Black hole

See also: Black hole (homonymy)

In Astrophysique, a black hole is a massive object whose gravitational Champ is so intense that it prevents any form of Matière or of Rayonnement to escape from it. Such objects thus do not emit a Lumière and are then Noir S. the black holes are described by the theory of the General relativity. They are not directly observable, but several techniques of indirect observation in different wavelengths were developed and make it possible to study the phenomena which they induce on their environment. In particular, the matter which is grabbed by a black hole is heated at considerable temperatures before being absorbed and emits of this fact an significant amount of X-rays. Thus, even if a black hole does not emit itself of radiation, it can nevertheless be detectable by its action on its environment. The existence of the black holes is a certainty for the near total of the Scientific community concerned (Astrophysicien S and physicists theorists).

Presentation and terminology

A black hole has a Masse given, concentrated in a point called gravitational Singularité. This mass makes it possible to define a Sphère called horizon of the black hole, centered on the singularity and whose ray is a maximum limit in on this side which the black hole prevents any radiation from escaping. This sphere represents to some extent the space extension of the black hole. For a black hole of mass equal to the mass of the Sun, its ray is worth approximately 3 kilometers. At an interstellar distance (in million kilometers), a black hole does not exert more attraction than any other of the same body masse  ; it thus is not about an irresistible “vacuum cleaner”. For example, if the Sun were replaced by an of the same mass black hole, the Orbite S of its Planet S would remain unchanged.

There exist several kinds of black holes. When they are formed following the gravitational collapse of a star, one speaks about stellar Black hole . When one finds them in the center of the Galaxie S, they have a mass being able to go until several billion solar masses and one then speaks about supermassif Black hole (or galactic black hole). Between these two scales of mass, one thinks that there exist intermediate black holes with a mass of a few thousands of solar masses. Black holes of mass much lower, who would have been trained at the beginning of the history of the universe, with the Big Bang, are also considered, and are called paramount Black holes . Their existence, at the present time, is not confirmed.

It is difficult to observe a black hole directly. It is however possible to deduce its presence by its gravitational action on its environment, in particular within the Microquasar S and of the active cores of galaxies, where matter in the vicinity falling on the black hole will be considerably heated and will emit a fort X-radiation. The observations thus make it possible to detect the existence of massive objects and very small size. The only objects that these observations imply and which are compatible within the framework of the General relativity are the black holes.

History

See also: Historical of the black holes

The concept of black hole emerged at the end of the 18th century within the framework of the Universal gravitation of Isaac Newton. The question was to know if there were objects whose mass was sufficiently large so that them Escape velocity is larger than the Speed of light. However, it is only at the beginning of the 20th century and the advent of the General relativity of Albert Einstein that the concept of black hole becomes more than one curiosity. Indeed, shortly after the publication of work of Einstein, a solution of the equation of Einstein implying the existence of a central black hole is published by Karl Schwarzschild. Fundamental work on the black holes goes back to the Années 1960, preceding by little the first solid observational indications in favor of their existence. The first “observation,” of an object containing a black hole was that of the source of X-rays Cygnus X-1 by the satellite Uhuru in 1971. The term of “black hole” emerged, in the current of the Années 1960, via the American Physicien Kip Thorne. Previously, one used the terms of “body of Schwarzschild” or “occluded star”. To note that the term of “black hole” met reserves in certain speech communities, in particular French-speaking and Russian speakers, which considered it somewhat improper.

Properties

A black hole is an astrophysical object like another. He is characterized by the fact that it is very difficult to observe directly (see below), and that its central area cannot be described in a satisfactory way by the physical theories in their state of the beginning of the 21e century because it shelters a gravitational Singularité. The latter cannot be described that within the framework of a theory of the quantum Gravitation, missing to date. On the other hand, one can perfectly describe the physical conditions which reign in its immediate vicinity, just as his influence on his environment, which makes it possible to detect them by various indirect methods.

