Pulsar is rotatingneutron star, which is named because it continuously sends electromagnetic pulse signals.Pulsars were first discovered in 1967.At that time, Bell, a female graduate student, found thatFoxOne star will send out a kind ofPeriodicityOfair waves。After careful analysis, scientists believe that this is an unknowncelestial bodies。Because such stars are constantly emittingelectromagnetic pulse The signal is called pulsar.
In the 50 years from the discovery of the first pulsar in 1967 to the discovery of the first pulsar by FAST in October 2017, only more than 3000 pulsars have been discovered in the world.
By April 2024, the 500 meter aperture spherical radio telescope (FAST), known as the "Chinese Celestial Eye", has found more than 900 new pulsars, including more than 650 pulsars in the galactic pulsar survey project, one of FAST's priority and major projects.Among more than 900 pulsars, there are at least 120 binary pulsars, 170 millisecond pulsars, and 80 weak occasional pulsars. These discoveries have greatly expanded the horizon of human observation of the universe.[13]
Pulsar, also called pulsar, isneutron starWhich can be periodically launchedPulse signalThe diameter is about 10km, and the rotation is extremely fast.[1]
Pulsar
People first thought thatfixed starIt will never change.And the change process of most stars is so long that people can't even notice it.However, not all stars are so peaceful.Later, people found that some stars are also "naughty" and changeable.So we gave a special name to those stars that like to change, called“Variable star”。
Pulsar emittingRadio pulseThe periodicity of is very regular.At the beginning, people were confused about this, and even thought that it might be aliens sending us a telegram.It is said that the first pulsar was called "Little Green Man 1".
After a year's efforts by several astronomers, it was finally confirmed that pulsars are fastrotationOfneutron star。Moreover, it is precisely because of its rapid rotation that it emits radiopulse。
Just as the earth hasmagnetic fieldSame,fixed starThere is also a magnetic field;Just as the earthrotationSimilarly, stars are also rotating;Like the earth, the magnetic field direction of a star is not necessarily the same asAutorotation shaftOn the same line.So, wheneverStellar rotationOne week, its magnetic field will draw a circle in space, and may sweep the earth once.So can't all stars pulse?Actually, it's not. It's like a pulsarRadio signal, need very strongmagnetic field。The smaller the size and the greater the mass of the star, the stronger its magnetic field.andneutron starIt is such a high densityfixed star。
On the other hand, the smaller the size and the greater the mass of the star, the shorter its rotation period.We are very familiarearth rotationIt takes twenty-four hours a week.The pulsar's rotation period is unexpectedly as small as 0.0014 seconds!To reach this speed, connectWhite dwarfNone.This also means that only high-speed rotatingneutron starTo play the role of pulsar.[1]
This conclusion caused a great sensation.Because although back in the 1930s,neutron starIt was put forward as a hypothesis, but it has not been confirmed, and people have not observed the existence of neutron stars.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.
Pulsar and its companion
untilpulseAfter the star is discovered, its pulse intensity and frequency are only asneutron starIn this way, small, dense and massive stars can reach.In this way, the neutron star really becomes a fact from the hypothesis.This is really an astronomical event of the last century.Therefore, the discovery of pulsars is known as one of the four major astronomical discoveries in the 1960s.
Pulsar is one of the four major astronomical discoveries in the 1960s.So far, we have found no less than 1620 pulsars, and we have learned that they are fast rotating neutron stars.
Pulsars have a strange characteristic - short and stable pulse period.The so-called pulse is like the pulse of a human being. A short radio signal appears once and again. For example, the first pulsar discovered by Bell, the interval between two pulses is 1.337 seconds. Other pulses are as short as 0.0014 seconds (No. PSR-J1748-2446), and the longest is only 11.765735 seconds (No. PSR-J1841-0456).So, how does this regular pulse come into being?
