The neutron star is the collapsed core of a large star that before it collapsed has a total of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars, excluding hypothetical quark stars and strange stars. Typically, neutron stars have a radius on the order of 10 kilometers (6.2 miles) and mass between 1.4 and 2.16 solar masses. They are generated from massive supernova explosions, combined with gravitational collapse, which compress the nucleus through the density of a white dwarf into an atomic nucleus. Once formed, they no longer actively generate heat, and cool over time; However, they may still develop further through collision or accretion. Most of the basic models for these objects imply that neutron stars are almost entirely composed of neutrons (subatomic particles without net electrical charge and with masses slightly larger than protons); electrons and protons present in the normal matter combine to produce neutrons under conditions in neutron stars. The neutron star is supported against further collapse by the pressure of neutron degeneration, a phenomenon described by the Pauli exclusion principle, as well as white dwarfs that are supported against collapse by electron degeneration pressure. If the remaining star has a mass greater than about 3 solar masses, it continues to collapse to form a black hole.
The observable neutron star is very hot and usually has a surface temperature of about 600 000 K . They are so dense that a normal-sized match box containing neutron star material will have a mass of about 3 billion tons, or 0.5 cubic kilometers of Earth's kilometers (cube with edges about 800 meters). Their magnetic field is between 10 8 and 10 15 (100 million to 1 quadrillion) times stronger than Earth. The gravitational field on the surface of the neutron star is about 2 ÃÆ' - 10 11 (200 billion) times from Earth.
When the star core collapses, its rotational rate increases as a result of the conservation of angular momentum, the newly formed neutron star rotates up to several hundred times per second. Some neutron stars emit electromagnetic radiation rays that make them detectable as pulsars. Indeed, the discovery of a pulsar by Jocelyn Bell Burnell in 1967 was the first observational suggestion that neutron stars exist. Radiation from pulsars is considered mainly emitted from areas near their magnetic poles. If the magnetic poles do not coincide with the axis of rotation of the neutron star, the light beam will sweep the sky, and when viewed from a distance, if the observer is somewhere in the path of light, it will appear as a radiation pulse. comes from a fixed point in space (the so-called "lighthouse effect"). The fastest spinning neutron star known is the PSR J1748-2446ad, spinning at a rate of 716 times per second or 43,000 revolutions per minute, giving a linear velocity on the surface in the order of 0.24Ã, c (ie almost a quarter of the speed of light).
It is estimated there are about 100 million neutron stars in the Milky Way, a figure obtained by estimating the number of stars that have experienced supernova explosions. However, most are old and cold, and neutron stars can only be easily detected in certain cases, such as if they are pulsars or parts of a binary system. Slow and non-accreted neutron stars are almost undetectable; however, since the detection of the Hubble Space Telescope from RX J185635-3754, some of the closest neutron stars that appear to emit only thermal radiation have been detected. Soft gamma repeaters are thought to be a type of neutron star with a very strong magnetic field, known as a magnetar, or alternatively, a neutron star with a fossil disk around it.
Neutron stars in binary systems can experience an increase that normally makes the system bright in X-rays while materials that fall into neutron stars can form hotspots that rotate inside and out of sight in an identified X-ray pulsar system. In addition, such increments can "recycle" old pulsars and potentially cause them to gain mass and rotate to very rapid rotation rates, forming pulsars called milliseconds. This binary system will continue to grow, and eventually the companions can become compact objects such as white dwarfs or neutron stars themselves, though other possibilities include the complete destruction of the companions through ablation or mergers. The incorporation of binary neutron stars may be a source of short-duration gamma rays and may be a powerful source of gravitational waves. By 2017, direct detection (GW170817) of the gravitational waves of such events is made, and gravitational waves have also been detected indirectly in a system in which two neutron stars orbit each other.