In addition, the black holes are astonishing in what they are described by very a small number of parameters. Indeed, their description, in the universe in which we live, depends only on three paramètres : the Mass, the electric Charge and the kinetic Moment. All the other parameters of the black hole (for example his size or its form) are fixed by these. By comparison, the description of a planet utilizes hundreds of parameters (chemical composition, differentiation of its elements, Convection, atmosphere, etc). The reason for which a black hole is not described that by these three parameters since 1967   is known;: it is the Théorème of baldness shown by Werner Israel. This one explains why only the fundamental interactions with long range being the Gravitation and the electromagnetism, the only measurable properties of the black holes are given by the parameters describing these interactions, namely the mass, the kinetic moment and the electric charge.

For a black hole, the mass and the electric Charge are usual properties which describes traditional physics ( i.e. not-relativist)  : the black hole has a gravitational Champ proportional to his mass and an electric field proportional to his load. The influence of the kinetic Moment is on the other hand specific to the General relativity. That one stipulates indeed that a body in rotation will tend “to involve” the space time in its vicinity. This phenomenon, not yet observed at present in the Solar system because of its extreme weakness for noncompact stars, is known under the name of Effet Lense-Thirring (also called frame dragging , in English). It takes a considerable amplitude in the vicinity of a black hole in rotation, so much so that an observer located in its immediate vicinity would be inevitably involved in the direction of rotation of the black hole. The area where this occurs is called Ergorégion.

Four possible theoretical types…

A black hole always has a nonnull mass. On the other hand, its two other characteristics, namely the kinetic moment (rotation) and the electric charge, can in theory take zero values (i.e. equal to Zero) or not null. The combination of these states makes it possible to define four types of black holes.

When the electric charge and the kinetic moment are null, one speaks about Black hole of Schwarzschild, of the name of Karl Schwarzschild which, the first, highlighted these objects as solutions of the equations of general relativity (the equations of Einstein), in 1916.

When the electric charge is nonnull and the kinetic moment no one, one speaks about Black hole of Reissner-Nordström. These black holes are not of notable astrophysical interest because no known process makes it possible to manufacture a compact object preserving an electric charge durably significative  ; this one is dissipated normally quickly by absorption of opposite electric charges taken with its environment. A black hole of Reissner-Nordström is thus a very improbable theoretical object in nature.

If the black hole has one kinetic moment (i.e. it is in rotation on itself) but does not have an electric charge, one speaks about Black hole of Kerr, of the name of the Mathématicien New Zealand Roy Kerr which found the formula describing these objects in 1963. Contrary to the black holes of Reissner-Nordström and Schwarzschild, the black holes of Kerr are of considerable astrophysical interest, because the models of training and evolution of the black holes indicate that those tend to absorb the surrounding matter via a Disque of accretion into which the matter falls while always spiralant in the same direction in the black hole. Thus, the matter communicates kinetic Moment with the black hole who absorbs it. The black holes of Kerr are thus the only ones that one really expects to meet in Astronomie. However, there remains possible that black holes at very weak kinetic time, being connected in practice with black holes of Schwarzschild, exist.

The version electrically charged with the black hole of Kerr, equipped like him with a rotation, is known under the name of Black hole of Kerr-Newman and presents like the black hole of Reissner-Nordström or that of astrophysical Schwarzschild only little interest have regard to its very weak probability.

… And a multitude of others

From a theoretical point of view, it can exist a multitude of other types of black holes with different properties. For example, there exists an analog of the black hole of Reissner-Nordström, but by replacing the electric Charge by a magnetic Charge, i.e. created by magnetic monopolies, whose existence remains extremely hypothetical to date. One can in the same way generalize the concept of black hole to spaces including/understanding more than three Dimension S. This allows exhiber types of black holes having properties sometimes different from those of the black holes introduced above.

The hole and black…

The existence of the black holes is considered as of the 18th century independently by John Michel and Pierre-Simon Laplace. They were then predicted objects as so much dense which them Escape velocity was higher than the Speed of light - i.e. even the light cannot overcome their gravitational force. Rather than such a force (which is a Newtonian concept), it is righter to say than the light undergoes in fact a shift towards the infinite red. This shift towards the red is of origin gravitationnelle : the light loses the totality of its energy while trying to leave the Puits of potential of a black hole. This shift towards the red is thus of a nature somewhat different from that due to the expansion of the universe, which one observes for the remote Galaxie S and which results from an expansion of a space not presenting a well of very major potentials. From this characteristic comes the “black” adjective, since a black hole cannot emit light. What is valid for the light is also for the matière : no particle can escape from a black hole once captured by this one, from where the term of extremely suitable “hole”.

