Lost in Space is an American science fiction television series, created and produced by Irwin Allen, which originally aired between 1965 and 1968. The series was inspired by the 1812 novel The Swiss Family Robinson and a comic book published by Gold Key Comics titled Space Family Robinson. The series follows the adventures of the Robinsons, a pioneering family of space colonists who struggle. The next generation of Galaxy has arrived. Discover Samsung Galaxy S10e, S10 and S10+'s cutting-edge performance, infinity display, all-day battery, and more.

.A black hole is a region of where is so strong that nothing—no or even such as —can escape from it. The theory of predicts that a sufficiently compact can deform to form a black hole.

The boundary of the region from which no escape is possible is called the. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, it has no locally detectable features. In many ways, a black hole acts like an ideal, as it reflects no light.

Moreover, predicts that event horizons emit, with as a of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a for, making it essentially impossible to observe.Objects whose are too strong for light to escape were first considered in the 18th century.

The first modern solution of general relativity that would characterize a black hole was found by in 1916, although its interpretation as a region of space from which nothing can escape was first published by in 1958. Black holes were long considered a mathematical curiosity; it was during the 1960s that theoretical work showed they were a generic prediction of general relativity.

The discovery of by in 1967 sparked interest in compact objects as a possible astrophysical reality.Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, of millions of may form. There is consensus that supermassive black holes exist in the centers of most.The presence of a black hole can be inferred through its interaction with other and with such as visible light. Matter that falls onto a black hole can form an external heated by friction, forming some of the. Stars passing too close to a supermassive black hole can be shred into streamers that shine very brightly before being 'swallowed.' If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location.

Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in, and established that the radio source known as, at the core of the galaxy, contains a supermassive black hole of about 4.3 million.On 11 February 2016, the collaboration of, which also represented the first observation of a black hole merger. As of December 2018, eleven have been observed that originated from ten merging black holes (along with one binary ).

On 10 April 2019, the first ever direct image of a black hole and its vicinity was published, following observations made by the in 2017 of the black hole in 's. Simulated view of a black hole in front of the. Note the effect, which produces two enlarged but highly distorted views of the Cloud. Across the top, the disk appears distorted into an arc.The idea of a body so massive that even light could not escape was briefly proposed by astronomical pioneer and English clergyman in a letter published in November 1784. Michell's simplistic calculations assumed such a body might have the same density as the Sun, and concluded that such a body would form when a star's diameter exceeds the Sun's by a factor of 500, and the surface exceeds the usual speed of light. Michell correctly noted that such supermassive but non-radiating bodies might be detectable through their gravitational effects on nearby visible bodies.

Scholars of the time were initially excited by the proposal that giant but invisible stars might be hiding in plain view, but enthusiasm dampened when the wavelike nature of light became apparent in the early nineteenth century.If light were a wave rather than a ', it is unclear what, if any, influence gravity would have on escaping light waves. Modern physics discredits Michell's notion of a light ray shooting directly from the surface of a supermassive star, being slowed down by the star's gravity, stopping, and then free-falling back to the star's surface.

General relativity. See also:In 1915, developed his theory of, having earlier shown that gravity does influence light's motion. Only a few months later, found a to the, which describes the of a and a spherical mass. A few months after Schwarzschild, Johannes Droste, a student of, independently gave the same solution for the point mass and wrote more extensively about its properties. This solution had a peculiar behaviour at what is now called the, where it became, meaning that some of the terms in the Einstein equations became infinite. The nature of this surface was not quite understood at the time. In 1924, showed that the singularity disappeared after a change of coordinates (see ), although it took until 1933 for to realize that this meant the singularity at the Schwarzschild radius was a non-physical.

Arthur Eddington did however comment on the possibility of a star with mass compressed to the Schwarzschild radius in a 1926 book, noting that Einstein's theory allows us to rule out overly large densities for visible stars like Betelgeuse because 'a star of 250 million km radius could not possibly have so high a density as the sun. Firstly, the force of gravitation would be so great that light would be unable to escape from it, the rays falling back to the star like a stone to the earth. Secondly, the red shift of the spectral lines would be so great that the spectrum would be shifted out of existence. Thirdly, the mass would produce so much curvature of the space-time metric that space would close up around the star, leaving us outside (i.e., nowhere).' In 1931, calculated, using special relativity, that a non-rotating body of above a certain limiting mass (now called the at 1.4 M ☉) has no stable solutions. His arguments were opposed by many of his contemporaries like Eddington and, who argued that some yet unknown mechanism would stop the collapse. They were partly correct: a slightly more massive than the Chandrasekhar limit will collapse into a, which is itself stable.

