# Black hole

**black holesblack-holeblackholedark starspin parameterBHBlack hole physicssingularitybachelor sunblack**

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it.wikipedia

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### Event horizon

**event horizonshorizoncosmic event horizon**

The boundary of the region from which no escape is possible is called the event horizon.

An event horizon is most commonly associated with black holes.

### Gravity

**gravitationgravitationalgravitational force**

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.

Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon.

### Pierre-Simon Laplace

**LaplaceLaplacianLaplace, Pierre-Simon**

Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.

He restated and developed the nebular hypothesis of the origin of the Solar System and was one of the first scientists to postulate the existence of black holes and the notion of gravitational collapse.

### Neutron star

**neutron starsdying starneutron star formation**

The discovery of neutron stars in the late 1960s sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality.

If the remnant star has a mass exceeding the Tolman–Oppenheimer–Volkoff limit, it continues collapsing to form a black hole.

### John Michell

**Michell, John**

Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace.

Considered "one of the greatest unsung scientists of all time", he was the first person known to propose the existence of black holes in publication, the first to suggest that earthquakes travel in waves, the first to explain how to manufacture artificial magnets, and the first to apply statistics to the study of the cosmos, recognizing that double stars were a product of mutual gravitation.

### Gravitational wave

**gravitational wavesgravitational radiationgravity wave**

On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves, which also represented the first observation of a black hole merger.

Gravitational-wave astronomy is a branch of observational astronomy that uses gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang.

### Mass

**inertial massgravitational massweight**

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. Through the work of Werner Israel, Brandon Carter, and David Robinson 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.

the mass of a very large star or black hole may be identified with its Schwarzschild radius (1 cm ≈ 6.73 kg).

### Binary star

**spectroscopic binaryeclipsing binarybinary**

In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

Examples of binaries are Sirius, and Cygnus X-1 (Cygnus X-1 being a well-known black hole).

### Subrahmanyan Chandrasekhar

**Chandrasekhar, SubrahmanyanChandrasekharS. Chandrasekhar**

In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at ) has no stable solutions.

His mathematical treatment of stellar evolution yielded many of the best current theoretical models of the later evolutionary stages of massive stars and black holes.

### Karl Schwarzschild

**SchwarzschildKarlSchwarzschild, Karl**

The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, although its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Only a few months later, Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties.

The Schwarzschild solution, which makes use of Schwarzschild coordinates and the Schwarzschild metric, leads to a derivation of the Schwarzschild radius, which is the size of the event horizon of a non-rotating black hole.

### Rotating black hole

**black holes spin demographicsKerr-Newman black holeKerr-Newmann black hole**

In 1963, Roy Kerr found the exact solution for a rotating black hole.

A rotating black hole is a black hole that possesses angular momentum.

### J. Robert Oppenheimer

**Robert OppenheimerOppenheimer[J. Robert] Oppenheimer**

But in 1939, Robert Oppenheimer and others predicted that neutron stars above another limit (the Tolman–Oppenheimer–Volkoff limit) would collapse further for the reasons presented by Chandrasekhar, and concluded that no law of physics was likely to intervene and stop at least some stars from collapsing to black holes.

With his students he also made important contributions to the modern theory of neutron stars and black holes, as well as to quantum mechanics, quantum field theory, and the interactions of cosmic rays.

### Schwarzschild metric

**SchwarzschildSchwarzschild solutionSchwarzschild vacuum**

Only a few months later, Karl Schwarzschild found a solution to the Einstein field equations, which describes the gravitational field of a point mass and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of Hendrik Lorentz, independently gave the same solution for the point mass and wrote more extensively about its properties.

A Schwarzschild black hole or static black hole is a black hole that has neither electric charge nor angular momentum.

### List of gravitational wave observations

**gravitational wave eventsdetectionseffective inspiral spin parameter**

, eleven gravitational wave events have been observed that originated from ten merging black holes (along with one binary neutron star merger).

### GW170817

**collision of two neutron starselectromagnetic radiation from a single sourcegravitational**

Observations of the neutron star merger GW170817, which is thought to have generated a black hole shortly afterward, have refined the TOV limit estimate to ~.

