what is the mass of a neutron star
Neutron star


its material would have a mass over , about 900 times the mass of the Great Pyramid of Giza. In the enormous gravitational field of a neutron star, that teaspoon of material would weigh , which is 15 times what the Moon would weigh if it were placed on the surface of the Earth. The entire mass of the Earth at neutron star density would fit into a sphere of 305m in diameter (the size of the Arecibo Observatory). The pressure increases from to from the inner crust to the center. The
2089576
Neutron star


likely radii for a given neutron star mass are bracketed by models AP4 (smallest radius) and MS2 (largest radius). BE is the ratio of gravitational binding energy mass equivalent to the observed neutron star gravitational mass of "M" kilograms with radius "R" meters, Given current values and star masses "M" commonly reported as multiples of one solar mass, then the relativistic fractional binding energy of a neutron star is A neutron star would not be more compact than 10,970 meters radius (AP4 model). Its
2089586
Neutron star


(the Tolman–Oppenheimer–Volkoff limit), although the recent estimate puts the upper limit at . The maximum observed mass of neutron stars is about . However in general, compact stars of less than (the Chandrasekhar limit) are white dwarfs, whereas compact stars with a mass between and should be neutron stars (though there is an interval of a few tenths of a solar mass where the masses of low-mass neutron stars and high-mass white dwarfs can overlap). It is thought that beyond the stellar
2089573
PSR J1614−2230


London. Neutron stars also have the property that as they become more massive, their diameter decreases. The mass of PSR J1614–2230 is the second highest of all the known neutron stars. The existence of a neutron star with such a high mass constrains the composition and structure of neutron stars, both of which are poorly understood. The reason for this is that the maximum mass of a neutron star is dependent upon its composition. A neutron star composed of matter such as hyperons or kaon condensates would collapse to form a black hole
5856238
Neutron star


A neutron star is the collapsed core of a giant star which before collapse had a total mass of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars, not counting black holes, hypothetical white holes, quark stars and strange stars. Neutron stars have a radius on the order of and a mass of about 1.4 solar masses. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei. Once
2089559
Neutron star


the companion star, the outer layers of which can be stripped off by the gravitational force of the neutron star if the two stars are sufficiently close. As the neutron star accretes this gas its mass can increase; if enough mass is accreted the neutron star may collapse into a black hole. Binaries containing two neutron stars are observed to shrink as gravitational waves are emitted. Ultimately the neutron stars will come into contact and coalesce. The coalescence of binary neutron stars is one of the leading models for the origin of short gamma
2089612
Tolman–Oppenheimer–Volkoff limit


neutrons in a neutron star formed a degenerate cold Fermi gas. They thereby obtained a limiting mass of approximately 0.7 solar masses, In a neutron star less massive than the limit, the weight of the star is balanced by short-range repulsive neutron–neutron interactions mediated by the strong force and also by the quantum degeneracy pressure of neutrons, preventing collapse. If its mass is above the limit, the star will collapse to some denser form. It could form a black hole, or change composition and be supported in some
18897774
Gravitational binding energy


neutron star pulsars) have radial density gradients plus relativistic corrections. Neutron star relativistic equations of state provided by Jim Lattimer include a graph of radius vs. mass for various models. The most likely radii for a given neutron star mass are bracketed by models AP4 (smallest radius) and MS2 (largest radius). BE is the ratio of gravitational binding energy mass equivalent to observed neutron star gravitational mass of "M" kilograms with radius "R" meters, Given current values and star masses "M" commonly reported as multiples
14959963
Tolman–Oppenheimer–Volkoff equation


George Volkoff in their 1939 paper, "On Massive Neutron Cores". In this paper, the equation of state for a degenerate Fermi gas of neutrons was used to calculate an upper limit of ~0.7 solar masses for the gravitational mass of a neutron star. Since this equation of state is not realistic for a neutron star, this limiting mass is likewise incorrect. Using gravitational wave observations from binary neutron star mergers (like GW170817) and the subsequent information from electromagnetic radiation (kilonova), the data suggest that the maximum mass
10224775
Be/X-ray binary


Be/X-ray binaries (BeXRBs) are a class of high-mass X-ray binaries that consist of a Be star and a neutron star. The neutron star is usually in a wide highly elliptical orbit around the Be star. The Be stellar wind forms a disk confined to a plane often different from the orbital plane of the neutron star. When the neutron star passes through the Be disk, it accretes a large mass of gas in a short time. As the gas falls onto the neutron star,
1339295
Neutron star


distance of the star. A fraction of the mass of a star that collapses to form a neutron star is released in the supernova explosion from which it forms (from the law of mass–energy equivalence, ). The energy comes from the gravitational binding energy of a neutron star. Hence, the gravitational force of a typical neutron star is huge. If an object were to fall from a height of one meter on a neutron star 12 kilometers in radius, it would reach the ground at around 1400 kilometers per second
2089584
Gravitational collapse


