WoU-MMA: Gravitational Lensing of Photons and Gravitational Waves in the Era of Multi-Messenger Astrophysics

University Of Texas At Dallas, Richardson TX

Investigators

Abstract

This award supports research in relativity and relativistic astrophysics and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. This award supports an integrated research program to investigate the confluence of three spectacular predictions of Einstein’s theory of general relativity: gravitational lensing, black holes (BHs), and gravitational waves (GWs). Gravitational lensing occurs when the gravitational field of a foreground object like a galaxy or galaxy cluster bends the path of radiation emitted by a background source as it travels towards the observer. BHs are massive objects so compact that they possess an event horizon from within which even light cannot escape. GWs are ripples in the fabric of spacetime that exert time-varying tidal forces on objects as they pass through them. This research program will investigate how gravitational lensing affects the GWs and electromagnetic (EM) radiation emitted by distant binary BHs and their surrounding gas. It has three main goals: (1) to determine the probability that GW sources are lensed and the strength of lensing magnification and distortion, (2) to assess whether lensing can be observationally distinguished from intrinsic changes to the properties of the background sources, and (3) to identify how joint (multi-messenger) GW and EM observations of gravitational lensing can reveal properties of the foreground lenses, background sources, and the lensing phenomenon itself that would be inaccessible to GW or EM observations individually. This research will promote the progress of science by significantly advancing the understanding of gravitational lensing as a multi-messenger phenomenon. This research program will also benefit society by supporting education and public outreach. It will fund research assistantships for two graduate students in the physics PhD program at the University of Texas at Dallas (UTD) and also provide opportunities for undergraduate research. Einstein’s legacy (especially the research topics in this proposal) has always fascinated the public and thus serves as a valuable tool for outreach to underrepresented groups. The team will present this research to diverse audiences including the TAG Magnet School in Dallas ISD, the UTD Women in Physics summer camp, the Texas Astronomical Society of amateur astronomers, and the Frontiers of Flight and Perot museums in Dallas. Current and future GW detectors will observe three classes of sources: (1) stellar-mass binary BH mergers like those seen by LIGO/Virgo, (2) supermassive black-hole (SMBH) mergers that are the primary target of LISA, and (3) extreme-mass-ratio inspirals (EMRIs) of compact objects into SMBHs. The proposed research will investigate strong gravitational lensing of these sources in three interrelated projects. (1) the PI's group will calculate the distribution of lensing amplification factors for sources at cosmological redshift, using wave or geometric optics as appropriate. They will then use this distribution to determine how strong lensing affects the three GW sources including the changes to the signal-to-noise ratio and the mismatch with the unlensed GW templates used for searches. (2) The team will explore the degeneracies between gravitational lensing and changes to the source parameters that define unlensed waveforms. In particular, they will determine the extent to which GW amplitude modulation due to misaligned spins can mimic the interference between multiple images, and whether changes to the waveform inclination and polarization angle can be distinguished from the coherent sum of lensed images with different polarization angles and parities. (3) The group will investigate the synergy between GW and EM observations of strongly lensed systems. This study will address whether upcoming EM surveys like LSST can provide catalogs to help identify the host galaxy of lensed GW events, if lensing reconstruction from EM observations can help identify time-delayed “images” in GW data, and whether combined EM and GW observations can improve the constraints on lens and source models. 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.