But in 1939, and others predicted that neutron stars above another limit (the ) 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. Their original calculations, based on the, gave it as 0.7 M ☉; subsequent consideration of strong force-mediated neutron-neutron repulsion raised the estimate to approximately 1.5 M ☉ to 3.0 M ☉. Observations of the neutron star merger, which is thought to have generated a black hole shortly afterward, have refined the TOV limit estimate to 2.17 M ☉.Oppenheimer and his co-authors interpreted the singularity at the boundary of the Schwarzschild radius as indicating that this was the boundary of a bubble in which time stopped. This is a valid point of view for external observers, but not for infalling observers. Because of this property, the collapsed stars were called 'frozen stars', because an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it to the Schwarzschild radius. Golden ageIn 1958, identified the Schwarzschild surface as an, 'a perfect unidirectional membrane: causal influences can cross it in only one direction'. This did not strictly contradict Oppenheimer's results, but extended them to include the point of view of infalling observers.

Extended the Schwarzschild solution for the future of observers falling into a black hole. A had already been found by, who was urged to publish it.These results came at the beginning of the, which was marked by general relativity and black holes becoming mainstream subjects of research. This process was helped by the discovery of by in 1967, which, by 1969, were shown to be rapidly rotating.

Until that time, neutron stars, like black holes, were regarded as just theoretical curiosities; but the discovery of pulsars showed their physical relevance and spurred a further interest in all types of compact objects that might be formed by gravitational collapse. In this period more general black hole solutions were found. In 1963, found for a. Two years later, found the solution for a black hole that is both rotating. Through the work of, and David Robinson the emerged, stating that a stationary black hole solution is completely described by the three parameters of the:, and.At first, it was suspected that the strange features of the black hole solutions were pathological artifacts from the symmetry conditions imposed, and that the singularities would not appear in generic situations.

This view was held in particular by, and, who tried to prove that no singularities appear in generic solutions. However, in the late 1960s and used global techniques to prove that singularities appear generically.Work by, Carter, and Hawking in the early 1970s led to the formulation of. These laws describe the behaviour of a black hole in close analogy to the by relating mass to energy, area to, and to.

The analogy was completed when Hawking, in 1974, showed that implies that black holes should radiate like a with a temperature proportional to the surface gravity of the black hole, predicting the effect now known as. EtymologyJohn Michell used the term 'dark star', and in the early 20th century, physicists used the term 'gravitationally collapsed object'.

Simple illustration of a non-spinning black holeThe postulates that, once it achieves a stable condition after formation, a black hole has only three independent physical properties:, and; the black hole is otherwise featureless. If the conjecture is true, any two black holes that share the same values for these properties, or parameters, are indistinguishable from one another.

The degree to which the conjecture is true for real black holes under the laws of modern physics, is currently an unsolved problem.These properties are special because they are visible from outside a black hole. For example, a charged black hole repels other like charges just like any other charged object. Similarly, the total mass inside a sphere containing a black hole can be found by using the gravitational analog of, the, far away from the black hole. Likewise, the angular momentum can be measured from far away using by the.

When an object falls into a black hole, any about the shape of the object or distribution of charge on it is evenly distributed along the horizon of the black hole, and is lost to outside observers. The behavior of the horizon in this situation is a that is closely analogous to that of a conductive stretchy membrane with friction and —the. This is different from other such as electromagnetism, which do not have any friction or resistivity at the microscopic level, because they are. Because a black hole eventually achieves a stable state with only three parameters, there is no way to avoid losing information about the initial conditions: the gravitational and electric fields of a black hole give very little information about what went in. The information that is lost includes every quantity that cannot be measured far away from the black hole horizon, including such as the total. This behavior is so puzzling that it has been called the.

Inside of the event horizon, all paths bring the particle closer to the center of the black hole. It is no longer possible for the particle to escape.The defining feature of a black hole is the appearance of an event horizon—a boundary in through which matter and light can pass only inward towards the mass of the black hole. Nothing, not even light, can escape from inside the event horizon. The event horizon is referred to as such because if an event occurs within the boundary, information from that event cannot reach an outside observer, making it impossible to determine whether such an event occurred.As predicted by general relativity, the presence of a mass deforms spacetime in such a way that the paths taken by particles bend towards the mass.

At the event horizon of a black hole, this deformation becomes so strong that there are no paths that lead away from the black hole.To a distant observer, clocks near a black hole would appear to tick more slowly than those further away from the black hole. Due to this effect, known as, an object falling into a black hole appears to slow as it approaches the event horizon, taking an infinite time to reach it. At the same time, all processes on this object slow down, from the view point of a fixed outside observer, causing any light emitted by the object to appear redder and dimmer, an effect known as.

