Seminars of fiscal year 2024

Test particle motion abound a black hole dressed with stationary and spherically symmetric fluid distribution

Recent theoretical research has been conducted to examine how the accumulation of matter affects the metrics of black hole solutions. One notable approach is to use perturbation methods to model and derive particle trajectories in the vicinity of these cosmic entities. This method provides a detailed understanding of how accretion affects the surrounding geometry.

This study focuses on scrutinizing the metric resulting from perfect fluid accretion onto a Schwarzschild black hole. By visualizing timelike geodesics and orbits around black holes, we deepen our understanding of the effects of accretion. Furthermore, we use the osculating element method to further analyze the impact of matter in the geodesic equation, enhancing our understanding of its implications. In addition, by examining the redshift of test particles orbiting a black hole, we investigate its observable effects.

Together, these multidimensional analyses enrich our understanding of the complex dynamics surrounding black holes and the influence of surrounding matter.

OJ 287: Potential Rosetta stone for the nascent multi-messenger nano-Hz GW astronomy

Recent observational campaigns and theoretical investigations strongly indicate the presence of a spinning supermassive black hole binary that spirals in due to the emission of nano-Hertz gravitational waves in bright blazar OJ 287. I will briefly describe these efforts while focusing on our August 2019 observations and their implications. Additionally, I will list our ongoing efforts, relevant to

i) the Event Horizon Telescope Consortium, and
ii) the International Pulsar Timing Array consortium which aims to detect GWs from such massive BH systems soon.

These efforts should be helpful in pursuing persistent multi-messenger nano-Hz GW astronomy, especially in the Square-Kilometer Array era.

Gravitational Waves Observations by LIGO-Virgo-KAGRA: neutron stars, black holes and dark matter

Gravitational-wave detectors have now led to several discoveries and shown themselves to be a powerful new tool for probing some of the most extreme astrophysical events in the universe. As more observations are made, new frontiers in our understanding of physics become accessible. Among those many promising avenues of gravitational-wave astronomy, this talk will discuss three observational aspects.
First some the latest results from the LIGO-Virgo-KAGRA collaboration, focusing on the analysis of the GW230529 event, and possible interpretations towards understanding its formation scenario. Then looking at how machine learning techniques can help address the gravitational-wave inference problem in general, and in particular handle real detector noise. Finally, presenting results from a direct search for scalar field dark matter using data from LIGO's third observing run.