Measuring the mass and distance of a gravitational wave (GW) source is a fundamental problem in GW astronomy. The issue is becoming even more pressing since LIGO and Virgo have detected massive black holes that in the past were thought to be rare, if not entirely impossible. The waveform templates used in the detection are developed under the assumption that the sources are residing in a...
We present new two-fluid models of accretion disks in active galactic nuclei (AGN) that aim to resolve the long-standing problem of Toomre instability in AGN outskirts. In the spirit of earlier work by Sirko Goodman 2003 and others, we argue that Toomre instability is eventually resolved via feedback produced by fragmentation and its aftermath. Unlike past semi-analytic models, which (i) adopt...
Extreme-mass-ratio inspirals (EMRIs) and intermediate-mass-ratio inspirals (IMRIs) are important gravitational-wave (GW) sources for the Laser Interferometer Space Antenna (LISA). So far, their formation and evolution are considered to be independent, but recent theories suggest that stellar-mass black holes (sBHs) and intermediate-mass black hole (IMBHs) can coexist in the accretion disk of...
Binary black holes (BBHs) are one of the most important types of gravitational wave (GW) sources. Recent studies show that BBHs may form and merge in the vicinity of a supermassive black hole (SMBH), which results in overestimated masses of black holes due to gravitational and Doppler redshift. One of the distinctive features of these GW sources is that they are accelerating around the SMBH,...
Estimating the spin of SgrA$^*$ is one of the current challenges we face in understanding the center of our Galaxy. In the present work, we show that detecting the gravitational waves (GWs) emitted by a brown dwarf inspiraling around SgrA$^*$ will allow us to measure the mass and the spin of SgrA$^*$ with unprecedented accuracy. Such systems are known as extremely large mass-ratio inspirals...
It is a great challenge to constrain the spin magnitude of the black holes (BHs). We have calculate a radio image of M87 in a flaring state using a part of time-dependent general relativistic radiative transfer code: CARTOON (Takahashi et al. 2022), and found that a time variable "crescent-shaped" shadow appears and its width depends on the BH spin magnitude. Following our previous work...
The "no-hair" theorem can, in principle, be tested at the center of the Milky Way by measuring the spin and the quadrupole moment of Sgr A* with the orbital precession of S-stars, measured over their full periods. Contrary to the original method, we show why it is possible to test the no-hair theorem using observations from only a single star, by measuring precession angles over a half-orbit....
