Islands and stretched horizon

Understand

Recently it was proposed that the entanglement entropy of the Hawking radiation contains the information of a region including the interior of the event horizon, which is called "island." In studies of the entanglement entropy of the Hawking radiation, the total system in the black hole geometry is separated into the Hawking radiation and black hole.

• In this paper, we study the entanglement entropy of the black hole in the asymptotically flat Schwarzschild spacetime.
• Consistency with the island rule for the Hawking radiation implies that the information of the black hole is located in a different region than the island.
• We found an instability of the island in the calculation of the entanglement entropy of the region outside a surface near the horizon.