Horizon of the events

See also: Horizon of the events

See also: Horizon (black hole)

The zone which delimits the area from where Lumière and Matière cannot escape, is called “Horizon of the events”. One speaks sometimes about “surface” of the black hole, though the term is somewhat unsuitable (it is not a question of a solid or gas surface as the surface of a Planet or a star). It is not a question of an area which shows characteristics particulières : an observer which would cross the horizon would not feel anything special at this time (see below). On the other hand, it would realize that it cannot escape any more from this area if it tried to make half-turn. It is a kind of Point nonreturn. In substance, it is a situation which is a little similar to that of a bather who would move away from the coast. If for example the bather can swim only two kilometers, it will not feel anything if it moves away to more than one kilometer of the coast. On the other hand, if it makes half-turn, it will realize that it does not have enough energy to reach bank.

On the other hand, an observer located in the vicinity of the horizon will notice that time passes differently for him and for an observer located far from the black hole. If this last sends to him light signals with regular intervals (for example a second), then the observer close to the black hole will receive energy signals (the Fréquence of the light signals will be raised, consequence of the shift towards the blue undergone by the light which fall towards the black hole), and the time intervals separating two consecutive signals will be brought closer (less than one second, therefore). This observer will thus have the impression which time more quickly passes for its fellow-member remained far from the black hole than for him. Contrary, the observer remained far from the black hole will see his colleague evolving/moving more and more slowly, time at this one giving the impression to run out more slowly.

If the distant observer sees an object falling into a black hole, the two phenomena of Dilatation of time and Décalage towards the red will combine. The possible signals emitted by the object increasingly red, less and less luminous (the emitted light loses more and more energy before arriving at the remote observer), and will be spaced more and more. In practice, the number of Photon S received by the distant observer will decrease very quickly, until becoming nul : at this time the object falling in the black hole became invisible. Even if the distant observer tries to approach the horizon in order to recover the object which it had the impression to see to stop right before the horizon, this one will remain invisible.

For an observer approaching a singularity, in fact the effects of tide will become important. These effects, which determine the deformations of an object (the body of an astronaut, for example) because of the inhomogeneousness of the gravitational Champ, will ineluctably be felt by an observer approaching too close to a black hole or a singularity. The area where these effects of tide become important is entirely located in the horizon for the black holes supermassifs, but encroaches notably out of the horizon for stellar black holes. Thus, an observer approaching a stellar black hole would be shredded before passing the horizon, whereas the same observer which would approach a supermassif black hole would pass the horizon without encumbers. It would on the other hand ineluctably be destroyed then by the effects of tide.

Singularity

See also: gravitational Singularity

At the center of a black hole an area is in which the gravitational field and the distortions of space (one speaks rather about curve of space) become infinite. This area is called a gravitational Singularité. The description of this area is delicate within the framework of general relativity since this one cannot describe areas where the curve becomes infinite.

Moreover, general relativity is a theory which cannot in general incorporate gravitational effects of quantum origin . However when the curve tends towards the infinite one, one can show that this one is necessarily prone for purposes of quantum nature. Consequently, only a theory of the gravitation incorporating all the quantum effects (one then speaks about quantum Gravitation) is able to describe the gravitational singularities correctly.

The description of a gravitational singularity is thus for the time being problematic. A black hole cannot be formed following the collapse of dwarf a blanche : this one, while crumbling initiates nuclear reactions which form Nucléon S heavier than those which compose it. By doing this, the release of energy which results from it is sufficient to dislocate the dwarf white one completely, which explodes in Supernova known as thermonuclear (or of Ia type).

A black hole is formed when the force of Gravité is sufficiently large to exceed the effect of the Pression, thing which occurs when the star progenitor exceeds a certain critical mass. In this case, plus any known force does not allow to maintain balance, and the object in question crumbles completely. In practice, several cases of figures are possibles : either a neutron star accrète of the matter resulting from another star, until reaching a critical mass, or it amalgamates with another neutron star (phenomenon a priori much rarer), or the heart of a massive star crumbles directly as a black hole.

