The surface surrounding a black hole, where the escape velocity equals the speed of light, is called the event horizon, and the radius of the surface is called the Schwarzschild radius. 24.5: Black Holes Theory suggests that stars with stellar cores more massive than three times the mass of the Sun at the time they exhaust their nuclear fuel will collapse to become black holes.When light or other radiation emerges from a compact smaller remnant, such as a white dwarf or neutron star, it shows a gravitational redshift due to the slowing of time. Curved spaces play an essential role in general relativity, where gravityis often visualized as curved space. Experiments on Earth and with spacecraft have confirmed this prediction with remarkable accuracy. Curved spaces can generally be described by Riemannian geometrythough some simple cases can be described in other ways. 24.4: Time in General Relativity General relativity predicts that the stronger the gravity, the more slowly time must run.For example, general relativity predicts that light or radio waves will be deflected when they pass near the Sun, and that the position where Mercury is at perihelion would change by 43 arcsec per century even if there were no other planets However, in the stronger gravity of the Sun, general relativity makes predictions that differ from Newtonian physics and can be tested. The popular phrase spacetime tells matter how to move, matter tells spacetime how to curve aptly encapsulates this equation. 24.3: Tests of General Relativity In weak gravitational fields, the predictions of general relativity agree with the predictions of Newton’s law of gravity. At the heart of GR lies Einsteins field equation that describes the interplay between space, time, and massive objects.Light must change its path near a massive object not because light is bent by gravity, but because spacetime is. ![]() The distribution of matter determines the curvature of spacetime other objects (and even light) entering a region of spacetime must follow its curvature.
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