In 1916, German astronomerKarl Schwarzschild (Karl Schwarzschild)Einstein field equationThis solution shows that if the actual radius of a static spherically symmetric star is less than a fixed value related to mass, a singular phenomenon will occur around it, that is, there is an interface -“Horizon”Once entering this interface, even light cannot escape.This fixed value is called Schwarzschild radius. This "incredible celestial body" was called "black hole" by Ann Ewing, a science journalist, in his article in 1964, and was later called "black hole" by American physicistsJohn Archibald Wheeler (John Archibald Wheeler) adopted and rapidly popularized.
In February 2024, a team led by researchers from the Australian National University published a paper in the British journal Nature Astronomy, saying that they had discovered the fastest growing black hole known so far, and the mass of matter it swallowed every day was equivalent to one sun[43]。
What is a black hole?It is an ancient astronomical prediction in the 18th century, and it is the ultimate fate and the possibility of rebirth of stars;It can change the trajectory of light and disturb the surrounding space-time... Although it is difficult for us to completely observe it, scientists have been trying to approach it by other methods for more than a hundred years.For black holes, this is just a short moment, but for humans, it is a long journey that constantly subverts the imagination.... Details
Because it does not emit light, black holes cannot be observed directly, but their existence and mass can be known indirectly, and their impact on other things can be observed.It emits X-ray andγThe "edge information" of X-ray can obtain the information about the existence of black holes.The existence of black holes can also be inferred from the indirect observation of the orbits of stars or interstellar clouds, and their positions and masses can also be obtained.
At 21:00 on April 10, 2019, Beijing time, the first photo of a black hole was released (see the photo of a black hole). The black hole is located at the center of a giant elliptical galaxy M87 in the constellation Virgo, 55 million light-years away from the Earth, and its mass is about 6.5 billion times that of the sun[4]。This picture is created by the eventHorizon telescope(Event Horizon Telescope, referred to as EHT) is essentially an image of the light emitted by the hot plasma accreted around the black hole after the gravitational deflection of the black hole.[2]
On October 6, 2020, the Royal Swedish Academy of Sciences awarded the 2020 Nobel Prize in Physics to three physicists who have made outstanding contributions to black hole research.Among them, British scientistsRoger Penrose Roger Penrose won the prize for finding that the formation of black holes is the direct evidence of general relativity. German scientist Reinhard Genzel and American female scientistAndrea GazAndrea Ghez won the prize for discovering a supermassive black hole in the center of the Milky Way Galaxy.Two scientific research teams of Genzel and Gates tracked the orbits of a group of brightest stars in the Sagittarius A * region in the center of the Milky Way Galaxy, proving that there is an invisible object in this region with a mass about 4 million times that of the sun and no more than the size of the solar system.
At 10:00 p.m. on March 24, 2021, Beijing time, the Event Horizon Telescope Cooperation Group released the polarization image of M87 supermassive black hole[23], revealing the magnetic field information of the hot gas surrounding M87 black hole.
At 9 p.m. on May 12, 2022 Beijing time, the Event Horizon Telescope Cooperation Organization officially released the first picture of the supermassive black hole Sagittarius A * (Sgr A *) in the center of the Milky Way Galaxy.[26]The black hole is about 26000 light-years away from the Earth, and its mass is about 4.3 million times that of the sun.May 24, 2023James Webb The space telescope (JWST) and Chandra X-ray Observatory have certified the most distant black hole observed so far. It is about 13.2 billion light years away from the Earth and has a mass of 10 million to 100 million times that of the sun, which is equivalent to the sum of the masses of all stars in its host galaxy.This supermassive black hole was formed only 500 million years after the Big Bang, so it tends to prove that the first generation of black holes in the universe came from the direct collapse of gas clouds, rather than the death of the first generation of stars.This achievement has been published to《Nature · Astronomy》Magazine.[27]
evolutionary process
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Two mutually devouring black holes
A black hole consists ofRiemannian curvature tensorScalar polynomials constructed from the starting point diverge heresingularityIt is composed of the surrounding space-time, and its boundary is a one-way membrane: event horizon, which is invisible within the event horizon.The gravitational collapse of massive stars is considered to be the cause of the formation of stellar mass black holes.basisEinsteinOfGeneral relativity, when a dyingfixed starWhen it collapses, it will collapse toward the center. If its mass is greater than the Tolman Oppenheimer Volkoff Equation (also known as TOV limit, estimated to be about 2.5-4 times the mass of the sun), it will collapse indefinitely, until it finally forms a star with nearly infinite volume and almost infinite density (almost a singularity).When its radius shrinks to less than the Schwarzschild radius, the space-time distortion caused by mass makes it impossible for even light to shoot out - "black hole" is born.
The generation process of black holes is similar toneutron starThe production process of: when a star is faced with destruction, it is generally because the fuel inside the star is insufficient and cannot maintain the temperature through nuclear synthesis;Or it is because stable stars accept foreign materials, but fail to raise their core temperature to maintain balance.In short, due to insufficient temperature, the core collapses rapidly under its own gravity, resulting in a powerful explosion, called a supernova explosion.This process causes most of the outer mass of the star to be ejected, leaving only a dense core in the inner layer.The size of the residual mass of a star determines its final fate, that is, what kind of compact star it will become.
When the mass of the remaining core is less than the TOV limit, it will become a neutron star, and the pressure supporting the star comes from the strong interaction between neutrons and the degenerate pressure.When the core mass is greater than the TOV limit, a black hole will be formed. At this time, its mass is large enough to make the contraction process go on endlessly, and even the repulsive force between neutrons cannot be stopped.Neutron itself is crushed into powder by its own gravity, leaving behind a substance with unimaginable density.[5]
What a black hole looks like from the equator (concept map)
From the perspective of stellar evolution, stars usually only contain hydrogen at the beginning, and the hydrogen nuclei in stars collide with each other all the time, resulting in fusion.Due to the large mass of the star, the energy generated by fusion counteracts the gravity of the star to maintain the stability of the star structure.The fusion of hydrogen nuclei produces a new element - helium, and then helium atoms also participate in the fusion to produce lithium.By analogy, according to the order of the periodic table of elements, beryllium, boron, carbon, nitrogen, etc. will be generated in turn until iron is generatedfixed starWill collapse.At this time, because the iron element is quite stable, the energy released when participating in fusion is less than the required energy, so the fusion stops, leading to the lack of enough energy inside the star to compete with the gravity of the massive star, thus causing the collapse of the star and eventually forming a black hole.
According to the stellar evolution theory, the original mass of stars that can form black holes should be more than 25 times the mass of the sun.Such stars will undergo violent supernova explosions in their later years, ejecting some material to form nebulae, and the remaining remnants will have a mass greater than the TOV limit, which can form black holes.
However, external observers cannot actually "see" the formation of black holes, because the gravitational time expansion of general relativity can only see that the collapsed matter gradually slows down above the event horizon until it stops.The light from collapsed matter will arrive at the observer longer and longer, and the light emitted at the moment before reaching the event horizon will be delayed indefinitely.Therefore, external observers have never seen the formation of the event horizon;In contrast, the collapsed material becomes darker and darker, and eventually gradually disappears from view.
Encyclopedia x ignorance: illustrating black holes
accretion
Black holes are usually produced by gathering the surrounding gasradiationThis process is known asaccretion 。high temperatureGaseous radiationThe efficiency of heat energy will seriously affect the geometric and dynamic characteristics of accretion flow.It has been observed thatThin discAnd thick disks with low radiation efficiency.When the accretion gas approaches the central black hole, the radiation they generate rotates the black hole and is the flow of the central extended matter system.Accretion is one of the most common processes in astrophysics, and it is precisely because of accretion that many common structures around us are formed.In the early universe, when gas moved fromdark substanceResultingGravitational potential wellGalaxies form when the center flows.Stars are formed byGas cloudIt is formed by collapse and fragmentation under its own gravity, and then by accretion of surrounding gas.planet(including the Earth) is also formed around newly formed stars by gathering gas and rocks.When the central object is a black hole, accretion will show its most spectacular side.