Astronomers have detected and concluded that the formation of pulses is due to the high-speed rotation of pulsars.Then why can rotation form pulses?The principle is just like the lighthouse we have seen when sailing in the sea by ship.Imagine a lighthouse is always on and moving regularly. Every time the lighthouse rotates, the light from its window will shine on our boat once.It keeps rotating. In our view, the light of the lighthouse is continuously on and off.The same is true for pulsars. When they rotate every week, we receive their radiation onceelectromagnetic wave, so it forms a continuous pulse.
Pulse is also called“Lighthouse effect”。The period of the pulse is actually the rotation period of the pulsar.However, the light of the lighthouse can only be emitted from the window. Does that mean that the pulsar can only be emitted from a certain "window"?Just like this, pulsars are neutron stars. Unlike other stars (such as the sun), neutron stars shine everywhere. Neutron stars can only radiate from two opposite small regions, and radiation cannot escape from other places.That is to say, neutronCatalogueThere are only two bright spots on the face, and the rest are dark.What is the reason?It turns out that there is a hugemagnetic fieldThe strong magnetic field closes the radiation, so that the neutron star radiation can onlyMagnetic axisDirection, from bothmagnetic poleThe two magnetic pole regions are the "windows" of neutron stars.
Fast rotating pulsar
The radiation of the neutron star comes out of two "windows" and spreads in the air, forming two conical radiation beams.If the earth is just in the direction of this radiation, we can receive the radiation, and every revolution, this radiation will sweep the earth once, forming the regular pulse signal we receive.lighthouse model It is now the most popular pulsar model.AnotherMagnetic field oscillation modelIt has not yet been universally accepted.
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.
The general symbol of a pulsar is PSR.For example, the first pulsar is recorded as PSR1919+21.1919 means the right ascension of the pulsar is 19 hours and 19 minutes+21 means that the declination of the pulsar is 21 degrees north latitude.
Double pulsarThe discovery of PSRJ0737-3039A/B made people ecstatic.It is a binary star system formed by two pulsars.It is indeed a very lucky thing to be able to discover the double pulsar system.After calculating PSRJ0737-3039A, scientists predicted that its pulse profile shape would evolve rapidly, and even predicted that its beam would be due to the axis around 2020PrecessionIt disappears from our sight, but careful observation results show that the expected pulse contour shape has not changed at all, which is a big blow to scientists.The failure of the prediction made us feel that there seems to be a problem with the pulsar beacon model.
In 1968, it was proposed that pulsars are fast rotating neutron stars.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.Because of the neutron starAutorotation shaftGenerally, it does not coincide with the magnetic axis. Every time the radio beam sweeps the earth, it receives a pulse.
Pulsar 2009-PSR004
At the end of the evolution, the star lacks the nuclear reaction materials needed for continued combustion, and its internal radiation pressure decreases. Due to its own gravityCollapse。The quality is not large enough (about several timesSolar mass）After collapsingElectronic degeneracy pressureAgainst gravity, it becomes a white dwarf. In a star with a mass larger than this, electrons are pressed intoNucleusNeutron is formed. At this time, the star relies on the neutron degenerate pressure to keep balance with gravity, which is called neutron star.
A typical neutron star has a radius of only a few kilometers to a dozen kilometers, but its mass is between 1-2 times the mass of the sun, so its density can reach hundreds of millions of tons per cubic centimeter.Because the angular momentum of the star is conserved when it collapses, the rotation speed of the star after collapsing into a neutron star with a very small radius is often very fast.Because the magnetic axis of the stellar magnetic fieldAutorotation shaftUsually it is not parallel, and some of the included angles even reach 90 degrees, while electromagnetic waves can only be emitted from the position of the magnetic pole, forming a conical radiation area.
In addition, in the evidence that pulsars are neutron stars, one of them is that weCrab Nebula(M1; Yuantianguan guest star, SN 1054) also found a period of about 0.033sPulsar 。
Spin precession observed in a pair of pulsars
Pulsars compensate for the radiated energy by consuming the rotational energy, so the rotation will gradually slow down.But this slowdown is so slow that the accuracy of the signal period can exceed that of atomic clocks.The pulsar's age can be inferred from its period. The shorter the period, the younger the pulsar.