Video Neutron star
Formation
Every major consecutive star with an initial mass above 8 times the mass of the sun (8Ã, M ? ) has the potential to produce a neutron star. As stars evolve away from the main sequence, subsequent nuclear combustion produces iron-rich nuclei. When all nuclear fuel in the core has run out, the nucleus must be supported by degeneration pressure only. Further mass deposits from burning the shell cause the core to exceed the Chandrasekhar limit. The electron degeneration pressure is overcome and the core collapses further, sending a soaring temperature to more than 5 ÃÆ' - 10 9 Ã, K . At this temperature, photodisintegration (iron core breakdown into alpha particles by high-energy gamma rays) occurs. As temperatures rise higher, electrons and protons combine to form neutrons through electron capture, releasing neutrino floods. When the density reaches the nuclear density 4 ÃÆ' - 10 17 kg/m 3 , the neutron degeneration pressure stops the contraction. The star's outer envelope stops and is thrown outward by the neutrino flux generated in the formation of a neutron, into a supernova. Left left is a neutron star. If the rest has a mass greater than about 3 M ? , it collapsed even further to become a black hole.
As the core of a massive star compressed during a Type II supernova, Type Ib or Type Ic supernova, and collapsing into a neutron star, it retains most of its angular momentum. But, since it only has a small portion of its parent fingers (and therefore the moment of inertia is sharply reduced), the neutron star is formed at a very high rotational speed, and then over a very long period it slows down. Neutron stars are known to have a rotation period of about 1.4 ms to 30 s. The density of neutron stars also provides very high surface gravity, with typical values ​​ranging from 10 12 to 10 13 m/s 2 (more than 10 11 times from Earth). One of the greatest gravitational measures is the fact that neutron stars have escape velocities ranging from 100,000 km/s to 150,000 km/sec, ie from a third to a half the speed of light. Gravity of neutron stars accelerates the tightening of matter into incredible speed. Its impact strength is likely to destroy the atoms of object components, making all things identical, in many ways, with the rest of the neutron stars.
Maps Neutron star
Properties
Mass and temperature
The neutron star has a mass of at least 1.1 and possibly up to 3 solar masses ( M ? ). The maximum observed mass of neutron stars is about 2.01 M ? . But in general, the compact star is less than 1.39 M ? (Chandrasekhar limit) is white dwarf, while compact star with mass between 1.4Ã, M ? and 3Ã, M ? (Tolman-Oppenheimer-Volkoff boundary) should be a neutron star (though there is an interval of some tenth of the mass of the sun where the mass of low-mass neutron stars and high-mass white dwarfs can overlap). Between 3Ã, M ? and 5Ã, M ? , hypothetical mass-mass stars such as quark stars and electro-tundak stars have been proposed, but nothing is proved to exist. More than 10 M ? The remaining stars will overcome the pressure of neutron degeneration and gravitational collapse will usually occur to produce black holes, although the smallest mass observed from the star black hole is about 5Ã, M ? .
The temperature inside the newly formed neutron star is from about 10 11 to 10 12 Ã, kelvin. However, a large number of emitted neutrinos carry so much energy that the temperature of the isolated neutron star falls within a few years to about 10 6 kelvin. At this lower temperature, most of the light generated by neutron stars is X-rays.
Density and pressure
The neutron star has an overall density of 3,7 ÃÆ' - 10 17 to 5,9 ÃÆ' - 10 17 ( 2.6 ÃÆ' - 10 14 span> to 4.1 ÃÆ' - 10 14 times the density of the Sun), which is proportional to the estimated atomic nuclear density 3 ÃÆ' - 10 17 Ã, kg/m 3 . The density of neutron stars varies from about 1 ÃÆ' - 10 9 kg/m 3 in crust-- increases with depth - up to about 6 ÃÆ' - 10 17 or 8 ÃÆ' - 10 17 Ã, kg/m 3 (denser than atomic nucleus) deeper. The neutron star is so dense that a teaspoon (5 milliliters) of its material will have a mass of more than 5.5 ÃÆ' - 10 12 Ã, kg , about 900 times the mass of the Great Pyramids of Giza. In the large gravitational field of a neutron star, its weight will be 1,1 ÃÆ' - 10 25 Ã, N , which is about 15 times the weight of the moon. Pressure increased from 3.2 ÃÆ' - 10 31 to 1,6 ÃÆ' - 10 34 Ã, Pa from the inner crust to the center.
Such high-density material state equations are not known precisely because of the theoretical difficulties associated with extrapolating the possible behavior of quantum chromodynamics, superconductivity, and material superfluidity under such circumstances along with the empirical difficulty of observing the neutron star characteristics. at least hundreds of parsecs away.
