Golden age
The first simulated image of a black hole,
created by Jean-Pierre Luminet in 1978 and featuring the characteristic
shadow, photon sphere, and lensed accretion disk. The disk is brighter on
one side due to the Doppler beaming.[38][39]
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.[40][41]: 258
In this period more general black hole solutions were found. 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.[42] Through the work of Werner
Israel,[43] Brandon Carter,[44][45] and David Robinson[46] the no-hair
theorem emerged, stating that a stationary black hole solution is
completely described by the three parameters of the Kerr–Newman
metric: mass, angular momentum, and electric charge.[47]
At first, it was suspected that the strange features of the black hole
solutions were pathological artefacts from the symmetry conditions
imposed, and that the singularities would not appear in generic situations.
This view was held in particular by Vladimir Belinsky, Isaak Khalatnikov,
and Evgeny Lifshitz, who tried to prove that no singularities appear in
generic solutions. However, in the late 1960s Roger
Penrose[48] and Stephen Hawking used global techniques to prove that
singularities appear generically.[49] For this work, Penrose received half of
the 2020 Nobel Prize in Physics, Hawking having died in 2018.[50]
Astronomical observations also made great strides during this era. In
1967 Antony Hewish and Jocelyn Bell Burnell discovered pulsars[51][52] and
by 1969, these were shown to be rapidly rotating neutron stars. [53] 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.[54] Based on observations
in Greenwich and Toronto in the early 1970s, Cygnus X-1, a galactic X-
ray source discovered in 1964, became the first astronomical object
commonly accepted to be a black hole.[55][56]
Work by James Bardeen, Jacob Bekenstein, Carter, and Hawking in the
early 1970s led to the formulation of black hole thermodynamics.[57] These
laws describe the behaviour of a black hole in close analogy to the laws of
thermodynamics by relating mass to energy, area to entropy, and surface
gravity to temperature. 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.[58]
Observation
An infographic explaining in detail the
appearance of a black hole.
On 11 February 2016, the LIGO Scientific Collaboration and the Virgo
collaboration announced the first direct detection of gravitational waves,
representing the first observation of a black hole merger. [59] On 10 April
2019, the first direct image of a black hole and its vicinity was published,
following observations made by the Event Horizon Telescope (EHT) in
2017 of the supermassive black hole in Messier 87's galactic centre.[60][61]
[62]
Gaia mission observations have found evidence of a Sun-like star
orbiting a black hole named Gaia BH1 around 1,560 light-
years (480 parsecs) away;[63] evidence suggests a brown dwarf
star orbits Gaia BH2.[64] Though only a couple dozen black holes have been
found so far in the Milky Way, there are thought to be hundreds of
millions, most of which are solitary and do not cause emission of radiation.
[65]
Therefore, they would only be detectable by gravitational lensing.
Etymology
In December 1967, a student reportedly suggested the phrase "black
hole" at a lecture by John Wheeler; Wheeler adopted the term for its
brevity and "advertising value", and Wheeler's stature in the field ensured
it quickly caught on.[36][66] leading some to credit Wheeler with coining the
phrase.[67] However the term was used by others around that time.
Science writer Marcia Bartusiak traces the term "black hole" to
physicist Robert H. Dicke, who in the early 1960s reportedly compared the
phenomenon to the Black Hole of Calcutta, notorious as a prison where
people entered but never left alive. The term "black hole" was used in
print by Life and Science News magazines in 1963, and by science
journalist Ann Ewing in her article "'Black Holes' in Space", dated 18
January 1964, which was a report on a meeting of the American
Association for the Advancement of Science held in Cleveland, Ohio.[36]
