Black hole

First real image in the history of a supermassive black hole located in the center of the galaxy M87, presented on April 10, 2019 by the international consortium Telescope of the event horizon.

A black hole is a finite region of space whose interior has a mass concentration high enough to generate a gravitational field such that no particle –not even light– can escape from it (in 2021 light reflections were observed in the farthest part of the black hole). Black holes may be capable of emitting a type of radiation, Hawking radiation, conjectured by Stephen Hawking in the 1970s. The radiation emitted by black holes such as Cygnus X-1 does not come from the black hole itself but from its disk. of accretion.

A black hole's gravity, or "space-time warp," causes a singularity enclosed by a closed surface, called an event horizon. This is predicted by the Einstein field equations. The event horizon separates the region of the black hole from the rest of the universe, and once inside it, no type of particle, material or electromagnetic, can leave, not even photons. This curvature is studied by general relativity, which predicted the existence of black holes and was its first indication. In the 1970s, Stephen Hawking, Ellis, and Penrose proved several important theorems about the occurrence and geometry of black holes. Previously, in 1963, Roy Kerr had shown that in four-dimensional spacetime all black holes must have a quasispherical geometry determined by three parameters: its mass M, its total electric charge e and its angular momentum L.

It is conjectured that at the center of most galaxies, including the Milky Way, are supermassive black holes.

On February 11, 2016, the LIGO, Virgo, and GEO600 collaborations announced the first detection of gravitational waves, produced by the merger of two black holes at about 410 million parsecs, megaparsecs, or Mpc, that is, about 1337 million light-years, mega-light-years or Mal from Earth. The observations demonstrated the existence of a binary system of stellar-mass black holes and the first observation of a merger of two black holes from a binary system. Previously, the existence of black holes was supported by astronomical observations indirectly, through the emission of X-rays by binary stars and active galaxies.

A black hole's gravity can pull in gas around it, which swirls and heats up to 12,000,000 °C, that is, 2000 times higher temperature than the surface of the Sun.

On April 10, 2019, the international Event Horizon Telescope consortium released the first image ever captured of a supermassive black hole located at the center of the galaxy M87.

Formation process

A proton and an electron are annihilated by emitting a neutron and a neutrino-electron

Black holes form in a process of gravitational collapse that was widely studied in the mid-XX century by various scientists, particularly Robert Oppenheimer, Roger Penrose and Stephen Hawking, among others. Hawking, in his informative book History of Time: From the Big Bang to Black Holes (1988), reviews some of the well-established facts about the formation of black holes.

This process begins after "death" of a red giant (star from 10 to 25 or more times the mass of the Sun), meaning "death" the total extinction of its energy. After several billion years of life, the gravitational force of said star begins to exert force on itself, causing a mass concentrated in a small volume, becoming a white dwarf. At this point, this process can continue until the collapse of said star due to the gravitational self-attraction that ends up turning this white dwarf into a black hole. This process ends up gathering a force of attraction so strong that it traps even light in it.

In simpler words, a black hole is the final result of the action of extreme gravity pushed to the limit possible. The same gravity that keeps the star stable begins to compress it to the point that the atoms begin to crush. The orbiting electrons get closer and closer to the atomic nucleus and eventually fuse with the protons, forming more neutrons in the process:

p++e− − → → n0+.. e{displaystyle p^{+}+e^{-}to n^{0}+{nu }_{e}}}

This process would involve the emission of a large number of neutrinos. The end result is a neutron star. At this point, depending on the mass of the star, the neutron plasma triggers an irreversible chain reaction, gravity increases enormously as the distance that originally existed between the atoms decreases. The neutron particles implode, squashing each other further, resulting in a black hole, which is a region of space-time bounded by the so-called event horizon. At present it is still unknown what happens to the matter that falls into the black hole crossing this limit, because for small scales only a quantum theory of gravity could adequately explain them, but there is no formulation completely consistent with such a theory.

History

M87 images made by Event Horizon Telescope on April 11, 2017 prior to your 2019 presentation

The concept of a body so dense that not even light can escape it was described in a 1783 paper submitted to the Royal Society by the English geologist and clergyman John Michell. By then Newton's theory of gravitation and the concept of escape velocity were well known. Michell calculated that a body with a density 500 times greater than that of the Sun, but with its same radius, would have, at its surface, an escape velocity equal to that of light and would be invisible. In 1796, the French mathematician Pierre-Simon Laplace explained the same idea in the first two editions of his book Exposition du Systeme du Monde, although, as the idea that light was a wave without mass, in the 19th century was discarded in later editions.

