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Black Holes Essay

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Black Holes

The American scientist John Wheeler coined the phrase “black hole” in 1969 to describe a massively compact star with such a strong gravitational field that light cannot escape. When a star’s central reserve of hydrogen is depleted, the star begins to die. Gravity causes the center to contract to higher and higher temperatures, while the outer regions swell up, and the star becomes a red giant. The star then evolves into a white dwarf, where most of its matter is compressed into a sphere roughly the size of Earth. Some stars continue to evolve, and their centers contract to even higher densities and temperatures until their nuclear reserves are exhausted and only their gravitational energy remain. The core then rushes …show more content…

Rays of light leaving a gravitating body are curved, and become more curved as the body shrinks. When the radius of the body is less than the radius of the photon sphere, a radius 1.5 times the Schwartzschild radius where the light rays circularly orbit a black hole, the exit cone begins to close. Rays within the exit cone escape while those outside are trapped and fall back. Since the photon sphere orbits are unstable, if a circulating rays is disturbed slightly, it either spirals around and is captured or spirals out and escapes at radius 3^.5=1.732 times that of the photon sphere. Both redshift and deflection allow no radiation to escape (Harrison 248-250).

At large distances from the black hole, gravity is weak and spacetime is the same as spacetime in special relativity. Close to the black hole, however, spacetime is deformed, causing differences in space and time between the stationary and distant observer. The effect of spacetime curvature near a black hole is such that lightcones are tilted so that the future lightcones tip toward the black hole. At the surface of the black hole (the event horizon), all rays emitted fall into the black hole. And no rays from the past are received from the black hole. A particle passing into a black hole receives no information of what lies ahead, and reaches the singularity in a time t= Rs /c. To a distant observer, however, it takes an infinite time for the

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