The neutron star has several properties of the atomic nucleus, including density (in order of magnitude) and composed of nucleons. In popular scientific writings, neutron stars are sometimes described as "gigantic nuclei". However, in other respects, neutron stars and atomic nuclei are very different. The nucleus is united by a strong interaction, while the neutron star is held together by gravity. The density of the nuclei is uniform, while the neutron stars are predicted to consist of many layers with varying composition and density.
Magnetic field
The strength of the magnetic field on the surface of the neutron star ranges from c. 10 4 to 10 11 Ã, tesla. This is an order of magnitude higher than in other objects: for comparison, a continuous 16 T field has been reached in the laboratory and sufficient to float a living frog due to diamagnetic levitation. Variations in magnetic field strength are likely to be major factors that allow different types of neutron stars to be differentiated based on their spectrum, and explain the pulsar's periodicity.
The neutron star known as magnetar has the strongest magnetic field, in the range of 10 8 to 10 11 Ã, tesla, and has become a widely accepted hypothesis for the type of soft gamma neutron star repeaters (SGRs) and pulsar X-ray anomalies (AXPs). The magnetic energy density of the 10 8 field Ã, T extreme, exceeds the mass-energy density of ordinary matter. This field of force is capable of polarizing the vacuum to the point that it is vacuum into a birefringent. Photons can merge or split into two, and virtual particle-antiparticle particles are generated. The field changes the energy levels of the electrons and the atoms are forced into thin cylinders. Unlike ordinary pulsars, magnetar spin-downs can be directly powered by their magnetic fields, and the magnetic field is strong enough to press the crust to the point of fracture. The fracture of the earth's crust causes a starfish, which is observed as a glowing, gamma-ray of millisecond rays. The fireball is trapped by a magnetic field, and comes and comes out of sight when the star is spinning, which is observed as a periodic soft gamma repeater (SGR) emission with a period of 5-8 seconds and that lasts for several minutes.
The origin of a strong magnetic field is unclear. One hypothesis is "freezing flux", or conserving the original magnetic flux during neutron star formation. If an object has a certain magnetic flux above its surface area, and the area shrinks to a smaller area, but the magnetic flux is preserved, then the magnetic field will increase as well. Similarly, the collapsing star begins with a much larger surface area than the resulting neutron star, and the conservation of magnetic flux will produce a much stronger magnetic field. However, this simple explanation does not fully explain the magnetic field strength of neutron stars.
Gravity and state equations
The gravitational field on the surface of the neutron star is about 2 ÃÆ' - 10 11 times stronger than on Earth, about 2.0 Ã kali - 10 12 m/s 2 . Such a strong gravitational field acts as a gravitational lens and deflects the radiation emitted by the neutron star in such a way that the invisible back surface parts become visible. If the radius of a neutron star is 3 GM / c 2 or less, then the photon may be trapped in orbit, thus making the entire surface of the neutron star visible from a single point of view , along with a destabilizing photon orbit at or below the distance of a star finger.
A small portion of the collapsing star's mass forming a neutron star is released in a supernova explosion from which it is formed (from the law of mass-energy equality,
Therefore, the typical gravitational force of the neutron star is very large. If an object falls from a height of one meter to a neutron star as far as 12 kilometers, it will reach the ground about 1400 kilometers per second. However, even before the impact, the tidal force will cause spaghettification, breaking down all kinds of ordinary objects into material streams.
Due to the enormous gravity, the widening of time between neutron and Earth stars is significant. For example, eight years can pass on the surface of a neutron star, but ten years will pass on Earth, not including the time-widening effect of rapid rotation.
Neutron stars of state relativistic equations illustrate the relation of radius vs. mass to various models. The radius most likely to be given to neutron star masses is given brackets by the AP4 model (the smallest radius) and MS2 (the largest radius). BE is the mass ratio of gravitational binding energy equivalent to the observed gravity mass of the neutron star from the "M" kilogram with "R" meter radius,
Diberikan nilai saat ini
dan massa bintang "M" biasanya dilaporkan sebagai kelipatan dari satu massa matahari,
maka energi fraksional relativistik dari bintang neutron adalah
The neutron star 2 M ? will not be more compact than the 10.970 meter radius (AP4 model). The energy of the gravitational mass fraction will be 0.187, -18.7% (exothermic). It's not near 0.6/2 = 0.3, -30%.