In addition to high-speed rotation, pulsars are also characterized by extremely strong magnetic fields. The electrons emitted from the magnetic poles have strong directionality.Because of the pulsarAutorotation shaftIt is not coincident with its magnetic axis. During rotation, when the radiation is toward the observer, the observer receives the pulse.By 1999, 1000 pulsars had been discovered.
Millisecond pulsar
In the 1980s, you discovered a class of so-called millisecond pulsars. Their cycles are too short, only in the order of milliseconds. Although previous instruments can detect them, it is difficult to distinguish them.It is found that millisecond pulsars are not young, which challenges the traditional theory of "the shorter the period, the younger".Further research finds that millisecond pulsars are associated withClose binaryof
The famous pulsar
The first pulsar discovered by humans: PSR1919+21, which is the pulsar discovered by Miss Bell above, located atFoxyDirection, period is 1.33730119227 seconds.
The first one discovered by human beingsPulsar binary：PSR B1913+16
The first belt discovered by humansplanetSystem pulsar: PSR B1257+12
The first double pulsar system discovered by man: PSRJ0737-3039
Pulse cause
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Although there is no very strong evidence yet, pulsar experts all over the world believe that pulsars emit a constant energy flow instead of flashing light or light.Just like the light of a flashlight, this energy converges into a very narrow beam and emits from the magnetic pole of the star.The magnetic axis of the neutron star is at a certain angle with the rotation axis (this is slightly different from the geographical position of the magnetic north pole of the Earth).When the star rotates, this beam sweeps like the beam of a lighthouse or the ambulance alarm lightSpace。Only when this beam directly shines on the earth can we detect the pulsar signal with some telescopes.In this way, the beam with constant current becomes pulsed light.[1]
Almost all experts believe this lighthouse model.However, some "deviant" opinions were raised.The new idea is that the pulsar's light comes not from its magnetic pole, but from its surroundings.At the same time, it is believed that the pulsar emits pulsed light because its magnetic field turns and oscillates at a high speed, and the violent magnetic field causes a very high induced electric field around the star.The peak value of the induced electric field appears near the zero crossing point of the magnetic field, and accelerates the charged particles to emit synchrotron radiation.This can explain the generation mechanism of the pulse signal.
The advantage of the magnetic field oscillation model is that it has the low frequency oscillation model of the sun.We know that the direction of the solar magnetic field will be reversed every 11 years. If the sun collapses into a neutron star, its rotation period can be shortened to seconds or even milliseconds. At the same time, its magnetic field reversal period can also reach milliseconds.The problem with the electromagnetic oscillation model lies in the following questions: Can the magnetic field of a star really flip so fast?Of course, the lighthouse model has its own problems: when the magnet rotates at a high speed, can it really shine from the magnetic pole?
The radiation of the pulse signal was once considered to be the unique behavior of the extreme magnetic field of the neutron star.But later people found that in someMain sequence starFor example, ultracold star TVLM 513-46546 and chemical special star CU Virginia have found very similar pulse radiation, and the magnetic field of these stars is very low (thousands of gauss).This is beneficial to the magnetic field oscillation model.Because the magnetic field oscillation model reduces the requirement for magnetic field strength.Most pulsars can be observed in the radio band.A few pulsars can alsovisible light、X-rayeven to the extent thatγradialIt can be observed in the wave band, for example, the famous Crab pulsar can be seen in radioγRays are observed in various wavebands.
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A young pulsar
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 PulsarPulsar )。
American film made in 1997《Hyperspace contact》The heroine in (Contact) deciphered the regular signals from outer space and made a special machine accordingly.But when we first determined the candidate for connecting with extraterrestrial intelligence by machine, we didn't choose her.This episode is considered to imply that Miss Bell didn't getNobel PrizeThings.
15-year-old girl discovers new pulsar
A high school student in West Virginia, using radio from Green BayAstronomical telescope（Robert C. Byrd Green Bank Telescope, GBT for short), a new pulsar has been found.
