Neutron star is divided byblack holeThe star with the highest external density, whose evolution reaches its final stage, occurs through gravitational collapseSupernova explosionLater, it may become one of the few endpoints. The mass of a star that does not reach the mass that can form a black hole collapses at the end of its lifeWhite dwarfThe density of stars between them and black holes is many times greater than that of any matter on the earth.
be-allPulsarAre all neutron stars[8]But neutron stars are not necessarily pulsars. Pulses are pulsars.
In 1932, shortly after the discovery of neutrons by Chadwick, the Soviet physicist Landau proposed that there was a class of stars that could all be composed of neutrons. Landau became the first scholar to propose the concept of neutron star.
In 1934, Bud and Zweiki published an article in Physical Review, believing that supernova explosion can transform an ordinary star into a neutron star, and pointing out that this process can accelerate particles and produce cosmic rays.
1939OppenheimerandVolkovThe first quantitative neutron star model was established through calculation, but the equation of state they used was an ideal degenerate neutron gas model.Neutron stars are stars in the late stage of evolution, which also form in the center of old stars.It's just that the stars that can form neutron stars are more massive.According to scientists' calculations, when the elderlyfixed starWhen its mass is greater than that of ten suns, it may eventually become a neutron star, while a star whose mass is less than eight suns can only become a neutron starWhite dwarf。
Although neutron star was proposed as a hypothesis in the 1930s, it has not been confirmed and people have never observed the existence of neutron star.Moreover, because the density of neutron stars predicted by the theory was too large for people to imagine, people were still generally skeptical of this hypothesis at that time.Until 1967, British scientistsHewishJoslyn Bell, a student ofPulsar。After calculation, its pulse intensity and frequency can only be reached by stars with small size, high density and large mass like neutron stars.In this way, the neutron star really becomes a fact from the hypothesis.This is really an astronomical event of this century.Therefore, the discovery of pulsars is known as one of the four major astronomical discoveries in the 1960s.
In 1967, astronomers accidentally received a strange radio wave.This kind of electric wave is transmitted every 1-2 seconds, just like the pulse of a person.People once thought it wasCosmic manThe call of was a sensation.Later, British scientist Hughes finally found out that this strange radio wave was originally from a special star that was unknown before, namely pulsar.This new discovery made Hewish obtain theNobel Prize。More than 300 pulsars have been foundGalaxyInside.Crab NebulaThere is a pulsar at the center of.
In 2007, astronomers discovered the fastest rotating neutron star so far with the help of the European Aeronautics Agency (ESA) Gamma Ray Astronomical Telescope (Integral).The neutron star, numbered XTE J1739-285, can rotate 1122 times along its axis every second.According to the concept of the Earth, if you turn around for one day, a second on this neutron star can last for more than three years.This discovery overturned the original thought of the 700 cycles per second speed limit of stars.
The diameter of this neutron star is about 10 kilometers, but its mass is similar to that of the sun. Its density is amazing, as high as 100 million tons per cubic centimeter.Its huge gravity constantly grabs a large amount of hot gas from nearby stars, and constantly induces thermonuclear explosions.[3]
On October 27, 2010, the Daily Telegraph reported that astronomers had discovered the largest neutron star in the universe so far, whose mass was almost twice that of the sun.
This neutron star named PSR J1614-223 is about the same size as a small city. It is not a big star relatively, but its density is surprisingly high. The mass of a small amount of material on it is as high as 500 million tons!
Evolutionary state
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Like white dwarfs, neutron stars are in the late stage of evolutionfixed starIt is also formed in the center of old stars.It's just that the stars that can form neutron stars are more massive.According to scientists' calculations, when the mass of an old star is about 8 to 2 or 30 times that of the sun, it may eventually become a neutron star, while a star with a mass less than 8 suns can only become a neutron starWhite dwarf。However, the difference between neutron stars and white dwarfs is not just the mass of the star that generated them.Their material existence state is completely different.