Black holes stretch, tear and devour stars
Jet
The greater the mass of the black hole, the greater the radiation produced by the accretion.Most galaxies in the universe are very quiet, but about 2% of them have intense activities, and their physical characteristics show rapid and obvious changes, mainly reflected in the strong radiation and explosion of galactic nuclei in the X-ray, ultraviolet, optical or radio bands.The energy emitted by these galaxies during the activity period is larger than the total energy released by the Milky Way in its lifetime, but the range of nuclear activity is very small. Only black holes can achieve such strong radiation efficiency.Such cores are calledActive galactic nucleus(Active Galactic Nucleus (AGN for short).At present, the mainstream AGN model believes that there is a supermassive black hole in the center of the active galaxy, which accretes the surrounding gas to form an accretion disk of several times to 1000 times the Schwarzschild radius, and ejects electrons and other ionized gases at a high speed in the direction perpendicular to the accretion disk, forming a spectacular jet with a gap of 0.1~second (pc) on both sides.The jet is due to the acceleration of electrons under the action of the strong magnetic field of the black hole, but under the constraint of the dense gas cloud around the black hole, electrons can only eject from the weakest part of the gas, forming a very fixed direction jet.The electrons ejected can approach the speed of light as quickly as possible.
Black hole is a strange celestial body in the universe, with super strong gravity, so that even light cannot escape its gravitational binding within the radius of the black hole.Astronomers more than 100 years ago discovered through observation that a black hole can eject a powerful outflow containing matter and energy at a speed close to the speed of light at a distance far from the radius of the black hole.At present, the main models in this field are "extracting the rotational energy of black holes" and "extracting the rotational kinetic energy of accretion disks".Astronomers try to analyze the energy source of the jet.By calculating the radiation predicted by the two models and comparing them with the observations, it is found that the jet predicted by the model of extracting the rotational kinetic energy of the black hole through the magnetic field is consistent with the actual observation results, while the other model of extracting the rotational kinetic energy of the accretion disk of the black hole through the magnetic field is difficult to explain the observation results[44]。
Further, this study analyzed the physical mechanism of "magnetic reconnection" in the black hole jet, and found that this was because the magnetic field in the accretion disk of M87 black hole would produce "magnetic explosion".This burst can produce a strong disturbance to the magnetic field, and this disturbance can spread far away, leading to magnetic reconnection in the jet[44]。
Stars are swallowed by black holes
evaporation
Black holes seem to absorb all matter, and their mass only increases, but they may also continue to radiate photons (although stellar mass black holes radiate very slowly).according toStephen Hawking(Stephen William Hawking) put forward a theory in 1974. In quantum physics, there is a phenomenon called "tunnel effect", that is, although the probability density distribution of a particle is as strong as possible in places with low energy, the probability density of the particle is still not zero even in places with quite high energy, in other words,Particles always have a certain probability to pass through those "walls" that cannot be penetrated in classical physics.The boundary of a black hole is a potential barrier with high energy for photons, but photons always have a certain probability of tunneling out.Hawking calculated that the temperature of photons emitted by the black hole is. This phenomenon is called Hawking radiation.
Hawking's theory is a leap of thinking dominated by inspiration. He combines general relativity and quantum theory. He finds that the gravitational field around the black hole releases energy and consumes the energy and mass of the black hole.
Suppose that a pair of particles will be created at any time and anywhere, and the created particles are positive particles and antiparticles. If this creation process occurs near the black hole, there will be four possible scenarios: two particles annihilate, two particles are sucked into the black hole, positive particles are sucked into the black hole, antiparticles escape, and antiparticles are sucked into the black hole, and positive particles escape.For the last case: one antiparticle of a pair of particles created near the black hole will be sucked into the black hole, while the positive particle will escape. Since energy cannot be created out of thin air, we assume that the antiparticle carries negative energy and the positive particle carries positive energy, and all the motion processes of the antiparticle can be regarded as the opposite of that of a positive particle,If an antiparticle is sucked into the black hole, it can be regarded as a positive particle escaping from the black hole.In this case, a particle carrying positive energy from the black hole escapes, that is, the total energy of the black hole is less. Einstein's mass energy equation shows that the loss of energy will lead to the loss of mass.
In the classical general relativity, because no photons can escape from the black hole, that is, the black hole does not produce radiation, the temperature of the black hole is absolute zero.But according to Hawking's theory, every black hole has a certain temperature, and the temperature is inversely proportional to the mass of the black hole.In other words, the temperature of the big black hole is low and the evaporation is weak;The temperature of the small black hole is high, and the evaporation is also strong, similar to a violent explosion.When the mass of the black hole is smaller and smaller, its Hawking radiation temperature will be higher and higher.Thus, when a black hole loses mass, its temperature and emissivity increase, and its mass loss is faster.This“hawking radiation ”It can be ignored for most black holes. Theoretically, a black hole equivalent to the mass of the sun will take about 1x years to evaporate completely.In fact, because the Hawking radiation temperature of the massive black hole is lower than the temperature of the cosmic microwave background radiation (about 2.7 Kelvin), the mass of the black hole at star level and above only increases, and only black holes smaller than the mass of the moon (less than 0.1 mm in diameter) will evaporate.Such a small black hole will radiate energy at a very high speed, and the black hole equivalent to the mass of an asteroid will evaporate completely in 1x seconds.Hawking radiation of black holes in the universe is difficult to observe, but some scholars proposed that the original black holes would release gamma ray bursts in the final stage of evaporation, but it has not been confirmed yet.NASAThe Fermi Gamma Ray Space Telescope launched in 2008 will continue to look for this explosion.
Gravitational lens
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A black hole with strong gravity.
For those inactive black holes, such as isolated black holes with no gas around them, if they are located between the Earth and a star or galaxy, the mass of the black hole can be calculated through the gravitational lens effect.
The space-time distortion of stellar gravity changes the path of light, making it different from the path without stars.Light deflects slightly inward near the surface of the star. This phenomenon can be seen by observing the light emitted by distant stars during the solar eclipse.When the star collapses inward, the space-time distortion caused by its mass becomes very strong, and the light deflects more inward, making it more difficult for photons to escape from the star.For the observer at a distance, the light becomes darker and redder.Finally, when the star shrinks to a certain critical radius（Schwarzschild radius ）Its mass causes the space-time distortion to become so strong that the light deflects inward so strongly that the light cannot escape.In this way, if no light escapes, nothing else can escape and will be pulled back.In other words, there is a collection of events or a space-time region, from which light or anything can not escape to reach the distant observer, which is a black hole.Its boundary is called the event horizon, which coincides with the trajectory of light that just cannot escape from the black hole.
Compared with other celestial bodies, black holes are very special.People cannot observe it directly, and scientists can only make various guesses about its internal structure.The reason why black holes hide themselves is the curved space-time.According to general relativity, spacetime will bend under the action of gravitational field.At this time, although light still travels along the shortest optical path between any two points, it appears to other observers that it has bent.When passing a dense celestial body, space-time will bend, and light will deviate from the original direction.
On the earth, due to the small effect of gravitational field, the distortion of space-time is minimal.Around the black hole, the deformation of space-time is very large.Even though some of the light from the stars blocked by the black hole will fall into the black hole and disappear, another part of the light will bypass the black hole through the curved space and reach the Earth.In this way, Earth's observers can see the star image distorted and magnified by the gravity of the black hole.The black hole acts like a magnifying glass, so it is also called strong gravitational lens effect.
More interesting is that some stars not only send light towards the Earth directly to the Earth, but also send light towards other directions that may be refracted by the strong gravity of the nearby black hole to reach the Earth.In this way, we can not only see the "face" of the star, but also its "side" and even its "back", which is also the "gravitational lens" effect in the universe.
