Discovering Neutron Stars and Black Holes with LIGO

Gravitational waves are tiny ripples in the fabric of space and time produced by accelerating masses such as the collisions of black holes and neutron stars. The first direct detection of gravitational waves in 2015 by NSF's Laser Interferometer Gravitational-wave Observatory (LIGO) opened an entirely new window on the universe, and in the decade since, hundreds of merging black holes and neutron stars have been observed. This award supports research at The Pennsylvania State University to discover new gravitational-wave sources with LIGO and its international partner observatories and to help produce the catalogs of merging black holes and neutron stars used by scientists around the world. These discoveries test Einstein's theory of general relativity in its most extreme regime, reveal how stars live and die, and may even shed light on the nature of dark matter, the mysterious substance that makes up most of the matter in the universe. This work serves the national interest by promoting the progress of science and by sustaining United States leadership in gravitational-wave physics and astronomy, a field pioneered with NSF support. The award also trains graduate students in data analysis, statistics, and scientific computing, skills vital for a highly educated STEM workforce, and supports a free summer camp in which high school students from central Pennsylvania engage with researchers and learn about gravitational-wave physics and astronomy. This award supports the Penn State group's work on searches for compact binary mergers within the LIGO/Virgo/KAGRA (LVK) collaboration and the emerging International Gravitational Wave Observatory Network (IGWN) from July 2026 through June 2028. The team will produce compact-binary search results for upcoming installments of the Gravitational Wave Transient Catalog, GWTC-6 (expected end of 2026) and GWTC-7 (estimated summer 2028), including the re-ranking of real-time search results, a dedicated search for intermediate-mass black hole binaries, and large-scale Monte Carlo injection campaigns that measure search sensitivity and selection effects, which are essential inputs for inferring the merger rates and population properties of neutron stars and black holes. The team will commission the Extended Search for Merger Events (ESME), which analyzes low-noise data collected outside of official observing runs during detector commissioning, running throughout the award period whenever such data are available and enabling discoveries that would otherwise be missed. A matched-filter search for sub-solar-mass compact objects, targeting binaries with primary masses of roughly 0.2-10 solar masses and secondary masses below one solar mass, will probe compact objects that cannot be formed by conventional stellar evolution and will constrain dark-matter models, including primordial black holes and dissipative (atomic) dark matter. These analyses will use the GstLAL pipeline and its next-generation successor, SGNL. In addition, the group will complete catalog-production infrastructure (gwtc-tools) integrated with the gravitational-wave candidate database GraceDB, and will develop the Gravitational-wave Resource Allocation and Science Planning (GRASP) platform used to manage the IGWN scientific program, membership contributions, and computing resources. 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.