Gravitational waves and black holes are among the most dramatic predictions of Einstein's General theory of Relativity. The Laser Interferometer Gravitational-wave Observatory (LIGO) is an ambitious NSF-funded project designed to directly detect gravitational waves and to use these waves to explore the universe. LIGO forms part of a world-wide network of gravitational-wave observatories which is probing probe black holes, neutron stars, supernovae and the early universe using gravitational-waves as an astronomical tool.

The LIGO Data Grid (LDG) is a distributed computational facility that hosts the software platforms and personnel needed to turn a collection of computer clusters into a powerful data analysis engine for gravitational-wave science. This award provided support for talented personnel to maintain the LDG and deliver the services, scalability and reliability needed by Advanced LIGO. The LDG team thus enabled gravitational-wave astronomy with Advanced LIGO and its international partners during the first two observing runs in 2015-2016 and 2016-2017. This award also supported the development of a platform (GraCEDb) to communicate between gravitational-wave astronomers and partners with electromagnetic telescopes and particle detectors.

On September 14, 2015, gravitational waves generated by the collision of two black holes passed the Earth. The Advanced LIGO detectors in Hanford, Washington and Livingston, Louisiana both registered the waves as they passed. Data recorded by these instruments was automatically transferred to Caltech, and on to Albert Einstein Institute, where it was analyzed. Just 3 minutes after the waves passed, the results were uploaded to GraCEDb and scientists across the Collaboration were alerted to the first direct measurement of gravitational waves. It took many months of analysis to confirm this first detection, to understand the properties of the black holes that collided, and to investigate the implications. This event is now known as GW150914. The likely direction to GW150914 was also communicated to partners via GraCEDb; while black-hole collisions are not likely to generate bright explosions, partners did look for light and particles coming from the collision. The tools and services developed, deployed and operated by this award were essential to the rapid identification of the signal and the subsequent analysis: they allowed the Collaboration to efficiently and robustly use computing facilities distributed around the world to understand the instrumental data and the gravitational-wave signal. This was a landmark discovery providing direct evidence of the gravitational waves and black holes predicted by Einstein’s theory. The collaboration published 11 papers about the event in February 2016 and made gravitational-wave observations part of the astronomer’s toolbox.

Even as the deep analyses of the September 14, 2015 event was going on. The LIGO detectors continued to acquire more data which was being analyzed within minutes of acquisition with the help of the LDG infrastructure and the LDG team. On 26 December 2015, a second measurable gravitational-wave signal passed Earth. This time the Collaboration was alerted just a minute after the wave passed. This signal, known as GW151226, also came from colliding black holes. Many more signals from colliding black holes have been identified since that time and searches for a vast array of signals from other types of astrophysical sources have also been completed using software and services provided under this award.  

Then, on 17 August 2017, the first gravitational wave from a binary neutron star collision, GW170817, was identified within 7 minutes of the waves passing Earth. An automated coincidence analysis confirmed that GW170817 was associated with the gamma-ray burst GRB170817a. GraCEDb provided all the information needed by astronomers to locate an optical counterpart of GW170817 within 10 hours. Observations from gamma-ray through radio were all reported in GraCEDb. GW170817 confirmed that neutron star mergers are the progenitors of some gamma-ray bursts, showed that gravitational waves travel at the same speed as light, provided an independent measurement of the expansion of our universe, ruled out physical theories that try to explain away dark matter as modified gravity, and provided a plausible mechanism to produce all or most of the gold and platinum found on Earth.

The first direct detection of gravitational waves was a watershed event in 21st century physics and astronomy. The scientific goals of the LIGO Scientific Collaboration rely on a substantial computational infrastructure, which spans astrophysical data analysis, detector and analysis platforms, software sustainability and computational hardware support. Cyber-infrastructure is as essential to gravitational-wave astronomy as the detectors themselves. This award provided cyber-infrastructure that allowed the LIGO Scientific Collaboration to carry out the transformative science that gravitational-wave observations bring.

In addition, we trained young scientisits to be experts in next-generation cyber-infrastructure, pushed the boundaries of LIGO's geographically distributed computational data grid, and sustained the operation of this cyber-infrastructure to support LIGO's science mission. Collaborations with external partners (including Internet2, Globus, Condor and Pegasus) continued to have significant impact outside the LSC.

Last Modified: 03/29/2018
Modified by: Patrick R Brady