The spatial relation between the event horizon and trapping horizon

Understand

The relation between event horizons and trapping horizons is investigated in a number of different situations with emphasis on their role in thermodynamics.

• A notion of constant change is introduced that in certain situations allows the location of the event horizon to be found locally.
• When the black hole is accreting matter the difference in area between the two different horizons can be many orders of magnitude larger than the Planck area.
• When the black hole is evaporating the difference is small on the Planck scale.