Name: CAREER: Enabling multimessenger astrophysics with real-time gravitational wave detection
Source: National Science Foundation (PHY-1454389)
Dates: 6/1/2015 - 5/30/2020
Roles: Chad Hanna (PI)
Sponsored Personnel: Becca Ewing, Ryan Magee, Cody Messick, Debnandini Mukherjee, Duncan Meacher, Sydney Chamberlain, Phoebe McClincy
Abstract
In the last decades, astrophysicists and astronomers have studied the Universe for clues about what causes some of the most energetic transient events. It has long been thought that truly extreme objects such as black holes and neutron stars are responsible. Advanced instruments spanning the electromagnetic spectrum have provided a wealth of information regarding the transient Universe; however, many observations are unable to directly probe the dynamics of the systems in question. General relativity provides a way to map out the dynamics of massive, dense objects from a distance by encoding the motion as ripples in space-time known as gravitational waves. The personnel on this project led efforts within the LIGO Scientific Collaboration to detect transient gravitational waves from the merger of black holes and neutron stars in real-time, enabling prompt multi-wavelength follow-up observations shed new light onto the origin of transients. Discoveries were relayed to a network of follow-up observatories so that scientists were able to learn as much as possible about these events before they fade away. This research increased understanding of the fundamental nature of space, time and the properties of exotic states of matter and energy that are not accessible to Earth-based laboratories.
Details
Research Highlights
PHY-1454389 funded in part the development and deployment of a real-time search for compact binary mergers known as GstLAL. The primary goal of this award was to discover compact binary mergers within seconds of the gravitational waves arriving at Earth in order to alert a broader astronomical community for prompt follow-up observations. The hope was to enable the identification of prompt electromagnetic and/or other astroparticle counterparts. The real-time gravitational wave search ran throughout advanced LIGO's first observing run from September 2015 to January 2016. From September to November the analysis targeted sources that have historically been thought to have the most likely electromagnetic counterparts, namely, sources containing at least one neutron star. Starting in November the real-time analysis parameter space was extended to include binary black holes with total mass up to 100 solar masses. The analysis identified candidates within approximately 1 minute of the signals arriving at Earth. Candidates were reported to the gravitational wave candidate database where rapid sky localization, parameter estimation and other follow-up task were started immediately. Once a candidate was identified, the rapid response team assembled at each LIGO observatory and analysts funded by this project joined by teleconference to help vet candidate events. Events that passed were circulated to the observing partners through a private gamma ray coordinates (GCN) circular.
The gravitational wave signal dubbed GW151226 was successfully detected by the gstlal inspiral pipeline and team members on Christmas day within 70s of the signal arriving at Earth. The online analysis was able to confidently establish that the system was likely to be a binary black hole and that its false alarm rate was less than 1 / 1000 years. This event firmly established gravitational wave astronomy by helping to refine the rate of binary black hole mergers as one that should yield regular detections over advanced LIGO's lifetime. GW151226 was the first gravitational wave event to be identified by a modeled search for compact binary mergers. The first event, GW150914, in part due to its high amplitude and in part due to its short duration, was first identified by a generic transient gravitational wave search and did not require matched filtering for detection. GW151226 on the other hand had a signal amplitude that was considerably lower than the noise and a duration in LIGO's band that was significantly longer. The generic transient gravitational wave algorithms did not detect GW151226. Thus real-time matched filtering was necessary for its identification, which is the major objective of this project. Throughout O1, the GstLAL analysis was also operated in an 'offline' mode to search the entire parameter space of compact binaries from 1-600 solar masses. Members of the team funded by PHY-1454389 helped to develop and run a search for binary black holes that detected the first ever gravitational wave event, GW150914, with a significance in excess of 5 sigma. Additionally, large simulation campaigns conducted in part by the team supported by PHY-1454389 helped to establish the first directly measured coalescence rate of binary black holes in the Universe.
Personnel supported by this award conducted a real-time search for neutron star and black hole mergers in advanced LIGO's second observing run (O2). Furthermore, personnel have conducted and are continuing to conduct an offline reanalysis of O2 data. Personnel conducted research and development efforts associated with these activities through co-developing the GstLAL software infrastructure. Our work was in collaboration with a team of other members of the LIGO and Virgo collaborations including University of Tokyo, University of Wisconsin-Milwaukee and Caltech. We aimed to enable a few novel features in O2 searches. Namely, we developed and depolyed a real-time single detector gravitational wave search. We also worked on and deployed some additional zero-latency signal processing algorithms, which should help us to meet our eventual goal of ~seconds of detection latency. Our team provided the promptest and most significant result for the first ever three detector gravitational wave detection involving advanced LIGO and advanced Virgo known as GW170814 with a 30 second detection time and a false alarm rate estimate of 1 / 80,000 years. Three days later our team provided the only detection of the first gravitational waves from a binary neutron star merger known as GW170817 within 7 minutes of arriving at earth with an estimated 1 / 10,000 years false alarm rate. It was detected in a single gravitational wave detector, which justified the effort put forward to enable this. GW170817 was the first multimessenger source including gravitational waves since it was also observed in gamma rays, x-rays, UV, optical, infra-red, and radio wavelengths. Additionally, our team provided offline significance estimates of GW170104 and GW170608.
After the end of O2, personnel on this project refined analysis techniques and worked to increase the reach of the compact binary search in preparation for advanced LIGO's third observing run (O3). In the interim between O2 and O3, personnel on this project conducted a search for sub-solar mass compact binaries and constrained such objects as a component of dark matter assuming that they were primordial black holes. Personnel on this project conducted offline analysis for Advanced LIGO's third observing run. This run marked the most sensitive gravitational wave data ever taken with an average of six gravitational wave detections per month. These results will appear soon as an update to the Gravitational Wave Transient Catalog (GWTC).
Outreach Highlights
The PI is committed as a teacher / scholar to engage in the education of students through participating in K-12 curriculum writing and hosting summer school education events as part of this award. During 2016, we developed curriculum on gravitational wave astronomy for high school students and provided hands on training at the first ever gravitational wave summer school at Penn State. This targeted local high school students, some from rural areas. Thanks to the support of this award as well as support from the Institute for Gravitation and the Cosmos and the Institute for CyberScience, we were able to offer the camp free of charge. Students learned about gravitational waves from compact binary signals, data analysis and high throughput computing. We assembed a small high throughput computing cluster to demonstrate how real-time gravitational wave searches work. On Halloween 2017 we celebrated dark matter day by hosting a booth in Penn State's HUB center in collaboration with the experimental dark matter faculty at PSU. The HUB center has tens of thousands of students, faculty and staff pass through daily. Among other things, our booth described how gravitational waves might help us to understand dark matter Personnel on this project developed a 'Carrilon of Black Holes' which explored how constructing a musical instrument from a set of black holes was possible (in theory by analogy between gravitational waves and sound) and had a timbre quite distinct from other musical instruments.