The assumption of the existence of a state more compact than that of neutron star was proposed in the current of the Années 1980   ; it would be that of stars with Quark S so called strange stars because of the name given for historical reasons to some of the quarks constituting the object, called “strange quarks. Indications of a possible indirect detection such stars were obtained since the current of the Années 1990, without slicing for as much definitively the question, but that does not change anything with the fact that beyond a certain mass this type of star ends up crumbling as a black hole, only the value limiting mass changes.

In 2006, one distinguishes four big classes from black holes according to their masse : black holes stellar, supermassifs, intermediaries and paramount (or micro black holes). The existence even the abundance of each type of black hole is directly related to the possibility of their formation.

Stellar black holes

See also: stellar Black hole

The stellar black holes have a mass of some solar masses. They are born following gravitational collapse from the residue from massive stars (approximately ten solar masses and more, initially). Indeed, when combustion by the thermonuclear reactions in the heart of massive star finishes, for lack of fuel, a Supernova occurs. The latter can leave behind it a heart which continues to crumble quickly.

In 1939, Robert Oppenheimer showed that if this heart has a mass higher than a certain limit (called Limite of Oppenheimer-Volkoff, and equal to approximately 3,3 solar masses), the gravitational force definitively carries it on all the other forces and a black hole is formed.

Collapse towards a black hole is likely to emit gravitational waves, which should be detected in a near future with instruments such as the detector Virgo of Cascina in Italy, or with both American interferometers of LIGO. The stellar black holes are today observed in the binary X and the Microquasar S and are responsible sometimes for the appearance of jets such as those observed in some active cores of galaxies.

Black holes supermassifs

See also: supermassif Black hole

The black holes supermassifs have a mass ranging between a few million and a few billion solar masses. They are in the center of the Galaxie S and their presence causes sometimes the appearance of jets and the X-radiation. The cores of galaxies which are thus more luminous than a simple star superposition are then called active cores of galaxies.

Our galaxy, the Milky Way, contains such a black hole, as it was shown by the observation of the extremely fast movements of stars close to the black hole. In particular, a named star S2 could be observed at the time of a complete revolution around an object sinks not detected in less than eleven years. The elliptic orbit of this star brought it to less than twenty astronomical units of this object (either a distance about that Uranus - Sun), and the speed to which the orbit is traversed makes it possible to assign a mass of approximately 2,3 million solar masses for the object sinks around of which it revolves. No model other than that of a black hole makes it possible to give an account of such a matter concentration in such a restricted volume.

The telescope Chandra also made it possible to observe in the center of the Galaxie NGC 6240 two black holes supermassifs orbits one around the other of it. The training of such giants is still discussed, but some think that they were formed very quickly at the beginning of the universe.

Intermediate black holes

See also: intermediate Black hole

The intermediate black holes are recently discovered objects and have a mass between 100 and: 10000 solar masses. In the Years 1970, the black holes of intermediate mass were supposed to create in the heart of the globular Amas S, but no observation came to support this assumption. Observations in the Années 2000 showed the existence of sources of ultralumineuses x-rays ( Ultra-luminous X-ray source in English, or ULX ). These sources are apparently not associated in the middle of the galaxies where the black holes supermassifs are found. Moreover, the quantity of x-rays observed is too important to be produced by a black hole of 20 solar masses, accrètant of the matter with a rate equal to the Limite of Eddington (maximum limit for a stellar black hole).

Paramount black holes

See also: paramount Black hole

The paramount black holes, so called micro black holes or quantum black holes , would have a very small size. They would have been formed during the Big Bang (from where name “paramount” black hole), following the gravitational collapse of small surdensities in the paramount Univers. In the Years 1970, the physicists Stephen Hawking and Bernard Carr studied a mechanism of training of the black holes in the paramount universe. They advanced the idea of a profusion of black, tiny mini-holes compared to those under consideration by the stellar formation. The density and the distribution in mass of these black holes are not known and depend primarily on the way in which a fast phase of expansion in the paramount universe occurs, the cosmic Inflation. These black holes, of low mass emit if they exist a gamma ray which could possibly be detected by satellite like INTEGRAL. Nonthe detection of this radiation makes it possible to put higher limits on abundance and the distribution in mass of these black holes.

According to certain models of high-energy physics, it could be possible to create similar black mini-holes in laboratory, in particle accelerator like LHC, installed close to Geneva, in Suisse.