Planck density (as there is nothing that can stop it). This is when the known laws of gravity cease to be valid. There are competing theories as to what occurs at this point, but it can no longer really be considered gravitational collapse at that stage. The radii of larger mass neutron stars (about 2.0 solar mass) are estimated to be about 12-km, or approximately 2.0 times their equivalent Schwarzschild radius. It might be thought that a sufficiently massive neutron star could exist within its Schwarzschild radius (1.0 SR
22081454
Stellar collision


mass of the remnant exceeds the Tolman–Oppenheimer–Volkoff limit. This creates a magnetic field that is trillions of times stronger than that of Earth, in a matter of one or two milliseconds. Astronomers believe that this type of event is what creates short gamma-ray bursts and kilonovae. If a neutron star collides with red giant of sufficiently low mass and density, both can survive in the form of a peculiar hybrid known as Thorne–Żytkow object, with a neutron star surrounded by a red giant. About half
7256013
Stellar black hole


exhibit localized explosions (thermonuclear bursts). Whenever such properties are observed, the compact object in the binary system is revealed as a neutron star. The derived masses come from observations of compact X-ray sources (combining X-ray and optical data). All identified neutron stars have a mass below 2.0 solar masses. None of the compact systems with a mass above 2.0 solar masses display the properties of a neutron star. The combination of these facts make it more and more likely that the class of compact stars with
21250949
Neutron star


is the fact that neutron stars have an escape velocity ranging from 100,000 km/s to 150,000 km/s, that is, from a third to half the speed of light. The neutron star's gravity accelerates infalling matter to tremendous speed. The force of its impact would likely destroy the object's component atoms, rendering all the matter identical, in most respects, to the rest of the neutron star. A neutron star has a mass of at least 1.1 and perhaps up to more than 2.1 solar masses ()
2089572
First observation of gravitational waves


) when they merged. That information showed that the objects had to be black holes, as any other kind of known objects with these masses would have been physically larger and therefore merged before that point, or would not have reached such velocities in such a small orbit. The highest observed neutron star mass is two solar masses, with a conservative upper limit for the mass of a stable neutron star of three solar masses, so that a pair of neutron stars would not have had sufficient mass to account for the merger (
262602
Neutron star


exclusion principle, just as white dwarfs are supported against collapse by electron degeneracy pressure. However neutron degeneracy pressure is not sufficient to hold up an object beyond 0.7 and repulsive nuclear forces play a larger role in supporting more massive neutron stars. If the remnant star has a mass exceeding the Tolman–Oppenheimer–Volkoff limit of around 2 solar masses, the combination of degeneracy pressure and nuclear forces is insufficient to support the neutron star and it continues collapsing to form a black hole. Neutron stars that can be observed are very hot
2089561
Lee Smolin


as a prediction of his theory that no neutron star should exist with a mass of more than 1.6 times the mass of the sun. Later this figure was raised to two solar masses following more precise modeling of neutron star interiors by nuclear astrophysicists. If a more massive neutron star was ever observed, it would show that our universe's natural laws were not tuned for maximal black hole production, because the mass of the strange quark could be retuned to lower the mass threshold for production of a black hole. A 1.97-solar-
7889871
Neutron star


remnant will overcome the neutron degeneracy pressure and gravitational collapse will usually occur to produce a black hole, though the smallest observed mass of a stellar black hole is about . Between and , hypothetical intermediate-mass stars such as quark stars and electroweak stars have been proposed, but none have been shown to exist. The temperature inside a newly formed neutron star is from around 10 to 10 kelvin. However, the huge number of neutrinos it emits carry away so much energy that the temperature of an isolated neutron star falls within a
2089574
Tolman–Oppenheimer–Volkoff limit


The Tolman–Oppenheimer–Volkoff limit (or TOV limit) is an upper bound to the mass of cold, nonrotating neutron stars, analogous to the Chandrasekhar limit for white dwarf stars. Observations of GW170817, the first gravitational wave event due to merging neutron stars (which are thought to have collapsed into a black hole within a few seconds after merging), suggest that the limit is close to 2.17 solar masses. A neutron star in a binary pair (PSR J2215+5135) has been measured to have a mass
18897769
Neutron star


these with unprecedented precision. In 2010, Paul Demorest and colleagues measured the mass of the millisecond pulsar PSR J1614−2230 to be , using Shapiro delay. This was substantially higher than any previously measured neutron star mass (, see PSR J1903+0327), and places strong constraints on the interior composition of neutron stars. In 2013, John Antoniadis and colleagues measured the mass of PSR J0348+0432 to be , using white dwarf spectroscopy. This confirmed the existence of such massive stars using a different method. Furthermore, this allowed
2089623
Compact star


Ic, and II. Such supernovae occur when the iron core of a massive star exceeds the Chandrasekhar limit and collapses to a neutron star. Like electrons, neutrons are fermions. They therefore provide neutron degeneracy pressure to support a neutron star against collapse. In addition, repulsive neutron-neutron interactions provide additional pressure. Like the Chandrasekhar limit for white dwarfs, there is a limiting mass for neutron stars: the Tolman-Oppenheimer-Volkoff limit, where these forces are no longer sufficient to hold up the star. As the
282169
1E 161348-5055


theory would account for the slower than expected rotation but not for the increase in brightness. An alternate explanation is that the star has a low-mass X-ray binary. The companion star would orbit in an elongated orbit. When the companion is close to the neutron star, it would feed mass into it, creating the increased brightness. The drag created by the companion on the neutron star's magnetic field would also slow the rotation of the neutron star. If this scenario is the case, it is the youngest
19924146
Compact star


forces in dense hadronic matter are not well understood, this limit is not known exactly but is thought to be between 2 and . If more mass accretes onto a neutron star, eventually this mass limit will be reached. What happens next is not completely clear. As more mass is accumulated, equilibrium against gravitational collapse reaches its breaking point. The star's pressure is insufficient to counterbalance gravity and a catastrophic gravitational collapse occurs in milliseconds. The escape velocity at the surface, already at least 1/3 light speed, quickly reaches the
282170
Stellar black hole