Shay Bloxton, 15 years old, participated in a project for students to analyze radio telescope data, and discovered an object that may be a pulsar on October 15, 2009.She and NRAOobservatoryOne month later, 30% of astronomers observed the object again and confirmed that it was indeed a pulsar.Bloxton said she was very excited. She went to Green Bay in November to participate in tracking observation.The project she is involved in is called Pulsar Search Collaboration (PSC)National Radio ObservatoryandUniversity of West VirginiaJoint project of.
Scientists first discovered pulsars in 1967.At the end of last year, another West Virginia student from South Harrison High School also found a pulsar like object while participating in the PSC project.
On May 7, 2021, it was reported that based on the observation of the "Chinese Celestial Eye", Chinese researchers found the evidence that the three-dimensional velocity of pulsars was collinear with the axis of rotation for the first time, marking that astronomers began to use the telescope to study pulsars in depth.[4]
On May 20, 2021, the research team of the National Astronomical Observatory officially released the discovery of 201 new pulsars by making use of the important progress made in the observation of the FAST telescope of the Chinese Celestial Eye.[5]
More than 500 new pulsars have been discovered by "China's Tianyan"
On December 15, 2021, since the first announcement of the discovery of pulsars on October 10, 2017, more than 500 new pulses have been found by the 500 meter aperture spherical radio telescope known as the "Chinese Celestial Eye" so farGo to the stars.[7]
After the Lunar New Year of the Rabbit in 2023, in the general control room of China's Tianyan, researchers are monitoring the operating status of the telescope, and collecting and recording data information from the universe.Jiang Peng, chief engineer of FAST, said that up to now, the total number of pulsars discovered by FAST has exceeded 740.The construction plan of the pilot array is also in preparation.[9]
More than 900 new pulsars have been found by "China Tianyan" FAST
By April 2024, the 500 meter aperture spherical radio telescope (FAST), known as the "Chinese Celestial Eye", has found more than 900 new pulsars, including more than 650 pulsars in the galactic pulsar survey project, one of FAST's priority and major projects.Among more than 900 pulsars, there are at least 120 binary pulsars, 170 millisecond pulsars, and 80 weak occasional pulsars. These discoveries have greatly expanded the horizon of human observation of the universe.[13]
Naming rules
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Pulsar is named by the abbreviation PSR of pulsar plus itsDeclinationCoordinate composition.asPSR B1937+211937 means that the pulsar is located at 19 37 right ascension,+21 means that it is located at+21 ° declination, and B means that the declination value is the value reduced to 1950 epoch.In addition, J indicates that the right ascension and declination value is the value reduced to the year 2000.
planet
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On that very day, at this meeting, another person prepared a similar speech. He was also a pulsar observer, and his name was Alex Wolzkan.
But unlike Lynn, his evidence shows that there is a pulsar not only surrounded by one planet, but also has a complete setPlanetary system！Before his speech, Wolzkan was a little uneasy, because Lynn's confession undoubtedly strengthened a deep-rooted concept;A pulsar cannot have planets around it.However, this time, it turned out that Wolzkan was right. He not only found the "wobble" of the pulsar, but also calculated that there were three planets orbiting the pulsar, and these planets met every 200 days. Each time, two of the larger planets would affect each other, so that their orbits would have some subtle changes.It was these changes that led him to discover the secret of the pulsar owning the planet.
This is how the pulsar planet was discovered, and it is still a complete onePlanetary systemHowever, at this time, those star hunters did not find a planet outside the solar system, which made them very confused, because pulsars have planets, which astronomers had never thought of in the past.A pulsar is an exploded neutron star. How could it possibly have planets?
This is how the first extrasolar planetary system was discovered. Because it does not conform to modern astronomical theories, this discovery always surprises people.
Pulsar binary
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Although the discovery that pulsars have planets seems unexpected, there is a more unexpected discovery in this regard, that is, pulsar binaries.
