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In astrophysics, an event horizon is a boundary beyond which events cannot affect an outside observer. Wolfgang Rindler coined the term in the 1950s. [1]In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive compact objects that even light cannot escape. [2]
Within an apparent horizon, light does not move outward; this is in contrast with the event horizon. In a dynamical spacetime, there can be outgoing light rays exterior to an apparent horizon (but still interior to the event horizon). An apparent horizon is a local notion of the boundary of a black hole, whereas an event horizon is a global notion.
For example, Schwarzschild spacetime contains an event horizon and so can be associated a temperature. In the case of Schwarzschild spacetime this is the temperature T {\displaystyle T} of a black hole of mass M {\displaystyle M} , satisfying T ∝ M − 1 {\displaystyle T\propto M^{-1}} (see also Hawking radiation ).
Horizon chart displaying the difference between greenhouse gas emissions of some European country and the corresponding European average for each year, ranging from 2012 to 2021. [8] When creating a horizon chart, the selection of the origin for the vertical axis, which determines the placement of the horizontal axis, is crucial.
The time for the event horizon or entropy of a black hole to halve is known as the Page time. [18] The calculations are complicated by the fact that a black hole, being of finite size, is not a perfect black body; the absorption cross section goes down in a complicated, spin -dependent manner as frequency decreases, especially when the ...
The difference between the forecast and the actual weather outcome for forecasts 3, 5, 7, and 10 days in advance. It was not until the 20th century that advances in the understanding of atmospheric physics led to the foundation of modern numerical weather prediction.
The curvature of the horizon is easily seen in this 2008 photograph, taken from a Space Shuttle at an altitude of 226 km (140 mi). The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all ...
The particle horizon, also called the cosmological horizon, the comoving horizon, or the cosmic light horizon, is the maximum distance from which light from particles could have traveled to the observer in the age of the universe. It represents the boundary between the observable and the unobservable regions of the universe, so its distance at ...