If it is a double black hole rotating around each other or merging, it will emit gravitational waves.Gravitational wave is the "ripple" of space-time, which will compress or stretch the objects passing by.On September 14, 2015, two gravitational wave detectors of the advanced Laser Interferometer Gravitational wave Observatory (aLIGO) in the United States detected the gravitational wave signal from the merger of two black holes for the first time.On December 26, 2015, LIGO again detected the gravitational wave signal of the merger of two black holes, which is the second gravitational wave signal detected by humans.
Figure: Two mutually rotating black holes (NGC6240's X-ray simulation of double black holes, which will be combined into one in the next 10 million to 100 million years)
physical characteristics
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According to the hairless theorem of black holes, a stable black hole can be described by only three physical quantities: mass M, angular momentum J, and charge Q.There should be no difference in physical properties between two black holes with the same parameter values, that is, the mass distribution and charge distribution inside the black hole have nothing to do with its external performance as a whole.Whether this theoretical speculation is true of black holes in reality is still an unresolved question.When an object falls into a black hole, the information about its shape and charge distribution is erased and transformed into the average properties of the black hole.At this time, the event horizon is like a dissipative system, which devours many physical information of the substance (such asBaryon number、Lepton numberThis contradicts the assumption that information is not lost in quantum mechanics, so it is called "black hole information paradox".A charged black hole repels or attracts charges just like other charged objects. Its total mass can be obtained by measuring the gravitational field in the distance, and its angular momentum can also be obtained by measuring the drag effect of the reference frame in the distance.
Although the mass of a black hole can be arbitrarily positive, its charge and angular momentum are limited by the mass
For a black hole with mass M, there are upper limits on the amount of charge and angular momentum.It should be noted that when the equation is equal, it means that there is a naked singularity, which violates the cosmic censorship conjecture (Penrose conjectures that there is a hidden law in nature that makes the starting point of the gravitational collapse of an object only exist within the event horizon and will not produce a naked singularity), so it is generally believed that the equal sign cannot be used.
According to its mass, black holes can be divided into supermassive black holes (~times the mass of the sun, with a radius of about 0.001~1000 times the distance between the sun and the earth), medium mass black holes (~times the mass of the sun, with a radius of about 1000 km), stellar black holes (3~100 times the mass of the sun, with a radius of about 30 km), and micro black holes (less than the mass of the moon, with a radius of less than 0.1 mm).The size of a black hole is generally defined as its event horizon radius. For a Schwarzschild black hole (a non charged and non rotating black hole), it is equal to its Schwarzschild radius, which is proportional to the mass:
Is the mass of the sun,
Is the Schwarzschild radius.For a charged black hole or a black hole with rotation, its outer horizon will become smaller, but it should not be less than
。
Event horizon
Event horizon is one of the most important characteristics of black holes. It is the interface of black holes in space-time. Light and matter can only enter the event horizon from the outside and cannot escape.This name comes from the fact that once an event occurs within the horizon, the information of the event can never be obtained by external observers, so it is impossible to judge whether the event has occurred.For general black holes, the size of the inner and outer event horizon is
(M, J and Q respectively represent the total mass, total angular momentum and total charge of the black hole.
Is unit mass angular momentum)
singularity
General relativity predicts that there is a physical gravitational singularity at the center of the black hole, where the curvature of space-time tends to infinity.For non rotating black holes, the region is a point shape;For a rotating black hole, it is a circular singularity uniformly distributed on a circle.In both cases, the volume of the singular region is zero.This indicates that the singularity region contains all the masses of the stable black hole.Therefore, the mass of the singular region can be considered as having infinite density.
Once an observer entering the Schwarzschild black hole (that is, a non rotating and non charged black hole) crosses the event horizon, he or she will inevitably be brought into the singularity.They can prolong this process and delay their decline by accelerating their departure, but they cannot be stopped or reversed.When they reach the singularity, they are pressed to an infinite density, and their mass is added to the total mass of the black hole.Before that, they will be stretched and torn by the increasing tidal force, which is usually called spaghetti or noodle effect.
Infinite redshift surface
The infinite redshift surface means that for the observer in a distant non rotating frame (LNRF), the photons on this surface can never reach the observer, or the redshift when arriving is infinite.For Schwarzschild black holes, the event horizon coincides with the infinite redshift surface, and only for spin black holes can they be separated.Only outside this surface can particles remain stationary under external force.The area between the infinite redshift surface and the event horizon becomes the energy layer.The size of the inner and outer infinite redshift surface is:
Different from the viewing surface, it is two ellipsoidal surfaces, so it is the included angle with polar coordinates
of
Minimum stable circular orbit (ISCO)
For Newton's law of universal gravitation, particles can stably circle around the central celestial body at any distance.However, under the general theory of relativity, there is a minimum stable circular orbit (ISCO). Any small inward disturbance will cause objects in the orbit to fall into the black hole along the spiral, and any outward disturbance (according to the energy of the disturbance) may cause objects to spin into the black hole, make a stable rotation at a farther distance, or escape to infinity.The size of ISCO is related to the rotation of the black hole. For Schwarzschild black hole, its size is:
For a rotating black hole, the minimum stable circular orbit of particles with the same rotation direction as the black hole will decrease.
Classification characteristics
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Physical property division
According to the physical characteristics of black holes, such as mass, angular momentum and charge, black holes can be divided into four categories:
Black hole type
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Non rotating and non charged black hole
Its space-time structure was calculated by Schwarzschild in 1916, called Schwarzschild black hole.
Non rotating charged black hole
It is called Reissner Nordstrom black hole.The space-time structure was calculated by Reissner and Nordstrom from 1916 to 1918.
Rotating uncharged black hole
It is called Kerr black hole.The space-time structure was calculated by Kerr in 1963.
Rotating charged black hole
It is called Kerr Newman black hole [MOU2].The space-time structure was calculated by Newman in 1965.
Kerr Newman black hole
Figure: Bright knots in M87 galactic nucleus and extragalactic jets (1999~2006 Hubble Space Telescope ultraviolet images).The brightness of this junction (called HST-1) is constantly changing, even brighter than M87 itself.Image from NASA 2009
A rotating and charged black hole is called a Kerr Newman black hole.The event horizon and the infinite redshift surface of the black hole with this structure will be separated, and the event horizon will be divided into two (outer horizon r+and inner horizon r -), and the infinite redshift surface will also be divided into two (rs+and rs -).The area between the outer horizon and the infinite redshift surface is called the energy layer, where energy is stored.Objects crossing the outer infinite redshift surface may still escape from the black hole, because the energy layer is not a unidirectional membrane region.
In the unidirectional membrane area, r is time and s is space.Objects passing through the outer horizon and entering the unidirectional membrane area will only be able to move forward and enter the black hole through the inner horizon.The area beyond the inner horizon is not a unidirectional membrane area, where there is a "odd ring", that is, the place where time ends.The object can move freely within the inner vision. Because the odd ring generates repulsion, the object will not hit the odd ring. However, there is an extremely interesting space-time zone near the odd ring, where there is a "closed time like line". Objects moving along this space-time curve can constantly return to their own past.
Supermassive black hole
Black holes accrete giant stars
A supermassive black hole is hidden in the center of most galaxies in the universe, including the Milky Way, where we live.These black holes have different masses, about 1 million to 40 billion solar masses.Astronomers detect the intense radiation and heat from the accretion disk around the black holeInfer the existence of these black holes.When matter falls under the gravity of a strong black hole, it will form an accretion disk around it and spiral down. In this process, potential energy will be released quickly, heating the matter to extremely high temperature, thus giving off strong radiation.The black hole consumes the surrounding material by accretion, which is one of its growth modes.
Figure: Black hole image, in the center of the Milky Way where we live, all stars in the Milky Way revolve around a supermassive black hole at the center of the silver center.
It is generally believed that there are several possible sources of supermassive black holes: first, the giant molecular clouds in the early universe directly collapsed into a seed black hole about 100000 times the mass of the sun;The second is that the first generation of super massive stars in the universe collapsed into seed black holes with about 10 to 100 solar masses after death.With the continuous accretion of the seed black holes and the merging of the two seed black holes, they eventually grow into supermassive black holes.
