Colloquia Schedule

Dr. Yuan Li (University of North Texas)
Wednesday, March 13, 2024
4:00 p.m.
LGRT 1033
Title:
Supermassive Black Hole Feeding and Feedback in Massive Systems
Abstract:
Supermassive black holes (SMBHs) play a crucial role in shaping the evolution of galaxies, especially the massive ones. In this talk, I will briefly review our current knowledge of three key aspects of SMBHs -- their feeding, feedback, and connections to host galaxies. I will discuss some of the efforts my group has made to advance our understanding in these research areas. In particular, I will highlight our recent "mesoscale" simulations which follow multiphase SMBH accretion flows from galaxy scales all the way down to scales relevant for accretion disks. I will also discuss our recent observational analysis of the turbulent motion of the cool clouds in centers of galaxy clusters, which has significant implications on how SMBH feedback operates in these systems. The results also put unprecedented constraints on microscopic transport processes in the weakly collisional, magnetized intracluster plasma. I will also discuss some recent and ongoing work on SMBH-host galaxy scaling relations and how machine learning may transform this field. Lastly, I will briefly discuss some exciting future directions of my research program.
Dr. Nicholas Stone (Hebrew University of Jerusalem)
Thursday, February 29, 2024
4:00 p.m.
LGRT 1033
Title:
Tidal Disruptions and other Dynamical Transients from Galactic Nuclei
Abstract:
The centers of galaxies feature the densest stellar environments in the Universe. In the gravitational blender of a galactic nucleus, close encounters between stars and compact objects can produce a variety of transients visible in electromagnetic and gravitational wave radiation. In this talk, I will give a detailed overview of one particular type of electromagnetic transient: stellar tidal disruption events, or TDEs. TDEs occur when unlucky stars wander too close to supermassive black holes (SMBHs). Long predicted by theorists, TDEs are now discovered by observers at a rate of dozens per year thanks to the last decade's advances in time domain astronomy. In the near future, the start of science operations at the Vera Rubin Observatory and the launch of ULTRASAT will make it possible to find thousands of TDEs per year. I will describe how TDEs can be used to measure SMBH masses and spins, to discover elusive "intermediate-mass" black holes, and to resolve long-standing questions on the origins and evolution of massive black holes over cosmic time. I will also discuss the puzzling dynamical origins of TDEs, including their surprising preference for rare "E+A" (post-starburst) host galaxies. I will conclude by briefly reviewing the other types of transients that can be produced in galactic nuclei, in particular the gravitational wave sources that will be detected by future space-based laser interferometers such as LISA.
Dr. Maria Charisi (Washington State University)
Monday, February 26, 2024
4:00 p.m.
LGRT 1033
Title:
Frontiers of multi-messenger astrophysics with pulsar timing arrays
Abstract:
A Pulsar Timing Array (PTA) is a galactic-scale detector that relies on precision timing of milli-second pulsars. As of last summer, all major PTA collaborations have found evidence of a low-frequency gravitational wave background. The most likely origin of this background is a population of supermassive black hole binaries (SMBHBs) formed in galaxy mergers. I will present the exciting recent results from the North American Nanohertz Observatory for Gravitational waves (NANOGrav) collaboration, and their meaning for extragalactic astronomy. I will also describe the next major milestone, which is likely the detection of an individual resolved binary. These systems, which should stand above the background, are also expected to be bright sources of electromagnetic emission, and can be detected as quasars with periodic variability. I will summarize the status of current electromagnetic searches and their challenges. Finally, I will discuss my plans to combine electromagnetic and gravitational-wave data and bring the first multi-messenger detection of a SMBHB within closer reach.