| Wednesday, September 6, 2023 |
| Two types of nuclear transients - tidal disruption events and disruptive collisions | |
| Taeho Ryu, Max Planck Institute for Astrophysics, Garching | |
| Event Type: Informal Astro Talk | |
| Time: 12:30 PM - 1:00 PM | |
| Location: 726 Broadway, 902, Lg Conf | |
| Abstract: Galactic nuclei are extreme environments where stars are densely packed around a supermassive black hole (SMBH). Occasionally, dynamical interactions in the galactic center lead the stars to interact violently at short distances with each other or with the SMBH, resulting in the formation of nuclear transients. In this talk, I will discuss two types of nuclear transients, tidal disruption events and high-velocity collisions between stars, based on the results of detailed hydrodynamics simulations. Tidal disruption events are one of the most dramatic nuclear transients in which a star is tidally disrupted by the SMBH in a few hours. The conventional picture has been that a star is fully disrupted at the first pericenter passage and the debris circularizes rapidly. However, these events are in fact more diverse and they can be categorized into several groups with different observational signatures depending on stellar pericenter distance, from partial disruption (i.e., partial mass loss and surviving remnant) to full disruption which is further sub-categorized depending on relativistic effects. On the other hand, disruptive collisions are the events where two stars collide at a very high relative velocity near the central SMBH. The collision product, a homologously expanding gas cloud, can generate a flare as bright as tidal disruption events. Subsequently, the expanding gas cloud would interact with the nearby SMBH, causing a second, possibly even brighter accretion-driven flare. Because these can happen near BHs at any mass scale, if the accretion is efficient, these disruptive collisions could contribute to the growth of black holes. | |
| HEP Journal Club | |
| Event Type: HEP Journal Club | |
| Time: 12:30 PM - 1:30 PM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Model G2-holonomy Singularities, M-theory and QFT’s in 3,4 and 5 dimensions. | |
| Bobby Acharya, ICTP | |
| Event Type: HEP Seminar | |
| Time: 2:00 PM - 3:15 PM | |
| Location: 726 Broadway, 940, CCPP Seminar | |
| Abstract: Understanding singularities in physics is significant in a broad range of contexts like cosmological initial conditions, black holes, renormalisation and scattering amplitudes. In string/M-theory we have learned that very special kinds of singularities in physical space have perfectly reasonable and interesting physical behaviour, often supporting interacting QFT’s and even conformal field theories. Models of the extra dimensions of space provided by G2-holonomy spaces provide a broad framework for investigating these systems. After introducing the exceptional Lie group G2 and G2-holonomy spaces we review earlier work in which conical singularities have provided insights into confining 4d gauge theories, including confining strings and domain walls. We then describe more recent investigations which in principle give rise to 3d and 4d QFT’s from rather intricate “interfaces” between 7d and 5d QFT’s. | |
| Zig Zag Zug | |
| Jack Donahue | |
| Event Type: Oral Defense | |
| Time: 5:00 PM - 7:00 PM | |
| Location: 726 Broadway, Room #802 | |
| Abstract: COMMITTEE Professor Sergei Dubovsky (Thesis Advisor) Professor Matthew Kleban Professor Aditi Mitra Professor Massimo Porrati Professor Yifan Wang | |