Gravitational waves are tiny ripples in the geometry of spacetime, generated by distant astrophysical objects such as black holes, neutron stars, and supernovas, that promise to provide unique insights into these intriguing and important astrophysical systems. The Laser Interferometer Gravitational-wave Observatory (LIGO) completed successful "science runs" in 2005-2007 and 2009-2010, collecting high-sensitivity data together with the GEO and Virgo gravitational-wave detectors located in Europe. This award supports a research program to use the data from those science runs to complete innovative multi-messenger searches for gravitational wave events in collaboration with optical and radio astronomers. The data will also be used to test alternative theories of gravity. Finally, preparations will begin for improved real-time multi-messenger searches using the Advanced LIGO and Virgo detectors when they begin science running in the 2014 to 2015 timeframe.
This project helps to maximize NSF's investment in LIGO and Advanced LIGO by exploring highly energetic astrophysical events with both gravitational-wave and radio and/or optical emissions. It thus connects the gravitational-wave detection effort with mainstream astronomy, maximizing the scientific potential through coordinated observations. In addition, it will explore the fundamental physics of gravity. In addition to the benefits to physics and astrophysics knowledge, this project will increase the participation of students and underrepresented minorities in scientific research, disseminate the results from this research to the general public, and improve the teaching and learning of science.
This NSF award supported the research of Prof. Peter Shawhan and several students at the University of Maryland as they worked on developing and improving ways to detect gravitational waves and learn about the astrophysical sources that produce them. As members of the LIGO Scientific Collaboration, Shawhan and his students had access to data from the LIGO gravitational wave detectors in the U.S. as well as the closely allied GEO600 and Virgo detectors in Europe. They co-authored many papers presenting the results of searches using past LIGO and Virgo data. One of special note, in which the Maryland group played a leading role, was a paper presenting the results of the first searches for optical counterparts to gravitational-wave candidate events, which involved LIGO/Virgo data collected in 2009-10 and many astronomers who looked for corresponding objects with a variety of telescopes. No convincing counterparts were found, but the techniques developed and tested in those searches will guide future "multi-messenger" searches. In fact, during the final year-and-a-half of the award, much of the Maryland group's effort was focused on getting ready for the Advanced LIGO era. The upgraded detectors will begin collecting science data in 2015, with better sensitivity and much better prospects for finding electromagnetic (visible light, infrared, ultraviolet, radio, X-ray or gamma-ray) counterparts. A framework for cooperation was worked out, after consulting with many astronomers, and in 2014 over 50 astronomy projects signed up to receive rapid alerts of gravitational-wave event candidates from Advanced LIGO (and Advanced Virgo when it starts operating in 2016). Shawhan played a major role in making those connections with the astronomy community, and graduate student Min-A Cho developed and tested the event selection algorithm that will identify interesting event candidates, package up the relevant information, and send it out to partner astronomers. Another focus of the Maryland group is the development of a joint search for gravitational waves and low-frequency radio pulses, which can be picked up by a new class of radio telescopes which use large arrays of dipole antennas. The Maryland group is working in particular with scientists who use the LWA1 radio telescope. Maryland graduate student Cregg Yancey has developed a joint analysis method and modeled the propagation of radio pulses from sources in other galaxies to determine how the signal arrival times will compare. This will be used to conduct an analysis with Advanced LIGO data starting next year. Besides carrying information about astrophysical objects such as neutron stars and black holes, gravitational waves are interesting in themselves. Einstein's general theory of relativity, the standard theory behind gravitational waves, predict that they have certain properties, such as having only "tensor" polarization modes. Some alternative theories predict that there is an additional "scalar" mode. Maryland undergraduate student Scott Sullivan did a study to determine how well scalar-mode gravitational-wave bursts can be detected using LIGO and Virgo. He found that a slightly modified analysis works well, so this is a promising type of signal to look for. However, it turns out that the standard tensor-mode analysis also does a pretty good job of detecting scalar-mode signals, just reconstructing them in the wrong location in the sky. Thus, the already-published LIGO-Virgo searches for ordinary (tensor) gravitational-wave bursts also can be interpreted as placing limits on scalar-mode bursts! These and related research projects have given several students valuable experience in scientific research, including broadening participation by members of underrepresented minorities. Another mission of the Maryland group is to share the excitement of research with the general public; Shawhan and students have talked with hundreds of visitors to science expos and career fairs over the past three years. And Shawhan has coordinated the production of "science summaries" for each new LIGO paper, written specifically for the general public and posted on the ligo.org web site.
