PhD defense Ka Wa Tsang @ University of Groningen

2021-03-05 16:15 | 2021-03-05 17:15

Ka Wa Tsang, PhD at Nikhef, will defend his thesis Friday 5 March 2021 online at the University of Groningen.

“The Final State – The fate of relativistic compact objects after merger”

In this thesis, we presented our work on probing the nature of the fi nal relativistic compact object after the binary merger via gravitational waves. This includes testing the black hole description given by the general relativity and obtaining the equation of state of a neutron star. There are relativisitic compact objects beyond the general relativity which may exist in the universe. A variety of alternative objects, called black hole mimickers, have been proposed such as wormholes, boson stars, and gravastars, which give di fferent gravitational wave signatures, especially gravitational wave echoes. The nature of the final excited black hole resulted from a binary black hole merger can be examined model-dependently by showing that any additional deviation parameters governing the waveforms are consistent with zero. We showed that the no-hair conjecture can be tested observationally with just a few plausible signals detected by the LIGO-Virgo detector network operating at its design sensitivity. If we have no any prior knowledge about the waveform, we can make use of the morphology-independent algorithm, especially BayesWave, which can detect any waveform by comparing the Bayesian evidences among signal, glitch and noise hypotheses. In our work, we modi ed the basis wavelet used in the algorithm so as to detect and characterise gravitational wave echoes speci cally. We applied the methods to the detected signals of the first gravitational wave transient catalog and did not find any evidence for echoes. Finally, in the future, we expect to see binary neutron star postmerger with third generation of gravitational wave interferometers. To extract the information about the equation of state, we need to have accurate waveform approximants. Currently the waveforms are poorly known because there have been no comprehensive numerical relativity simulations incorporating all necessary microphysical processes. Nevertheless,
the discovery of quasi-universal relations, especially for the f2 frequency, serves as building blocks for modelling the postmerger. By constraining f2 which contains rich information about the equation of state at ultra-high density, we can
in turn constrain the equation of state. In our work, we discovered new quasiuniversal relations and improved existing ones, and demonstrated the possibility of performing inspiral-merger-postmerger consistency tests.

“The Final State – The fate of relativistic compact objects after merger” (pdf)

The defense will be broadcasted on the youtubechannel of the University of Groningen:

Supervisors: prof. dr. C.F.F. Van Den Broeck and prof. dr. A. Mazumdar

contact: Ka Wa Tsang