In terms of formation process, neutron stars are similar toWhite dwarfIt is very similar.WhenStellar crustWhen it expands outward, its nucleusReaction forceAnd shrink.A series of complexphysical changeAnd finally form a neutron star core.The whole star will end its life with a spectacular explosion.This is famous in astronomy“SupernovaExplosion ".
Neutron starStellar evolutionTo the end, viaGravitational collapsehappenSupernova explosionAfter that, it may become one of the few destinations.Hydrogen, helium, carbon and other elements in the core of starsnuclear fusionThey are exhausted in the reaction, and when they are finally transformed into iron, they cannot obtain energy from nuclear fusion.The peripheral materials that lose the pressure support of thermal radiation will fall rapidly to the core under the traction of gravity, which may cause the kinetic energy of the shell to be converted into heat energy and burst outwardSupernovaExplosions, or depending on the mass of the star, the inner region of the star is compressed intoWhite dwarf, neutron stars and evenblack hole。
When a white dwarf is compressed into a neutron star, the star is subjected to intense compression, so that the electrons in its constituent matter are incorporatedprotonConvert toneutronThe diameter is only about ten kilometers, but the first cubic centimeter of material can weigh up to one billion tons.
The predecessor of a neutron star is usually a star whose mass is 10-29 times the mass of the sun.The huge pressure generated in the process of collapse makes its material structure undergo tremendous changes.In this case, not only the shell of the atom is broken, but alsoNucleusIt was also crushed.The protons and neutrons in the nucleus are squeezed out, and the protons and electrons are squeezed together to form neutrons.Finally, all the neutrons are squeezed together to form a neutron star.Obviously, the density of neutron stars, even white dwarfs composed of atomic nuclei, cannot be compared with it.On a neutron star, every cubic centimeter of material weighs 100 million tons or even 1 billion tons.
Neutron star magnetic ore star
Whenfixed starAfter shrinking into a neutron star, its rotation will be accelerated to several to dozens of cycles per second.At the same time, the contraction makes the neutron star a very strong“magnet”This "magnet" emits electric waves from some part of it.When it rotates rapidly, like the searchlight on the lighthouse, it regularly scatters radio waves towards the earth.
When launchingair wavesWhen the part of is facing the earth, we receive radio waves;When this part follows the star'sturnWhen we deflect, we cannot receive the radio waves.Therefore, the radio waves we receive are intermittent.This phenomenon is also called "lighthouse effect".
The neutron star is not the final state of the star, and it needs further evolution.Because of its high temperature and fast energy consumption, it maintains luminosity by slowing down its rotation to consume angular momentum.When its angular momentum is consumed, the neutron star will become non luminousBlack dwarf。
The exterior of the neutron star is a solid iron shell, about 1 km thick, and the density is between 10 ^ 11~10 ^ 14 g/cm3;The interior is almost completely composed of neutrons, with a density of 10 ^ 14~10 ^ 15 g/cm3.[4]
A typical neutron star has a mass between 1.35 and 2.1 times of the sun's mass and a radius between 10 and 20 kilometers (the larger the mass, the larger the radius shrinks), that is, 30000 to 70000 times of the sun's radius.Therefore, the overall density of the neutron star is
G to
Grameen,Equivalent to more than 100 million tons per cubic centimeter[1]This density is approximatelyNucleusIts density is one hundred trillion times that of water.Compared with tens of tons/cubic centimeter of white dwarfs, the latter seems not worth mentioning.If we compress the earth like this, the diameter of the earth will be only 22 meters.In fact, the density of neutron stars is so large that the mass of a neutron star with a radius of 10 kilometers is equivalent to the mass of the sun.