a compact star — either a white dwarf (for masses below the Chandrasekhar limit) or a neutron star or a (hypothetical) quark star. If the collapsing star has a mass exceeding the TOV limit, the crush will continue until zero volume is achieved and a black hole is formed around that point in space. The maximum mass that a neutron star can possess (without becoming a black hole) is not fully understood. In 1939, it was estimated at 0.7 solar masses, called the TOV limit. In 1996
21250944
PSR J1614−2230


delay is dependent upon the mass of the white dwarf companion. The best fit companion mass was . Knowing the companion mass and orbital elements then provided enough information to determine the mass of PSR J1614–2230 to be . The conditions in neutron stars are very different from those encountered on Earth, as a result of the high density and gravity of neutron stars; their masses are of order the mass of a star, but they have sizes around in radius, which is comparable to the size of the center of large cities such as
5856237
X-ray burster


immediately be classified as a neutron star, since black holes do not have a surface and all of the accreting material disappears past the event horizon. The donor star's mass falls to the surface of the neutron star where the hydrogen fuses to helium which accumulates until it fuses in a burst, producing X-rays. The mass of the donor star is used to categorize the system as either a high mass (above 10 solar masses ()) or low mass (less than ) X-ray binary, abbreviated as
19044713
Cygnus X-1


appears to determine the distance at which the surrounding plasma begins to emit these QPOs, with the emission radius decreasing as the mass decreases. This technique has been used to estimate the mass of Cygnus X-1, providing a cross-check with other mass derivations. Pulsations with a stable period, similar to those resulting from the spin of a neutron star, have never been seen from Cygnus X-1. The pulsations from neutron stars are caused by the neutron star's magnetic field; however, the no-hair theorem guarantees that black
5267555
Neutron star


In 2017, a direct detection (GW170817) of the gravitational waves from such an event was made, and gravitational waves have also been indirectly detected in a system where two neutron stars orbit each other. Any main-sequence star with an initial mass of above 8 times the mass of the sun () has the potential to produce a neutron star. As the star evolves away from the main sequence, subsequent nuclear burning produces an iron-rich core. When all nuclear fuel in the core has been exhausted, the
2089568
History of X-ray astronomy


binary system with a normal star. In these "X-ray binaries," the X-rays originate from material traveling from the normal star to the neutron star in a process called accretion. The binary nature of the system allowed astronomers to measure the mass of the neutron star. For other systems, the inferred mass of the X-ray emitting object supported the idea of the existence of black holes, as they were too massive to be neutron stars. Other systems displayed a characteristic X-ray pulse, just
6750357
Neutron star


formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star. Neutron stars are partially supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli
2089560
GW170817


in binary neutron stars that will merge within a Hubble time, the total mass is . The masses of the component stars have greater uncertainty. The larger () has a 90% chance of being between , and the smaller () has a 90% chance of being between . Under the low spin assumption, the ranges are for and for . The chirp mass, a directly observable parameter which may be very roughly equated to the geometric mean of the masses, is measured at . The neutron star merger event is thought
20023809
James Lattimer


David N. Schramm first argued that the mergers of neutron stars and black holes would result in the ejection of neutron-rich matter in sufficient quantities to explain the origin of r-process elements such as gold and platinum. Later, with collaborators, he demonstrated decompressing neutron-star matter from both neutron star-black hole and neutron star-neutron star mergers would form a natural r-process that would match observed patterns. Mass ejection and r-process nucleosynthesis from decompression has been apparently observed in the aftermath of GW170817,
4771041
Stellar rotation


. The mass of a neutron star is in the range of 1.2 to 2.1 times the mass of the Sun. As a result of the collapse, a newly formed neutron star can have a very rapid rate of rotation; on the order of a hundred rotations per second. Pulsars are rotating neutron stars that have a magnetic field. A narrow beam of electromagnetic radiation is emitted from the poles of rotating pulsars. If the beam sweeps past the direction of the Solar System then the pulsar will produce a periodic pulse that can
15027346
The Magnificent Seven (neutron stars)


best laboratory to study neutron star atmospheres and, probably, internal structure. The holy grail of neutron star astrophysics is the determination of the equation of state (EOS) of matter at supra-nuclear densities. The most direct way of constraining the EOS is to measure simultaneously the neutron star mass and radius. If a neutron star emits blackbody radiation from its surface of radius formula_1 at homogeneous temperature formula_2, the received flux at distance formula_3 is: So, if distance formula_3 is known and formula_2 can be determined by spectral analysis
683922
GR Muscae


GR Muscae, also known as 2S 1254-690 is a binary star system in the constellation Musca composed of a neutron star of between 1.2 and 1.8 times the mass of the Sun and a low-mass star likely to be around the mass of the Sun in close orbit. A magnitude 19 blue star was pinpointed as the optical counterpart of the X-ray source in 1978. Its apparent magnitude varies from 18 to 19.1 over a period of 0.16 days. The neutron star has an accretion disk that takes around 6.74
10115496
Gravitational wave


, allowed for constraining the masses of the neutron stars involved between 0.86 and 2.26 solar masses. Further analysis allowed a greater restriction of the mass values to the interval 1.17–1.60 solar masses, with the total system mass measured to be 2.73–2.78 solar masses. The inclusion of the Virgo detector in the observation effort allowed for an improvement of the localization of the source by a factor of 10. This in turn facilitated the electromagnetic follow-up of the event. In contrast to the case of binary black hole mergers, binary neutron star
1246156
Neutron star merger