Eventually, the falling object fades away until it can no longer be seen. Typically this process happens very rapidly with an object disappearing from view within less than a second.On the other hand, indestructible observers falling into a black hole do not notice any of these effects as they cross the event horizon. According to their own clocks, which appear to them to tick normally, they cross the event horizon after a finite time without noting any singular behaviour; in classical general relativity, it is impossible to determine the location of the event horizon from local observations, due to Einstein's.The of the event horizon of a black hole at equilibrium is always spherical.

For non-rotating (static) black holes the geometry of the event horizon is precisely spherical, while for rotating black holes the event horizon is oblate. Main article:The photon sphere is a spherical boundary of zero thickness in which that move on to that sphere would be trapped in a circular orbit about the black hole. For non-rotating black holes, the photon sphere has a radius 1.5 times the Schwarzschild radius. Their orbits would be, hence any small perturbation, such as a particle of infalling matter, would cause an instability that would grow over time, either setting the photon on an outward trajectory causing it to escape the black hole, or on an inward spiral where it would eventually cross the event horizon.While light can still escape from the photon sphere, any light that crosses the photon sphere on an inbound trajectory will be captured by the black hole. Hence any light that reaches an outside observer from the photon sphere must have been emitted by objects between the photon sphere and the event horizon.

The ergosphere is a pumpkin-shaped region outside of the event horizon, where objects cannot remain stationary.Rotating black holes are surrounded by a region of spacetime in which it is impossible to stand still, called the ergosphere. This is the result of a process known as; general relativity predicts that any rotating mass will tend to slightly 'drag' along the spacetime immediately surrounding it. Any object near the rotating mass will tend to start moving in the direction of rotation. For a rotating black hole, this effect is so strong near the event horizon that an object would have to move faster than the speed of light in the opposite direction to just stand still.The ergosphere of a black hole is a volume whose inner boundary is the black hole's event horizon and a pumpkin-shaped outer boundary, which coincides with the event horizon at the poles but noticeably wider around the equator. The outer boundary is sometimes called the ergosurface.Objects and radiation can escape normally from the ergosphere.

Through the, objects can emerge from the ergosphere with more energy than they entered. This energy is taken from the rotational energy of the black hole causing the latter to slow. A variation of the Penrose process in the presence of strong magnetic fields, the is considered a likely mechanism for the enormous luminosity and relativistic jets of and other.Innermost stable circular orbit (ISCO). Simulation of two black holes collidingPenrose demonstrated that once an event horizon forms, general relativity without quantum mechanics requires that a singularity will form within. Shortly afterwards, Hawking showed that many cosmological solutions that describe the have singularities without or other (see '). The, the, and the laws of showed that the physical properties of black holes were simple and comprehensible, making them respectable subjects for research.

Conventional black holes are formed by of heavy objects such as stars, but they can also in theory be formed by other processes. Gravitational collapse.

Main article:Gravitational collapse occurs when an object's internal is insufficient to resist the object's own gravity. For stars this usually occurs either because a star has too little 'fuel' left to maintain its temperature through, or because a star that would have been stable receives extra matter in a way that does not raise its core temperature. In either case the star's temperature is no longer high enough to prevent it from collapsing under its own weight.The collapse may be stopped by the of the star's constituents, allowing the condensation of matter into an exotic.

The result is one of the various types of. Which type forms depends on the mass of the remnant of the original star left after the outer layers have been blown away. Such explosions and pulsations lead to. This mass can be substantially less than the original star. Remnants exceeding 5 M ☉ are produced by stars that were over 20 M ☉ before the collapse.If the mass of the remnant exceeds about 3–4 M ☉ (the ), either because the original star was very heavy or because the remnant collected additional mass through accretion of matter, even the degeneracy pressure of is insufficient to stop the collapse. No known mechanism (except possibly quark degeneracy pressure, see ) is powerful enough to stop the implosion and the object will inevitably collapse to form a black hole. Artist's impression of supermassive black hole seedThe gravitational collapse of heavy stars is assumed to be responsible for the formation of.

In the early universe may have resulted in very massive stars, which upon their collapse would have produced black holes of up to 10 3 M ☉. These black holes could be the seeds of the supermassive black holes found in the centers of most galaxies.

It has further been suggested that supermassive black holes with typical masses of 10 5 M ☉ could have formed from the direct collapse of gas clouds in the young universe. Some candidates for such objects have been found in observations of the young universe.While most of the energy released during gravitational collapse is emitted very quickly, an outside observer does not actually see the end of this process. Even though the collapse takes a finite amount of time from the of infalling matter, a distant observer would see the infalling material slow and halt just above the event horizon, due to.