In 1915, Einstein developed general relativity and showed that light was influenced by gravitational interaction. A few months later, Karl Schwarzschild found a solution to Einstein's equations, where a heavy body would absorb light. It is now known that the Schwarzschild radius is the radius of the event horizon of a non-rotating black hole, but this was not well understood at the time. Schwarzschild himself thought that it was nothing more than a mathematical solution, not a physics. In 1930, Subrahmanyan Chandrasekhar showed that a body with a critical mass (now known as the Chandrasekhar limit) and emitting no radiation would collapse under its own gravity because there would be nothing known to slow it down (for such a mass the force of attraction gravitational force would be greater than that given by the Pauli exclusion principle). However, Eddington objected to the idea that the star would reach zero size, implying a singularity stripped of matter, and that there would have to be something to inevitably stop it from collapsing, a line taken by most scientists.

In 1939, Robert Oppenheimer predicted that a massive star could undergo gravitational collapse and therefore black holes could be formed in nature. This theory did not receive much attention until the 1960s, because after World War II there was more interest in what was happening on an atomic scale.

In 1967, Stephen Hawking and Roger Penrose proved that black holes are solutions to Einstein's equations and that in certain cases a black hole could not be prevented from creating from a collapse. The idea of a black hole gained strength with the scientific and experimental advances that led to the discovery of pulsars. Shortly after, in 1969, John Wheeler coined the term "black hole" during a meeting of cosmologists in New York, to designate what was previously called a "star in complete gravitational collapse".

On April 10, 2019, the international Event Horizon Telescope consortium released the first image ever captured of a supermassive black hole located at the center of the galaxy M87. In turn, the announcement of another real image of a black hole in Sagittarius A* was expected; however, they clarified that it had not been obtained because the source was very variable during the observation periods, being resolved in the future.

Theoretical classification

Simulation of gravitational lens by a black hole that distorts the light from a galaxy in the background

Artistic representation of a black hole

Depending on their origin, theoretically there can be at least two kinds of black holes:

According to the mass

• Supermassive black holes: with several million solar masses. They would be found in the center of several galaxies, for example in ours, calling ''Satigario A'. They form in the same process that gives rise to the spherical components of the galaxies.
• Intermediate black holes: (IMBH) is a kind of black hole with a mass in the range of 100 to a million solar masses, significantly more than stellar black holes, but less than supermassive black holes.
• Black star mass holes: They form when a star of more than 30-70 solar masses becomes supernova and implosion. They have more than three solar masses. Its core concentrates on a very small volume that is increasingly shrinking. This is the type of black holes first postulated within the theory of general relativity.
• Black micro holes: They are hypothetical objects, something smaller than star objects. If they are small enough, they can evaporate in a relatively short period by Hawking radiation. This type of physical entities is postulated in some approaches of quantum gravity, but cannot be generated by a conventional process of gravitational collapse, which requires masses superior to that of the Sun.

According to its charge and angular momentum

There is a theorem about the properties of black holes that are usually stated saying that "a black hole has no hair" (in English) No-hair theorem); theorem states that any object that suffers a gravitational collapse reaches a stationary state as a black hole described only by three parameters: its mass M{displaystyle M}Your burden Q{displaystyle Q} and its angular moment J{displaystyle J}. Considering these last two physical properties, we have the following classification for the final state of a black hole:

• The simplest black hole possible is the black hole of Schwarzschild, which does not rotate or has load.
• If it does not rotate but has electric charge, it has the so-called black hole of Reissner-Nordstrøm.
• A black hole in rotation and without load is a black Kerr hole.
• If it has rotation and load, we talk about a black Kerr-Newman hole.

The four previous solutions can be systematized as follows:

Theoretical description

Observable zones

Artistic representation of a black hole with a companion star moving in orbit around, exceeding its Roche limit. The material that falls forms a growing disc, with some material expelled in highly energetic collided polar jets.

In the vicinity of a black hole, an accretion disk is usually formed, made up of matter with angular momentum, electric charge and mass, which is affected by its enormous gravitational attraction, causing it to inexorably cross the event horizon and therefore increase the size of the hole.

As for the light that passes through the area of the disk, it is also affected, as predicted by the theory of Relativity. The effect is visible from Earth due to the momentary deviation that it produces in known stellar positions, when the beams of light coming from them pass through said area.

Until today it is impossible to describe what happens inside a black hole; its effects on matter and energy can only be imagined, assumed, and observed in the outer zones and near the event horizon and the ergosphere.

