From the 1 of 6 linked papers with an AI index.
6 papers
Odd-parity ringdown gravitational waves of a spherically symmetric black hole with perfect fluid accretion
Rikuto Ohashi, Yasutaka Koga, Hiroyuki Nakano +2
The paper analyzes how the odd‑parity ringdown gravitational waves of a Schwarzschild black hole are affected by steady, spherically symmetric accretion of a perfect fluid, derivin…
Shadow formation in gravitational collapse: Redshift and blueshift by spacetime dynamics
Yasutaka Koga, Nobuyuki Asaka, Masashi Kimura +1
A black hole illuminated by a background light source is observed as a black hole shadow. For a black hole formed by gravitational collapse of a transmissive object, redshift of li…
AdS gravastar and bulk-cone singularities
Heng-Yu Chen, Yasuaki Hikida, Yasutaka Koga
The horizon of black hole is surrounded by the photon sphere and an outside observer cannot easily examine the geometry inside the photon sphere. In this note, we propose a way to…
Test particle motion around a black hole dressed with a spherically symmetric stationary fluid
Ariadna Uxue Palomino Ylla, Yasutaka Koga, Chul-Moon Yoo
We investigate the motion of a massive particle around a spherically symmetric black hole surrounded by a stationary and radial inflow of perfect fluid. The background spacetime is…
Geometrical origin for the compaction function for primordial black hole formation
Tomohiro Harada, Hayami Iizuka, Yasutaka Koga +1
We propose a geometrical origin for the Shibata-Sasaki compaction function, which is known to be a reliable indicator of primordial black hole formation at least during radiation d…
Revisiting spins of primordial black holes in a matter-dominated era based on peak theory
Daiki Saito, Tomohiro Harada, Yasutaka Koga +1
We estimate the probability distribution for the spins of the primordial black holes (PBHs) that formed during an early matter-dominated era in the Universe. We employ the Zel'dovi…