Light from the collapsing material takes longer and longer to reach the observer, with the light emitted just before the event horizon forms delayed an infinite amount of time. Thus the external observer never sees the formation of the event horizon; instead, the collapsing material seems to become dimmer and increasingly red-shifted, eventually fading away. Primordial black holes and the Big BangGravitational collapse requires great density.

In the current epoch of the universe these high densities are found only in stars, but in the early universe shortly after the densities were much greater, possibly allowing for the creation of black holes. High density alone is not enough to allow black hole formation since a uniform mass distribution will not allow the mass to bunch up. In order for to have formed in such a dense medium, there must have been initial density perturbations that could then grow under their own gravity. Different models for the early universe vary widely in their predictions of the scale of these fluctuations. Various models predict the creation of primordial black holes ranging in size from a to hundreds of thousands of solar masses.Despite the early universe being extremely —far denser than is usually required to form a black hole—it did not re-collapse into a black hole during the Big Bang.

Models for of objects of relatively constant size, such as, do not necessarily apply in the same way to rapidly expanding space such as the Big Bang. High-energy collisions. Simulated event in the CMS detector: a collision in which a micro black hole may be createdGravitational collapse is not the only process that could create black holes. In principle, black holes could be formed in collisions that achieve sufficient density.

As of 2002, no such events have been detected, either directly or indirectly as a deficiency of the mass balance in experiments. This suggests that there must be a lower limit for the mass of black holes. Theoretically, this boundary is expected to lie around the ( m P= √ / ≈ 1.2 ×10 19 ≈ 2.2 ×10 −8 kg), where quantum effects are expected to invalidate the predictions of general relativity. This would put the creation of black holes firmly out of reach of any high-energy process occurring on or near the Earth.

However, certain developments in quantum gravity suggest that the Planck mass could be much lower: some scenarios for example put the boundary as low as 1 TeV/ c 2. This would make it conceivable for to be created in the high-energy collisions that occur when hit the Earth's atmosphere, or possibly in the at. These theories are very speculative, and the creation of black holes in these processes is deemed unlikely by many specialists. Even if micro black holes could be formed, it is expected that they would in about 10 −25 seconds, posing no threat to the Earth.

GrowthOnce a black hole has formed, it can continue to grow by absorbing additional. Any black hole will continually absorb gas and from its surroundings. This is the primary process through which supermassive black holes seem to have grown.

A similar process has been suggested for the formation of found in. Black holes can also merge with other objects such as stars or even other black holes. This is thought to have been important, especially in the early growth of supermassive black holes, which could have formed from the aggregation of many smaller objects. The process has also been proposed as the origin of some. Main article:In 1974, Hawking predicted that black holes are not entirely black but emit small amounts of thermal radiation at a temperature ℏ c 3/(8 π G M ); this effect has become known as.

By applying to a static black hole background, he determined that a black hole should emit particles that display a perfect. Since Hawking's publication, many others have verified the result through various approaches. If Hawking's theory of black hole radiation is correct, then black holes are expected to shrink and evaporate over time as they lose mass by the emission of photons and other particles. The temperature of this thermal spectrum is proportional to the of the black hole, which, for a Schwarzschild black hole, is inversely proportional to the mass.

Hence, large black holes emit less radiation than small black holes.A stellar black hole of 1 M ☉ has a Hawking temperature of 62. This is far less than the 2.7 K temperature of the radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrinking. To have a Hawking temperature larger than 2.7 K (and be able to evaporate), a black hole would need a mass less than the.

Such a black hole would have a diameter of less than a tenth of a millimeter.If a black hole is very small, the radiation effects are expected to become very strong. A black hole with the mass of a car would have a diameter of about 10 −24 m and take a nanosecond to evaporate, during which time it would briefly have a luminosity of more than 200 times that of the Sun. Lower-mass black holes are expected to evaporate even faster; for example, a black hole of mass 1 TeV/ c 2 would take less than 10 −88 seconds to evaporate completely. For such a small black hole, effects are expected to play an important role and could hypothetically make such a small black hole stable, although current developments in quantum gravity do not indicate this is the case.The Hawking radiation for an astrophysical black hole is predicted to be very weak and would thus be exceedingly difficult to detect from Earth.

A possible exception, however, is the burst of gamma rays emitted in the last stage of the evaporation of primordial black holes. Searches for such flashes have proven unsuccessful and provide stringent limits on the possibility of existence of low mass primordial black holes. NASA's launched in 2008 will continue the search for these flashes.If black holes evaporate via, a solar mass black hole will evaporate (beginning once the temperature of the cosmic microwave background drops below that of the black hole) over a period of 10 64 years. A supermassive black hole with a mass of 10 11 (100 billion) M ☉ will evaporate in around 2×10 100 years.