Hers is a graduate student. He was sent to Arecibo, Puerto Rico as Taylor's assistantradio telescopeObserving pulsars was the best radio telescope at that time. Maybe it was the reason why he used this telescope. He found a strange radio wave. At that time, it was only seven years since the first pulsar was discovered. People's understanding of pulsars was still very shallow. At that time, Hulls could not immediately be sure that the periodic changes he saw were true. After repeated observation,Only then did he determine that the system was dual.He telegraphed the news to Taylor, who immediately rushed to Arecibo. After further study, they thought it was a pulsar binary, and together determined the period of the binary and the distance between the two celestial bodies.
Thus, the first pulsar binary was discovered in this way. This discovery was awarded the Nobel Prize in 1993, so there were two Nobel Prizes for the discovery of pulsars.
Double pulsar
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In December 2003, a research report on Nature announced the discovery of pulsar PSR J0737-3039, which appeared in pairs with a star that looked like a neutron star.One month later, when he came from Parkes, AustraliaAstronomical telescopeWhen the data were re analyzed, the researchers found that the neutron star was actually another pulsar.So this is the first discovered double pulsar system, named PSR J0737-3039 A/B.
Pulsar binaries and double pulsars
Pulsar binaryAndDouble pulsarThere are differences.In pulsebinary star A pulsar is accompanied by another non pulsar (which can be a neutron star, a white dwarf star, or even an ordinary main sequence star).In a double pulsar system, two pulsars must accompany each other.There have been 120 pulsar binary systems discovered, and only one PSRJ0737-3039A/B pulsar system has been discovered.
research meaning
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Since pulsars were found in the wreckage of collapsed supernovae, they can help us understand what happens when stars collapse.We can also reveal the mystery of the birth and evolution of the universe through their research.Moreover, as time goes by, the behavior of pulsars will change in a variety of ways.
The period of each pulsar is not constant.What we can detect is the rotational energy of the neutron star（electromagnetic radiationSource).When a pulsar emits electromagnetic radiation, it will lose part of its rotational energy and its rotational speed will decrease.By measuring their rotation period month after month and year after year, we can accurately infer how much their rotational speed has decreased, how much energy has been lost in the process of evolution, and even how long they can live before they can't emit light because their rotational speed is too low.
It has also been proved that each pulsar has something different.Some are extremely bright;Some will happenStarquake, rapidly increase the speed;Some have companion stars in binary orbits;There are also dozens of pulsars with extremely fast speed (up to 1000 times per second).Every new discovery will bring some new and rare information, which scientists can use to help us understand the universe.
Discoverer
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Jocelyn Bell Bonnell and the 1974 Nobel Prize in Physics
Bonaire is a graduate student of Antony Hewish, who discovered pulsars for the first time.In 1968, she and Hewish jointly published the discovery in the journal Nature.In 1973, they jointly received the Michelson Medal issued by the Franklin Institute of Management.Unfortunately, in 1974, when the Nobel Prize was awarded to astronomers for the first time, Bonaire's mentor Hughes and colleague Martin Ryer were all on the list, but she was excluded from the Nobel Hall.Many astronomers expressed their anger at this, but others believed that Bonaire only did the work of collecting data, and Hewish's interpretation of the data was the key.Bonaire never argued about her defeat, but most reports showed that what she did was not just an early observation.
Related information
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At 7:42 on November 10Jiuquan Satellite Launch CenteruseLong March 11 carrier rocket, successfully launched the pulsar test satellite.The satellite is mainly used to verify the performance index of pulsar detector and space environment adaptability, accumulate in orbit test data, and lay a technical foundation for the verification of pulsar detection system.Pulsars are called lighthouses in the universe. They have obvious characteristics, are easy to identify, and are positioned accurately in the universe.