White dwarfAlthough its density is large, it is still within the maximum density range that can be reached by normal material structure: electrons or electrons,NucleusstillNucleus, the atomic structure is complete.In neutron stars,pressureIt's so bigelectron degeneracy pressure Can no longer afford it: electrons are compressed into the atomic nucleus, neutralized with protons as neutrons, making the atom only composed of neutrons, and the neutron degenerate pressure supports the neutron star, preventing it from further compression.The whole neutron star is formed by such atomic nuclei close together.It can be said that a neutron star is a huge atomic nucleus.The density of a neutron star is the density of its nucleus.The mass of the neutron star is so large that the huge gravity makes the lightparabolaBreak free.
If the mass of a compact star is less than 1.44 times the mass of the sun, it may beWhite dwarfBut neutron stars with mass greater than the Oppenheimer limit will continue to occurGravitational collapse, it is inevitable thatblack hole。[2]
The surface area of neutron stars is about 30-300 square kilometers, and the earth is 510 million square kilometers. The surface area of the earth is about 1.7-17 million times that of neutron stars.
Neutron stars are extremely hot.The surface temperature of a neutron star is about 1.1 million degrees.[5]It is estimated that the central temperature of the newborn neutron star is about
reach
Kelvin.When we compare the sun, we can have a slightly more specific concept: the surface temperature of the sun is less than 6000 ℃, and the temperature is higher the farther inside, and the central temperature is about 15 million degrees.
At the initial stage of the formation of a neutron star, its cooling is through the so-called Urca process. When the internal temperature drops to 100 million K, the Urca process stops, and other neutrino processes continue to dominate the cooling.After 1000 years, the cooling is dominated by light radiation.Since then, the surface temperature has been maintained at
K around.
The pressure inside the neutron star is amazing.The pressure at the center of our earth is about three millionAtmospheric pressureThat is what we usually call 1Standard atmospheric pressureMore than 3 million times.The central pressure of the pulsar is believed to reach
Three atmospheres, stronger than the geocentric pressure
Times, stronger than the center of the sun
Times.
Scientists find that neutron stars emit strong currents from the poles
neutron starmagnetic fieldExtremely strong.On the earth, the magnetic field strength of the earth's magnetic pole is the largest, but only 0.7Gs (Gauss is the unit of magnetic field strength, 1Gs=
T）。SunspotThe magnetic field of about 1000~4000Gs is extremely strong.Most pulsesCatalogueThe magnetic field intensity in the surface polar region is as high as 100 billion Gs, or even 20 trillion Gs.The strong magnetic field of the neutron star causes the neutron star to emit beam like radio waves (radio waves) along the direction of the magnetic pole.The magnetic poles of the neutron star usually do not coincide with the two poles, so if the magnetic poles of the neutron star just face the earth, then with its rotation, the radio beam emitted by the neutron star will sweep the earth again and again like a rotating lighthouse, forming radio pulses.People also call such objects "pulsars".[5]
Because neutron stars retain most of theangular momentum, but the radius is only a tiny amount of the parent star,Moment of inertiaThe decrease of leads to the rapid increase of the rotating speed, resulting in a very high rotation rate, with the period fromMillisecond pulsarFrom 700 to 30 seconds.The high density of the neutron star also makes it powerfulSurface gravity, the intensity is the earth's
reach
Times.
Escape speedIt is the speed required to move an object from the gravity field to an infinite distance, and is an indicator of gravity measurement.The escape speed of a neutron star is about 10000 to 150000 km/s, which is half of the speed of light.In other words, the maximum speed of the object falling on the surface of the neutron star will reach 150000 km/s.More specifically, if a person with an average weight (70kg) encounters a neutron star, the energy he hits the surface of the neutron star will be equivalent to the power of a 200 million ton nuclear explosion (four times that of the world's largest nuclear bombGreat CzarOf course, this is only a hypothesis. If this is the case, this person will be torn apart by the powerful tidal force as he gets closer to the neutron star.
