34 citations · 102 across the 8 of their papers we have counts for
8 papers
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…
Radiative gravastar with thermal spectrum; Sudden vacuum condensation without gravitational collapse
Ken-ichi Nakao, Kazumasa Okabayashi, Tomohiro Harada
The gravastar is an exotic compact object proposed as a final product of gravitational collapse of a massive object in order to resolve problems associated with black holes. It is…
Radiative gravastar with Gibbons-Hawking temperature
Ken-ichi Nakao, Kazumasa Okabayashi, Tomohiro Harada
We study the quantum particle creation in a toy model of spherically symmetric gravitational collapse whose final product is not a black hole but a gravastar. Precedent studies rev…
Dynamical photon sphere and time evolving shadow around black holes with temporal accretion
Yasutaka Koga, Nobuyuki Asaka, Masashi Kimura +1
A photon sphere is known as the geometrical structure shaping a black hole shadow. The mechanism is well understood for static or stationary black hole spacetimes such as the Schwa…
Robustness of particle creation in the formation of a compact object
Kazumasa Okabayashi, Tomohiro Harada, Ken-ichi Nakao
Hawking has predicted that the formation of a black hole by gravitational collapse causes quantum particle creation and the spectrum of the particles is almost thermal. This phenom…
Do black hole shadows merge?
Kazumasa Okabayashi, Nobuyuki Asaka, Ken-ichi Nakao
The so-called black hole shadow is not a silhouette of a black hole but an image of a collapsing object or a white hole. Hence it is non-trivial whether black hole shadows merge wi…
Maximal Efficiency of Collisional Penrose Process with Spinning Particle II
Kazumasa Okabayashi, Kei-ichi Maeda
We analyze the collisional Penrose process between a particle on the ISCO orbit around an extreme Kerr black hole and a particle impinging from infinity. We consider both cases wit…
Maximal Efficiency of Collisional Penrose Process with Spinning Particles
Kei-ichi Maeda, Kazumasa Okabayashi, Hirotada Okawa
We analyze collisional Penrose process of spinning test particles in an extreme Kerr black hole. We consider that two particles plunge into the black hole from infinity and collide…