Pedro Marronetti - US grants

The NSF's LIGO gravitational wave detectors are among a number of new and planned facilities all over the world which are designed to directly detect and measure gravitational waves. The observation of gravitational waves will open a new window on the universe by enabling us to study exotic objects such as black holes, supernovae, neutron stars, collapsars and gamma-ray bursts in a completely different way. The work in this project is aimed at continuing the development of a generic numerical code capable of simulating what is expected to be one of the most important sources of gravitational radiation, namely binary systems consisting of black holes. The specific focus of this project is to improve such binary black hole simulations by (i) providing more realistic initial conditions for the simulations, (ii) improving the quality and accuracy of the simulations and (iii) studying the validity and utility of approximation schemes such as the periodic standing-wave approximation.
This work is important because only accurate simulations, which start from realistic initial conditions, will be able to produce reliable theoretical predictions of the gravitational waves which will be observed in the near future. In addition, this investigation makes key contributions to synergistic efforts, ranging from numerical and mathematical relativity to gravitational wave astrophysics. It is carried out in collaboration with the relativity groups at the University of Texas in Brownsville and the University of Jena in Germany. Regular exchanges benefit students from all three institutions.

The NSF's LIGO gravitational wave detectors are among a number of new and planned facilities all over the world which are designed to directly detect and measure gravitational waves. The observation of gravitational waves will open a new window on the universe by enabling us to study exotic objects such as black holes, supernovae, neutron stars, collapsars and gamma-ray bursts. The research in this project is aimed at simulating on the computer what is expected to be one of the most important sources of gravitational radiation, namely binary systems consisting of black holes. The black holes in such systems spiral towards each other until they form a larger merged black hole. The plan for this project is to investigate these systems in order to make predictions about the gravitational waves emitted during their inspiral and merger. In the course of this work, several key physics questions will be addressed: (i) What is the maximum possible recoil velocity after the two black holes have merged? (ii) For what configurations can spin flips occur? (iii) What is the maximum achievable angular momentum of the final merged black hole? (iv) How sensitive are the simulations to the choice of the initial conditions?
This work is important because gravitational wave detectors (such as LIGO) need reliable theoretical predictions of the gravitational waves which will be observed in the near future. Other aspects of this work have implications for a variety of astrophysical models. For example, the magnitude of the recoil of the final black hole is an important input parameter for the cosmological evolution of supermassive black holes or the growth and retention of intermediate-mass black holes in dense stellar clusters. In addition, this investigation makes key contributions to synergistic efforts, ranging from numerical and mathematical relativity to gravitational wave astrophysics. It is carried out in collaboration with the relativity group at the University of Jena in Germany. Regular exchange with this institution through visits by faculty, post-docs and students will have educational benefits for both the students at Florida Atlantic University and the students in Jena.

OCI-0749242
Messer
OCI 0749248
Blondin
OCI 0749204
Marronetti

The advent of petascale computing brings with it the promise of substantial increases in physical fidelity for a host of scientific problems, but the architectural features of petascale machines will require considerable innovation for effective use. This three-part collaborative project addresses several of the most immediate development needs for CHIMERA, a massively parallel multi-physics code designed expressly to simulate core-collapse supernovae. These stellar explosions produce most of the elements in the Universe; are prodigious sources of neutrinos, gravitational waves, and photons, and lead to the formation of neutron stars and black holes. The extension of CHIMERA to petascale platforms will proceed through: 1) a complete, tested, three-dimensional spatial domain decomposition for the hydrodynamics, including a strategy to handle coordinate singularities in spherical polar coordinates; 2) a scalable three-dimensional Poisson solver for the gravitational field, both Newtonian and general relativistic; 3) a flexible, modular system for parallel I/O; 4) multi-core solutions for the linear systems dominating the thermonuclear kinetics and neutrino transport; 5) investigating Partitioned Global Address Space (PGAS) languages to overlap computation and communication; and 6) improvements to the physical models and algorithms.

Students and postdocs trained under this project will be well versed in virtually every important aspect of computational science, including numerical linear algebra, computational fluid dynamics, radiation transport, and stiff system solution, and will gain real world experience with the management, analysis, and visualization of large data sets, and the attendant hardware and software environments of petascale computing. The generalized methods will be applicable in other fields, and the popular allure of astrophysics makes it especially effective in public outreach for supercomputing. The team expects to continue with tours, talks, and presentations on computational astrophysics, reaching each year over 400 K-12 students and teachers, more than 200 college undergraduates, and hundreds of other non-scientists.

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

This project continues the development of the numerical codes necessary to simulate the merger of two neutron stars or two black holes and the modeling of the gravitational waves generated by these phenomena. In particular, the work concentrates of the study of more realistic physics in the modeling of the neutron stars, including the effects of neutrino radiation and the creation of initial data sets that will include neutron stars with arbitrary spins (in magnitude and orientation). Research on black hole mergers will continue, this time enhanced by a collaboration with the NINJA Group: a large (more than 80 investigators) international effort dedicated to ease the introduction of numerically generated gravitational waveforms into the data analysis pipeline of LIGO and VIRGO.

This work is particularly important in the light of the advent of the new generation of gravitational wave detectors such as LIGO. The possibility of detecting gravitational waves directly has created a new branch of astronomical sciences. Direct detection of these waves will provide unique insights into some of the most fascinating objects in the universe: black holes and neutron stars. Due to the matter that clouds the mergers of neutron stars with black holes or other neutron stars, gravitational waves and neutrino radiation are the only vehicles that can convey information about the last few moments of a binary system, the merger and the creation of a new object (most likely a black hole). Furthermore, this project supports a recently-formed relativity group at a developing research institution, Florida Atlantic University with a culturally diverse student body.