The energy radiation of a neutron star is one million times that of the sun, about
watt.According to the world's electricity consumption, if the total energy radiated in one second is converted intoelectric energy, which will last our earth for billions of years.
neutron star
From the surface to the center of the neutron star, the density increases rapidly from the usual iron crystal density to
g/
。There is a layer outside the neutron starPlasma, inside the surface is a solid shell, which is mainly composed of lattice lattice of Fe atomic nucleus and degenerate free electron gas, with a density of
。The density gradually increases from the outside to the inside, and then forces the electron to combine with the proton in the nucleus to form a series of neutron rich nuclei, such as Ni, Ge, Zn, Mo, Kr, and then transits to the core, starting to have freedomneutronThis process is called neutron drain
The atomic nucleus will completely dissociate and disappear, and the neutron star material will become a continuous neutron fluid with a few electrons and protons mixed.
According to the estimates of some scholars, the total number of neutron stars in the Milky Way should be at least 200000. By the end of the 1980s, less than five thousandths of the estimated number had been found.The task of observation and research in the future is still arduous.
Since the discovery of neutron stars, it has only been 20 to 30 years. However, no matter howCelestial evolutionIn terms of research, it has provided scientists with very rich and rare observational data and made contributions to promoting the research of physical processes and change laws of substances under extreme conditions.At the same time, it also puts forward a series of questions and puzzles to people in this newly developed field.
“Magnetostar”Magnetar is a kind of neutron star. They all have extremely strong magnetic field. Through the decay generated by them, the energy source will continuously release high-energy electromagnetic radiationγMainly ray.In 1992, the theory of magnetostar was developed by Robert Duncan andChristoChristopher Thompson first proposed that in the following years, this assumption was widely accepted to explain the softγSoft gamma repeater and irregularityX-ray pulsar(anomalous X-ray pulsar) and other observable objects.
When a black hole meets a neutron star
When the distance between the two is 20~30 billion kilometers, the surface material of the neutron star is unstable, and the magnetic field has obvious abnormal fluctuations.When the distance between the two reaches 10 billion kilometers, the external matter of the neutron star will fly out and orbit around the black hole at a high speed, and then the neutron star will spiral downward toward the "singularity" of the black hole.When it reaches 5 billion kilometers, the magnetic field of the black hole and the neutron star collides violently, and a large number of electrons and light are released. Then the energy of the neutron star will be slowly consumed, and then be swallowed by the black hole. The time depends on the volume of the neutron star, but generally does not exceed 6 hours.
Astronomical information
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Astronomical telescopeFound the fastest rotating neutron star so far, rotating 1122 cycles per secondearth rotation100 million times faster.The first Spanish astronomer who observed this star, Kuchler, said that he had discovered this star, code namedJ1739-285But not long ago, its rotational speed was calculated through a telescope.The diameter of this neutron star is about 10 kilometers, but its mass is similar to that of the sun. Its density is amazing, as high as 100 million tons per cubic centimeter.Its huge gravity constantly grabs a large amount of hot gas from nearby stars, and constantly induces thermonuclear explosions.
Astronomers discovered it through this phenomenon.The previous record of neutron star rotation is 716 cycles per second, and the rotation speed of stars is generally 270-715 cycles per second.700 circles was once considered as the limit of celestial rotation. According to modern physics theory, if the rotational speed exceeds this limit, stars will be destroyed or turned into black holes by strong centripetal force.But the latest findings contradict this view.Theoretically, 1122 revolutions per second is not the rotation limit, and the rotation speed of large neutron stars may be as high as 3000 revolutions.What puzzles astronomers is why the celestial bodies still shrink without losing their own material under the powerful centrifugal force of high-speed rotation.
neutron star
Discover pulsars
October 1967, Cambridge UniversityCavendish Laboratory Joslyn Bell, a 24-year-old graduate student of Professor Anthony Hewish, testedradio telescopeWhen receiving the signal, I found some regular pulse signals unintentionally. Their period is very stable, 1.337 seconds.At first, she thought it was the signal sent by the alien "Little Green Man", but in the next less than half a year, she found several such pulse signals again and again.Later, people confirmed that this is a new kind of celestial body, and named it Pulsar (also known as pulsar).Pulsars anda quasar、Cosmic microwave background radiation、Interstellar molecules Together, they were called the "four major discoveries" of astronomy in the 1960s.