The average density of supermassive black holes can be very low, even lower than that of air.This is because the Schwarzschild radius is proportional to its mass, while the density is inversely proportional to its volume.Since the volume of a sphere (such as the event horizon of a non rotating black hole) is proportional to the radius cube, and the mass increases almost in a straight line, the volume growth rate will be greater.Therefore, the density will decrease as the radius of the black hole increases.
May 24, 2023James Webb Space TelescopeJames Webb Space Telescope (JWST for short) and Chandra X-ray Observatory have certified that the most distant black hole observed so far is about 13.2 billion light-years away from the Earth, with a mass about 10 million to 100 million times that of the sun, which is equivalent to the sum of the masses of all stars in its host galaxy.The supermassive black hole in the adjacent universe generally accounts for only 0.1% of the mass of its host galaxy.It is located in the center of the UHZ1 galaxy. Since Abell 2744 galaxy cluster is sandwiched between it and the Earth, the infrared ray emitted by the UHZ1 galaxy and the X-ray emitted by the gas around the black hole are amplified through the gravitational lens, which can be observed by us.
This supermassive black hole was formed only 470 million years after the Big Bang. If it is a black hole formed by the collapse of the first generation of stars, it is not old enough to grow into such a huge black hole, so it tends to prove that the first generation of black holes in the universe came from the direct collapse of gas clouds.This achievement has been published in the journal Nature Astronomy.[4]
At present, the most massive black hole directly observed by humans is TON 618.This behemoth has about 66 billion solar masses.The shadow area it forms (the light entering the area is severely deflected, about twice the size of the event horizon), and it takes several weeks for the light to go through.[7]
Medium mass black hole
Since the 1990s, astronomers have successively found a number of objects with extremely high X-ray luminosity in distant galaxies. They may be the medium mass black holes that people have been looking for, or several or dozens of solar mass stellar black holes with special radiation mechanisms.The international astronomical and astrophysical circles have always been difficult to reach a conclusion on this.Medium mass black holes are between stellar black holes and supermassive black holes, with a mass of 1 to 1 million times that of the sun.[MOU2] Since such objects are very far away from us, usually tens of millions of light years, and the light pollution caused by X-ray irradiation of black hole accretion disk is also very strong, it is extremely difficult to measure them.
November 2020, Laser Interferometer Gravitational Wave Observatory VirgoGravitational wave detector(LIGO Virgo) cooperation group announced that they had detected for the first time the gravitational wave generated by a medium mass black hole.This gravitational wave detection study involving more than 1500 researchers shows that about 7 billion years ago, two black holes with masses 66 times and 85 times of the sun respectively formed a new medium mass black hole after a violent collision.This is also the first medium mass black hole detected so far.The medium mass black hole detected this time has a mass 142 times that of the sun.[8]
Stellar black hole
In the early morning of November 28, 2019, international scientific journals《natural》A major discovery made by the National Astronomical Observatory of the Chinese Academy of Sciences was released.[9]Relying on China's self-developed National Major Science and Technology Infrastructure Guo Shoujing Telescope (LAMOST), the research team found a stellar black hole with the largest mass so far, and provided a new method to find black holes by taking advantage of LAMOST's sky survey.This black hole with a mass of 70 times that of the sun has exceeded the upper limit of the mass of a stellar black hole predicted by theory[10], overturning people's understanding of the formation of stellar black holes, which is expected to promote the innovation of stellar evolution and black hole formation theory.
On April 29, 2020《natural》A magazine article questioned that there is no conclusive evidence that the mass of a black hole is greater than 50 times the mass of the sun.[11]Later, the team that discovered the black hole replied that the observation data still showed that the black hole had 23~65 times the mass of the sun.[12]
Explore History
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Early exploration
In 1970, the US "Freedom" satellite discovered Cygnus X-1, which is different from other ray sources. On Cygnus X-1 is a huge blue planet that weighs more than 30 times more than the sun. The planet is pulled by an invisible object weighing about 21 solar masses.Astronomers agree that this object is a black hole, which is the first black hole discovered by humans.
In 1928, astrophysicistChandraseka, SubramanianSubrahmanyan Chandrasekhar went to Cambridge, England to study under the English astronomer Sir Arthur Eddington.Chandraseka realized that there is a limit to the repulsive force that Pauli exclusion principle can provide.The maximum velocity difference of particles in stars is limited to the speed of light by relativity.This means that when the star mass is large enough, the repulsion force caused by the incompatibility principle will be smaller than the role of gravity.Chandraseka calculated that;A cold star about 1.4 times the mass of the sun cannot support itself against its own gravity (this mass is called the Chandraseka limit).Lev Davidovich Landau, a former Soviet scientist, found a similar conclusion almost at the same time.
If the mass of a star is smaller than the Chandraseka limit, it will eventually stop shrinking and finally become a "white dwarf" with a radius of several thousand miles and a density of several hundred tons per cubic inch.White dwarfs are supported by the repulsive force of the principle of incompatibility between electrons in their matter.The first observed white dwarf is a companion star of Sirius (the brightest star in the night sky)（Sirius B ）。
Landau also pointed out that there is another possible final state for stars.Its ultimate mass is about twice to twice the mass of the sun, but its volume is even much smaller than that of a white dwarf star.These stars are supported by the repulsive force of the incompatibility principle between neutrons and protons, not electrons.So they are called neutron stars.Their radius is only about 10 miles, and their density is several hundred million tons per cubic inch.When neutron star was first predicted, there was no way to observe it. It was a long time later that people found pulsar, a neutron star that rotates at high speed and emits periodic signals.
In 1967, a graduate student in CambridgeJocelyn Bell(Jocelyn Bell) discovered an object that emits regular pulses of radio waves from the sky, which further encouraged the prediction of the existence of black holes.At first Bell and her mentor Anthony Hervish thought that they might have contacted the alien civilization in our galaxy.At the seminar announcing their discovery, they called the four earliest sources LGM1-4, which means "Little Green Man".Eventually they and everyone else concluded that these objects, called pulsars, were actually rotating neutron stars.
On the other hand, when stars whose mass is greater than the Chandraseka limit run out of fuel, they will have a big problem: under certain circumstances, they will explode or throw out enough material to reduce their mass below the limit, so as to avoid the catastrophic gravitational collapse. No matter how big the star is, this will always happen.Eddington refused to believe Chandraseka's results.Eddington believes that a star cannot collapse into a point.This is the view of most scientists: Einstein himself wrote a paper announcing that the volume of the star would not shrink to zero.The hostility of other scientists, especially his former teacher, Eddington, the main researcher of star structure, made Chandraseka abandon this work and turn to other astronomical problems such as the movement of star clusters.However, when Chandraseka won the 1983 Nobel Prize, at least in part because of his early work on the mass limit of cold stars.
Chandraseka pointed out that the Pauli incompatibility principle of electrons cannot prevent the collapse of stars whose masses are greater than the Chandraseka limit. At this time, the electrons in the stars will be pressed into the protons to form neutrons, and the whole star will also evolve into a neutron star.What would happen if a star collapsed beyond the mass limit of a neutron star was unknown at that time.This problem was first solved by Robert Oppenheimer, a young American, in 1939. He showed that a star with a mass greater than a certain value would directly collapse into a black hole, and this mass limit was the Ptoleman Oppenheimer Volkow limit.However, the results he obtained showed that there would be no more results with the telescope at that time.Later, due to the interference of World War II, Oppenheimer was involved in the atomic bomb program.After the war, most scientists were attracted to physics at the atomic and nuclear scales, so the problem of gravitational collapse was forgotten by most people.
When the concept of black hole was first proposed, there were two light theories: one was the particle theory of light approved by Newton;The other is the wave theory of light.Because of the wave particle duality of quantum mechanics, light can be regarded as both wave and particle.In the wave theory of light, it is not clear how light responds to gravity.But if light is composed of particles, people can expect that they are just as affected by gravity as shells, rockets and planets.At first people thought that light particles moved infinitely fast, so gravity could not slow them down. But in 1676, Danish astronomersRomer(Ole R ø mer) The discovery of the limited speed of light shows that gravity can have an important effect on it.
