Talk detail

Participant	Harada, Tomohiro
Institution	Rikkyo University - Toshima - Tokyo - Tokyo - Japan

Session	BH3	Accepted	Yes	Order	7	Time	10'
Talk	Oral abstract	Title	High-velocity collision of an ISCO particle around a Kerr black hole
Co-authors	Masashi Kimura
Abstract	Banados, Silk and West (2009) indicated that Kerr black holes act as particle accelerators to arbitrarily high energy. In this context, we discuss the relevance of an ISCO particle around a nearly maximally rotating black hole. This implies that high-velocity collisions of compact objects are naturally expected around a rapidly rotating supermassive black hole. Implications to accretion flows onto a rapidly rotating black hole are also discussed. We finally discuss that the particle acceleration would not be so sensitive to gravitational radiation reaction if the mass ratio of the inspiraling particle to the black hole is sufficiently small.

Session	BH3	Accepted	Yes	Order	8	Time	10'
Talk	Oral abstract	Title	High-velocity collision of two general geodesic particles around a Kerr black hole
Co-authors	Masashi Kimura
Abstract	We present an expression for the center-of-mass (CM) energy of two colliding general geodesic massive and massless particles around a Kerr black hole. We show that the CM energy can be arbitrarily high only in the limit to the horizon and then derive a formula for the CM energy of two general geodesic particles colliding near the horizon. To have an arbitrarily high CM energy, the angular momentum of either of the two particles must be fine-tuned to the critical value. We show that, in the direct collision scenario, the collision with an arbitrarily high CM energy can occur near the horizon of maximally rotating black holes not only at the equator but also on a belt centered at the equator. This belt lies between latitudes $\pm acos(\sqrt{3}-1)\simeq \pm 42.94^{\circ}$.