Some monster black holes in the universe are predicted to continue to grow up to perhaps 10 14 M ☉ during the collapse of superclusters of galaxies. Even these would evaporate over a timescale of up to 10 106 years. Observational evidence. By nature, black holes do not themselves emit any electromagnetic radiation other than the hypothetical, so astrophysicists searching for black holes must generally rely on indirect observations. For example, a black hole's existence can sometimes be inferred by observing its gravitational influence upon its surroundings.On 10 April 2019 an image was released of a black hole, which is seen in magnified fashion because the light paths near the event horizon are highly bent. The dark shadow in the middle results from light paths absorbed by the black hole.

The image is in false color, as the detected light halo in this image is not in the visible spectrum, but radio waves. This artist's impression depicts the paths of photons in the vicinity of a black hole. The gravitational bending and capture of light by the event horizon is the cause of the shadow captured by the Event Horizon Telescope.The (EHT), run by MIT's, is an active program that directly observes the immediate environment of the event horizon of black holes, such as the black hole at the centre of the Milky Way. In April 2017, EHT began observation of the black hole in the center of Messier 87.

Ending of infinity war. Read More: Avengers: Infinity War’s Ending Was Very Different In The Comics Spider-Man: Far From Home (2019) release date: Jul 02, 2019. Avengers: Infinity War / The Avengers 3 (2018) release date: Apr 27, 2018. The Avengers 4 / Avengers: Endgame (2019) release date: Apr 26, 2019. Ant-Man & The. The final act of Infinity War takes place on multiple fronts, with Thanos facing off with Iron Man, Doctor Strange, Spider-Man and half of the Guardians of the Galaxy on his home world - Saturn's. There's only one cure for the post-Infinity War blues, and that's diving straight into the ending and trying to figure out what the hell just happened — and what the hell is going to happen next. The ending of Infinity War feels like Marvel relying on that old trick once again, and it arguably cheapens the emotional impact of that last moment. What's the point in mourning Doctor Strange.

'In all, eight radio observatories on six mountains and four continents observed the galaxy in Virgo on and off for 10 days in April 2017' to provide the data yielding the image two years later in April 2019. After two years of data processing, EHT released the first direct image of a black hole, specifically the supermassive black hole that lies in the center of the aforementioned galaxy. What is visible is not the black hole, which shows as black because of the loss of all light within this dark region, rather it is the gases at the edge of the event horizon, which are displayed as orange or red, that define the black hole.The brightening of this material in the 'bottom' half of the processed EHT image is thought to be caused by, whereby material approaching the viewer at relativistic speeds is perceived as brighter than material moving away. In the case of a black hole this phenomenon implies that the visible material is rotating at relativistic speeds (1,000 km/s), the only speeds at which it is possible to centrifugally balance the immense gravitational attraction of the singularity, and thereby remain in orbit above the event horizon.

This configuration of bright material implies that the EHT observed from a perspective catching the black hole's accretion disc nearly edge-on, as the whole system rotated clockwise. However, the extreme associated with black holes produces the illusion of a perspective that sees the accretion disc from above. In reality, most of the ring in the EHT image was created when the light emitted by the far side of the accretion disc bent around the black hole's gravity well and escaped such that most of the possible perspectives on M87. can see the entire disc, even that directly behind the 'shadow'.Prior to this, in 2015, the EHT detected magnetic fields just outside the event horizon of Sagittarius A., and even discerned some of their properties. The field lines that pass through the accretion disc were found to be a complex mixture of ordered and tangled. The existence of magnetic fields had been predicted by theoretical studies of black holes.

Predicted appearance of non-rotating black hole with toroidal ring of ionised matter, such as has been proposed as a model for. The asymmetry is due to the resulting from the enormous orbital speed needed for centrifugal balance of the very strong gravitational attraction of the hole. Detection of gravitational waves from merging black holesOn 14 September 2015 the gravitational wave observatory made the first-ever successful.

The signal was consistent with theoretical predictions for the gravitational waves produced by the merger of two black holes: one with about 36, and the other around 29 solar masses. This observation provides the most concrete evidence for the existence of black holes to date. For instance, the gravitational wave signal suggests that the separation of the two objects prior to the merger was just 350 km (or roughly four times the Schwarzschild radius corresponding to the inferred masses). The objects must therefore have been extremely compact, leaving black holes as the most plausible interpretation.More importantly, the signal observed by LIGO also included the start of the post-merger, the signal produced as the newly formed compact object settles down to a stationary state. Arguably, the ringdown is the most direct way of observing a black hole. From the LIGO signal it is possible to extract the frequency and damping time of the dominant mode of the ringdown.

