Event Calendar

Location: MP 15th Floor Conference Room

Title: Probing Dark Energy with Galaxy Clusters

Abstract: Galaxy cluster surveys have been recognized as one of the most powerful probes of dark energy, but their constraining power is limited by the accuracy of mass calibration. I will present my research on using simulations to improve mass calibration methods, including galaxy dynamics, weak gravitational lensing, clustering, and X-ray observations. These results not only mitigate the systematic uncertainties in current cluster surveys but also help the optimization for future ground- and space-based missions.

Host: Alex van Engelen

Location: MP1318A

Location: MP1318A

The schedule of speakers: https://tinyurl.com/cita-blackboard Location: MP 1318A

Location: MP 1318A, 60 St. George Street

Location: 15th floor conference room

Location: MP 15th Floor Conf Room

Open discussion of stars- and planets-related topics or more specialized discussion of dynamics-related papers on alternating weeks. See here for details. Location: MP 1318A

The schedule of speakers: https://tinyurl.com/cosmo-rota  
Location: 15th floor conference room

Local gravity and high-energy astro group meeting. Contact for questions is Aaron Zimmerman. For a list of upcoming discussions see: https://gravity.cita.utoronto.ca/doku.php Location: MP1318A

Weekly paper discussion focussing on pulsars, compact objects, and propagation effects. For a list of upcoming discussions, see: https://docs.google.com/spreadsheets/d/16TXacDDCk5FxMyw_842h5JHuq0h0RNhlWvp4li64edM/edit?usp=sharing If you would like to sign up for the presenter rota, email: simard@astro.utoronto.ca Location: CITA lounge

Location: MP 15th Floor Conference Room

Title: Accelerating compact object mergers and collisions in binaries in galactic nuclei, and in quadruple star systems — implications for gravitational wave sources and Type Ia supernovae

Abstract: We consider mergers and collisions of compact objects induced by dynamical interactions in two contexts. In the first part of the talk, we discuss mergers of stellar-mass black holes (BHs) in binary systems in galactic nuclei. Most galactic nuclei are known to harbor a massive BH (MBH). Binaries in these environments are susceptible to the Lidov-Kozai (LK) mechanism due to the torque of the central MBH, which can drive binaries to high eccentricities and trigger strong interactions such as the emission of gravitational waves (GWs), and, ultimately, BH mergers. These events are potential sources for GW detectors such as aLIGO and VIRGO. The LK mechanism is only effective if the binary is highly inclined with respect to the MBH, implying low rates compared to the inferred aLIGO rates. However, close to an MBH, \sqrt{N}-torques from the stellar cluster give rise to vector resonant relaxation (VRR), which affects the orientation of the binary around the MBH. This process can bring a binary with low inclination into an `active' LK regime in which high eccentricities, and, subsequently, strong interactions are triggered. We study the coupled LK-VRR dynamics, and investigate the potential enhancement of LK dynamics due to VRR. In the second part of the talk, we consider Type Ia supernovae (SNe Ia) produced by colliding white dwarfs (WDs). Katz & Dong showed in 2012 that high-eccentricity LK oscillations in triple star systems can lead to collisions of WDs, which are known to likely result in SNe Ia explosions. However, other authors subsequently showed that the rates are likely low compared to observations because many potential progenitor systems (i.e., highly inclined systems) would experience mergers during the pre-WD evolution. An alternative pathway has been proposed in quadruple star systems, in which the typically longer secular time-scales might alleviate these problems. Here, we consider the dynamical and stellar evolution of quadruple systems, in both the 2+2 (two binaries orbiting each other’s barycentre) and 3+1 (triple orbited by a fourth star) configurations. We demonstrate the existence of several pathways that lead to WD collisions, and estimate their rates. We find that the collision-induced SNe Ia rates from quadruples are comparable to those previously found for stellar triples. However, these rates are several orders of magnitude lower compared to the observations, indicating that collision-induced SNe Ia from triples and quadruples are rare.

Host: Cristobal Petrovich

Location: MP 1318

Location: MP1318A

The schedule of speakers: https://tinyurl.com/cita-blackboard Location: MP 1318A

Location: MP 1318A, 60 St. George Street

Location: 15th floor conference room

Location: MP 15th Floor Conf Room

Title: TBA

Abstract: TBA

Host: Laura Keating / George Stein

The schedule of speakers: https://tinyurl.com/cosmo-rota  
Location: 15th floor conference room

Local gravity and high-energy astro group meeting. Contact for questions is Aaron Zimmerman. For a list of upcoming discussions see: https://gravity.cita.utoronto.ca/doku.php Location: MP1318A

Weekly paper discussion focussing on pulsars, compact objects, and propagation effects. For a list of upcoming discussions, see: https://docs.google.com/spreadsheets/d/16TXacDDCk5FxMyw_842h5JHuq0h0RNhlWvp4li64edM/edit?usp=sharing If you would like to sign up for the presenter rota, email: simard@astro.utoronto.ca Location: CITA lounge