The pulsar test satellite belongs to the sun synchronous orbit satellite. After the satellite is put into orbit, it will carry out in orbit technical tests to verify the performance indicators and space environment adaptability of the on-board pulsar detector, accumulate the measured pulsar data in orbit, and lay a technical foundation for pulsar detection and technical system verification.[2]
In astronomical research, it is usually difficult to measure the distance between the celestial body and the earth, but the distance is the most basic parameter.Pulsar distance is the most basic parameter for further research on the origin, evolution, distribution and radiation characteristics of pulsars.Only about one tenth of the more than 2000 pulsars that have been found so far have a measurement distance (independent of the distance of the model).In recent years, fast radio bursts are a kind of radio pulses with unknown origin, large dispersion and millisecond duration found in astronomical observations.The distance of fast radio bursts is very important for analyzing their origin and the location relationship with the Milky Way (Hanoi source or extragalactic source).Only two of the 17 fast radio storms detected have redshift measurements.
Shortly after the discovery of pulsars, scientists found that using pulsars to measure distance and dispersion (DM) can build an electron density model of the Milky Way.The model can be used to estimate the distance of all pulsars in the Milky Way with dispersion measurement, and the accuracy of the model distance greatly depends on the number and accuracy of pulsars measured at the known distance.The most recent electron density model of the Milky Way is the NE2001 model, which mainly describes theFree electron densityDistribution of.
the near future,Xinjiang Observatory, Chinese Academy of SciencesYao Jumei, a doctoral student, constructed a new electron density model (YMW16 for short).Compared with the existing models, YMW16 has the following advantages through observation in the past decade: 1. The number of pulsars with measurement distance has doubled, and the accuracy of structural parameters of the Milky Way has improved;IIMagellan CloudThe number of pulsars increases, and the understanding of Magellanic cloud structure is improved;3、 The rapid radio burst was found, and theIntergalactic mediumThe distribution of free electron density.Researchers seized the opportunity to propose YMW16, which not only improved the distance accuracy of the Milky Way pulsar model, which was nearly 40% better than NE2001 within the 95% confidence interval, but also was the first model that can be used to estimate the distance of Magellanic cloud pulsars and rapid radio bursts.Yao Jumei teaches RN. Manchester completed this work under the guidance of his tutor Wang Na.Relevant research results have been published in The Astrophysical Journal (2017, 835, 29)[3]。
In terms of pulsar research, in May 2021, the "China Tianyan" team found the evidence that the three-dimensional velocity of pulsars is collinear with the axis of rotation for the first time."This discovery cannot be explained by the current supernova simulation, which challenges the existing neutron star origin model, and also expands human's understanding of the origin of special celestial bodies under extreme physical conditions."[6]
As of August 2022, FAST has discovered more than 660 pulsars.FAST has carried out the development of pulsar timing system and advanced receiver system. In the future, FAST will also go deep into the scientific research of pulsar search.[8]
In June 2023, scientists discovered a pulsar binary system with an orbital period of only 53 minutes by using the "Chinese Celestial Eye" FAST, which is the pulsar binary system with the shortest orbital period found so far, and confirmed the theory of the evolution of spider pulsars from the "red back" to the "black widow" system from observation.The research was completed by the scientific research team of the National Astronomical Observatory of the Chinese Academy of Sciences and domestic and foreign collaborators, and the relevant results were published online in the international academic journal Nature on June 21.[10]
In July 2023, it was learned from the FAST Operation and Development Center that more than 800 new pulsars have been found in the 500 meter aperture spherical radio telescope (FAST) known as the "Chinese Celestial Eye".[11]
In October 2023, the "Wang Shouguan Sky Survey Commando" led by Han Jinlin, a researcher from the National Astronomical Observatory of the Chinese Academy of Sciences, discovered 76 accidental pulsars in the "Galactic Plane Pulsar Snapshot (GPPS) Sky Survey" using China's Tianyan FAST, including the most faint group of pulsars known to mankind, which only occasionally radiate pulses in a few rotation cycles,It is internationally known as "Rotating Radio Transient Sources (RRAT)".[12]
Chinese scientists have systematically analyzed the public observation data of "China's Celestial Eye" FAST by developing a search scheme based on the fast folding algorithm, found two long-period pulsars in the globular cluster M15, and revealed a new evolution path of the globular cluster pulsars.This paper was published in Science in China: Physics, Mechanics and Astronomy in 2024.[14]
