A century after Einstein predicted their existence, the NSF-funded Laser Interferometer Gravitational-wave Observatory (LIGO) and the Virgo Detector have given us a new sense to observe the universe. Gravitational waves are ripples of warped spacetime that travel at the speed of light. Following the first observation of gravitational waves in September, 2015, LIGO and Virgo have continued to observe gravitational waves, and these waves are giving us new insight into the most extreme events in the universe: the collisions of black holes and neutron stars.

In this project, researchers at California State University, Fullerton used supercomputer calculations to model merging black holes and neutron stars and the gravitational waves they emit. To do this, we used the Spectral Einstein Code (https://www.black-holes.org/code/SpEC.html), which we and others in the Simulating eXtreme Spacetimes (SXS) Collaboration develop. We calculated the gravitational waves for merging black holes, including the first simulations of merging black holes that are both significantly different and size and spinning nearly as rapidly as possible. We have shared our numerical results with other scientists and the public (https://black-holes.org/waveforms), and they have helped others create better approximate models that are crucial for finding gravitational waves in detector data and for learning as much as possible about the waves? sources. We have explored implications of our results, such as how well our detectors can tell if merging black holes were spinning rapidly. We have compared our results to calculations from other numerical-relativity codes and directly with gravitational-wave observations, finding good agreement. 

We also applied similar computational techniques to help model one of the most important sources of noise in gravitational-wave detectors: Brownian thermal noise in the mirrors? reflective coatings. Even the loudest gravitational waves only change the lengths of detectors? arms by a fraction of the size of a proton as they pass by; measurements of these length changes are limited by random thermal motions in the detectors? mirrors?especially the thermal motions in the mirrors? reflective coatings. We developed an open-source code (https://github.com/geoffrey4444/NumericalCoatingThermalNoise) based on the deal-ii framework for calculating thermal noise in mirror coatings made of different materials, including crystalline coatings, a promising but not yet fully understood alternative to conventional coatings. We used the code to assess how important crystalline effects are when computing coating thermal noise.

More than a dozen undergraduate and master?s students at Cal State Fullerton directly participated in these activities. Reflecting our university?s diversity, the majority of student researchers who participated in this project are female, members of underrepresented minority groups, or both. Students have contributed at every level of these activities, including writing code, performing supercomputer calculations, analyzing results, and creating figures and text for technical publications reporting our results. Along the way, they learned skills they will take into their future careers, such as how to perform and analyze large data sets from large computations and how to present their work orally and in writing.

Students and the PI shared the excitement of gravitational-wave astronomy with other scientists and with the public. This includes presenting lectures to K-12 students and to the public, speaking at national and international scientific meetings, and creating visualizations of merging black holes and gravitational waves featured in the national and international media.

Last Modified: 10/26/2019
Modified by: Geoffrey Lovelace