One of the most controversial effects implied by the existence of a black hole is its apparent ability to decrease the entropy of the Universe, which would violate the fundamentals of thermodynamics, since all matter and electromagnetic energy that crosses said event horizon, have an associated level of entropy. Stephen Hawking proposes in one of his books that the only way for entropy not to increase would be for the information of everything that crosses the event horizon to continue to exist in some way.

Another of the implications of a supermassive black hole would be the probability that it would be able to generate its complete collapse, becoming a singularity naked of matter.

Entropy in Black Holes

S=14c3kG A{displaystyle S={frac {1}{4}}{frac {c^{3k}{Ghbar }A}

The Bekenstein-Hawking formula for the entropy of a black hole

According to Stephen Hawking, black holes merge the second law of thermodynamics, giving rise to speculation about space-time travel and wormholes. The issue is being reviewed; Hawking retracted his initial theory and admitted that the entropy of matter is conserved inside a black hole (see external link). According to Hawking, despite the physical impossibility of escape from a black hole, they can end up evaporating by the so-called Hawking radiation, a source of X-rays that escapes the event horizon.

The hypothesis that black holes contain an entropy and that, moreover, this is finite, requires to be consistent that such holes emit thermal radiation, which at first seems incredible. The explanation is that the emitted radiation escapes from the black hole, from a region of which the outside observer knows only its mass, its angular momentum and its electric charge. That means that all combinations or configurations of radiation from particles that have the same energy, angular momentum, and electric charge are equally likely. There are many possibilities of entities, even the most exotic if you like, that can be emitted by a black hole, but this corresponds to a small number of configurations. By far the largest number of configurations corresponds to an emission with a spectrum that is near thermal.

Physicists such as Jacob D. Bekenstein have linked black holes and their entropy to information theory. Bekenstein's work on information theory and black holes suggested that the second law would still hold if generalized entropy (S_gen) were introduced.) that would add to the conventional entropy (S_conv), the entropy attributable to black holes that depends on the total area (A) of holes blacks in the universe Specifically, this generalized entropy must be defined as:

Sgen=Scornv+c3k4G A{displaystyle S_{gen}=S_{conv}+{frac {c^{3k}{4Ghbar }}A}

Where, k It's Boltzmann's constant, c is the speed of light, G is the constant universal gravitation and {displaystyle hbar } is the constant of rationalized Planck, and A the area of the event horizon.

Definition of a black hole

Although there are intuitive explanations for the behavior of a black hole, in theoretical cosmology there is no simple definition of what constitutes a black hole, and all theorists work with sophisticated topological definitions of what constitutes a black hole. In fact, in a compact space-time there is no adequate and general way to define what conditions a region must meet to be considered a black hole. In non-compact space-time some technical conditions are required to decide whether a region is a black hole, so in an asymptotically flat and predictable space-time (containing a Cauchy hypersurface that satisfies certain requirements), it is said that there is a black hole region if the causal past of the light-like hypersurface located at future infinity does not contain all of spacetime (that means that said hypersurface is unreachable from some spacetime points, precisely those contained in the area of black hole). The causal past boundary of the future light-like hypersurface is the event horizon.

Theoretical impossibility of black holes?

Black holes contain all the mass of the star in a mathematical point, which is what is known as a singularity. Einstein never accepted that, but thought that the mass should occupy a finite region even if it was small and for this reason he opposed the existence of black holes, which nobody called that at the time (they were known as "Schwarzschild singularities"). The name black hole was proposed by the American physicist Wheeler, 10 years after Einstein's death.

There are strong mathematical results under which a metric theory of gravitation (such as general relativity) predicts the formation of black holes. These results are known as singularity theorems that predict the occurrence of space-time singularities (and if the cosmic censorship hypothesis is accepted, therefore the formation of black holes). Einstein's field equations for general relativity admit situations for which the conditions for the occurrence of singularities are fulfilled and therefore, the singularity theorems show that black holes are possible within general relativity. However, some alternative metric theories such as the relativistic theory of gravitation, very similar to general relativity in almost all respects and which also explains the observed events in the solar system and the expansion of the universe, use slightly different field equations where It always holds that in the local absence of matter and by virtue of the causality conditions of the theory, for any isotropic vector field (light-type vectors) defined over space-time the inequality holds:

Rμ μ .. vμ μ v.. ≤ ≤ 0{displaystyle R_{mu nu }v^{mu }v^{nu }leq 0}

This condition implies that the conditions of the previously mentioned theorems will not be fulfilled and, therefore, they cannot be applied to predict the existence of singularities and therefore black holes.