In 1783, the supervisor of CambridgeJohn Mitchell On the basis of this assumption, John Michell published an article in the Philosophical Journal of the Royal Society of London.He pointed out that a star with enough mass and enough compactness would have such a strong gravitational field that even light could not escape - any light emitted from the surface of the star would be attracted back by the star's gravity before reaching far away.Michel suggested that there may be a large number of such stars. Although we cannot see them because the light emitted from them will not reach us, we can still feel their gravitational attraction.This is what we call a black hole.[11]
In fact, because the speed of light is fixed, it is not rigorous to treat light as artillery shells in Newton's theory of gravity.(The projectile launched from the ground to the sky decelerates due to gravity, and finally stops rising and returns to the ground; however, a photon must continue to rise at a constant speed, so how Newton's gravity affects light.) Before Einstein put forward the general theory of relativity in 1915, there was no theory about how gravity affects the coordination of light,Then the meaning of this theory for massive stars was understood.
When observing a star collapsing and forming a black hole, because there is no absolute time in relativity, each observer has his own time measurement.Because of the gravitational field of the star, someone's time on the star will be different from someone's time in the distance.Suppose there is a fearless astronaut on the surface of the collapsing star collapsing inward with the star. According to his watch, a signal is sent every second to a spaceship orbiting the star.At a certain time in his watch, such as 11 o'clock, the star just shrinks to its critical radius. At this time, the gravitational field is strong enough that nothing can escape, and his signal can no longer be transmitted to the spacecraft.When he arrived at 11 o'clock, his partner in the spaceship found that the time interval of a series of signals sent by astronauts was getting longer and longer.But this effect was very small before 10:59:59.Between the two signals sent at 10:59:58 and 10:59:59, they only need to wait a little longer than one second. However, they must wait an infinite amount of time for the signal sent at 11:00.According to the astronauts' watches, light waves are emitted from the surface of stars between 10:59:59 and 11:00;Seen from the spaceship, the light wave is scattered to an infinite time interval.The time interval for receiving this string of light waves on the spaceship becomes longer and longer, so the light from the star becomes more and more red and lighter. Finally, the star becomes so dim that it can no longer be seen from the spaceship, and all that remains is a black hole in space.However, this star continues to act on the spaceship with the same gravity, making the spaceship continue to revolve around the black hole formed.
Black hole engulfs neutron star (computer simulation)
However, the above scenario is not completely realistic due to the following problems.The farther away from the star, the weaker the gravity is, so the gravity acting on the fearless astronaut's feet is always greater than that acting on his head.Before the star has shrunk to the critical radius and formed the event horizon, the difference in force has pulled the astronaut into the shape of spaghetti, or even torn him apart!However, there are objects with much greater mass in the universe, such as the central region of galaxies, which suffer gravitational collapse and produce black holes;An astronaut on such an object will not be torn apart before the black hole forms.In fact, when he reached the critical radius, he would not have any strange feeling, even when he passed the point of never returning, he did not notice.However, as this area continues to collapse, within a few hours, the difference between the gravity applied to his head and feet will become so large that it will be torn apart again.
Roger Penrose Roger Penrose's research between 1965 and 1970 pointed out that according to the general relativity, there must be a singularity of infinite density and space time curvature in a black hole.This is quite similar to the Big Bang at the beginning of time, except that it is the end of time for a collapsed object and astronauts.At this singularity, both the laws of science and the ability to predict the future have failed.However, any observer remaining outside the black hole will not be affected by the failure of predictability, because neither light nor any other signal from the singularity can reach.This amazing fact led Roger Penrose to put forward the cosmic surveillance conjecture, which can be interpreted as: "God hates naked singularities." In other words, singularities generated by gravitational collapse can only occur in places like black holes, where it is gracefully covered by the event horizon and not seen by the outside world.Strictly speaking, this is the so-called weak cosmic surveillance conjecture: it prevents the observers left outside the black hole from being affected by the predictable failure at the singularity, but it cannot help the poor astronaut who unfortunately fell into the black hole.
General Relativity Correlation
There are some theoretical solutions to the general relativistic equation, which make it possible for our astronauts to see naked singularities.He may be able to avoid hitting the singularity and go through a "wormhole" to another region of the universe.It seems that this provides a huge possibility for space time travel.Unfortunately, all these solutions seem to be very unstable;A minimal interference, such as the existence of an astronaut, will change it, so that he can't see the singularity before he hits it and ends his time.In other words, the singularity always occurs in his future, and never in the past.The strong cosmic surveillance conjecture means that in a realistic solution, the singularity always or completely exists in the future (such as the singularity of gravitational collapse), or in the past (such as the Big Bang).Because it is possible to travel to the past near the bare singularity, there is great hope that some form of cosmic surveillance conjecture will be established.
The event horizon, that is, the boundary of the non escape region in space and time, is just like the one-way film surrounding the black hole: objects, such as careless astronauts, can fall into the black hole through the event horizon, but nothing can escape from the black hole through the event horizon.(Remember that the event horizon is the space time orbit of light trying to escape from the black hole, and nothing can move faster than light.) People can apply the words of Dante, the poet, to the event horizon: "People entering from here must abandon all hope." Once anything or anyone enters the event horizon,It will soon reach the end of the infinite dense area and time.
General relativity predicts that the moving weight will cause the radiation of gravitational waves, which are ripples of space time curvature propagating at the speed of light.Gravitational waves are similar to ripples in electromagnetic fields, but it is much more difficult to detect them.Like light, it takes away the energy of the objects that emit them.Because any energy in motion will be carried away by the radiation of gravitational waves, it can be expected that the system of a large mass object will eventually tend to a constant state.(This is quite similar to throwing a piece of cork into the water. At first, it turned up and down for a long time, but when the ripple took its energy away, it finally calmed down.) For example, the earth orbiting the sun produced gravitational waves.The effect of its energy loss will change the Earth's orbit, making it gradually closer to the sun, and finally hit the sun, in this way, it will return to the final unchanged state.In the case of the Earth and the sun, the rate of energy loss is very small - only about one can be ignitedElectric heaterThis means that it will take about 100 billion years for the earth to collide with the sun. There is no need to worry about it immediately.The process of changing the Earth's orbit is so slow that it can't be observed at all.However, this effect was observed in PSR1913+16 (PSR stands for "pulsar", a special neutron star that emits regular radio pulse) binary star system discovered in 1974.This system consists of two neutron stars moving around each other. Due to the radiation of gravitational waves, their energy losses make them close to each other in spiral orbits.
When a star collapses to form a black hole, it will move much faster, so the rate of energy being carried away is much higher.So it will not take too long to reach the same state.People would think that it would depend on all the complex characteristics of the star that formed the black hole - not only its mass and rotation speed, but also the different densities of different parts of the star and the complex movement of the gas in the star.If black holes are as changeable as the original objects that collapsed to form them, it will be very difficult to predict them in general.
However, Werner Israel, a Canadian scientist, revolutionized the study of black holes in 1967.He pointed out that according to general relativity, non rotating black holes must be very simple spheres;Its size only depends on their mass, and any two such black holes with the same mass must be equal.In fact, they can be described by Einstein's special solution, which was found by Karl Schwarzenegger in 1916, shortly after the discovery of general relativity.At the beginning, many people (including Israel himself) believed that since a black hole must be spherical, a black hole can only be formed by the collapse of a spherical object.Therefore, any actual non spherical star will only collapse to form a naked singularity.
However, some people, especiallyRoger Penrose andJohn Wheeler (John Archibald Wheeler) advocates a different interpretation.They argue that the rapid motion involving the collapse of the star shows that the gravitational wave released by it makes it more and more spherical, and when it finally becomes static, it will become an accurate sphere.According to this view, any non rotating star, no matter how complex its shape and internal structure are, will end up in a spherical black hole after gravitational collapse, and its size only depends on its mass.This view was further supported by the calculation and was soon accepted by everyone.