From these it is possible to infer the mass and angular momentum of the final object, which match independent predictions from numerical simulations of the merger. The frequency and decay time of the dominant mode are determined by the geometry of the photon sphere.

Hence, observation of this mode confirms the presence of a photon sphere, however it cannot exclude possible exotic alternatives to black holes that are compact enough to have a photon sphere.The observation also provides the first observational evidence for the existence of stellar-mass black hole binaries. Furthermore, it is the first observational evidence of stellar-mass black holes weighing 25 solar masses or more.Since then many more have since been observed. Proper motions of stars orbiting Sagittarius A.The of stars near the center of our own provide strong observational evidence that these stars are orbiting a supermassive black hole. Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source.

By fitting their motions to, the astronomers were able to infer, in 1998, that a 2.6 million object must be contained in a volume with a radius of 0.02 to cause the motions of those stars. Since then, one of the stars—called —has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass to 4.3 million M ☉ and a radius of less than 0.002 light years for the object causing the orbital motion of those stars.

The upper limit on the object's size is still too large to test whether it is smaller than its Schwarzschild radius; nevertheless, these observations strongly suggest that the central object is a supermassive black hole as there are no other plausible scenarios for confining so much invisible mass into such a small volume. Additionally, there is some observational evidence that this object might possess an event horizon, a feature unique to black holes. Accretion of matter. Blurring of X-rays near black hole (; 12 August 2014)When the accreting object is a or a black hole, the gas in the inner accretion disk orbits at very high speeds because of its proximity to the. The resulting friction is so significant that it heats the inner disk to temperatures at which it emits vast amounts of electromagnetic radiation (mainly X-rays). These bright X-ray sources may be detected by telescopes.

This process of accretion is one of the most efficient energy-producing processes known; up to 40% of the rest mass of the accreted material can be emitted as radiation. (In nuclear fusion only about 0.7% of the rest mass will be emitted as energy.) In many cases, accretion disks are accompanied by that are emitted along the poles, which carry away much of the energy. The mechanism for the creation of these jets is currently not well understood, in part due to insufficient data.As such, many of the universe's more energetic phenomena have been attributed to the accretion of matter on black holes.

In particular, and are believed to be the accretion disks of supermassive black holes. Similarly, X-ray binaries are generally accepted to be systems in which one of the two stars is a compact object accreting matter from its companion. It has also been suggested that some may be the accretion disks of.In November 2011 the first direct observation of a quasar accretion disk around a supermassive black hole was reported. X-ray binaries. A image of, which was the first strong black hole candidate discoveredare systems that emit a majority of their radiation in the part of the spectrum.

These X-ray emissions are generally thought to result when one of the stars (compact object) accretes matter from another (regular) star. The presence of an ordinary star in such a system provides an opportunity for studying the central object and to determine if it might be a black hole.If such a system emits signals that can be directly traced back to the compact object, it cannot be a black hole. The absence of such a signal does, however, not exclude the possibility that the compact object is a neutron star. By studying the companion star it is often possible to obtain the orbital parameters of the system and to obtain an estimate for the mass of the compact object. If this is much larger than the (the maximum mass a star can have without collapsing) then the object cannot be a neutron star and is generally expected to be a black hole.The first strong candidate for a black hole, was discovered in this way by, Louise Webster and Paul Murdin in 1972.

Some doubt, however, remained due to the uncertainties that result from the companion star being much heavier than the candidate black hole. Currently, better candidates for black holes are found in a class of X-ray binaries called soft X-ray transients. In this class of system, the companion star is of relatively low mass allowing for more accurate estimates of the black hole mass. Moreover, these systems actively emit X-rays for only several months once every 10–50 years. During the period of low X-ray emission (called quiescence), the accretion disk is extremely faint allowing detailed observation of the companion star during this period. One of the best such candidates is.

Quiescence and advection-dominated accretion flowThe faintness of the accretion disk of an X-ray binary during quiescence is suspected to be caused by the flow of mass entering a mode called an (ADAF). In this mode, almost all the energy generated by friction in the disk is swept along with the flow instead of radiated away.

If this model is correct, then it forms strong qualitative evidence for the presence of an event horizon, since if the object at the center of the disk had a solid surface, it would emit large amounts of radiation as the highly energetic gas hits the surfacean effect that is observed for neutron stars in a similar state. Quasi-periodic oscillations. Magnetic waves, called, flow from the base of black hole jets.Astronomers use the term ' to describe galaxies with unusual characteristics, such as unusual emission and very strong radio emission. Theoretical and observational studies have shown that the activity in these active galactic nuclei (AGN) may be explained by the presence of, which can be millions of times more massive than stellar ones.

