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## Escape probability of a photon emitted near the black hole horizon

- Kota Ogasawara, Takahisa Igata, T. Harada, U. Miyamoto
- Physics, MathematicsPhysical Review D
- 3 October 2019

We investigate the escape of photons from the vicinity of the horizon to infinity in the Kerr-Newman black hole spacetime. We assume that a light source is at rest in a locally nonrotating frame on… Expand

## Photon emission from inside the innermost stable circular orbit

- Takahisa Igata, K. Kohri, Kota Ogasawara
- PhysicsPhysical Review D
- 26 February 2021

We consider a situation where a light source orbiting the innermost stable circular orbit (ISCO) of the Kerr black hole is gently falling from the marginally stable orbit due to an inﬁnitesimal… Expand

## Complete conformal classification of the Friedmann–Lemaître–Robertson–Walker solutions with a linear equation of state

- T. Harada, B. Carr, Takahisa Igata
- Mathematics
- 5 January 2018

We completely classify Friedmann–Lemaître–Robertson–Walker solutions with spatial curvature and equation of state , according to their conformal structure, singularities and trapping horizons. We do… Expand

## Stable Bound Orbits of Massless Particles around a Black Ring

- Takahisa Igata, H. Ishihara, Y. Takamori
- Physics
- 1 February 2013

We study the geodesic motion of massless particles in singly rotating black ring spacetimes. We find stable stationary orbits of massless particles in toroidal spiral shape in the case that the… Expand

## Constants of motion for constrained Hamiltonian systems: A particle around a charged rotating black hole

- Takahisa Igata, T. Koike, H. Ishihara
- Physics
- 11 May 2010

We discuss constants of motion of a particle under an external field in a curved spacetime, taking into account the Hamiltonian constraint, which arises from the reparametrization invariance of the… Expand

## Effect of a Weak Electromagnetic Field on Particle Acceleration by a Rotating Black Hole

- Takahisa Igata, T. Harada, M. Kimura
- Physics
- 22 February 2012

We study high energy charged particle collisions near the horizon in an electromagnetic field around a rotating black hole and reveal the condition of the fine-tuning to obtain arbitrarily large… Expand

## The essence of the Blandford-Znajek process

- Shunichiro Kinoshita, Takahisa Igata
- Physics
- 25 October 2017

From a spacetime perspective, the dynamics of magnetic field lines of force-free electromagnetic fields can be rewritten into a quite similar form for the dynamics of strings, i.e., dynamics of… Expand

## Observability of spherical photon orbits in near-extremal Kerr black holes

- Takahisa Igata, H. Ishihara, Y. Yasunishi
- Physics, MathematicsPhysical Review D
- 30 March 2019

We investigate the spherical photon orbits in near-extremal Kerr spacetimes. We show that the spherical photon orbits with impact parameters in a finite range converge on the event horizon.… Expand

## Escape probability of the super-Penrose process

- Kota Ogasawara, T. Harada, U. Miyamoto, Takahisa Igata
- Physics
- 10 September 2016

We consider a head-on collision of two massive particles that move in the equatorial plane of an extremal Kerr black hole, which results in the production of two massless particles. Focusing on a… Expand

## Complete classification of photon escape in the Kerr black hole spacetime

- Kota Ogasawara, Takahisa Igata
- Physics
- 9 November 2020

We consider necessary and sufficient conditions for photons emitted from the vicinity of a Kerr black hole horizon to escape to infinity. The radial equation of motion determines necessary conditions… Expand

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