A neutron star merger is a type of stellar collision. It occurs in a fashion similar to the rare brand of type Ia supernovae resulting from merging white dwarfs. When two neutron stars orbit each other closely, they spiral inward as time passes due to gravitational radiation. When the two neutron stars meet, their merger leads to the formation of either a more massive neutron star, or a black hole (depending on whether the mass of the remnant exceeds the Tolman–Oppenheimer–Volkoff limit). The merger can also create
21845973
Magnetar


the neutron star (where neutrons predominate by mass). A similar magnetohydrodynamic dynamo process produces even more intense transient fields during coalescence of pairs of neutron stars. When in a supernova, a star collapses to a neutron star, and its magnetic field increases dramatically in strength. Halving a linear dimension increases the magnetic field fourfold. Duncan and Thompson calculated that when the spin, temperature and magnetic field of a newly formed neutron star falls into the right ranges, a dynamo mechanism could act, converting heat and rotational energy into magnetic
934991
Matter


, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons. In other words, most of what composes the "mass" of ordinary matter is due to the binding energy of quarks within protons and neutrons. For example, the sum of the mass of the three quarks
15534707
Degenerate matter


(which includes all measured neutron stars). In the case of neutron stars and white dwarfs, this phenomenon is compounded by the fact that the pressures within neutron stars are much higher than those in white dwarfs. The pressure increase is caused by the fact that the compactness of a neutron star causes gravitational forces to be much higher than in a less compact body with similar mass. The result is a star with a diameter on the order of a thousandth that of a white dwarf. There is an upper limit to the
14267815
Axion


and allow much greater sensitivities than currently achievable. The International Axion Observatory (IAXO) is a proposed fourth generation helioscope. Axions may be produced within neutron stars, by nucleon-nucleon bremsstrahlung. The subsequent decay of axions to gamma rays allows constraints on the axion mass to be placed from observations of neutron stars in gamma-rays using the Fermi LAT. From an analysis of four neutron stars, Berenji et al. obtained a 95% CL upper limit on the axion mass of 0.079 eV. It was reported in 2014 that
19190548
X-ray astronomy


-ray background. The X-ray continuum can arise from bremsstrahlung, black-body radiation, synchrotron radiation, or what is called inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions. An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate mass star. Hercules
209180
Supernova


ejected from the star creates the narrow absorption lines and causes a shock wave through interaction with the newly ejected material. When a stellar core is no longer supported against gravity, it collapses in on itself with velocities reaching 70,000 km/s (0.23"c"), resulting in a rapid increase in temperature and density. What follows next depends on the mass and structure of the collapsing core, with low mass degenerate cores forming neutron stars, higher mass degenerate cores mostly collapsing completely to black holes, and non-degenerate cores undergoing
8016025
Neutron star


pressure halts the contraction. The infalling outer envelope of the star is halted and flung outwards by a flux of neutrinos produced in the creation of the neutrons, becoming a supernova. The remnant left is a neutron star. If the remnant has a mass greater than about , it collapses further to become a black hole. As the core of a massive star is compressed during a Type II supernova, Type Ib or Type Ic supernova, and collapses into a neutron star, it retains most of its angular momentum. But,
2089570
Nuclear physics


and neutrons — and that neutrons were spin particles which explained the mass not due to protons. The neutron spin immediately solved the problem of the spin of nitrogen-14, as the one unpaired proton and one unpaired neutron in this model each contributed a spin of in the same direction, giving a final total spin of 1. With the discovery of the neutron, scientists could at last calculate what fraction of binding energy each nucleus had, by comparing the nuclear mass with that of the protons and neutrons which composed it. Differences between
1590087
Binary star


-ray binaries are semidetached binaries in which gas from a late-type donor star or a white dwarf overflows the Roche lobe and falls towards the neutron star or black hole. Probably the best known example of an X-ray binary is the high-mass X-ray binary Cygnus X-1. In Cygnus X-1, the mass of the unseen companion is estimated to be about nine times that of the Sun, far exceeding the Tolman–Oppenheimer–Volkoff limit for the maximum theoretical mass of a neutron star. It is
7800845
Norma (constellation)


neutron star orbiting a blue-white supergiant approximately 20 times as massive as the Sun. The stellar wind from the more massive star is drawn to the magnetic poles of the neutron star, forming an accretion column and producing X-rays. Located 19,000 light-years away, QX Normae is an active low mass X ray binary composed of a neutron star and its companion star that is smaller and cooler than the Sun. The neutron star is 1.74 ± 0.14 times as massive as the Sun, yet its radius is a
14829349
Magnetar


explanation for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs). Like other neutron stars, magnetars are around in diameter and have a mass 2–3 times that of the Sun. The density of the interior of a magnetar is such that a tablespoon of its substance would have a mass of over 100 million tons. Magnetars are differentiated from other neutron stars by having even stronger magnetic fields, and by rotating comparatively quicker. Most neutron stars rotate once every one to ten seconds, whereas magnetars rotate once
934985
Degenerate matter


, formed by the gradual shrinking of the cores of stars that run out of fuel. During this shrinking, an electron-degenerate gas forms in the core, providing sufficient degeneracy pressure as it is compressed to resist further collapse. Above this mass limit, a neutron star (partially supported by neutron degeneracy pressure) or a black hole may be formed instead. Neutron degeneracy is analogous to electron degeneracy and is demonstrated in neutron stars, which are partially supported by the pressure from a degenerate neutron gas. The collapse may happen
14267812
Neutron star