The models of these AGN consist of a central black hole that may be millions or billions of times more massive than the; a disk of and called an accretion disk; and two perpendicular to the accretion disk. Detection of unusually bright flare from, a black hole in the center of the galaxy on 5 January 2015Although supermassive black holes are expected to be found in most AGN, only some galaxies' nuclei have been more carefully studied in attempts to both identify and measure the actual masses of the central supermassive black hole candidates. Some of the most notable galaxies with supermassive black hole candidates include the, and the.It is now widely accepted that the center of nearly every galaxy, not just active ones, contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's, known as the, strongly suggests a connection between the formation of the black hole and the galaxy itself. Simulation of gas cloud after close approach to the black hole at the centre of the Milky Way.

Microlensing (proposed)Another way the black hole nature of an object may be tested in the future is through observation of effects caused by a strong gravitational field in their vicinity. One such effect is: The deformation of spacetime around a massive object causes light rays to be deflected much as light passing through an optic. Observations have been made of weak gravitational lensing, in which light rays are deflected by only a few.

However, it has never been directly observed for a black hole. One possibility for observing gravitational lensing by a black hole would be to observe stars in orbit around the black hole.

There are several candidates for such an observation in orbit around. See also:The evidence for stellar black holes strongly relies on the existence of an upper limit for the mass of a neutron star. The size of this limit heavily depends on the assumptions made about the properties of dense matter. New exotic could push up this bound. A phase of free at high density might allow the existence of dense, and some models predict the existence of. Some extensions of the posit the existence of as fundamental building blocks of quarks and, which could hypothetically form.

These hypothetical models could potentially explain a number of observations of stellar black hole candidates. However, it can be shown from arguments in general relativity that any such object will have a maximum mass.Since the average density of a black hole inside its Schwarzschild radius is inversely proportional to the square of its mass, supermassive black holes are much less dense than stellar black holes (the average density of a 10 8 M ☉ black hole is comparable to that of water). Consequently, the physics of matter forming a supermassive black hole is much better understood and the possible alternative explanations for supermassive black hole observations are much more mundane. For example, a supermassive black hole could be modelled by a large cluster of very dark objects.

However, such alternatives are typically not stable enough to explain the supermassive black hole candidates.The evidence for the existence of stellar and supermassive black holes implies that in order for black holes to not form, general relativity must fail as a theory of gravity, perhaps due to the onset of corrections. A much anticipated feature of a theory of quantum gravity is that it will not feature singularities or event horizons and thus black holes would not be real artifacts. For example, in the model based on, the individual states of a black hole solution do not generally have an event horizon or singularity, but for a classical/semi-classical observer the statistical average of such states appears just as an ordinary black hole as deduced from general relativity.A few theoretical objects have been conjectured to match observations of astronomical black hole candidates identically or near-identically, but which function via a different mechanism. These include the, the, and the. Open questions Entropy and thermodynamics. The formula for the Bekenstein–Hawking entropy ( S) of a black hole, which depends on the area of the black hole ( A).

The constants are the ( c), the ( k), ( G), and the ( ħ). In, this reduces to S = A / 4.In 1971, Hawking showed under general conditions that the total area of the event horizons of any collection of classical black holes can never decrease, even if they collide and merge. This result, now known as the, is remarkably similar to the, which states that the total of an isolated system can never decrease. As with classical objects at temperature, it was assumed that black holes had zero entropy. If this were the case, the second law of thermodynamics would be violated by entropy-laden matter entering a black hole, resulting in a decrease of the total entropy of the universe. Therefore, Bekenstein proposed that a black hole should have an entropy, and that it should be proportional to its horizon area.The link with the laws of thermodynamics was further strengthened by Hawking's discovery that predicts that a black hole radiates at a constant temperature.

This seemingly causes a violation of the second law of black hole mechanics, since the radiation will carry away energy from the black hole causing it to shrink. The radiation, however also carries away entropy, and it can be proven under general assumptions that the sum of the entropy of the matter surrounding a black hole and one quarter of the area of the horizon as measured in is in fact always increasing. This allows the formulation of the as an analogue of the, with the mass acting as energy, the surface gravity as temperature and the area as entropy.One puzzling feature is that the entropy of a black hole scales with its area rather than with its volume, since entropy is normally an that scales linearly with the volume of the system. This odd property led and to propose the, which suggests that anything that happens in a volume of spacetime can be described by data on the boundary of that volume.Although general relativity can be used to perform a semi-classical calculation of black hole entropy, this situation is theoretically unsatisfying. In, entropy is understood as counting the number of microscopic configurations of a system that have the same macroscopic qualities (such as, etc.). Without a satisfactory theory of, one cannot perform such a computation for black holes.