The state equation for neutron stars is unknown. It is assumed that it differs significantly from the white dwarf, whose country equation is that the degenerated gas can be explained in close agreement with special relativity. However, with neutron stars, the effects of increased general relativity can no longer be ignored. Several state equations have been proposed (FPS, Act, APR, L, SLy, etc.) and current research is still trying to limit the theories to make predictions of neutron star matter. This means that the relationship between density and mass is not fully known, and this causes uncertainty in the radius estimate. For example, the neutron star 1.5Ã, M ? can have a radius of 10.7, 11.1, 12.1 or 15.1 kilometers (for EOS FPS, Act, APR or L respectively).
Structure
An understanding of the current neutron star structure is determined by the existing mathematical model, but it is possible to deduce some details through the study of neutron star oscillations. Asteroseismology, a study applied to ordinary stars, can reveal the inner structure of neutron stars by analyzing the observed spectra of star oscillations.
The current model shows that the matter on the surface of a neutron star consists of ordinary atomic nuclei that are crushed into solid lattices with an ocean of electrons flowing through the gap between them. It is possible that the core on the surface is iron, due to the high binding energy of iron per nucleon. It is also possible that heavy elements, such as iron, simply drown beneath the surface, leaving only the light cores like helium and hydrogen. If the surface temperature exceeds 10 6 kelvin (as in the case of young pulsars), the surface must be a liquid, not a solid phase that may exist in colder neutrons (temperature <10 6 kelvin).
The "atmosphere" of a neutron star is hypothesized at most a few micrometers thick, and its dynamic is entirely controlled by a neutron star magnetic field. Under the atmosphere, one finds solid "crust". The crust is very hard and very smooth (with maximum surface deviation ~ 5 mm), due to extreme gravity fields.
Continuing inward, a person meets with nuclei with increasing numbers of neutrons; Such nuclei will decay rapidly on Earth, but are kept steady by tremendous pressure. As this process continues at increasing depth, neutron droplets become extraordinary, and free neutron concentrations increase rapidly. In the region, there are nuclei, free electrons, and free neutrons. The nucleus becomes smaller (gravity and pressure flooding strong forces) until the core is reached, by the definition of the point at which most neutrons exist. The expected nuclear phase phase hierarchy in the inner crust has been characterized as a "nuclear paste", with less space and larger structures leading to higher pressures. The composition of superdense material at the core remains uncertain. One model describes the nucleus as a neutron-degeneration superfluid material (mostly neutrons, with some protons and electrons). More exotic forms of matter may occur, including the decline of strange material (containing strange quarks in addition to up and down quarks), materials containing pawns and high-energy kaons besides neutrons, or ultra-solid matter quark-degenerate.
Radiation
Pulsar
Neutron stars are detected from their electromagnetic radiation. The neutron star is usually observed in pulsed radio waves and other electromagnetic radiation, and the neutron star observed with pulses is called a pulsar.
Pulsar radiation is thought to be caused by particle acceleration near its magnetic poles, which need not be aligned with the axis of neutron star rotation. It is estimated that large electrostatic fields are formed near the magnetic pole, which causes electron emission. These electrons are magnetically accelerated along the field lines, leading to the radiation of curvature, with highly polarized radiation toward the curvature plane. In addition, high energy photons can interact with lower energy photons and magnetic fields for the production of electron-positron pairs, which by destruction of electrons-positrons lead to higher energy photons.
The radiation derived from the neutron star magnetic poles can be described as magnetosphere radiation , referring to the magnetosphere of the neutron star. This is not to be confused with magnetic dipole radiation , which is emitted because the magnetic axis is not aligned with the rotation axis, with the same radiation frequency as the neutron star rotation frequency.
If the axis of rotation of the neutron star is different from the magnetic axis, the external viewers will only see this radiation beam each time the magnetic axis points toward them during the rotation of the neutron star. Therefore, periodic pulses are observed, at a rate equal to the rotation of a neutron star.