Unlike the five previous GW detections, which were of merging black holes not expected to produce a detectable electromagnetic signal, the aftermath of this merger was also seen by 70 observatories on seven continents and in space, across the electromagnetic spectrum, marking a significant breakthrough for multi-messenger astronomy.

### First observation of gravitational waves

**direct detection of gravitational wavesdirectly detecteddirectly detected gravitational waves**

On 11 February 2016, the LIGO collaboration announced the first direct detection of gravitational waves, which also represented the first observation of a black hole merger.

One case where gravitational waves would be strongest is during the final moments of the merger of two compact objects such as neutron stars or black holes.

### No-hair theorem

**no hair theoremBlack holes have no hairno-hair**

Through the work of Werner Israel, Brandon Carter, and David Robinson 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.

The no-hair theorem postulates that all black hole solutions of the Einstein-Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three externally observable classical parameters: mass, electric charge, and angular momentum.

### Chandrasekhar limit

**limit(Chandrasekhar) limitChandrasekhar's work on limits**

In 1931, Subrahmanyan Chandrasekhar calculated, using special relativity, that a non-rotating body of electron-degenerate matter above a certain limiting mass (now called the Chandrasekhar limit at ) has no stable solutions.

Consequently, a white dwarf with a mass greater than the limit is subject to further gravitational collapse, evolving into a different type of stellar remnant, such as a neutron star or black hole.

### Eddington–Finkelstein coordinates

**Eddington chartEddington–Finkelstein formEddington–Finkelstein null coordinates**

In 1924, Arthur Eddington showed that the singularity disappeared after a change of coordinates (see Eddington–Finkelstein coordinates), although it took until 1933 for Georges Lemaître to realize that this meant the singularity at the Schwarzschild radius was a non-physical coordinate singularity.

In general relativity, Eddington–Finkelstein coordinates are a pair of coordinate systems for a Schwarzschild geometry (i.e. a spherically symmetric black hole) which are adapted to radial null geodesics.

### Stephen Hawking

**HawkingProfessor Stephen HawkingDr. Stephen Hawking**

However, in the late 1960s Roger Penrose and Stephen Hawking used global techniques to prove that singularities appear generically.

His scientific works included a collaboration with Roger Penrose on gravitational singularity theorems in the framework of general relativity and the theoretical prediction that black holes emit radiation, often called Hawking radiation.

### Neutron star merger

**mergercollision of two neutron starsmerger of neutron stars**

, eleven gravitational wave events have been observed that originated from ten merging black holes (along with one binary neutron star merger).

When the two neutron stars meet, their merger leads to the formation of either a more massive neutron star, or a black hole (depending on whether the mass of the remnant exceeds the currently poorly known Tolman–Oppenheimer–Volkoff limit).

### Milky Way

**galaxyMilky Way Galaxyour galaxy**

In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.

The Milky Way may also contain perhaps ten billion white dwarfs, a billion neutron stars, and a hundred million black holes.

### Kruskal–Szekeres coordinates

**complete extensionKruskal extensionKruskal–Szekeres diagrams**

A complete extension had already been found by Martin Kruskal, who was urged to publish it.

In general relativity Kruskal–Szekeres coordinates, named after Martin Kruskal and George Szekeres, are a coordinate system for the Schwarzschild geometry for a black hole.

### Brandon Carter

Through the work of Werner Israel, Brandon Carter, and David Robinson 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.

Brandon Carter, FRS (born 1942) is an Australian theoretical physicist, best known for his work on the properties of black holes and for being the first to name and employ the anthropic principle in its contemporary form.

### John Archibald Wheeler

**John WheelerWheelerJohn A. Wheeler**

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 it quickly caught on, leading some to credit Wheeler with coining the phrase.

He is best known for linking the term "black hole" to objects with gravitational collapse already predicted early in the 20th century, for coining the terms "quantum foam", "neutron moderator", "wormhole" and "it from bit", and for hypothesizing the "one-electron universe".