(FPS, UU, APR, L, SLy, and others) and current research is still attempting to constrain the theories to make predictions of neutron star matter. This means that the relation between density and mass is not fully known, and this causes uncertainties in radius estimates. For example, a neutron star could have a radius of 10.7, 11.1, 12.1 or 15.1 kilometers (for EOS FPS, UU, APR or L respectively). Current understanding of the structure of neutron stars is defined by existing mathematical models
2089588
PSR J1614−2230


star at the time of discovery, and rules out many neutron star equations of state that include exotic matter such as hyperons and kaon condensates. In 2013, a slightly higher neutron star mass measurement was announced for PSR J0348+0432, . This confirmed the existence of such massive neutron stars using a different measuring technique. Pulsars were discovered in 1967 by Jocelyn Bell and her adviser Antony Hewish using the Interplanetary Scintillation Array. Franco Pacini and Thomas Gold quickly put forth the idea that pulsars are highly magnetized rotating neutron stars, which
5856232
Astrophysical X-ray source


the Milky Way. Scorpius X-1 is some 9,000 ly from Earth and after the Sun is the strongest X-ray source in the sky at energies below 20 keV. Its X-ray output is 2.3 × 10 W, about 60,000 times the total luminosity of the Sun. Scorpius X-1 itself is a neutron star. This system is classified as a low-mass X-ray binary (LMXB); the neutron star is roughly 1.4 solar masses, while the donor star is only 0.42 solar masses. In the late 1930s
6492181
Neutron star


. However, even before impact, the tidal force would cause spaghettification, breaking any sort of an ordinary object into a stream of material. Because of the enormous gravity, time dilation between a neutron star and Earth is significant. For example, eight years could pass on the surface of a neutron star, yet ten years would have passed on Earth, not including the time-dilation effect of its very rapid rotation. Neutron star relativistic equations of state describe the relation of radius vs. mass for various models. The most
2089585
Neutron star


time that the release of the gravitational binding energy of the neutron stars powers the supernova: "In the supernova process, mass in bulk is annihilated". Neutron stars were thought to be too faint to be detectable and little work was done on them until November 1967, when Franco Pacini pointed out that if the neutron stars were spinning and had large magnetic fields, then electromagnetic waves would be emitted. Unbeknown to him, radio astronomer Antony Hewish and his research assistant Jocelyn Bell at Cambridge were shortly to detect radio pulses from
2089617
Quark-nova


masses between 1.5 and 1.8 solar masses are theoretically the best candidates for conversion due to spin down of the star within a Hubble time. This amounts to a small fraction of the projected neutron star population. A conservative estimate based on this, indicates that up to two quark-novae may occur in the observable universe each day. Theoretically, quark stars would be radio-quiet, so radio-quiet neutron stars may be quark stars. Direct evidence for quark-novae is scant; however, recent observations of supernovae SN
16294752
Hexaquark


could notionally result from the combination of two uds hyperons A number of experiments have been suggested to detect dibaryon decays and interactions. In the 1990s several candidate dibaryon decays were observed but they were not confirmed. There is a theory that strange particles such as hyperons and dibaryons could form in the interior of a neutron star, changing its mass–radius ratio in ways that might be detectable. Accordingly, measurements of neutron stars could set constraints on possible dibaryon properties. A large fraction of the neutrons in a neutron star could turn
11020469
Astrophysical X-ray source


eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion. Vela X-1 is the prototypical detached HMXB. An intermediate-mass X-ray binary (IMXB) is a binary star system where one of the components is a neutron star or a black hole. The other component is an intermediate
6492179
Indium


-lasting (up to thousands of years) s-process (slow neutron capture) in low-to-medium-mass stars (which range in mass between 0.6 and 10 solar masses). When a silver-109 atom (the isotope that comprises approximately half of all silver in existence) catches a neutron, it undergoes a beta decay to become cadmium-110. Capturing further neutrons, it becomes cadmium-115, which decays to indium-115 by another beta decay. This explains why the radioactive isotope is more abundant than the stable one.
14895383
Thorne–Żytkow object


If their combined mass exceeds the Tolman-Oppenheimer-Volkoff limit then the two will collapse into a black hole, resulting in a supernova that disperses the outer layers of the star. Otherwise, the two will coalesce into a single neutron star. If a neutron star and a white dwarf merge, this could form a Thorne–Żytkow object with the properties of an R Coronae Borealis variable. The surface of the neutron star is very hot, with temperatures exceeding 10 K: hotter than the cores of all but the most
8959024
Nuclear pasta


structures resembles various types of pasta. Neutron stars form as remnants of massive stars after a supernova event. Unlike their progenitor star, neutron stars do not consist of a gaseous plasma. Rather, the intense gravitational attraction of the compact mass overcomes the electron degeneracy pressure and causes electron capture to occur within the star. The result is a compact ball of nearly pure neutron matter with sparse protons and electrons in between in a space several thousand times smaller than the progenitor star. At the surface, the pressure is low enough that
10370869
Fermi gas


radiation) against gravitational forces. At the end of the star lifetime, when thermal processes are weaker, some stars may become white dwarfs, which are only sustained against gravity by electron degeneracy pressure. Using the Fermi gas as a model, it is possible to calculate the Chandrasekhar limit, i.e. the maximum mass any star may acquire (without significant thermally generated pressure) before collapsing into a black hole or a neutron star. The latter, is a star mainly composed of neutrons, where the collapse is also avoided by neutron
13586441
Type II supernova


formation of a black hole from fallback of material onto the neutron star core, the collapsar model; interaction with a dense envelope of circumstellar material, the CSM model; the highest mass pair instability supernovae; possibly others such as binary and quark star model. Stars with initial masses between about 25 and 90 times the sun develop cores large enough that after a supernova explosion, some material will fall back onto the neutron star core and create a black hole. In many cases this reduces the luminosity of the supernova, and above
13246328
Tolman–Oppenheimer–Volkoff limit