Israel's results only deal with black holes formed by non rotating objects.In 1963, Roy Kerr, a New Zealander, found a family of solutions to the general relativistic equation describing a rotating black hole.These "Kerr" black holes rotate at a constant speed, and their size and shape only depend on their mass and rotation speed.If the rotation is zero, the black hole is spherical, and this solution is the same as the Schwarzschild solution.If there is rotation, the equator of the black hole will bulge out (just as the earth or the sun bulges out due to rotation), and the faster the rotation, the more bulges.From this, it is speculated that if Israel's result is extended to include the case of rotating bodies, any rotating body collapsing to form a black hole will finally end in a static state described by Kerr's solution.
The study of black holes is one of the rare cases in the history of science. Without any observed evidence to prove its theory is correct, it has been developed to a very detailed level as a mathematical model.Indeed, this is often the main argument against black holes: how can one believe an object whose basis is only a calculation based on the suspect general relativity?However, in 1963, astronomer Maarten Schmidt of Paloma Observatory in California measured the redshift of a dim quasar in the direction of the radio source called 3C273 (i.e. 273 in the third category of the Cambridge Radio Source Catalogue).He found that the gravitational field could not cause such a large red shift - if it was gravitational red shift, such stars must have such a large mass and be so close to the Earth that they would interfere with the orbits of planets in the solar system.This suggests that the redshift is caused by the expansion of the universe, which further indicates that the object is very far away from the Earth.Since it can be observed at such a distance, it must be very bright, that is, it must radiate a lot of energy.One would think that the mechanism for generating such a large amount of energy seems to be not just a star, but the gravitational collapse of the entire central region of a galaxy.The gravitational collapse in such a small area is reminiscent of a black hole.Later research on quasars showed that.It is one of the active galactic nuclei, with a supermassive black hole at its center.
Black hole magnetic field
On December 4, 2015, with the help of the Event Horizon Telescope (EHT), astronomers detected the magnetic field outside the event horizon of the supermassive black hole Sagittarius A * in the center of the Milky Way Galaxy.Scientists found that some regions near the black hole were chaotic, with disordered magnetic circles and vortices, like spaghetti mixed together.On the contrary, the magnetic field in other regions is much more orderly, which may be the region generated by the material jet.The magnetic field around the black hole will change significantly in a period as short as 15 minutes.[13]On March 24, 2021, the Event Horizon Telescope Cooperation Group released the polarization image of M87 supermassive black hole[3], revealing the magnetic field information of the hot gas surrounding M87 black hole.
Hawking's theory
At the beginning of 2014, Hawking pointed out that the black hole in the classical theory does not exist, and proposed a new "gray hole" theory.The theory holds that matter and energy will be released into the universe again after being trapped by black holes for a period of time.The concept of grey hole is mainly to solve the contradiction between general relativity and quantum mechanics firewall paradox.[14]
In January 2016, Hawking, together with physicists Malcolm Perry and Andrew Strominger, put forward a new theory: the gap of the black hole that allows information to "escape" is composed of "soft charged hairs", which are particles composed of photons and gravitons located on the horizon line,These particles with extremely low or even zero energy can capture and store the information of particles falling into the black hole.[15]
Black hole photograph
April 5, 2017, according to the United Kingdom《New scientist》The online version of the magazine said that the "Earth sized" telescope was ready to "penetrate the heart of the galaxy".It consists of 8 radio observatories around the world, simulating an astronomical equipment with planetary scale.This group of giant astronomical equipment is called the Event Horizon Telescope (EHT), which includes radio telescopes located in Spain, the United States and Antarctica.The telescope targets the Sagittarius A * black hole 25000 light-years away from the Earth and M87 galaxy black hole 55 million light-years away from the Earth.The former is a very bright and dense radio wave source located in the center of the Milky Way Galaxy, which is part of the Sagittarius A radio source. The "heart" of the radio source is where the supermassive black hole is located. This 4 million solar mass black hole is also regarded as the best object to study black hole physics;The mass of the black hole at the core of M87 galaxy is estimated to reach 6.5 billion solar masses.EHT hopes to see the truth of these two black holes through continuous observation of their directions.
At 9:00 on April 10, 2019 (21:00 on April 10, Beijing time), astronomers from all over the world simultaneously announced the "truth" of M87 black hole.The black hole is located at the center of a giant elliptical galaxy M87 in the constellation Virgo, 55 million light-years away from Earth, and its mass is about 6.5 billion times that of the sun.There is a shadow in its core area, surrounded by a crescent halo.Einstein's general theory of relativity has been proved to hold under extreme conditions.
M87 center supermassive black hole (ESO, European Southern Observatory, 2019)[1]
At 10:00 p.m. on March 24, 2021, Beijing time, the event horizon telescope (ETH) cooperative organization, which Chinese scientists participated in, announced the latest research results: the image of M87 supermassive black hole in polarized light.This is the latest progress after successfully capturing the first black hole picture in human history two years ago, and it is also the first time that humans have measured the polarization information characterizing the magnetic field near the edge of a black hole.This result is crucial to explain how M87 galaxy, 55 million light-years away from our Earth, propagates huge jets of energy outward from its core.[3]
Polarization image of M87 black hole (EHT cooperation group 2021)[16]
Figure: The first picture of the black hole at the center of the Milky Way Galaxy was made like this (EHT cooperation group 2022)
In May 2022, at the press conference held at the same time around the world, including Shanghai, astronomers showed the first picture of the supermassive black hole at the center of our Milky Way Galaxy.[17]This result provides an empirical evidence that this object is a black hole, and provides valuable clues for understanding the behavior of this "monster" that is considered to reside at the center of most galaxies.This photo was "taken" by the international research team, the Event Horizon Telescope (EHT), through a global network of radio telescopes.
This is the first picture of the supermassive black hole Sgr A * in the center of our Milky Way Galaxy, and the first direct visual evidence of the existence of this black hole.This photo was captured by a virtual telescope (EHT) as large as the earth, which is composed of eight radio telescopes distributed on the earth.The telescope is named after the event horizon (that is, the boundary of a black hole where light cannot escape).
Because the black hole does not emit light, we cannot see the black hole itself, but the revolving luminous gas gives a signal of its existence: a dark central region (called shadow) surrounded by a bright ring structure.The (radio) light shown in the photo is caused by the strong gravitational bending of the black hole, whose mass is more than four million times the mass of the sun.
This photo is an average of different photos extracted by the EHT team from Sgr A *'s 2017 observation data.[29]
Figure: Full resolution M87 black hole image obtained by machine learning method (Princeton Institute of Advanced Research, 2023)
In 2023, the research team of Princeton Institute of Advanced Studies used the“Event horizon telescope”The data obtained by the cooperation organization (EHT) uses the machine learning technology of principal component interferometric modeling (PRIMO) to achieve the resolution of the black hole image to the physical resolution of the array for the first time, and finally generate a new M87 black hole image.[18]
fractal geometry
Black hole concept map
In 2015, an international research team composed of scientists from the United States, Britain, Italy and Austria found that black holes, gravitational waves and dark matter all have fractal geometric characteristics according to previous research and supercomputer simulation.Some experts believe that this major discovery will lead to a profound understanding of many different fields of astronomy and even physics.
Black hole is a kind of celestial body with infinite density and infinitely small volume in the space of the universe. All physical theorems will fail when they encounter black holes;It is produced by gravitational collapse of a star with enough mass after the fuel of nuclear fusion reaction is exhausted and "dies".When the black hole "burps", it means that some celestial body is "swallowed" by the black hole, and the black hole "grows" by swallowing the matter falling into it;When a black hole "eats" a large amount of material, a high-speed plasma jet will escape from the edge of the black hole.Scientists use the theories of fluid dynamics and gravity and use supercomputers to simulate them and conclude that the growing black hole will form a fractal surface if it "eats".