Non-pulsated neutron star
In addition to pulsars, neutron stars have also been identified without a clear periodicity of their radiation. This appears to be a characteristic of an X-ray source known as the Central Compact Objects in Supernova remnants (CCOs in SNRs), which are considered young, neutron-insulated radio-quiet stars.
Spectra
In addition to radio emissions, neutron stars have also been identified in other parts of the electromagnetic spectrum. These include visible light, near infrared, ultraviolet, X-rays and gamma rays. Pulsars observed in X-rays are known as X-ray pulsars if powered by accretion; while those identified in light appear as optical pulsars. The majority of detected neutron stars, including those identified in optical rays, X-rays and gamma rays, also emit radio waves; Pulsar crabs produce electromagnetic emissions across the entire spectrum. However, there are neutron stars called quiet radio-neutron stars, with no detectable radio emissions.
Rotation
Neutron stars spin very quickly after their formation due to the conservation of angular momentum; like spinning ice spins that pull on their arms, the slow rotation of the original star's core accelerates as it shrinks. The newborn neutron star can rotate many times in one second.
Play down
Over time, neutron stars are slow, because their rotating magnetic fields have the effect of radiating energy associated with rotation; Older neutron stars may take a few seconds for each revolution. This is called spinning down . The rate at which a neutron star slows the rotation is usually constant and very small.
Waktu periodik ( P ) adalah periode rotasi, waktu untuk satu putaran bintang neutron. Tingkat spin-down, laju perlambatan rotasi, kemudian diberi simbol ( P -dot), turunan negatif P sehubungan dengan waktu. Ini didefinisikan sebagai penurunan waktu berkala per satuan waktu; itu adalah kuantitas tanpa dimensi, tetapi dapat diberikan unit s? s -1 (detik per detik).
The spin-down ( P -dot) level of the neutron star is usually in the range of 10 -22 to 10 -9 Ã,? s -1 , with shorter periods (or faster spins) observed neutron stars typically have smaller P -dot. However, as neutron star stars, the neutron star slows ( P increases) and the deceleration rate decreases ( P -dot decreases). Finally, the rotation rate becomes too slow to ignite the radio-emission mechanism, and neutron stars can no longer be detected.
P and P -not allow minimum magnetic field neutron stars to be estimated. P and P -dot can also be used to calculate the characteristic age of the pulsar, but gives a somewhat larger estimate than the actual age when it was applied to the young pulsar.
P dan P -dot juga dapat dikombinasikan dengan momen inersia bintang neutron untuk memperkirakan kuantitas yang disebut luminositas spin-down , yang diberikan simbol ( E -dot). Bukan luminositas yang terukur, melainkan tingkat kerugian dihitung dari energi rotasi yang akan memanifestasikan dirinya sebagai radiasi. Untuk bintang neutron di mana luminositas spin-down sebanding dengan luminositas yang sebenarnya, bintang neutron dikatakan "rotasi bertenaga". Luminositas yang diamati dari Kepiting Pulsar sebanding dengan luminositas spin-down, mendukung model yang kekuatan energi kinetik rotasi radiasi darinya. Dengan bintang-bintang neutron seperti magnetar, di mana luminositas sebenarnya melebihi luminositas spin-down dengan sekitar faktor seratus, diasumsikan bahwa luminositas didukung oleh disipasi magnetik, bukannya rotasi bertenaga.
P and P -dot can also be plotted for a neutron star to create P - P -the point of the diagram. It encodes a large amount of information about the pulsar population and its properties, and has been likened to the Hertzsprung-Russell diagram in importance to neutron stars.
Play
The speed of neutron star rotation can be increased, a process known as spin up. Sometimes the neutron star absorbs the orbiting material from the companion star, increasing the rotational rate and reshaping the neutron star into an oblate spheroid. This leads to an increase in the rate of rotation of neutron stars over a hundred times per second in the case of millisecond pulsars.
The fastest-spinning neutron star known today, PSR J1748-2446ad, spins at 716 revolutions per second. However, a 2007 paper reported the detection of an X-ray oscillation, which gives an indirect rotation size, from 1122 Hz of the XTE J1739-285 neutron star, showing 1122 rotations per second. However, at present, this signal is only seen once, and should be regarded as temporary until it is confirmed in another explosion of that star.
