Under these conditions, an apparent horizon is present in the particle's ( accelerating ) reference frame, representing a boundary beyond which events are unobservable.
12.
The " apparent horizon " is then defined as the boundary of these surfaces essentially, it is the outermost surface of the black hole, in this sense.
13.
But it's interesting that if you look at the very furthest blue spot at full resolution, it seems to be displaced upward, just a little, from the apparent horizon.
14.
Note, however, that a " black hole " is defined with respect to the " event horizon ", which is not always the same as the apparent horizon.
15.
Thus the apparent horizon can be thought of as the boundary of black hole for light at this instant, whereas the event horizon is the boundary of the black hole for light in the future.
16.
In practice the " apparent horizon " has a slight negative altitude due to the curvature of the Earth, the value of which gets more negative as the observer ascends higher above sea level.
17.
For example, it is possible to slice the Schwarzschild geometry in such a way that there is " no " apparent horizon, ever, despite the fact that there is certainly an event horizon.
18.
He is network director of the Boston Institute for Nonprofit Journalism ( BINJ ), an investigative reporting group and regional wire service that he co-founded with Chris Faraone in 2015, and writes the syndicated column Apparent Horizon.
19.
Studies have shown that the illusion can be created without using walls and a ceiling; it is sufficient to create an apparent horizon ( which in reality will not be horizontal ) against an appropriate background, and the eye relies on the apparent relative height of an object above that horizon.
20.
It is possible for light to be currently moving away from the black hole ( and so outside the apparent horizon ), but in the future will not be able to escape ( e . g . because the mass of the black hole is growing ) and therefore inside the event horizon.