Observation of the black holes

See also: Observation and detection of the black holes

The two only classes of black holes for whom one has many observations (indirect, but increasingly precise, to see following paragraph) are the stellar black holes and supermassifs. The supermassif black hole nearest is that which is in the center of our galaxy to approximately 8 kilo Parsec S.

One of the first methods of detection of a black hole is the determination of the mass of the two components of a binary star, starting from the orbital parameters. One thus observed stars of low mass with a very marked orbital movement (amplitude of several tens of km/s), but whose companion is invisible. The invisible massive companion can generally be interpreted like a neutron star or a black hole since a normal star with such a mass would be seen very easily. The mass of the companion (or the function of masses, if the angle of inclination is unknown) is then compared with the mass maximum limit of the neutron stars (approximately 3,3 solar masses). If it exceeds this limit, it is considered that the object is a black hole. If not, it can be a white Naine.

It is also considered that certain stellar black holes appear at the time of the starts of gamma rays (or GRB , for gamma-ray burst in English). Indeed, the latter would be formed via the explosion of a massive star (like a star Wolf-Rayet) in Supernova, and that in certain cases (described by the model Collapsar), a flash of gamma rays is produced at the time when the black hole is formed. Thus, a GRB could represent the signal of the birth of a black hole. Black holes of lower mass can also be formed by traditional supernovas. The remanent one of the supernova 1987A is suspected of being a black hole, for example.

A second phenomenon directly connected to the presence of a black hole, this time not only of stellar type, but so supermassif, is the presence of jets observed mainly in the field of the radio waves. These jets result from the changes of Magnetic field to large scales occurring in the disc of accretion of the black hole.

Towards the observation directe ?

The smallness of a stellar black hole (a few kilometers) makes his observation direct impossible. As an example, and even if the angular Taille of a black hole is larger than that of a traditional object, a black hole of a mass solar and located at a Parsec (approximately 3,26 light-years) would have a micro Diamètre angular of 0,1 Seconde of arc. However, the situation is more favorable for a supermassif black hole. Indeed, the size of a black hole is proportional to his mass. The black hole of the galactic center has a mass, estimated well, approximately 2,6 million solar masses. Its Rayon of Schwarzschild is thus of approximately 7 million kilometers. The angular size of this black hole, located at approximately 8,5 Kiloparsec S is about 30 microseconds of arc. This resolution is inaccessible in the visible Domaine, but is currently rather close to the limits atteignables in Interférométrie radio. The technique of radio interferometry, with a sufficient sensitivity, is limited in frequency to the millimetre-length field. A profit of an order of magnitude in frequency would allow a resolution better than the angular size of the black hole. The direct imagery of the black hole of the galactic center is thus possible in the years which come. The supermassif black hole located at the center of the galaxy M87 is approximately 2000 times more distant (18,7 Mpc), but estimated nearly 1300 times more massive. This black hole could thus become the second black hole coloured after that of the Milky Way.

Stellar examples of black holes

Cygnus X-1, detected in 1965, is the first known astrophysical object containing a black hole. It is a binary system consisted of a black hole in rotation and a giant star.

The stellar binary systems which contain a black hole with a forming accretion disc of the jets are called Microquasar S, in reference to their parents extragalactiques : the Quasar S. the two classes of objects share in fact the same physical processes. Among the most studied microquasars, one will note GRS 1915+105, discovered in 1994 to have supraluminic jets . Another case of such jets was detected in the system GRO J1655-40. But its distance is prone to controversy and its jets could not be supraluminic. Let us note also the very special microquasar S 433, which has persistent jets in Précession, and where the matter moves per packages at speeds of some fractions speed of light.

Examples of black holes supermassifs

The candidates black holes supermassifs firstly were the active cores of galaxy and the Quasar S discovered by the radioastronomers in the years 1960. However, the most convincing observations of the existence of black holes supermassifs are those of the orbits of stars around the galactic Center called Sagitarius A*. The orbit of these stars and speeds reached, made it possible today to exclude any other type of object that a supermassif black hole at this place of the galaxy. Thereafter, of the black holes supermassifs were detected in many other galaxies.