However, the attribution of honor has been controversial.1974The nobel prize in physicsThe laurel was only worn on the head of the tutor Hughes, completely ignoring the contribution of student Bell, and the public opinion was in an uproar.Sir Hoyle, a famous British astronomer, is in London《The Times》Speaking, he believed that Bell should share the Nobel Prize with Hewish, and criticized the poor investigation of the Nobel Committee before awarding the prize. He even thought that this event was a scandal and a case of gender discrimination in the history of the Nobel Prize.Hoyle also believes that Bell's discovery is very important, but her tutor has withheld this discovery for half a year, which is objectively a theft.More scholars pointed out that "Miss Bell's remarkable discovery has won her mentor HughesNobelPhysics Award ".The title page of the book Pulsar, written by famous astronomers Manchester and Taylor, reads: "Dedicated to Jocelyn Bell, without her intelligence and persistence, we cannot obtain the joy of pulsars."
The controversy about the real discoverer of pulsars and the challenge to the Nobel Committee have gone through 40 years.Today, 40 years later, it has become a topic of concern again.Looking back, as a tutor, Hewish won the Nobel Prize, which is understandable, but Bell lost the honor, which is regrettable.Without Bell's meticulous investigation of "interference" signals, they might have missed the discovery of pulsars.If theNobel Prize"Competition" is compared to the scientific "Olympic Games", so the "judges" 40 years ago obviously blew "black whistle", or at least miscalculated, which stained the scientific fairness and authority of the Nobel Prize.
During Bell's visit to Beijing, the author talked with her about the discovery of pulsars and her views on the Nobel Prize.In 1993, two American astronomers discovered a pulsarKonductraWhen the Nobel Prize was awarded, the Nobel Prize Committee was particularly careful to invite Bell to participate in the award ceremony, which is a kind of compensation.In 1968, after leaving Cambridge, she and Hewish did not cooperate any more. It was not until the 1980s that they met at an international conference and shook hands.Since the discovery of pulsar, in addition to the Nobel Prize, she has won more than a dozen world-class science awards and become a science ambassador.
The difference between neutron star and pulsar
All pulsars are neutron stars with high-speed rotation, which means that pulsars are a kind of neutron stars, but neutron stars are not all pulsars, and we need to receive pulse signals.The neutron star has a strong magnetic field, and the moving charged particles emit synchrotron radiation, forming a radio beam rotating with the neutron star.Since the rotation axis and magnetic axis of the neutron star generally do not coincide, each time the radio beam sweeps the earth, it receives a pulse.At this time, this neutron star is also called pulsar.Pulsars are one of the four major astronomical discoveries in the 1960s (the other three are:a quasar、Interstellar molecules 、Cosmic 3K microwave radiation）。Because it keeps sending radio pulses, and the interval (pulse period) between the two pulses is very stable, the accuracy can be compared withatomic clockComparable.The periods of various pulsars are different, ranging from 4.3 seconds long to 0.3 seconds short, or even milliseconds.
As the neutron star rotates, it emits something like an electron beamElectric pulse。Like the light from a lighthouse, the electric pulse sweeps across the earth at a certain time interval.When it just passes the earth, we can measure its relevant value.
Pulsars are fast rotating neutron stars, but not all neutron stars are pulsars.Because when the radiation beam of the neutron star does not sweep the earth, we will not receive the pulse signal, and the neutron star will not behave as a pulsar at this time.
Neutron stars and black holes
Neutron stars and black holes are two kinds of mysterious objects with the strongest density and gravity in the universe.Neutron stars alone are incredible enough, and black holes must be added.It is a death trap and bottomless abyss in the universe. No matter can escape its strong gravity, including light.Near it, all the laws of physics today seem inapplicable.
