Apparent horizon

Apparent Horizon is a concept in astrophysics and general relativity that refers to the boundary of a black hole from which light cannot escape. The term is used in contrast to the event horizon, which is a fixed boundary that defines the region of space from which light cannot escape. The apparent horizon, on the other hand, can change its location and shape based on the matter and energy present in the black hole.

Definition

The apparent horizon is defined as the boundary of the region of a black hole from which light cannot escape. It is a surface in spacetime that separates the region of spacetime that is causally connected to infinity from the region that is not. The apparent horizon is a local concept, meaning it is defined only in terms of the properties of the spacetime at a particular point and does not depend on the global structure of the spacetime.

Properties

The apparent horizon has several important properties. First, it is a null surface, meaning that light rays that hit the apparent horizon can neither escape from the black hole nor fall into it. Second, the apparent horizon is a dynamical horizon, meaning it can change its location and shape based on the matter and energy present in the black hole. This is in contrast to the event horizon, which is a fixed boundary that does not change with time.

Significance

The concept of the apparent horizon is important in the study of black holes and general relativity. It provides a way to define the boundary of a black hole in a way that is local and can be determined from the properties of the spacetime at a particular point. This makes it a useful tool in numerical simulations of black holes and in the study of the cosmological horizon in cosmology.

See also

• Black hole
• Event horizon
• General relativity
• Cosmological horizon

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