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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Black hole | 3/13 | https://en.wikipedia.org/wiki/Black_hole | reference | science, encyclopedia | 2026-05-05T13:31:52.244381+00:00 | kb-cron |
The era from the mid-1960s to the mid-1970s was the "golden age of black hole research", when general relativity and black holes became mainstream subjects of research.
In this period, solutions to the equations of general relativity under various different physical constraints were discovered. In 1963, Roy Kerr found the exact solution for a rotating black hole. Two years later, Ezra Newman found the axisymmetric solution for a black hole that is both rotating and electrically charged.
In the late 1960s and early 1970s scientists from research groups formed by Yakov Zeldovich, John Archibald Wheeler and Dennis W. Sciama discovered a series of important mathematical properties of black hole models dubbed "a black hole has no hair" by Wheeler. The first hints came from work by Vitaly Ginzburg who studied a series of increasing compact stars threaded with intense magnetic fields. He discovered that the fields get trapped on the black hole surface.
In 1967, Werner Israel showed that any non-spinning, uncharged collapsing star gives a spherically symmetric black hole: any asymmetry must somehow vanish. In 1972, Richard H. Price found that the asymmetry was converted into gravitational waves. It took another 15 years and many physicists to produce a body of work that became known as the no-hair theorem, which states that a stationary black hole is completely described by the three parameters of the Kerr–Newman metric: mass, angular momentum, and electric charge.
At first, it was suspected that the strange mathematical singularities found in each of the black hole solutions only appeared due to the assumption that a black hole would be perfectly spherically symmetric, and therefore the singularities would not appear in generic situations where black holes would not necessarily be symmetric. This view was held in particular by Vladimir Belinski, Isaak Khalatnikov, and Evgeny Lifshitz, who tried to prove that no singularities appear in generic solutions, although they would later reverse their positions. However, in 1965, Roger Penrose proved that general relativity predicts that singularities appear in all black holes, although this may not still hold when quantum mechanics is taken into account.
Astronomical observations also made great strides during this era. In 1967, Antony Hewish and Jocelyn Bell Burnell discovered pulsars and by 1969, these were shown to be rapidly rotating neutron stars. Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities, but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse. However, experimental evidence confirming a black hole was very difficult to obtain and ultimately required efforts from many astronomers. X-ray telescope observations by Riccardo Giacconi's team in 1971 showed that Cygnus X-1 emitted x-rays in rapid, sporadic fashion consistent with a compact source. This became the first candidate black hole. Optical spectroscopy and detailed astrophysical models for Cygnus X-1 were consistent with a binary system of a massive star and compact star generating x-rays as gas from the massive but ordinary star was sucked into its invisible compact companion. (In 2011, the masses of these stars was estimated to be 14.1±1.0 M☉ for the black hole and 19.2±1.9 M☉ for the optical stellar companion.) By 1974 the object was widely considered to be a black hole, but 100% confidence for Cygnus X-1 may not be possible.
Work by James Bardeen, Carter, and Hawking in the early 1970s led to the formulation of black hole thermodynamics. These laws describe the behaviour of a black hole in a manner analogous to the laws of thermodynamics. Jacob Bekenstein strengthened this analogy with the properties of mass, surface area, and surface gravity for a black hole related to the thermodynamical concepts of energy, entropy, and temperature respectively. The analogy was completed when Hawking, in 1974, showed that quantum field theory implies that black holes should radiate like a black body with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as Hawking radiation.