Yasutaka Koga (Rikkyo University, Japan) will give a CENTRA seminar titled “Photon surface and relevant phenomena”.
The seminar will take place on 30th April 2020, at 13:30, using ZOOM video conferencing (contact justin.feng@tecnico.ulisboa.pt for URL).
Abstract:
Photon surface is a geometrical object which generalizes the photon sphere of Schwarzschild spacetime. Due to its geometrical features, there are interesting phenomena concerning the photon surface.
In this talk, after reviewing a photon surface and its stability, we see two theoretical phenomena in the following. “SP/PS correspondence”: In analysis of accretion and outflow of fluid, the existence of the sonic point (SP) plays a key role for finding physical solutions. If the matter is radiation fluid, there is a one-to-one correspondence between the sonic points and photon surfaces (PS) of the spacetime. “Photon surface as a wormhole throat”: Wormhole spacetime is constructed by truncating two spacetimes at some boundaries and sewing them together along the boundaries. The sewn boundary is called a throat. Such a wormhole spacetime is said to be a solution of Einstein equation if Israel’s junction conditions are satisfied with an adequate matter distribution on the throat. If the throat with the matter distribution is a pure tension brane, the corresponding boundaries of the original spacetimes must be photon surfaces.