other way (for example, by quark degeneracy pressure if it becomes a quark star). Because the properties of hypothetical, more exotic forms of degenerate matter are even more poorly known than those of neutron-degenerate matter, most astrophysicists assume, in the absence of evidence to the contrary, that a neutron star above the limit collapses directly into a black hole. A black hole formed by the collapse of an individual star must have mass exceeding the Tolman–Oppenheimer–Volkoff limit. Theory predicts that because of mass loss
18897775
Stellar collision


rapidly heat up the interior of the combined star and spread, causing a supernova explosion. In a matter of seconds, all of the white dwarf's mass is thrown into space. Neutron star mergers occur in a fashion similar to the rare type Ia supernovae resulting from merging white dwarfs. When two neutron stars orbit each other closely, they spiral inward as time passes due to gravitational radiation. When they meet, their merger leads to the formation of either a heavier neutron star or a black hole, depending on whether the
7256012
Binary star


to become hotter and emit radiation. Cataclysmic variable stars, where the compact object is a white dwarf, are examples of such systems. In X-ray binaries, the compact object can be either a neutron star or a black hole. These binaries are classified as low-mass or high-mass according to the mass of the donor star. High-mass X-ray binaries contain a young, early-type, high-mass donor star which transfers mass by its stellar wind, while low-mass X
7800844
Neutron star


mass fraction gravitational binding energy would then be 0.187, −18.7% (exothermic). This is not near 0.6/2 = 0.3, −30%. The equation of state for a neutron star is not yet known. It is assumed that it differs significantly from that of a white dwarf, whose equation of state is that of a degenerate gas that can be described in close agreement with special relativity. However, with a neutron star the increased effects of general relativity can no longer be ignored. Several equations of state have been proposed
2089587
Oppenheimer security hearing


Serber explored the properties of white dwarf stars. This was followed by one co-written with one of his students, George Volkoff, in which they demonstrated that there was a limit, the so-called Tolman-Oppenheimer-Volkoff limit, to the mass of stars beyond which they would not remain stable as neutron stars and would undergo gravitational collapse. In 1939, with another of his students, Hartland Snyder, he went further and predicted the existence of what are today known as black holes. It would be decades
17682856
Nuclear drip line


more and more neutrons are created in nuclei the energy levels for neutrons get filled up to an energy level equal to the rest mass of a neutron. At this point any electron penetrating a nucleus will create a neutron, which will "drip" out of the nucleus. At this point we have: And from this point onwards the equation applies, where "p" is the Fermi momentum of the neutron. As we go deeper into the neutron star the free neutron density increases, and as the Fermi momentum increases with
982453
47 Tucanae


neutron star. 47 Tucanae has 25 known millisecond pulsars, the second largest population of pulsars in any globular cluster. These pulsars are thought to be spun up by the accretion of material from binary companion stars, in a previous X-ray binary phase. The companion of one pulsar in 47 Tucanae, 47 Tuc W, seems to still be transferring mass towards the neutron star, indicating that this system is completing a transition from being an accreting low-mass X-ray binary to a millisecond pulsar. X-ray
10956235
PSR J0348+0432


PSR J0348+0432 is a neutron star in a binary system with a white dwarf. It was discovered in 2007 with the Green Bank Telescope in a drift-scan survey. In 2013, a mass measurement for this neutron star was announced: . This measurement was done with a combination of radio timing and precise spectroscopy of the white dwarf companion. This is slightly higher than, but statistically indistinguishable from, the mass of PSR J1614−2230, which was measured using the Shapiro delay. This measurement confirmed the existence of such massive
2554250
Black hole


the mass of the compact object. If this is much larger than the Tolman–Oppenheimer–Volkoff limit (that is, the maximum mass a neutron star can have before it collapses) then the object cannot be a neutron star and is generally expected to be a black hole. The first strong candidate for a black hole, Cygnus X-1, was discovered in this way by Charles Thomas Bolton, Louise Webster and Paul Murdin in 1972. Some doubt, however, remained due to the uncertainties that result from the companion
4412806
Degenerate matter


mass of a neutron-degenerate object, the Tolman–Oppenheimer–Volkoff limit, which is analogous to the Chandrasekhar limit for electron-degenerate objects. The limit for objects supported by ideal neutron degeneracy pressure is only 0.75 solar masses. For more realistic models including baryon interaction, the precise limit is unknown, as it depends on the equations of state of nuclear matter, for which a highly accurate model is not yet available. Above this limit, a neutron star may collapse into a black hole or into other, denser
14267816
Strange matter


definition, strange matter might occur inside neutron stars, if the pressure at their core is high enough (i.e. above the critical pressure). At the sort of densities and high pressures we expect in the center of a neutron star, the quark matter would probably be strange matter. It could conceivably be non-strange quark matter, if the effective mass of the strange quark were too high. Charm quarks and heavier quarks would only occur at much higher densities. A neutron star with a quark matter core is often called
15619800
Qu Qinyue


curve and energy spectrum. They created a model for a neutron star binary system, and provided detailed explanation of the observational data using the mechanism of Bremsstrahlung and Kruskal-Schwarzschild instability. Their work was reported at the 17th International Cosmic Ray Conference held in 1981. About the same time, Fang Lizhi, Qu Qinyue, Wang Zhenru and others proposed a theory that abnormal neutron stars, in which neutrons are in a state that their effective mass become zero or nearly zero, are a form of stars during their final period.
1876519
Gravitational wave


neutron stars can be constituents of binaries. For example, a pair of solar mass neutron stars in a circular orbit at a separation of 1.89 m (189,000 km) has an orbital period of 1,000 seconds, and an expected lifetime of 1.30 seconds or about 414,000 years. Such a system could be observed by LISA if it were not too far away. A far greater number of white dwarf binaries exist with orbital periods in this range. White dwarf binaries have masses in the order of the Sun, and diameters in the
1246108
S-process