Professor John Wheeler, a famous American physicist, once said that anyone who is not familiar with fractal geometry in the future cannot be called a cultural person in science.Professor Zhou Haizhong, a famous Chinese scholar, once pointed out that fractal geometry not only shows the beauty of mathematics, but also reveals the essence of the world, thus changing the way people understand the mysteries of nature;It can be said that fractal geometry is the geometry that truly describes nature, and its research has greatly expanded the cognitive domain of human beings.It can be seen that fractal geometry has an extremely important scientific position.
Black hole is the most mysterious natural phenomenon in the universe.The reason why it has fractal geometry is still a mystery.
Black hole recording
In August 2022, the National Aeronautics and Space Administration (NASA) released an audio clip. The sound was synthesized based on the gravitational wave of the Perseus black hole 200 million light years away.It is reported that this sound wave is from NASAChandra X-ray Observatory。[19]
Heartbeat of black hole
With the help of the X-ray telescope, we can see the periodic light changes produced by the accretion disk around the black hole, just like the "heartbeat" of the black hole.The first object to discover heartbeat was GRS 1915+105 discovered by the Granat X-ray satellite in 1992, which is also the first radio super bright source of the Milky Way Galaxy discovered by humans.It is an X-ray black hole binary system, including a black hole and a star. The masses of both have reliable measurements, which are about 12 solar masses and 0.7 solar masses, respectively.[20]
frontier research
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Plasma
Researchers from the Max Planck Institute for Nuclear Physics and the Helmholtz Berlin Center in Germany have successfully generated plasma around black holes in the laboratory using the Berlin Synchrotron (BESSY Ⅱ).Through this research, astrophysical experiments that can only be carried out in space by artificial satellites can also be carried out on the ground, and many astrophysical problems are expected to be solved.The gravity of a black hole is very large, and it will absorb all materials.After entering the black hole, nothing can escape from the boundary of the black hole.As the temperature of the inhaled object increases, a high-temperature plasma will be generated that separates the nucleus from the electron.
The absorption material of black holes will produce X-rays, which in turn will stimulate a large number of chemical elements in them to emit X-rays with unique lines (colors).Analyzing these lines can help scientists learn more about the density, velocity and composition of the plasma near the black hole.
Iron plays a key role in this process.Although the reserves of iron in the universe are not as rich as lighter hydrogen and helium, it can better absorb and re emit X-rays, and the emitted photons therefore have higher energy and shorter wavelength (making them have different colors) than the photons emitted by other lighter atoms.
X-rays emitted by iron will also be absorbed when passing through the medium around the black hole.In this so-called photoionization process, the iron atom usually undergoes several times of ionization, and more than half of the 26 electrons it contains will be removed, eventually producing charged ions, which will gather into plasma. Researchers can reproduce this process in the laboratory.
The core of the experiment is the electron beam ion trap designed by Max Planck Institute for Nuclear Physics.In this ion trap, the iron atom is heated by a strong electron beam and is ionized 14 times.The experimental process is as follows: a mass of iron ions (only a few centimeters long and as thin as hair) is suspended in an ultrahigh vacuum under the action of magnetic and electric fields. The photon energy of X-ray emitted by the synchrotron is selected by a "monochromator" with high accuracy and applied to iron ions as a very thin but concentrated beam.
The spectral lines measured in the laboratory match the results observed by the Chandra X-ray Observatory and the XMM Newton Telescope.In other words, researchers artificially created black hole plasma in space in the ground laboratory.
This novel method combines the ion trap of charged ions with the synchrotron radiation source, so that people can better understand the plasma around the black hole or the active galactic nucleus.The researchers hope that the combination of the EBIT spectroscope with the clearer third-generation (PETRA III, a synchrotron radiation source that began operating in Hamburg, Germany, in 2009) and fourth generation (X-ray free electron laser XFEL) X-ray sources will bring more fresh vitality to this research field.
Artificial black hole
The idea of an artificial black hole was first put forward by Professor William Unruh of the University of British Columbia in Canada in the 1980s. He believed that the behavior of sound waves in fluid is very similar to that of light in black holes. If the velocity of fluid exceeds that of sound, then an artificial black hole has actually been established in the fluid.However, due to the lack of sufficient gravity, the artificial black holes that Dr. Leonhardt intends to create cannot "swallow everything around" like real black holes except light.
When a particular star larger than our sun explodes in the final stage of life, nature will form a black hole.They concentrate large amounts of material in very small spaces.Suppose that during the process of proton collision in the Large Hadron Collider to produce particles, a tiny black hole is formed, and the energy of each proton is equivalent to that of a mosquito in flight.Astronomical black holes weigh more than anything produced by the Large Hadron Collider.According to the gravity property described by Einstein's theory of relativity, it is impossible to generate a small black hole in the LHC.However, some pure theories predict that the Large Hadron Collider will produce such micro black holes.All of these theories predict that such black holes produced by the Large Hadron Collider will evaporate instantaneously.Therefore, the black hole it produces will have no time to accumulate matter, producing results visible to the naked eye.
On September 10, 2008, with the first proton beam running through the whole colliderHadron collider(LHC) officially started.Up to now, LHC has not seen black holes in the laboratory.
Black hole bomb
In January 2001, Ulf Leonhardt, a theoretical physics scientist at the University of St. Andrews, announced that he and other British researchers would create a black hole in the laboratory. No one was surprised at that time.But Russia《Pravda》Recently, it was revealed that Russian scientists predicted that black holes could not only be made in laboratories, but also that in 50 years' time, the "black hole bomb" with huge energy would dwarf the "atomic bomb" that has turned people pale.
A. P. Trofimenko, a Russian scientist, believes that a real black hole in the universe that can devour everything can also be "manufactured" through the laboratory: a black hole the size of an atomic nucleus will have more energy than a nuclear factory.If human beings one day create a black hole bomb, the energy generated by the explosion of a black hole bomb will be equivalent to the simultaneous explosion of several atomic bombs, which can cause at least one billion deaths. "[21]
Capture nebula
The nebula is approaching the central black hole of the Milky Way (concept map)
In December 2011, an international research team using the European Southern Observatory's Very Large Telescope (VLT) found that a nebula was approaching the black hole at the center of the Milky Way Galaxy and would be swallowed by it.
This is the first time astronomers have observed the process of black holes "catching" nebulae.Observations show that the mass of this nebula is about three times that of the Earth, and its position is gradually close to the "Sagittarius A *" black hole.The mass of this black hole is about 4 million times that of the sun, and it is the nearest large black hole.Researchers believe that by 2013, this nebula will be very close to the black hole and may be gradually swallowed by the black hole.[22]
Black hole hairless
There are only three significant physical quantities inside a black hole: mass, charge and angular momentum.
In 1973, Hawking, B. Carter and others strictly proved the "black hole hairless theorem": "no matter what kind of black hole, its final property is only determined by a few physical quantities (mass, angular momentum, charge)".That is, after the formation of a black hole, only these three conserved quantities that cannot be transformed into electromagnetic radiation remain, and all other information ("hair") is lost. The black hole has almost no complex properties of the matter that formed it, and has no memory of the shape or composition of its predecessor.So the term "black hole" inventor Wheeler jokingly called this characteristic "black hole hairless".
For physicists, a black hole or a piece of sugar cube are extremely complex objects, because their complete description, including their atomic and nuclear structures, requires billions of parameters.In contrast, a physicist who studies the outside of black holes has no such problem.A black hole is an extremely simple object. If you know its mass, angular momentum and charge, you will know everything about it.Black holes hardly retain any of the complex properties of the matter that formed them.It has no memory of the shape or composition of its predecessor, but only maintains mass, angular momentum and electric charge.Simplification is perhaps the most basic feature of black holes.The inventor of most terms about black holes, York Wheeler, called this feature "black hole hairless" 60 years ago.
Black hole information paradox
For decades, cosmologists have been puzzled by the problem that black holes can destroy the information that makes them.Black hole is a celestial body determined by its mass, angular momentum and electric charge.Any complex data absorbed by it will only retain these three information.If so, it is impossible to know other characteristics of the object that initially formed the black hole, as well as other characteristics of the object that the black hole sucked in.However, information in quantum mechanics will be preserved forever, and you can use that information to reconstruct the past of an object.
