Gravitational Wave Astrophysics with LIGO: The Oregon Experimental Relativity Group

The initial discovery of gravitational waves in 2015 by LIGO confirmed a crucial prediction of General Relativity made by Einstein a century earlier. The gravitational waves observed by LIGO in 2015 resulted from the collision of two black holes, each roughly thirty times more massive than our sun. Although this was an amazing natural event, it was only observable by gravitational waves -- the ripples in spacetime which propagate outward across the cosmos for millions of light-years and may eventually be noticed by the LIGO observatories. It underscores the potential of LIGO to make unique contributions to astronomy, astrophysics, and cosmology. Since 2015, LIGO has recorded approximately 300 such collisions, mostly of pairs of black holes, but also of black holes with neutron stars, and pairs of neutron stars. Indeed, with this unique collection in hand, LIGO has been able to make new statements about the origins of massive stars in the universe, and, paired with more conventional astronomical observations, provided new insights into the origin of heavy elements, which are crucial to life on Earth. Meanwhile, the LIGO observatories have become increasingly sensitive to ever smaller spacetime ripples. This has enabled the potential for discoveries -- the observation of gravitational waves from different types of astrophysical objects, objects which are not pairs of black holes and/or neutron stars. This award will set up LIGO gravitational wave searches from two promising new sources, namely collapsing black holes and extremely magnetized neutron stars. The former are associated with the explosive phenomena known as (long) gamma-ray bursts (GRBs), while the latter are associated with magnetar x-ray flares and fast radio bursts. This award will support graduate students at University of Oregon (UO), who will develop new methods to carry out novel searches and to develop methodology to make astrophysical inferences from the results, i.e. what we have learned about the death throes of massive stars and the inner workings of neutron stars. It is expected that these students will either continue in the field or will enter the private sector, where they will carry their expertise in data science and analysis. The UO group will continue to carry out workshops for Oregon high school teachers, and this award will spawn a new activity in direct public outreach via “pub talks.”

This award will combine two emerging areas of astrophysics to probe sources of gravitational waves from progenitors that are not compact binary mergers. The first area is multi-messenger astronomy (MMA). The second area is the search for gravitational-wave signals without waveform templates – the so-called burst analyses. The searches will fundamentally rely on MMA observational results. X-ray, gamma-ray, or radio transient signals from astrophysically energetic events provide a time and sky location that also mark an episode of putative gravitational-wave emission. These provide the so-called triggers for the gravitational-wave data analysis, which labels the time near the trigger as the “on-source” (or signal) data segment, and the off-source data as the background. Excess signal power relative to background is an indicator of a potential gravitational-wave detection in association with the triggering gamma-ray burst (GRB), magnetar x-ray flare, or optical supernova breakout observation. This method does not rely on any predetermined mathematical form for the gravitational waves. Astrophysical inference with gravitational waves to date has involved analyses that rely on systems of compact (black hole or neutron star) binary systems. The team will explore a new pathway for astrophysical inference, one involving the gravitational wave burst analyses of non-binary systems. It is crucial to not only develop methods to confidently detect gravitational waves from novel sources but also to infer new and unique statements about the astrophysical properties of the emitting systems. This new window of opportunity is made possible by its reliance on multi-messenger data, including new observations by the Vera Rubin Observatory, and by the ever-increasing sensitivity of the LIGO, Virgo, and KAGRA gravitational wave observatories.

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.

Award Number: 2513356
Principal Investigator: Raymond Frey
Funds Obligated: $400,000
State: OR