Since the experimental data do not allow discerning which of the two theories (Einstein's general relativity or Logunov's relativistic gravitational theory) is the correct one, since both coincide for the majority of well-proven observational facts, it is not it can be taken for granted that black holes are a necessary consequence of gravitation.

Absence of central singularity according to other theories

On December 10, 2018, Abhay Ashtekar, Javier Olmedo and Parampreet Singh published a scientific paper in the field of loop theory of gravity, proving the absence of central singularity inside the black hole, without geometrically specifying the future of matter at this point, while the Janus model proposes an explanation.

This new study gives the same conclusions as those obtained by previous work based on general relativity.

Black holes in current physics

Physical phenomena are explained by two theories that are somewhat opposed and based on incompatible principles: quantum mechanics, which explains the nature of "the very small", where chaos and statistics predominate and admits cases of temporal evolution not deterministic, and general relativity, which explains the nature of "the very heavy" and which states that at all times it is possible to know exactly where a body is, this theory being totally deterministic. Both theories are experimentally confirmed but, when trying to explain the nature of a black hole, it is necessary to discern whether quantum is applied because it is something very small or relativity because it is something so heavy. It is clear that until more advanced physics is available, it will not be possible to really explain the nature of this phenomenon.

Recent Discoveries

In 1995, a team of UCLA researchers led by Andrea Ghez using computer simulations demonstrated the possibility of the existence of supermassive black holes in the nuclei of galaxies. After these calculations using the adaptive optics system, it was verified that something distorted the light rays emitted from the center of our galaxy (the Milky Way). Such deformation is due to an invisible supermassive black hole that has been named Sgr.A (or Sagittarius A). In 2007-2008, a series of interferometry experiments from radio telescope measurements began to measure the size of the supermassive black hole at the center of the Milky Way, which is estimated to have a mass 4.5 million times greater than that of the Sun. and a distance of 26,000 light years (about 255,000 trillion km from Earth). The supermassive black hole at the center of our galaxy would currently be inactive as it has consumed much of the baryonic matter, which is found in the area of its immediate gravitational field and emits large amounts of radiation.

For her part, the astrophysicist Feryal Özel has explained some probable characteristics around a black hole: anything, including empty space, that enters the tidal force caused by a black hole would be accelerated to extreme speed as in a vortex and all the time within the area of attraction of a black hole would be heading towards the same black hole.

At present it is considered that, despite the destructive perspective that black holes have, by condensing matter around themselves, they serve in part to the constitution of galaxies and the formation of new stars.

In June 2004 astronomers discovered a supermassive black hole, Q0906+6930, at the center of a distant galaxy some 12.7 billion light-years away. This observation indicated a rapid creation of supermassive black holes in the early Universe.

The formation of micro black holes in particle accelerators has been reported, but not confirmed. For now, there are no observed candidates for primordial black holes.

On February 11, 2016, the LIGO collaboration announced the first direct observation of gravitational waves, generated by the merger of two stellar-mass black holes. What was also the first direct observation of two black holes merging.

On April 10, 2019, the Event Horizon Telescope (EHT) photographed for the first time a black hole, the supermassive black hole of between 6,400 and 6,600 solar masses located at the center of the galaxy M87. This is the first direct evidence of the existence of these bodies and may open the door to future research on a theory of everything that joins Einstein's theory of Relativity and quantum mechanics.

On May 5, 2022, the US space agency NASA released the "sound" of black holes, the audio is considered theoretical since it was produced through a computer process that sounds the electromagnetic waves received in a radio telescope.

The eldest

Leaving aside the supermassive black holes that are usually in the nuclei of galaxies and whose masses are millions of times our Sun, the largest stellar-mass black hole known to date, was discovered in 2007 and was called IC 10 X-1. It is in the dwarf galaxy IC 10 located in the constellation Cassiopeia, at a distance of 1.8 million light-years (17 trillion kilometers) from Earth, with a mass between 24 and 33 times that of our Sun.

Subsequently, in April 2008, the journal Nature published a study carried out at the University of Turku (Finland). According to this study, a team of scientists led by Mauri Valtonen discovered a binary system, a blazar, called OJ 287, in the constellation of Cancer. Such a system appears to be made up of a smaller black hole orbiting a larger one, with the mass of the larger one being 18 billion times that of our Sun, making it the largest known black hole. It is assumed that in each rotation interval the smaller black hole, which has a mass of 100 million suns, hits the ergosphere of the larger one twice, generating a quasar. Located 3.5 billion light-years from Earth, it is relatively close to Earth for a quasar.