The slow neutron-capture process , or "s"-process is a series of reactions in nuclear astrophysics that occur in stars, particularly AGB stars. The "s"-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron. In the "s"-process, a seed nucleus undergoes neutron capture to form an isotope with one higher atomic mass. If the new isotope is stable, a series of increases in mass can occur, but if it is unstable, then beta decay will occur, producing an element
2440006
Spacetime


spacetime how to curve. General relativity predicts that pressure acts as a gravitational source with exactly the same strength as mass-energy density. The inclusion of pressure as a source of gravity leads to dramatic differences between the predictions of general relativity versus those of Newtonian gravitation. For example, the pressure term sets a maximum limit to the mass of a neutron star. The more massive a neutron star, the more pressure is required to support its weight against gravity. The increased pressure, however, adds to the gravity acting on
9203141
SN 1997D


SN 1997D, discovered on January 1997 in galaxy NGC 1536 in Reticulum constellation is a first clearly identified example of atypical Type II supernova with a very low luminosity and expansion velocity. There are two alternatives, a high-mass 25-40 solar masses star or smaller star with mass of 8-10 solar masses. As there is no evidence that neutron star was formed during the collapse of the star, it is likely that star was in upper spectrum of the mass. Observations of the light curve from SN 1997D showed
4161769
X-ray binary


or a black hole. The other component is an intermediate-mass star. An intermediate-mass X-ray binary is the origin for Low-mass X-ray binary systems. A high-mass X-ray binary (HMXB) is a binary star system that is strong in X rays, and in which the normal stellar component is a massive star: usually an O or B star, or a blue supergiant. The compact, X-ray emitting, component is a neutron star or black hole.
17877835
Preon star


particles, and then particles. However, the theory postulates that it is possible for some stars made of the sub-subatomic particles to remain. It is believed that they may also form out of massive stars that collapse too unstably to become neutron stars, but not enough to become black holes. The mass of a preon star is predicted to be where The radius of a preon star is estimated to be The maximum mass of a preon star is predicted to be formula_3. where is the mass of the earth. The
16209318
R-process


of this material seems to consist of two types: hot blue masses of highly radioactive "r"-process matter of lower-mass-range heavy nuclei () and cooler red masses of higher mass-number "r"-process nuclei () rich in actinides (such as uranium, thorium, and californium). When released from the huge internal pressure of the neutron star, these ejecta expand and form seed heavy nuclei that rapidly capture free neutrons, and radiate detected optical light for about a week. Such duration of luminosity would not be
2440003
Degenerate matter


occur in hypothetical quark stars, formed by the collapse of objects above the Tolman–Oppenheimer–Volkoff mass limit for neutron-degenerate objects. Whether quark-degenerate matter forms at all in these situations depends on the equations of state of both neutron-degenerate matter and quark-degenerate matter, both of which are poorly known. Quark stars are considered to be an intermediate category among neutron stars and black holes. At densities greater than those supported by any degeneracy, gravity overwhelms all other forces. The stellar body collapses to
14267820
Neutron star


such accretion can "recycle" old pulsars and potentially cause them to gain mass and spin-up to very fast rotation rates, forming the so-called millisecond pulsars. These binary systems will continue to evolve, and eventually the companions can become compact objects such as white dwarfs or neutron stars themselves, though other possibilities include a complete destruction of the companion through ablation or merger. The merger of binary neutron stars may be the source of short-duration gamma-ray bursts and are likely strong sources of gravitational waves.
2089567
Neutron star


, a value that placed fundamental constraints on the mass and radius of neutron stars. Many millisecond pulsars were later discovered, but PSR B1937+21 remained the fastest-spinning known pulsar for 24 years, until PSR J1748-2446ad (which spins more than 700 times a second) was discovered. In 2003, Marta Burgay and colleagues discovered the first double neutron star system where both components are detectable as pulsars, PSR J0737−3039. The discovery of this system allows a total of 5 different tests of general relativity, some of
2089622
Pauli exclusion principle


also known as Fermi pressure. This exotic form of matter is known as degenerate matter. The immense gravitational force of a star's mass is normally held in equilibrium by thermal pressure caused by heat produced in thermonuclear fusion in the star's core. In white dwarfs, which do not undergo nuclear fusion, an opposing force to gravity is provided by electron degeneracy pressure. In neutron stars, subject to even stronger gravitational forces, electrons have merged with protons to form neutrons. Neutrons are capable of producing an even higher degeneracy pressure
4899835
Soft X-ray transient


rare, about 100 systems are known. SXTs are a class of low-mass X-ray binaries. A typical SXT contains a K-type subgiant or dwarf that is transferring mass to a compact object through an accretion disk. In some cases the compact object is a neutron star, but black holes are more common. The type of compact object can be determined by observation of the system after an outburst; residual thermal emission from the surface of a neutron star will be seen whereas a black hole will not show
7132532
X-ray transient


neutron star) and some type of "normal", low mass star (i.e. a star with a mass of some fraction of the Sun's mass). These objects show changing levels of low-energy, or "soft", X-ray emission, probably produced somehow by variable transfer of mass from the normal star to the compact object. In effect the compact object "gobbles up" the normal star, and the X-ray emission can provide the best view of how this process occurs. Soft X
21915922
Michiel van der Klis