In February 2005, a blue giant star, called SDSS J090745.0+24507 was observed leaving our galaxy with a speed twice higher than the Escape velocity of the Milky Way, that is to say 0,0022 times speed of light. When the trajectory of this star is gone up, it is seen that it crosses the immediate vicinity of the galactic center. Its speed and its trajectory thus consolidate also the idea of the presence of a supermassif black hole at this place whose gravitational influence would have caused the ejection of this star of the Milky Way.

In November 2004, a team of astronomers brought back the discovery of the first intermediate black hole of mass in our galaxy and orbiting to only three light-years of the galactic center. This black hole would have a mass of approximately 1300 solar masses and is in a cluster of only seven stars. This cluster is probably the residue of a massive star cluster which was stripped by the presence of the central black hole. This observation consolidates idea that the black holes supermassifs grow by absorbing stars and other black holes, who could be confirmed by the direct observation of the gravitational waves emitted by this process, via the space Interféromètre LISA.

In June 2004, of the Astronome S found a black hole supermassif, called Q0906+6930, in the center of a remote Galaxie of approximately 12,7 billion light-years, i.e. when the universe was still very young. This observation shows that the training of the black holes supermassifs in the galaxies is a relatively fast phenomenon.

Black holes and fundamental physics

Theorems on the singularities

A crucial question in connection with the black holes is to know under which conditions they can be formed. If the requirements with their formation are extremely specific, the chances that the black holes are numerous can be weak. A whole of mathematical theorems due to Stephen Hawking and Roger Penrose showed that it was not rien : the training of the black holes can occur in a variety of extremely generic conditions. For obvious reasons, this work was named Théorèmes on the singularities. These theorems date from the beginning of the Années 1970, time when there was hardly observational confirmation of the existence of the black holes. The later observations actually confirmed that the black holes were very frequent objects in the universe.

Naked singularities and censures cosmic

See also: cosmic Principle of censure

At the center of a black hole a gravitational Singularité is located. For any type of black hole, this singularity “is hidden” of the outside world by the horizon of the events. This situation proves heureuse  very;: current physics cannot certainly describe a gravitational singularity, but that has little importance because, that one being inside the zone delimited by the horizon, it does not influence the events of the outside world. It is however that there exist mathematical solutions with the equations of the general relativity in which a singularity exists without being surrounded by a horizon. It is for example the case for the solutions of Kerr or Reissner-Nordström when the load or the kinetic moment exceeds a certain breaking value. In this case, one does not speak any more a black hole (there is no more horizon, therefore more “hole”) but of naked Singularité. Such configurations are extremely difficult to study in practice, because the prediction of the behavior of the singularity remains always impossible  ; but this time, it influences the universe in which we live. The existence of naked singularities thus has as a consequence the impossibility of a deterministic evolution of the universe in the state of current knowledge.

These elements, as well as more fundamental considerations, led the English mathematician Roger Penrose to formulate in 1969 the assumption known as of the censures cosmic, stipulating that no physical process could allow the appearance of naked singularities in the universe. This assumption, which has several possible formulations, was the object of a bet between Stephen Hawking on the one hand and Kip Thorne and John Preskill on the other hand, the latter having bet that naked singularities could exist. In 1991, Stuart L. Shapiro and Saul A. Teukolsky showed on faith of digital simulations that naked singularities could be formed in the universe. A few years later, Matthew Choptuik highlighted a whole important of situations from which the formation of naked singularities was possible. These configurations remain however extremely particular, and require a fine Ajustement initial conditions to lead to the formation of the naked singularities. Their formation is thus possible , but in practice extremely improbable . In 1997 Stephen Hawking recognized that it had lost its bet with Kip Thorne and John Preskill. Another bet has had for launched summer, where more restrictive conditions on the initial conditions being able to lead to naked singularities were added.

Entropy of the black holes

See also: Entropy of the black holes

In 1971, the British physicist Stephen Hawking showed that the entire surface of the horizons of the events of any traditional black hole can never decrease. This property is completely similar to the Second law of thermodynamics, with surface playing the part of the Entropie. Within the framework of traditional physics, one could violate this law of the Thermodynamique by sending matter in a black hole, which would make it disappear from our universe, with the consequence of a waning of the total entropy of the universe.