Stephen Hawking proposed a solution. He believed that a black hole would generate Hawking radiation until it evaporated, so its past can only be found from the information of its radiation.How to restore this information from radiation is still a mystery.
Since Hawking proposed that black holes can radiate energy, the debate on whether black holes can retain the complete information before matter has never stopped.Some people think that to understand the data running into a black hole, we need to see not only the particles emitted by Hawking radiation, but also the interactions between them.These interactions include gravity and the exchange of interacting media (such as photons).Through these interactions, an observer can theoretically restore the information of objects in the black hole.[23]
Time reversal
From the thermodynamic point of view, space-time is also considered as hologram. According to the holographic principle, it is related to the surface area in a given area, and can also be further explained as the time direction of thermodynamics.Since the past and future holographic screen areas increase in different directions, the direction of time can correspond to two different types of holographic screens.[24]
J1144
On June 15, 2022, an international research team from Australian National University unexpectedly discovered the fastest growing black hole in 9 billion years.This black hole, code named J1144 for short, has a mass of 3 billion times that of the sun. On average, it can "devour" an Earth sized object every second, and its quasar brightness is 7000 times the brightness of all the lights in the Milky Way.[25]
Jet precession
On September 27, 2023, astronomers captured the direct evidence of the rotation of M87 black hole, providing new insights into the most mysterious celestial body in the universe, which was published in the journal Nature.[26]The 22 year long radio observation results show that the magnetic field around the black hole's rotation cuts the charged particles to accelerate and produce a jet, and the jet periodically precesses around the black hole with a period of 11 years.This indicates that there is a dislocation between the rotation axis of the black hole and the accretion disk, causing the jet to swing like a gyroscope.[27]This phenomenon is in line with Einstein's general theory of relativity's prediction that "if the black hole is in a rotating state, it will lead to the dragging effect of the reference frame".
Observation results
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On February 26, 2015, a team from Peking University published an article in the journal Nature, saying that a black hole with a mass of 12 billion times that of the sun was found in a super bright quasar (a kind of AGN) 12.8 billion light years away, and that the black hole had existed in the early days of the formation of the universe.[28]
In 2017, Polish astronomer Szymon KozłWski), using Sloan Digital Sky Survey (SDSS) data, pointed out that the black hole mass of quasar J140821.67+025733.2 is about 196 billion solar mass.However, this value is controversial in the academic community and is considered to be problematic.[29]
On December 7, 2017, scientists from the Carnegie Institution of Science found a distant supermassive black hole whose mass is 800 million times that of the sun.[30]
In April 2019, the Event Horizon Telescope (EHT) cooperation team first released the central black hole of M87 galaxy, which is also the first black hole photo taken by humans.[1]
On April 14, 2021, the Shanghai Astronomical Observatory announced the latest observation results, and the multi band "fingerprint" of M87 black hole was successfully captured.[31]
In May 2022, the picture of the supermassive black hole Sagittarius A * in the center of the Milky Way was first released by the EHT cooperation group.
In August 2022, researchers from the National Astronomical Observatory of the Chinese Academy of Sciences released the first batch of wide field X-ray images and energy spectra of celestial bodies observed by EP-WXT pathfinders.The instrument can simultaneously detect X-ray sources in multiple directions in one observation.These include stellar mass black holes and neutron stars.[32]
On November 4, 2022, researchers from the Harvard Smithsonian Center for Astrophysics in the United States published a report that they found that the black hole that is currently known to be the closest to the Earth is located 1600 light-years away from the Earth.The researchers said that the black hole, named Gaia BH1, is located in the Ophiuchus galaxy, about 10 times the mass of the sun, and its distance from its companion star is equivalent to the distance between the Earth and the sun.The previously known nearest black hole is located 3000 light-years away from Earth.Researchers found the black hole when analyzing the data collected by the European Space Agency's space probe Gaia, and then confirmed its existence with the observations of the North Gemini telescope on Mauna Kea Mountain, Hawaii, USA.In addition to being closest to the Earth, Gaia BH1 is also a dormant black hole, which is different from more than 20 other black holes known in the Milky Way.Scientists discovered the "Gaia BH1" black hole by observing the movement of the companion star. The companion star revolves around the black hole, and its orbital distance is roughly the same as the distance of the Earth around the sun.[33-34]
In 2022, scientists observed an extremely rare astronomical spectacle - Tidal Disruption Event (TDE). At the same time, they detected that there was a matter jet "rushing" from the black hole to the earth at a speed close to the speed of light.[35]
On March 29, 2023, the University of Durham announced that a research led by the University had discovered a super black hole with a mass about 30 billion times that of the sun by using the gravitational lens effect.[36]
On April 10, 2023, according to the American Funny Science Network, American astronomers found a "runaway" black hole, which seemed to be running away from its host galaxy in space, dragging some gas and stars behind.The research team points out that if this discovery is confirmed, it will be the first observational evidence that a supermassive black hole can eject from its host galaxy and roam in interstellar space.Relevant research was published in Astrophysical Journal Letters.[37]
In May 2023, a team of astronomers led by the University of Southampton in the UK captured the largest ever cosmic explosion, which is believed to be caused by a huge gas cloud swallowed by a supermassive black hole.[38]
On January 9, 2023, scientists found that two supermassive black holes ate side by side.They grow at the same time, only 750 light-years apart. They are the closest black holes observed by scientists, and they will eventually melt into a huge black hole.[39]
In July 2023, it was reported that the international cooperation team led by Chinese scientists found that the black hole of the famous micro quasar GRS 1915+105 had a sub second low-frequency radio quasi periodic oscillation phenomenon, just like a weak radio "pulse".This is the first time that the "pulse" of a black hole has been observed in the radio band internationally, which is expected to open up new ideas for radio observation and theoretical research of black holes.The research was led by the Department of Astronomy of Wuhan University and the National Astronomical Observatory of the Chinese Academy of Sciences, and the relevant results were published in the international academic journal Nature on July 27.[40]
On September 1, 2023, Science published the latest research results of black hole accretion magnetic field mainly based on the observation results of Huiyan satellite in the form of a long article.The study found direct observational evidence for the formation of magnetic trapping accretion disks around black holes using the observation data of China's first space X-ray astronomical satellite, Insight, combined with ground radio and optical telescope observations.[41]
In February 2024, a team led by researchers from the Australian National University published a paper in the British journal Nature Astronomy, saying that they had discovered the fastest growing black hole known so far, and the mass of matter it swallowed every day was equivalent to one sun[43]。
According to the press release issued by the Australian National University on February 20, 2024, this research was completed by the university in cooperation with the University of Melbourne, the European Southern Observatory and the Sorbonne University in Paris, France.The mass of this black hole is 17 billion times that of the sun, and it is more than 12 billion light years away from the Earth.
The bulletin issued by the European Southern Observatory pointed out that the quasar code of the black hole is J0529-4351, which is not only the brightest quasar observed so far, but also the brightest object observed so far.
In April 2024, it was reported that an international research team composed of scientists from the United States, Italy and other countries detected the "burping" of a black hole for the first time: a giant black hole would "burp" once every 8.5 days, and the "burping" ejected from the black hole's accretion disk.The research team pointed out that a smaller black hole that constantly passes through the accretion disk of the black hole may be the reason for its hiccups.Relevant research papers were published in the journal Science Report on March 27.[45]
world record
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The densest object in the universe:Black holes are remnants of stars, which ended their lives in the form of supernovae.They are characterized by a space area where gravity is so strong that even light cannot escape.The boundary of this region is called the event horizon. At the center of the black hole is a singularity, and the mass of the dead star is compressed to a single point of zero size and infinite density.It is this singularity that produces the strong gravitational field of the black hole.(Guinness World Records)
scientific problems
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On June 27, 2022, at the closing ceremony of the 24th annual meeting of the Chinese Association for Science and Technology, the Chinese Association for Science and Technology solemnly released 10 cutting-edge scientific questions that guide scientific development, including "How did black holes in the universe form and evolve?"[42]。
