Activities
Merging Supermassive Black Hole Binaries
Speaker: Zoltan Haiman (Columbia University)
Supermassive black hole (SMBH) binaries are inevitably produced during galaxy formation, but observational evidence for them remains elusive. I will discuss the coupled dynamics of a SMBH binary with a circumbinary gas disk, and the expected characteristics of electromagnetic (EM) emission from such a system. In particular, the emission is likely time-variable, and contain unique spectral signatures, which should aid in the identification of SMBH binaries. We have performed hydrodynamical simulations and found that binaries can be fueled efficiently, and that the accretion rates onto the BHs have quasi-periodic modulations. The periodicity pattern depends on the mass ratio, and the strong periodic emission persists all the way to the merger. This may be used to identify unique counterparts of gravitational wave sources expected to be detected by Pulsar Timing Arrays and by LISA, and to discover wider binary SMBHs in time-domain EM surveys. We have identified a handful of quasars with periodic optical variability on the timescale of O(year). I will comment on the interpretation of these quasars as SMBH binary candidates, and on the possibility of seeing an analogous "X-ray chirp" during the late-stage inspiral a LISA binary.
Place: KIAA-PKU Auditorium
Time: Thursday, July 4, 2019 - 4:00pm to 5:00pm
Merger and mass ejection of neutron-star binaries in numerical relativity
Speaker: Masaru Shibata (Max-Planck-Institute)
On August 17th, 2017, merger of binary neutron stars was observed for the first time by gravitational-wave and electromagnetic telescopes. Optical and infrared observations in particular agree broadly with the prediction by numerical relativity. From this April, advanced LIGO and VIRGO are in O3 observation and already had a few candidates of neutron-star mergers. We expect several more observations of neutron-star mergers (including black hole-neutron star merger). I will review our current understanding for neutron-star mergers and related mass ejection that are obtained by numerical relativity simulations and summarize predicted observational (optical and infrared) features.
Place: KIAA-PKU Auditorium
Time: Thursday, June 27, 2019 - 4:00pm to 5:00pm
Gravitational wave astronomy around 0.1-10 Hz
Speaker: Naoki Seto (Kyoto University)
I discuss the prospects of gravitational wave astronomy around 0.1-10Hz. This frequency regime is just between the two bands probed byground-based detectors (LIGO, Virgo, KAGRA,..) and the proposed spacedetectors (LISA, TianQin, Taiji). I briefly introduce the Japaneseplan DECIGO targeting this band and then discuss its main sciencetargets, including primordial stochastic background and compactbinaries.
Place: KIAA-PKU Auditorium
Time: Thursday, May 16, 2019 - 4:00pm to 5:00pm
Extracting Physics from Gravitational Waves (2/2)
Speaker: Tjonnie Li (The Chinese University of Hong Kong)
Place: 1st floor meeting room, KIAA-PKU
Time: 10:00AM, Apr 5
Gravitational Lensing of Gravitational Waves
Speaker: Tjonnie Li (The Chinese University of Hong Kong)
Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. I examine gravitational wave events in the limit of geometric optics, where one expects to see multiple signals from the same event with different arrival times and amplitudes, and wave optics, where one expects to see effects such as interference and diffraction.
Recent studies are showing that second generation gravitational-wave detectors may observe more than one lensed event. I present the results from a search for signatures of gravitational lensing in the binary black hole events detected by Advanced LIGO and Virgo during their first two observational runs. In particular, we look for three effects: 1) evidence of lensing magnification in the individual signals due to galaxy lenses, 2) evidence of multiple images due to strong lensing by galaxies, 3) evidence of wave optics effects due to point-mass lenses. We find no compelling evidence of any of these signatures in the observed gravitational wave signals. Finally, I will also look ahead to the microlensing effects due to substructure on top of strong lensing by (clusters of) galaxies.
Place: KIAA-PKU Auditorium
Time: Thursday, April 4, 2019 - 4:00pm to 5:00pm
Extracting Physics from Gravitational Waves (1/2)
Speaker: Tjonnie Li (The Chinese University of Hong Kong)
Place: K208, KIAA-PKU
Time: 10:00AM, Apr 3
Morningside/Silk Road/PKU Seminar on Gravitational Wave and Relativistic Astrophysics
Speaker: Chris Belczynski
Title: BH-BH/NS-NS mergers with LIGO/Virgo
Place: KIAA auditorium room
Time: 16:00 Thursday (22 Nov 2018)