what it is today. Van der Klis pioneered special mathematical analysis techniques that are now regarded as the “gold standard” within his discipline. Van der Klis's research focuses on X-ray binaries, pairs of stars orbiting each other that emit X-ray radiation. Some binary star systems contain a compact object like a neutron star or a black hole. By studying the dynamics of materials in the vicinity of such objects one can learn about their mass, radius and rotational speed. Moreover, this kind of research provides
12820194
Neutron


and coworkers reported that they observed, for the first time, the dineutron emission in the decay of Be. The dineutron character is evidenced by a small emission angle between the two neutrons. The authors measured the two-neutron separation energy to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region. At extremely high pressures and temperatures, nucleons and electrons are believed to collapse into bulk neutronic matter, called neutronium. This is presumed to happen in neutron stars. The extreme
1589266
Degenerate matter


when the core of a white dwarf is above the vicinity of 1.4 solar masses, which is the Chandrasekhar limit, and the collapse is not halted by the pressure of degenerate electrons. As the star collapses, the Fermi energy of the electrons increases to the point where it is energetically favorable for them to combine with protons to produce neutrons (via inverse beta decay, also termed electron capture and "neutronization"). The result is an extremely compact star composed of nuclear matter, which is predominantly a degenerate neutron gas,
14267813
Nucleosynthesis


of neutrons converts iron into elements heavier than iron and nickel. The products of stellar nucleosynthesis are generally dispersed into the interstellar gas through mass loss episodes and the stellar winds of low mass stars. The mass loss events can be witnessed today in the planetary nebulae phase of low-mass star evolution, and the explosive ending of stars, called supernovae, of those with more than eight times the mass of the Sun. The first direct proof that nucleosynthesis occurs in stars was the astronomical observation that interstellar gas has become enriched with
4346546
PSR J0348+0432


neutron stars using a different measuring technique. The notable feature of this binary pulsar is its combination of high neutron star mass and short orbital period: 2 hours and 27 minutes. This allowed a measurement of the orbital decay due to the emission of gravitational waves, as observed for PSR B1913+16 and PSR J0737−3039. Pulsars were discovered in 1967 by Jocelyn Bell and her adviser Antony Hewish using the Interplanetary Scintillation Array. Franco Pacini and Thomas Gold quickly put forth the idea that pulsars are highly magnetized rotating neutron stars, which
2554251
Future of an expanding universe


will properly begin. Stars of very low mass will eventually exhaust all their fusible hydrogen and then become helium white dwarfs. Stars of low to medium mass, such as our own sun, will expel some of their mass as a planetary nebula and eventually become white dwarfs; more massive stars will explode in a core-collapse supernova, leaving behind neutron stars or black holes. In any case, although some of the star's matter may be returned to the interstellar medium, a degenerate remnant will be left behind whose mass
9274499
Blitzar


Blitzars are a hypothetical type of astronomical object in which a spinning pulsar rapidly collapses into a black hole. They are proposed as an explanation for fast radio bursts (FRBs). The idea was proposed in 2013 by Heino Falcke and Luciano Rezzolla. A blitzar is thought to start from a neutron star with a mass that would cause it to collapse into a black hole if it were not rapidly spinning. Instead, the neutron star spins fast enough so that its centrifugal force keeps the collapse from happening. This makes the neutron
12698213
Stellar black hole


of black hole natal kicks. The velocity distribution of black hole natal kicks seems similar to that of neutron star kick velocities. One might have expected that it would be the momenta that were the same with black holes receiving lower velocity than neutron stars due to their higher mass but that doesn't seem to be the case, which may be due to the fall-back of asymmetrically expelled matter increasing the momentum of the resulting black hole. Our Milky Way galaxy contains several stellar-mass Black Hole Candidates (BHCs) which
21250951
Gamma-ray burst


or superluminous supernova as a high-mass star implodes to form a neutron star or a black hole. A subclass of GRBs (the "short" bursts) appear to originate from the merger of binary neutron stars. The cause of the precursor burst observed in some of these short events may be the development of a resonance between the crust and core of such stars as a result of the massive tidal forces experienced in the seconds leading up to their collision, causing the entire crust of the star to shatter. The sources
4345438
Future of an expanding universe


; white dwarfs, produced by stars with initial masses between about 0.08 and 8 solar masses; and neutron stars and black holes, produced by stars with initial masses over . Most of the mass of this collection, approximately 90%, will be in the form of white dwarfs. In the absence of any energy source, all of these formerly luminous bodies will cool and become faint. The universe will become extremely dark after the last star burns out. Even so, there can still be occasional light in the universe.
9274508
PSR B1620−26 b


when the core of star collapses to a neutron star and ejects most of its mass in a supernova explosion, it is unlikely that a planet could remain in orbit after such an event. It is more likely that the planet formed in orbit around the star that has now evolved into the white dwarf, and that the star and planet were only later captured into orbit around the neutron star. Stellar encounters are not very common in the disk of the Milky Way, where the Sun is, but in the dense core of
19748279
Compact star


density (c. 2 kg/m) of an atomic nucleus. At this point the matter is chiefly free neutrons, with a small amount of protons and electrons. In certain binary stars containing a white dwarf, mass is transferred from the companion star onto the white dwarf, eventually pushing it over the Chandrasekhar limit. Electrons react with protons to form neutrons and thus no longer supply the necessary pressure to resist gravity, causing the star to collapse. If the center of the star is composed mostly of carbon and oxygen then
282166