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A stellar black hole (or stellar-mass black hole) is a
black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
formed by the
gravitational collapse Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formati ...
of a
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
. They have masses ranging from about 5 to several tens of
solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es. They are the remnants of
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
explosions, which may be observed as a type of
gamma ray burst In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic events occurring in distant galaxies which represent the brightest and most powerful class of explosion in the universe. These extreme electromagnetic emissions are second ...
. These black holes are also referred to as collapsars.


Properties

By the
no-hair theorem The no-hair theorem states that all stationary black hole solutions of the Einstein–Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three independent ''externally'' observabl ...
, a black hole can only have three fundamental properties: mass, electric charge, and angular momentum. The angular momentum of a stellar black hole is due to the
conservation of angular momentum Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of Momentum, linear momentum. It is an important physical quantity because it is a Conservation law, conserved quantity – the total ang ...
of the star or objects that produced it. The
gravitational collapse Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity. Gravitational collapse is a fundamental mechanism for structure formati ...
of a star is a natural process that can produce a black hole. It is inevitable at the end of the life of a massive star when all stellar energy sources are exhausted. If the mass of the collapsing part of the star is below the Tolman–Oppenheimer–Volkoff (TOV) limit for
neutron-degenerate matter Degenerate matter occurs when the Pauli exclusion principle significantly alters a state of matter at low temperature. The term is used in astrophysics to refer to dense stellar objects such as white dwarfs and neutron stars, where thermal pres ...
, the end product is a
compact star In astronomy, the term compact object (or compact star) refers collectively to white dwarfs, neutron stars, and black holes. It could also include exotic stars if such hypothetical, dense bodies are confirmed to exist. All compact objects have a ...
– either a
white dwarf A white dwarf is a Compact star, stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very density, dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place i ...
(for masses below the Chandrasekhar limit) or a
neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
or a (hypothetical) quark star. If the collapsing star has a mass exceeding the TOV limit, the crush will continue until zero volume is achieved and a black hole is formed around that point in space. The maximum mass that a neutron star can possess before further collapsing into a black hole is not fully understood. In 1939, it was estimated at 0.7 solar masses, called the TOV limit. In 1996, a different estimate put this upper mass in a range from 1.5 to 3 solar masses. The maximum observed mass of neutron stars is about for PSR J0740+6620 discovered in September, 2019. In the theory of
general relativity General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...
, a black hole could exist of any mass. The lower the mass, the higher the density of matter has to be in order to form a black hole. (See, for example, the discussion in Schwarzschild radius, the radius of a black hole.) There are no known stellar processes that can produce black holes with mass less than a few times the mass of the Sun. If black holes that small exist, they are most likely primordial black holes. Until 2016, the largest known stellar black hole was solar masses. In September 2015, a rotating black hole of solar masses was discovered by
gravitational waves Gravitational waves are oscillations of the gravitational field that travel through space at the speed of light; they are generated by the relative motion of gravitating masses. They were proposed by Oliver Heaviside in 1893 and then later by H ...
as it formed in a merger event of two smaller black holes. , the binary system 2MASS J05215658+4359220 was reported to host the smallest-mass black hole currently known to science, with a mass 3.3 solar masses and a diameter of only 19.5 kilometers. There is observational evidence for two other types of black holes, which are much more massive than stellar black holes. They are
intermediate-mass black hole An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range of one hundred to one hundred thousand (102–105) solar masses: significantly higher than stellar black holes but lower than the hundred thousand to more than ...
s (in the center of
globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...
s) and
supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...
s in the center of the
Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...
and other galaxies.


X-ray compact binary systems

Stellar black holes in close binary systems are observable when the matter is transferred from a companion star to the black hole; the energy released in the fall toward the compact star is so large that the matter heats up to temperatures of several hundred million degrees and radiates in
X-rays An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
. The black hole, therefore, is observable in X-rays, whereas the companion star can be observed with
optical telescopes An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electronic image sensors. ...
. The energy release for black holes and
neutron stars A neutron star is the gravitationally collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star—combined with gravitational collapse—that compresses the core past white dwarf star density to th ...
are of the same order of magnitude. Black holes and neutron stars are therefore often difficult to distinguish. The derived masses come from observations of compact X-ray sources (combining X-ray and optical data). All identified neutron stars have a mass below 3.0 solar masses; none of the compact systems with a mass above 3.0 solar masses display the properties of a neutron star. The combination of these facts makes it more and more likely that the class of compact stars with a mass above 3.0 solar masses are in fact black holes. Note that this proof of the existence of stellar black holes is not entirely observational but relies on theory: we can think of no other object for these massive compact systems in stellar binaries besides a black hole. A direct proof of the existence of a black hole would be if one actually observes the
orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...
of a particle (or a cloud of gas) that falls into the black hole.