To avoid violating this law, the physicist Jacob Bekenstein proposed that a black hole has an entropy (without specifying true nature of it), and that it is proportional to the surface of its horizon. Bekenstein thought whereas the black holes do not emit radiation and that the bond with thermodynamics was only one simple analogy and not a physical description of the properties of the black hole. Nevertheless Hawking shortly after showed by a calculation of Quantum theory of the fields that the result on the entropy of the black holes is much more than one simple analogy and than it is possible to rigorously define a temperature associated with the radiation with the black holes (see below).

Using the equations of the thermodynamics of the black holes, it appears that the entropy of a black hole is proportional to the surface of its horizon. It is a universal result which can be applied in another context to the cosmological model comprising them also a horizon such as for example the Univers of Sitter. The microscopic interpretation of this entropy remains on the other hand an opened problem, to which the Théorie of the cords however succeeded in bringing partial brief replies.

It was then shown that the black holes are objects with maximum entropy, i.e. the maximum entropy of an area of space delimited by a given surface is equal to that of the of the same black hole surfaces , . This report brought the physicists Gerald' T Hooft and then Leonard Susskind to propose in the same way a whole of ideas, called holographic Principe, based on the fact that the description of the surface of an area makes it possible to reconstitute all the relative information with its contents, that Hologramme code of the relative informations to a volume on a simple surface, thus making it possible to give an effect of relief starting from a surface.

The discovery of the entropy of the black holes thus allowed the development of an extremely major analogy between black holes and Thermodynamique, the Thermodynamique of the black holes, which could help in the comprehension of a theory of the quantum Gravité.

See also: Thermodynamic of the black holes

Evaporation and radiation of Hawking

See also: Evaporation of the black holes

In 1974, Stephen Hawking applied the Quantum theory of the fields to the Espace-temps curved general relativity, and discovered that as opposed to what predicted traditional mechanics, the black holes could indeed emit a radiation (near to a thermal radiation) now called Rayonnement of Hawking  : the black holes are thus not completely “black”.

The radiation of Hawking corresponds in fact to a spectrum of black Corps. One can thus associate with it the “Température” of the black hole, who is inversely proportional to his size. So more the black hole is important, plus his temperature is low. A black hole of the mass of the Planet Mercure would have a temperature equal to that of the radiation of cosmological diffuse Fond (about 2,73 Kelvin S). If the hole is more massive, it will be thus colder than the temperature of the bottom and will increase its energy more quickly than it will not lose of it via the radiation of Hawking, becoming thus even more cold. A stellar black hole thus has a temperature of a few microkelvins, which completely makes the detection direct of its evaporation inenvisageable. However, for less massive black holes, the temperature is higher, and the loss of associated energy enables him to see its mass varying on cosmological scales. Thus, a black hole of a few million tons will evaporate it in one duration lower than that of the age of the universe. Whereas the black hole evaporates, the black hole becomes smaller, therefore hotter. Certain astrophysicists proposed that complete evaporation black holes would produce a flash of gamma rays. This would be a signature of the existence of black holes of very low mass. They would be then paramount black holes. Current research explores this possibility with the data of the satellite European INTEGRAL.

Paradox of information

See also: Theorem of baldness

A question of still irresolute fundamental physics at the beginning of the 21e century is the famous Paradoxe of information. Indeed, because of the Théorème of baldness already quoted, it is not possible to determine a posteriori what entered the black hole. However, seen of an observer moved away, information never is completely destroyed since the matter falling into the black hole disappears only after an infinitely long time. Then, is the information which trained the black hole lost or pas ?

General considerations on what of the quantum Gravité should be a theory suggest that there can be only one finished and limited quantity entropy (i.e a maximum and finished quantity information) associated with space close to the horizon of the black hole. But the variation of the entropy of the horizon plus that of Hawking radiation is always sufficient to take into account all the entropy of the matter and energy falling into the black hole… But remain many questions. In particular at is the quantum level, the quantum state of the radiation of Hawking given in a single way by the history from what fell into the hole noir ? In the same way, the history from what fell is given in a single way by the quantum state of the black hole and of its radiation ? In other words, are the black holes, or are not, déterministes ? This property is of course preserved in general relativity as in traditional physics, but not in the quantum Mécanique.

