Gravity Initiative
The TAP Gravity Initiative brings together researchers from astronomy and physics to study the fundamental laws of gravity and their manifestation in the observable universe, primarily in the extreme environments of black holes and neutron stars. Our members perform theoretical, computational, and observational studies of these extreme physical systems.
Visit the websites of Gravity Initiative Co-Chairs Sam Gralla and Vasileios Paschalidis for more information about current research and publications.
TAP Gravity Lectures
Luis Lehner, Perimeter Institute for Theoretical Physics
Luis Lehner visited October 7 – 11, 2024, hosted by Vasilis Paschalidis.
YouTube recording of the talk
TITLE: Inquiring Through Black Holes
ABSTRACT: Black holes have become unique tools in the understanding of a plethora of phenomena in vastly different fronts. From understanding spectacularly energetic events in our universe, gaining insights on potential new particles to unraveling seemingly unrelated phenomena. As we move through the 2nd century of General Relativity, the combination of observations together with a deeper understanding of the theory will catalyze new breakthroughs touching, arguably, all areas of physics. In this talk, we will connect with several of these fronts, and discuss opportunities from-and-to black holes.
BIO: Luis Lehner is an Argentinian-Canadian gravitational physicist who focuses on understanding strongly gravitating systems. His research covers a range of topics, from fundamental questions on the nature of gravity to its role in powering the most energetic events in the universe as well as connections with dark energy and dark matter. He obtained his PhD in 1998 at the University of Pittsburgh, was a postdoctoral fellow at the University of Texas at Austin and the University of British Columbia. He was faculty at Louisiana State University and joined Perimeter Institute in 2009. He has received numerous distinctions like the Nicholas Metropolis Award, an Alfred Sloan Fellowship, selected among the 10 most influential Hispanic Canadians in 2019. He is also the theorist in residence in the Gravitational Wave International Committee, is on the scientific boards of the Oskar Klein Center at the University of Stockholm and the ICTP-SAIFR at the University of Sao Paulo.
Neal Dalal, Perimeter Institute for Theoretical Physics
The Gravity and Cosmology Initiatives jointly hosted Neal Dalal, February 15-21, 2024, as part of the TAP Lectureship Series.
No recording is available.
Title: AGN HBT OMG
Abstract: I’ll discuss an old technique called intensity interferometry, pioneered by Hanbury Brown and Twiss (HBT) that allows us to achieve sub-microarcsecond angular resolution using ordinary ground-based optical telescopes observing visible light. This technique is best suited for compact, bright sources, and I will discuss applications of intensity interferometry observations of bright, supermassive black holes called active galactic nuclei (AGN). I’ll discuss possible applications, including measurement of the Hubble constant H0, and probing the innermost structure of quasar accretion disks.
Bio: Neal Dalal is a theoretical cosmologist with interests in large-scale structure, dark matter, gravitational lensing, and cosmic inflation. He received his PhD from UCSD, and then held postdoctoral fellowships at the IAS and CITA, before joining the faculty of the University of Illinois in 2011. He has been faculty at the Perimeter Institute since 2017.
Aaron Zimmerman, University of Texas at Austin
Aaron Zimmerman visited March 21-30, 2024, hosted by Sam Gralla and Vasilis Paschalidis.
YouTube recording of the talk
TITLE: Gravitational Waves and Searching for the Unexpected ABSTRACT: The detection of gravitational waves has revealed an invisible side of the Universe. Observations of gravitational waves from black holes and neutron stars allow us to test our understanding of dynamical spacetime, study matter at extreme densities, and measure the expansion history of our Universe in new ways. Gravitational wave data also provides opportunities for unexpected discoveries. In this talk I will give an overview of gravitational wave detections made by the LIGO, Virgo and KAGRA collaborations. I will then discuss two avenues for future discovery with gravitational waves: direct searches for exotic stars, and black hole spectroscopy using ringdown. BIO: Aaron Zimmerman is an Assistant Professor at the University of Texas at Austin. He is a member of the LIGO Scientific Collaboration, and his research focus is gravitational wave modeling and data analysis. He did his PhD at Caltech with Yanbei Chen, where he studied the ringdown of black holes and methods to visualize curved spacetimes. After graduating in 2013 he moved to the Canadian Institute for Theoretical Astrophysics (CITA) in Toronto as a CITA Fellow and then Senior Research Associate. He began at UT Austin in 2018.
Opportunities to Engage
Talks
More information on future Gravity Initiative lecturers and their schedule can be found at TAP Lectureships. Join the Gravity listserv for up-to-date information.
Images
Volume rendering of rest-mass density (color coded) for a circumbinary accretion disk around a binary black hole with spinning black holes. The magnetic field lines (white) are those intersecting the black hole horizons. Twin jets are visible above and below each black hole (see inset for a zoomed-in view). The black spheres indicate the resolved black hole apparent horizons in the simulations. Source: Paschalidis et al. The Astrophysical Journal Letters, 910:L26, 2021
Credit: SXS, the Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org)