Disorders and starquakes
Sometimes the neutron star will experience a mistake, increase the speed of a sudden rotation or spin. Disturbance is thought to be the effect of starfish - because the rotation of the neutron star slows, its shape becomes more rounded. Due to the rigidity of the "neutron" crust, this occurs as a discrete event when the crust breaks out, creating an earthquake similar to an earthquake. After starquake, the star will have smaller equatorial radius, and since the angular momentum is conserved, its rotational speed increases.
Starquakes that occur in magnetars, with the resulting error, are the main hypothesis for gamma ray sources known as soft gamma repeaters.
The latest work, however, shows that starquake will not release enough energy for neutron star errors; It has been argued that glitches may be caused by a vortex transition in the theoretical superfluid nucleus of a neutron star from one state of metastatic energy to a lower one, thereby releasing the emerging energy as an increase in the rate of rotation.
"Anti-glitches"
An "anti-error", a small decrease in rotational velocity, or spin down, of a neutron star has also been reported. This occurs in magnetars, which in one case results in an increase in the X-ray luminosity of factor 20, and significant changes in spin-down rates. Current neutron star models do not predict this behavior. If the cause is internal, it shows the differential rotation of the solid outer crust and the superfluid component of the inner magnetar structure.
Population and distance
Currently, there are about 2,000 known neutron stars in the Milky Way and the Magellan Cloud, most of which have been detected as radio pulsars. The neutron star is concentrated mostly along the Milky Way disk although its spread perpendicular to the disk is large because the supernova explosive process can provide high translational speed (400 km/sec) to the newly formed neutron star.
Some of the best known neutron stars are the RX J1856.5-3754, which is about 400 light-years away, and PSR J0108-1431 about 424 light-years away. RX J1856.5-3754 is a member of a group near a neutron star called The Magnificent Seven. Another neutron star nearby detected transit background constellation Ursa Minor has been nicknamed Calvera by its Canadian and American inventors, after the villain in the 1960 movie The Magnificent Seven . This fast-moving object is found using the ROSAT/Bright Source Catalog.
Binary binary star system
About 5% of all known neutron stars are members of the binary system. The formation and evolution of binary neutron stars can be a complex process. Neutron stars have been observed in binaries with regular main sequence stars, red giants, white dwarfs or other neutron stars. According to the modern theory of binary evolution, it is expected that neutron stars also exist in binary systems with black hole friends. The binary incorporation containing two neutron stars, or neutron stars and black holes, is expected to be the primary source for the emission of detectable gravitational waves.
X-ray binaries
Binary systems containing neutron stars often emit X-rays, emitted by hot gases when they fall onto the surface of neutron stars. The gas source is a companion star, an outer layer that can be released by the gravitational force of a neutron star if two stars are close enough. When a neutron star adds to this gas, its mass may increase; if enough mass increases, the neutron star will fall into the black hole.
Star binary and nucleosynthesis incorporation Neutron
Binaries containing two neutron stars are observed to shrink when gravitational waves are emitted. In the end the neutron star will come into contact and unite. Coalescence of binary neutron stars is one of the leading models for the origin of short gamma-ray bursts. The strong evidence for this model comes from the observation of kilonova associated with short duration GRB 130603B gamma-ray bursts, and finally confirmed by the detection of GW170817 and GRB 170817A gravitational waves short by LIGO, Virgo and 70 observatories covering the observed electromagnetic spectrum. event. The light emitted in kilonova is believed to be derived from the decay of radioactive material released by the incorporation of two neutron stars. This material may be responsible for the production of many chemical elements outside of iron, as opposed to the theory of nucleosynthesis of supernovae.
Planet
Neutron stars can host exoplanets. It can be original, circumcised, captured, or the result of a second round of planetary formation. Pulsars can also cut off the atmosphere of a star, leaving the rest of the planet-mass, which can be understood as a chthonian planet or star object depending on its interpretation. For pulsars, such pulsar planets can be detected by the pulsar timing method, which allows for higher precision and much smaller planet detection than with other methods. Two systems have been confirmed definitively. The first Ekoplanet ever detected were three Draugr, Poltergeist and Phobetor planets around PSR B1257 12, found in 1992-1994. Of these, Draugr is the smallest extrasolar planet ever detected, with twice the mass of the Moon. Another system is the PSR B1620-26, where the circular planet orbits the dwarf-white binary neutron binary system. Also, there are some unconfirmed candidates. The pulsar planet receives little visible light, but a large amount of ionizing radiation and high energy star wind energy, which makes them into a rather hostile environment.