Black hole kicks

The large distances above the
galactic plane The galactic plane is the plane (geometry), plane on which the majority of a disk-shaped galaxy's mass lies. The directions perpendicular to the galactic plane point to the galactic poles. In actual usage, the terms ''galactic plane'' and ''galac ...
achieved by some
binaries A binary file is a computer file that is not a text file. The term "binary file" is often used as a term meaning "non-text file". Many binary file formats contain parts that can be interpreted as text; for example, some computer document files ...
are the result of black hole natal kicks. The velocity distribution of black hole natal kicks seems similar to that of neutron star kick velocities. One might have expected that it would be the momenta that were the same with black holes receiving lower velocity than neutron stars due to their higher mass but that doesn't seem to be the case, which may be due to the fall-back of asymmetrically expelled matter increasing the momentum of the resulting black hole.


Mass gaps

It is predicted by some models of stellar evolution that black holes with masses in two ranges cannot be directly formed by the gravitational collapse of a star. These are sometimes distinguished as the "lower" and "upper" mass gaps, roughly representing the ranges of 2 to 5 and 50 to 150
solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es (), respectively. Another range given for the upper gap is 52 to 133 . has been regarded as the upper mass limit for stars in the current era of the universe.


Lower mass gap

A lower mass gap is suspected on the basis of a scarcity of observed candidates with masses within a few solar masses above the maximum possible neutron star mass. The existence and theoretical basis for this possible gap are uncertain. The situation may be complicated by the fact that any black holes found in this mass range may have been created via the merging of binary neutron star systems, rather than stellar collapse. The
LIGO The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Prior to LIG ...
/
Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...
collaboration has reported three candidate events among their gravitational wave observations in run O3 with component masses that fall in this lower mass gap. There has also been reported an observation of a bright, rapidly rotating giant star in a binary system with an unseen companion emitting no light, including x-rays, but having a mass of solar masses. This is interpreted to suggest that there may be many such low-mass black holes that are not currently consuming any material and are hence undetectable via the usual x-ray signature.


Upper mass gap

The upper mass gap is predicted by comprehensive models of late-stage stellar evolution. It is expected that with increasing mass, supermassive stars reach a stage where a
pair-instability supernova A pair-instability supernova is a type of supernova predicted to occur when pair production, the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays, temporarily reduces the internal radiatio ...
occurs, during which
pair production Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers ...
, the production of free
electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
s and
positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
s in the collision between
atomic nuclei The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford at the University of Manchester based on the 1909 Geiger–Marsden gold foil experiment. Aft ...
and energetic
gamma ray A gamma ray, also known as gamma radiation (symbol ), is a penetrating form of electromagnetic radiation arising from high energy interactions like the radioactive decay of atomic nuclei or astronomical events like solar flares. It consists o ...
s, temporarily reduces the internal pressure supporting the star's core against gravitational collapse. This pressure drop leads to a partial collapse, which in turn causes greatly accelerated burning in a runaway thermonuclear explosion, resulting in the star being blown completely apart without leaving a stellar remnant behind. Pair-instability
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
e can only happen in stars with a mass range from around 130 to 250 solar masses () and low to moderate
metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...
(low abundance of elements other than hydrogen and helium – a situation common in
Population III stars In 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926. Baade observed tha ...
). However, this mass gap is expected to be extended down to about 45 solar masses by the process of pair-instability pulsational mass loss, before the occurrence of a "normal" supernova explosion and core collapse. In nonrotating stars the lower bound of the upper mass gap may be as high as 60 . The possibility of direct collapse into black holes of stars with core mass > 133 , requiring total stellar mass of > 260 has been considered, but there may be little chance of observing such a high-mass supernova remnant; i.e., the lower bound of the upper mass gap may represent a mass cutoff. Observations of the LB-1 system of a star and unseen companion were initially interpreted in terms of a black hole with a mass of about 70 solar masses, which would be excluded by the upper mass gap. However, further investigations have weakened this claim. Black holes may also be found in the mass gap through mechanisms other than those involving a single star, such as the merger of black holes.


Candidates

Our
Milky Way galaxy The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galaxy, which are ...
contains several stellar-mass black hole candidates (BHCs) which are closer to us than the supermassive black hole in the
galactic center The Galactic Center is the barycenter of the Milky Way and a corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a ...
region. Most of these candidates are members of X-ray binary systems in which the compact object draws matter from its partner via an accretion disk. The probable black holes in these pairs range from three to more than a dozen
solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...
es.


Extragalactic

Candidates outside our galaxy come from
gravitational wave Gravitational waves are oscillations of the gravitational field that Wave propagation, travel through space at the speed of light; they are generated by the relative motion of gravity, gravitating masses. They were proposed by Oliver Heaviside i ...
detections: Candidates outside our galaxy from X-ray binaries: The disappearance of N6946-BH1 following a failed supernova in NGC 6946 may have resulted in the formation of a black hole.


See also

* Black holes in fiction *
Supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...
* Rogue black hole * Primordial black hole


References


External links


Black Holes: Gravity's Relentless Pull
Award-winning interactive multimedia Web site about the physics and astronomy of black holes from the Space Telescope Science Institute
Black hole diagrams
*
Heaviest Stellar Black Hole Discovered in Nearby Galaxy, Newswise, 17-Oct-2007
{{DEFAULTSORT:Stellar Black Hole + Compact stars