, and the wide variety of events and processes that can affect the development of those stars. For that work, astrophysicists require large collections of very efficient computers, such as the computer cluster that will be purchased with these funds, to run massive simulations that help us explore these questions. In addition to the pure research that will be done with this cluster, the PI's group is also well known for generating award-winning visualizations of their simulations, which will be used at a variety of Science, Technology, Engineering, and Mathematics (STEM) education and public-outreach events. The entire team also has extensive experience in attracting a diverse group of researchers to STEM research and fields; this cluster will help that group to train a new generation of diverse researchers in data-science methods and scientific computing, contributing to the technical workforce of the nation.

This grant will allow the acquisition of a high-performance computing (HPC) cluster that will enable research in the emerging area of gravitational physics. The cluster will be essential to the development and optimization of codes needed for both gravitational-wave (GW) data analysis as part of the Laser-Interferometer Gravitational-wave Observatory (LIGO) Scientific Collaboration, and GW source modeling for the physical interpretation of the detections. The equipment consists of a large computer cluster (56 nodes) with InfiniBand networking and 70 TB of usable storage. This cluster will incorporate three innovative Graphics-Programming-Unit nodes (using GPUs appropriate for scientific computing) which will be used as accelerators for special-purpose massively parallel computations. The cluster will be housed at a top-of-the-line HPC data center on the Northwestern University campus and will be operated and managed by an experienced team of HPC professionals led by one of the co-PIs. In more detail, the cluster will be used for GW research focused on binaries with two compact objects (neutron stars and/or black holes) in interdisciplinary collaborations between GW data analysts (members of the LIGO Scientific Collaboration), astrophysicists, and computer scientists. The goals are to optimize data searches for GW signals (through effective detector characterization), to extract as promptly as possible and accurately the physical properties of the signal sources (through continuous improvements of our parameter-estimation algorithms), and to advance the astrophysical interpretation of the discoveries so we can better understand the sources' origin and constrain theoretical models using our GW observations (through the development of state-of-the-art formation models in different environments and comparing predictions to data). The team is led by PI Kalogera and co-PI Rasio, who are well recognized for their significant impact in these research areas and for their innovative development of new computational tools for GW data analysis and astrophysical modeling of GW sources.

Most stars form in dense clusters. The largest star clusters contain many millions of stars. The masses of these stars, when born, cover a broad range. The most massive stars end their lives in as little as a few million years and leave behind remnant black holes or neutron stars. Much larger numbers of massive white dwarf remnants are produced from intermediate-mass stars in a few billion years. The star clusters themselves often continue to live for many billions of years. Therefore, many of the star clusters observed today can contain large numbers of black holes and neutron stars formed a long time ago, as well as large populations of white dwarfs. The investigators will use computer simulations to study the dynamical interactions of all compact remnants (black holes, neutron stars, and white dwarfs) in dense star clusters. These models will help astronomers interpret observational data. This work also has applications beyond astronomy. In particular, the computing methodology developed for this work will be of interest to scientists outside of physics and astronomy, since the techniques used to model dense clusters of interacting stars have broad relevance in science and engineering. This work will also help maintain the investigators' student-oriented research program in computational astrophysics. The graduate students involved will mentor and work closely with undergraduate students. The investigators will strive to recruit students from traditionally underrepresented groups. Education and public outreach activities will take advantage of the investigators' close ties to the Adler Planetarium in Chicago and the Dearborn Observatory on the Northwestern University campus.

State-of-the-art N-body simulations will be performed to study the formation and evolution of compact objects in a variety of star cluster environments. The main focus will be on the production of compact binaries, which can be strong sources of gravitational waves and high energy radiation, as well as transient sources triggered by collisions and close encounters of compact objects. The work will address key questions concerning the formation and dynamical evolution of compact objects in dense star clusters, including their strong interactions with other stars. The electromagnetic transients produced through interactions of compact remnants with other stars potentially include a variety of X-ray and gamma-ray burst sources, as well as many optical transients of great current interest in the new era of large time-domain astronomy surveys. Additionally, all compact binaries formed through dynamical interactions are strong sources of gravitational waves, and some will have strong electromagnetic counterparts, making them key targets for multi-messenger astronomy. This award thus advances the goals of the NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" Big Idea.

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.