The minor

Not counting the possible microblack holes that are almost always ephemeral when produced at subatomic scales; macroscopically in April 2008 the team coordinated by Nikolai Saposhnikov and Lev Titarchuk has identified the smallest of the black holes known to date; It has been called J1650, it is located in the constellation Ara (or Altar) of the Milky Way (the same galaxy of which the Earth is a part). J 1650 has a mass equivalent to 3.8 suns and only 24 km in diameter, it would have been formed by the collapse of a star; such dimensions were predicted by Einstein's equations. It is considered that they are practically the minimum dimensions that a black hole can have since a star that collapsed and produced a phenomenon of lower mass would become a neutron star. It is considered that many more black holes of similar dimensions may exist.

Plasma Jets

In April 2008, the journal Nature published a study conducted at Boston University led by Alan Marscher in which he explains that collimated plasma jets originate from magnetic fields located near the edge of black holes. In punctual zones of such magnetic fields the plasma jets are oriented and accelerated to velocities close to c (speed of light), such a process is comparable to the acceleration of particles to create a jet stream (jet) in a reactor. When the plasma jets originated by a black hole are observable from Earth, such a type of black hole falls into the category of blazar.

The fact that a black hole "emits" radiation seems to be a contradiction, however this can be explained: any object (suppose a star) that is trapped by the gravitation of a black hole, before being completely "swallowed", before passing behind the event horizon, it is pushed so strongly by the tidal forces of the black hole in the ergosphere zone that a small part of its matter shoots out at speeds close to the speed of light (as when an orange is squeezed hard).: part of the material in the orange is ejected in the form of jets of juice, in the case of objects trapped by a black hole, part of its mass is centrifugally ejected in the form of radiation outside the gravitational field of the singularity).

Star formation by the influx of black holes

New stars could form from elliptical disks around black holes; such elliptical disks are produced by ancient gas clouds previously disintegrated by the same black holes; stars produced by condensation or accretion from such elliptical disks appear to have highly elliptical orbits around supermassive black holes.

Hawking Radiation

Until the early 1970s it was thought that black holes did not directly emit any type of matter, and their ultimate destiny was to continue growing by accreting more and more matter. However, a consideration of quantum effects at the event horizon of a hole led Hawking to discover a physical process by which the hole could emit radiation. According to the uncertainty principle of quantum mechanics, there is the possibility that short-lived particle-antiparticle pairs will form on the horizon, given that the probability that one of the elements of the pair will fall into the hole irreversibly and the other member of the escape pair, the conservation principle requires that the hole decrease in mass to compensate for the energy that the escaping pair takes from the vicinity of the event horizon. Note that in this process the pair is formed strictly on the outside of the black hole, so it does not contradict the fact that no material particle can leave the interior. However, there is a net effect of energy transfer from the black hole to its surroundings, which is Hawking radiation, the production of which does not violate any physical principle.

Appearance and optics

Infographic that explains in detail the appearance of a black hole. The different parts of the visible image of a black hole and its acreation disc are explained. The lateral and upper schematics show the trajectory of light rays deflected by gravity from each part of the black hole to the observer.

Linguistic note

In countries like Spain or Argentina, where a difference is made between a hole (concavity) and a hole (opening) the term “black hole” should be used. In countries like Mexico or Chile where hole and hole are synonymous, "black hole" and "black hole" are also synonymous.

See also

References

Bibliography

• Hawking, S. W. & Ellis, G. F. R.: The Large Scale Structure of Space-time, Cambridge, Cambridge University Press, 1973, ISBN 0-521-09906-4.
• Logunov, A.A. 1998, Theory of Relativity and Gravitation Course, Lomonósov State University, Moscow, ISBN 5-88417-162-5.
• Wald, R. M.: General the Relativity(Chapter 12 "Black Holes"), Chicago, The University of Chicago Press, 1984, ISBN 0-226-87032-4.

External links

• Wikimedia Commons hosts a multimedia gallery on Black hole.
• Celestia Project Educational video to understand black holes (video No. 28).
• Hundreds of black holes ready to devour everything in their way in our galaxy
• Finnish scientists managed to calculate the mass of the greatest black hole known in space
• Video that simulates the fall in a black hole (in English)
• Video of a conference on black holes by Enrique Fernández Borja
• Conference video Black holes and the nature of space time by Juan Maldacena