Neutron Star Formation Research Articles

Binary Pulsars

There are now three radio frequency pulsars known to be in binary systems: PSRs 1913+16, 0820+02, and 0655+64. The first of these, discovered in 1974, moves in a tight, highly eccentric orbit with a period of approximately 7h 45m. Its companion has not yet been identified with certainty, but must be a compact object of mass comparable to that of the pulsar. PSRs 0820+02 and 0655+64, recognized as binaries during the past fifteen months, have nearly circular orbits with periods of over three years and about one day, respectively. All three objects are of great interest for the opportunity they provide to measure the masses of neutron stars. In addition, the first has proven to be a useful probe of gravitational theories, and the study of all of them should yield important information concerning the evolution of binary systems and the formation of neutron stars.

Supernovae — Birthplace of Pulsars?

Recent developments in the theory of the light from supernovae indicate that while Type II supernovae probably involve the explosion of a massive star with an extended envelope, Type I supernovae may involve the total thermonuclear disruption of a white dwarf. The energy release in a Type II supernova is presumably related to the contraction of the core to a neutron star and pulsar formation is likely. The hypothesis that Type II supernovae leave pulsars while Type I supernovae do not leave compact remnants is shown to be consistent with the available information on X-ray sources containing neutron stars, young supernova remnants, and the distribution of pulsars in the galaxy. Some pulsars are probably formed in the explosion of a massive star that has lost its envelope. These events may not be accompanied by a bright supernova display.

General Relativistic Collapse of an Axially Symmetric Star Leading to the Formation of Neutron Stars and Black Holes

Using the [(2+1)+1]-dimensional representation of the Einstein equations, we have computed the general relativistic collapse of a rotating star. We adopt the cylindrical coordinate. The system is assumed to be axially and plane symmetric. The number of meshes is 28×28 in R and Z direction. The equation of state is P=1/3ρε for ρ< ρ*≡3×1014 g/cm3 and P=(ρ-ρ*)ε+1/3ρ*ε for We use the following initial conditions; ρ∝exp(-(R2+Z2)/λ), Ω∝exp(-R2/λ) where Ω and λ are angular velocity and a size parameter, respectively. We have calculated three models; (1)Model 1 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.05.(2)Model 2 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.12.(3)Model 3 M=10M⊙, ρc=3×1013g/cm3, α=0.20, β=0.22. where α=Eint/|Egrav| and β=Erot/|Egrav|. In all models, an apparent horizon was formed, that is, a black hole was formed. In Model 1, the final density distribution is oblate shape. In Model 2, there is a ringlike peak of the proper mass density distribution at the final stage. In Model 3, the determinant of the metric tensor goes to nearly zero at the ring in the equatorial plane, so that the proper mass density shows strong ringlike peak which is inside the apparent horizon. As the curvature invariant made from the Riemann tensor becomes very large at this ring, this may be a ring singularity of the space-time. These rotating black holes look like the Kerr black hole.

Supernova Explosions in Degenerate Stars —Detonation, Deflagration, and Electron Capture—

Presupernova evolution and the hydrodynamic behavior of supernova explosions in stars having electron-degenerate cores are summarized. Carbon deflagration supernovae in C+O cores disrupt the star completely. On the other hand, in electron capture supernovae, O+Ne+Mg cores collapse to form neutron stars despite the competing oxygen deflagration.Also discussed are white dwarf models for Type I supernovae (SN I). Supernova explosions in accreting white dwarfs are either the detonation or deflagration type depending mainly on the accretion rate. The carbon deflagration model reproduces many of the observed features of SN I.

The collapse of carbon-oxygen white dwarfs

view Abstract Citations (50) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The collapse of carbon-oxygen white dwarfs. Canal, R. ; Isern, J. ; Labay, J. Abstract Carbon-oxygen white dwarfs formed in close binary systems may become unstable by mass accretion. Recent results concerning carbon-oxygen separation at the freezing point during the phase of cooling may have very important consequences for the problem of neutron star formation. The central, high-density regions of the star are then made of pure oxygen, the carbon being rejected to lower-density layers. When the star is compressed, carbon ignition can only happen after neutronization of the central (oxygen) regions. It is shown that, in this case, the chances of collapse to a neutron star are independent from the rate of mass accretion, in contrast with previous studies. A likely mechanism for neutron star formation emerges from this picture. Publication: The Astrophysical Journal Pub Date: October 1980 DOI: 10.1086/183354 Bibcode: 1980ApJ...241L..33C Keywords: Binary Stars; Carbon Stars; Gravitational Collapse; Neutron Stars; Stellar Evolution; White Dwarf Stars; Oxygen; Stellar Mass Accretion; X Ray Sources; Astrophysics; Close Binaries:White Dwarfs; Collapse:White Dwarfs; White Dwarfs:Evolution full text sources ADS |