Stellar telophase
We know that after a star has completed its long life, a small and medium mass star will become a white dwarf, and a large and super massive star will cause a supernova explosion.How stars evolve after supernova explosion depends on the mass of the remaining star cores.Indian astrophysicistChandrasekaIn the late 1930s, it was found that when the mass of the left star core reached 1.4 times of the sun, its gravity would be large enough to compress the atoms in the star core to the extent that electrons and protons would combine into neutrons.At this time, the core of the star becomes a neutron star, whose density is equivalent to putting the mass of one and a half suns into a core with a diameter of about 24 kilometers.
This is a single neutron star with a surface temperature of 1.2 million degrees and a diameter of only 28 kilometers.(HST)
The neutron star, which is moving at a high speed of 200 times the speed of sound, is about 200 light-years away from the Earth.Three hundred thousand years later, it will have a slight impact on the earth.（HST）
A single stellar black hole floating in a galaxyGravitational lensThe phenomenon creates two images of the star behind it.（HST）
There may be a giant dust disk in the center of NGC6251 that emits strong ultraviolet radiationblack hole。（HST）
Elliptical galaxyIn the dust disk at the center of NGC7052, there may be a supermassive black hole with a mass 300 million times that of the sun.（HST）
SagittariusThe dust disk at the center of galaxy A (NGC5128) contains a huge supermassive black hole.（HST）
The center of the Milky WaySagittarius A*It is said that it is also a black hole.
Research value
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Like black holes, neutron stars were an exciting discovery in the 20th century, opening up a new field for human exploration of nature, and had a profound impact on the development of modern physics, becoming one of the four major discoveries in astronomy in the 1960s.
Gravitational wave research
At 22:00 on October 16, 2017 Beijing time,National Science FoundationA press conference was held to announce that the Laser Interference Gravitational Wave Observatory (LIGO) and Virgo Gravitational Wave Observatory (Virgo) first discovered the double neutron star merging gravitational wave event on August 17, 2017, and the International Union for the Observation of Gravitational Wave Electromagnetic Counterparts discovered the electromagnetic counterpart of the gravitational wave event.[6]
Scientists believe that gold, platinum and other heavy metals on the earthmetallic elementIt may come from the big explosion of neutron star collision hundreds of millions of years before the birth of the solar system.
It has long been generally believed that ordinary elements, such as oxygen and carbon, are generated when a dying star explodes into a new star, but researchers are puzzled that the data shows that these star explosions cannot produce such a large number of elements as exist on the earthHeavy metal elements。From the University of Lycester andUniversity of Basel These scientists believe that the answer lies in rare neutron star pairs.
Neutron stars are super dense cores that generate new large stars. They contain as much material as our sun, but only about the size of a city.Sometimes two neutron stars will be found orbiting each other, which is the legacy of a binary galaxy. There are four known pairs in our Milky Way Galaxy.Scientists used the supercomputer of the Lycester Astrophysical Fluid Facility, 100 miles north of London, England, to simulate what would happen if they slowly rotated close to the explosion.
It takes supercomputers several weeks to perform such a calculation, which only happens in the last few milliseconds of the lives of the two planets.The results show that when the intermediate sub stars approach, the huge force will split them, releasing enough energy to illuminate the whole universe for several milliseconds.This collision is more likely to produce a black hole - a crack in space that engulfs light - and eject ash when a nuclear reaction occurs, shooting protons into the nucleus of light elements to generate heavy elements.The ejected material mixes and collides with the gas and dust between stars to form a new generation of stars, which slowly makes heavy metals disperse in the Milky Way.
The probability of this rare phenomenon in the universe is more than 10 billion years, which is consistent with the analysis results of element spectra in the solar system with a life span of 5 billion years, providing strong evidence for this theory.Surprisingly, the number of elements produced by the model is very close to the universe, which partly answers the question of where our world comes from.[7]
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.This instrumentOne observation can simultaneously detect X-ray sources in multiple directions.These include stellar mass black holes and neutron stars.[9]
