2004/09/07 | 黑洞[Black Hole]
类别(Ω〖物理〗) | 评论(0) | 阅读(70) | 发表于 17:02
A massive astrophysical object that is theorized to be created from the collapse of a neutron star. The gravitational forces are so strong in a black hole that they overcome neutron degeneracy pressure and, roughly speaking, collapse to a point (known as a singularity). Even light cannot escape the gravitational pull of a black hole within the black hole's so-called Schwarzschild radius.
Uncharged, zero angular momentum black holes are called Schwarzschild black holes. Uncharged nonzero angular momentum black holes are called Kerr black holes. Nonspinning charged black holes are called Reissner-Nordström black holes. Charged, spinning black holes are called Kerr-Newman black holes. The black hole no hair theorem shows that mass, charge, and angular momentum are the only properties which a black hole can possess.

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In 1965, R. Penrose proved the singularity theorem, which says that a singularity must reside inside every imploding star, and therefore every black hole. In 1969, Lifschitz, Khalatnikov, and Belinsky showed that tidal gravity oscillates chaotically near the singularity. They also found the particular type of singularity, now known as a BKL singularity. Black holes can pulsate, as was recognized by Press (1971). Over the next decade or so, the pulsations were shown to always be stable using perturbation methods. In 1973, S. Hawking showed that black holes radiate as if they have a temperature proportional to their surface gravity, and therefore evaporate over time. In 1974, Hawking proposed that black hole radiation laws were equivalent to thermodynamic lawse showed that the entropy is
(1)

where A is the surface area, c is the speed of light, G is the gravitational constant, and is h-bar.
Tidal forces at the horizon are smaller for larger black holes. They are given by
(2)

where C is the circumference around the black hole at the given position. There are no circular orbits with radii less than times the horizon circumference. Spinning black holes can store up to 29% of their energy as spin energy. When a spherical, electrically charges star implodes to form a black hole, the star and other objects falling into the black hole can travel from the hole's interior to another universe.However, this conclusion breaks down with the small perturbations which always exist.
The two body problem of general relativity (Einstein and Rosen 1935) is still unsolved. It cannot be treated analytically. The first numerical solution of the head-on collision of two black holes of equal mass was obtained by Smarr (1979), and Matzner et al. (1995) determined the details of the coalescence.
Two black holes of mass M each orbiting each other will coalesce after time
(3)

(Misner et al. 1973, equation 36.17b).


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