For long years, Stephen Hawking maintained its position original of 1975 wanting that the radiation of Hawking is entirely thermal, and thus completely random, thus representing a new not-determinist information source. However, the 21 July 2004, it presented a new argument, going contrary to its first position , , . In its new calculations, the Entropie associated with a black hole would be indeed inaccessible to an external observer. Moreover in the absence of this information, it is impossible to connect in a univocal way information of the radiation of Hawking (contained in its internal correlations) at the initial state of the system. However, if the black hole evaporates completely, this univocal identification can be made and the Unitarité is preserved (the information is thus stored). It is not clear that the Scientific community specialized either absolutely convinced by the arguments presented by Hawking. But Hawking itself was sufficiently convinced to regulate the bet that it had made in 1997 with the physicist John Preskill of Caltech, thus causing an enormous interest of the media.

In July 2005, the advertisement of Hawking gave place to a publication in the review Physical Review and was discussed thereafter with the center of the scientific community without a consensus Net not emerging as for the validity from the approach suggested by Hawking , .

Black holes and holes of worm

See also: Hole of worm

General relativity indicates that there would exist configurations in which two black holes are connected one to the other. Such a configuration is usually called Trou of worm or more rarely bridge of Einstein-Rosen. Such configurations inspired much the authors of Science-fiction (see for example the references of the section Popular culture) because they propose a means of travelling very quickly at long distances, even to travel in time. In practice, such configurations, if they are authorized by general relativity, seem completely unrealizable in an astrophysical context, because no known process seems to allow the formation of such objects.

Popular culture

When one speaks about “popular culture” in connection with black hole, one often thinks of Science-fiction. One finds there, with the cinema or in the literary field, much of inspiration.

In films

  • '' The Black Hole '' (1979), of Gary Nelson, is a film of the studios Disney.
  • '' Event horizon '' (1997), of Paul W.S. Anderson.
  • '' Sphere '' (1998), of Barry Levinson.
  • '' The Void '' (2002), of Gilbert Mr. Shilton.
  • In the mythology of the Star Wars , Evona, one of the two suns of the system in which the people in the Hutt are originating was absorbed by a black hole.
  • In " the planet of the singes" the hero travels in time while passing in a black hole…

In the literature

In the televised series

  • Andromeda, the protagonist and his vessel (Andromeda) are grabbed by a black hole and there are prisoners in time during 300 years.
  • Babylon 5 , the space voyage is made possible by zones of singularity created artificially.
  • Stargate SG-1 , in episode 15 of the season 2, SG-10 on mission on P3W-451 is confronted with the appearance of a black hole.
  • Stargate SG-1 , in episode 6 of season 9, a planet crumbles in a black hole by the will of the Ori, in order to activate a giant door of stars.
  • Stargate SG-1 , the interplanetary vessels move quickly thanks to a “jump in the hyperspace”. This one is connected to the theory of the black holes (see graphic on the holes of worm).
  • Stargate SG-1 , in episode 3 of the season 10, SG-1 uses a black hole to block super-carries it of Oris.

In music

  • the song Cygnus X-1 of the album has Farewell to Kings (1977) by the group Rush
  • the song Black Holes of the album Great White North (1981) by Bob & Doug MacKenzie
  • the song Supermassive Black hole of the album Black Holes and Revelations (2006) by the group MUSE
  • the song Black Hole Sun of the album Superunknown (1994) by the group Soundgarden

In Cartoon

  • the Comics Warheads (published by Marvel the U.K.) described the adventures of mercenaries serving black holes to move through space.
  • In the Cartoon Lobo/The Mask (published by cd. Comics and Dark Horse), the adventure brings together the 2 heroes in a hunting against a monster having destroyed several galaxies. One finds there a bar improvised on a piece of meteorite floating close to a Black hole. Lobo, being seized the Mask, is transported in the past thanks to a Trou of worm. It becomes thus the monster with the continuation of which it had launched out.

In the field of the Video game

  • Outcast where the Earth is threatened to be absorbed by a black hole, after an accident.
  • Star Fox or the Arwing can travel of part of space to another thanks to a black hole.
  • Freelancer in which the player travels of a system to another while passing by " brêches of jump " or of the " doors of jump " being connected with holes of worm.

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