Some progress has been made in various approaches to quantum gravity. In 1995, and showed that counting the microstates of a specific black hole in reproduced the Bekenstein–Hawking entropy. Since then, similar results have been reported for different black holes both in string theory and in other approaches to quantum gravity like. Information loss paradox. Utopian mining walkthrough game.

Is lost in black holes?Because a black hole has only a few internal parameters, most of the information about the matter that went into forming the black hole is lost. Regardless of the type of matter which goes into a black hole, it appears that only information concerning the total mass, charge, and angular momentum are conserved. As long as black holes were thought to persist forever this information loss is not that problematic, as the information can be thought of as existing inside the black hole, inaccessible from the outside, but represented on the event horizon in accordance with the holographic principle. However, black holes slowly evaporate by emitting. This radiation does not appear to carry any additional information about the matter that formed the black hole, meaning that this information appears to be gone forever.The question whether information is truly lost in black holes (the ) has divided the theoretical physics community (see ).

In quantum mechanics, loss of information corresponds to the violation of a property called, and it has been argued that loss of unitarity would also imply violation of conservation of energy, though this has also been disputed. Over recent years evidence has been building that indeed information and unitarity are preserved in a full quantum gravitational treatment of the problem.One attempt to resolve the black hole information paradox is known as. In 2012, the ' was introduced with the goal of demonstrating that black hole complementarity fails to solve the information paradox. According to, a of involves two mutually particles. The outgoing particle escapes and is emitted as a quantum of Hawking radiation; the infalling particle is swallowed by the black hole. Assume a black hole formed a finite time in the past and will fully evaporate away in some finite time in the future.

Then, it will emit only a finite amount of information encoded within its Hawking radiation. According to research by physicists like and, there will eventually be a time by which an outgoing particle must be entangled with all the Hawking radiation the black hole has previously emitted. This seemingly creates a paradox: a principle called 'monogamy of entanglement' requires that, like any quantum system, the outgoing particle cannot be fully entangled with two other systems at the same time; yet here the outgoing particle appears to be entangled both with the infalling particle and, independently, with past Hawking radiation.

In order to resolve this contradiction, physicists may eventually be forced to give up one of three time-tested principles: Einstein's, or local. One possible solution, which violates the equivalence principle, is that a 'firewall' destroys incoming particles at the event horizon. In general, which if any of these assumptions should be abandoned remains a topic of debate. Ferguson, Kitty (1991). Black Holes in Space-Time. Watts Franklin. CS1 maint: ref=harv.

(1988). Bantam Books, Inc. CS1 maint: ref=harv.; (1996). Princeton University Press.

CS1 maint: ref=harv. (2003). Princeton U Press. CS1 maint: ref=harv. Melia, Fulvio (2003).

Cambridge U Press. CS1 maint: ref=harv.

Pickover, Clifford (1998). Black Holes: A Traveler's Guide. Wiley, John & Sons, Inc. (1994).

& Company, Inc. CS1 maint: ref=harv.

(2008). Little, Brown and Company. CS1 maint: ref=harv. Wheeler, J. Craig (2007).

Cosmic Catastrophes (2nd ed.). Cambridge University Press. CS1 maint: ref=harv University textbooks and monographs. Carroll, Sean M. Spacetime and Geometry. Addison Wesley. CS1 maint: ref=harv , the lecture notes on which the book was based are available for free from Sean Carroll's.

(1973). 'Black hole equilibrium states'. In; DeWitt, C.

CS1 maint: ref=harv. (1999). Mathematical Theory of Black Holes. Oxford University Press. CS1 maint: ref=harv. Frolov, V. P.; Novikov, I.

'Black hole physics'. Cite journal requires journal= CS1 maint: ref=harv. Frolov, Valeri P.; Zelnikov, Andrei (2011). Oxford: Oxford University Press.

CS1 maint: ref=harv.; Ellis, G. Cambridge University Press. CS1 maint: ref=harv.

(2007). The Galactic Supermassive Black Hole.

Princeton U Press. CS1 maint: ref=harv.;; (1973). Freeman and Company. CS1 maint: ref=harv.

Taylor, Edwin F.; (2000). Exploring Black Holes. Addison Wesley Longman. CS1 maint: ref=harv. (1984). University of Chicago Press. CS1 maint: ref=harv.

Wald, Robert M. Space, Time, and Gravity: The Theory of the Big Bang and Black Holes. University of Chicago Press. CS1 maint: ref=harv. Price, Richard; Creighton, Teviet (2008).

'Black holes'. 3 (1): 4277.:.Review papers.