History of discovery
At the American Physical Society meeting in December 1933 (the process was published in January 1934), Walter Baade and Fritz Zwicky proposed the existence of a neutron star, less than two years after the discovery of neutrons by Sir James Chadwick. In searching for an explanation of the origin of supernovae, they tentatively proposed that in supernovae explosions the stars were converted into stars consisting of very dense neutrons they called neutron stars. Baade and Zwicky rightly proposed at the time that the release of gravity binding energy from neutron stars of supernova forces: "In the process of supernovae, mass in large quantities are destroyed". The neutron stars were considered too dim to be detected and little work was done on them until November 1967, when Franco Pacini pointed out that if neutron stars rotate and have a large magnetic field, the electromagnetic waves will be emitted. Unbeknownst to him, radio astronomer Antony Hewish and his research assistant Jocelyn Bell in Cambridge soon detected radio pulses from now widely believed magnetic stars, fast-spinning neutron stars, known as pulsars.
In 1965, Antony Hewish and Samuel Okoye discovered "an unusual source of high temperature radio brightness in the Crab Nebula". This source turns out to be the Pulsar Crab produced from a large 1054 supernova.
In 1967, Iosif Shklovsky examined X-rays and optical observations of Scorpius X-1 and correctly concluded that the radiation originated from neutron stars at the incremental stage.
In 1967, Jocelyn Bell Burnell and Antony Hewish invented regular radio pulses from PSR B1919 21. These pulsars were then interpreted as spinning and separate neutron stars. The source of the pulsar energy is the neutron star's rotational energy. The majority of known neutron stars (around 2000, in 2010) have been found as pulsars, emitting regular radio pulses.
In 1971, Riccardo Giacconi, Herbert Gursky, Ed Kellogg, R. Levinson, E. Schreier, and H. Tananbaum discovered a 4.8 second pulsation in an X-ray source in the Centaurus constellation Cen X-3. They interpret this as a result of hot spinning neutron stars. The source of energy is gravity and the result of rain of gasses that fall to the surface of neutron stars from companion stars or interstellar mediums.
In 1974, Antony Hewish was awarded the Nobel Prize in Physics "for his decisive role in the discovery of the pulsar" without Jocelyn Bell sharing in the discovery.
In 1974, Joseph Taylor and Russell Hulse invented the first binary pulsar, PSR B1913 16, consisting of two neutron stars (one seen as pulsars) orbiting around their center of mass. Einstein's general theory of relativity predicts that large objects in short binary orbit must emit gravitational waves, and thus their orbits will decay over time. This is indeed observed, exactly as the estimates of general relativity, and in 1993, Taylor and Hulse were awarded the Nobel Prize in Physics for this discovery.
In 1982, Don Backer and colleagues discovered the first millisecond pulsar, PSR B1937 21. This object rotates 642 times per second, a value that places a fundamental constraint on the mass and radius of a neutron star. Many millisecond pulsars were later found, but PSR B1937 21 remained the fastest known pulsar spinning for 24 years, until PSR J1748-2446ad (which rotates more than 700 times per second) was found.
In 2003, Marta Burgay and colleagues discovered the first neutron double star system in which both components could be detected as pulsars, PSR J0737-3039. The discovery of this system allows a total of 5 different general relativity tests, some of them with unprecedented precision.
In 2010, Paul Demorest and colleagues measured the millisecond pulsar mass of PSR J1614-2230 to 1.97 Â ± 0.04 M ? , using Shapiro delay. This is substantially higher than the mass of previously measured neutron stars (1.67 M ? , see PSR J1903 0327), and places a strong constraint on the interior composition of the neutron star.
In 2013, John Antoniadis and colleagues measured PSR J0348 0432 mass to 2.01 Â ± 0.04Ã, M ? , using white dwarf spectroscopy. This confirms the existence of big stars using different methods. Furthermore, this allows, for the first time, general relativity tests to use massive neutron stars.
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