International Journal of Modern Physics D 32(16) 2350105 2023年12月 [査読有り]
We consider the periapsis shifts of bound orbits of stars on static clouds around a black hole. The background spacetime is constructed from a Schwarzschild black hole surrounded by a static and spherically symmetric self-gravitating system of mas...
Tomohiro Harada   Takahisa Igata   Sato, Takuma   Carr, Bernard   
Classical and Quantum Gravity 39(14) 145008 2022年6月 [査読有り]
We completely classify the Friedmann–Lemaître–Robertson–Walker solutions with spatial curvature K = 0, ±1 for perfect fluids with linear equation of state p = wρ, where ρ and p are the energy density and pressure, without assuming any energy condi...
Kota Ogasawara   Takahisa Igata   
Physical Review D 105(2) 024031 2022年1月 [査読有り]
We consider necessary and sufficient conditions for photons emitted from an arbitrary spacetime position of the extremal Kerr black hole to escape to infinity. The radial equation of motion determines necessary conditions for photons emitted from ...
Journal of Physics: Conference Series 314 012113-012113 2011年9月 [査読有り]
We study stable bound orbits of a free particle around a black ring. Unlike the higher-dimensional black hole case, we find that there exist stable bound orbits in toroidal spiral shape near the ring axis and stable circular orbits on the axis. In...