Thermodynamic laws of neutrino and photon emission

From the analogous properties of neutrinos and photons as quantized energy waves, the generalized ’’blackbody’’ radiation law for the total power radiated Rν per unit area per unit frequency ν is derived as Rν?k3/c2h2) × T3{(hν/kT)3/ [exp(hν/kT)−1] +3(hν/kT)3/ [exp(hν/kT)+1]}, where c is the speed of light, h is Planck’s constant, k is Boltzmann’s constant, and T is the absolute temperature. The first term in the brackets is the usual Planck radiation law for photon emission. The second term is the corresponding expression describing blackbody neutrino and antineutrino emission, which contains a factor of 3 because three different types of neutrinos are presently suspected. Otherwise the photon and neutrino terms only differ in the sign of the unity term due to the different spin statistics of photons compared with neutrinos. For photons, the spin =h/ and Bose–Einstein statistics apply, while for neutrinos the spin =h//2 and Fermi–Dirac statistics are appropriate. The wavelength (λm) at which the maximum energy is radiated is λmT=2.898 μ kK for photons and λmT=2.859 μ kK for neutrinos, while the total power radiated per unit area is R=T4 (σp+σn), where σp=5.67 W/cm2(kK)4 for photons and σn = 14.88 W/cm2(kK)4 for three types of neutrinos. Note that kK represents kilo degrees Kelvin. As is well known, the form of the blackbody law for photons demands the possibility of stimulated emission by light flux, thus allowing light to be amplified. On the other hand, the neutrino blackbody law demands that neutrino radiating transitions are suppressed in the presence of a neutrino flux. There are applications of these neutrino concepts in particle physics and astrophysics. It appears that neutrino blackbodies or graybodies may exist in nature associated with black holes, the formation of neutron stars, and the formation of the universe itself.

Neutron Star Formation by Collapse of White Dwarfs

Abstract.Mass-accreting carbon-oxygen white dwarfs become thermally and dynamically unstable when they reach high enough central densities. Carbon ignition at the star’s center likely propagates subsonically and, in the case of an initially solid core, leads to collapse if the rate of increase of the core’s mass is sufficiently fast. Recent results indicate, however, that solidification of the core induces carbon-oxygen separation. The central regions are then made of pure oxygen while carbon is rejected to lower-density layers. Carbon ignition happens only after neutronization of the central (oxygen) regions. Collapse to a neutron star is then independent from the rate of mass increase and the only possible restrictions are set by the behaviour of the outer, accreted layers. X-ray sources, pulsars and Type I supernovae are likely outcomes of this process.

An upper limit to the rate of formation of neutron stars in the Galaxy. II

In a recent paper Endal found the rate of formation of neutron stars in the Galaxy to be about one every 4 years, which is substantially larger than the maximum rate of one every 27 years which I found in an earlier paper. The principal reason for this large difference is that Endal assumes that the representative stellar population in the Galaxy is that in the galactic plane near the Sun while I assume it is that in an infinitely long cylinder perpendicular to the galatic plane. Because the OB stars, which are the neutron-star progenitors, are much more highly concentrated toward the galactic plane than are most other stars in the galactic disk, Endal's procedure greatly overestimates the number of these objects in the Galaxy and the rate of neutron-star formation. Endal's rate of neutron-star formation and his value for the amount of photon energy emitted by the average neutron-star progenitor require that the integrated photon luminosity of the neutron-star progenitors in the Galaxy be 3.2 x 10/sup 10/ L/sub sun/, which is about 50% larger than the total photon luminosity of all stars in the Galaxy. Using more recently published observational data, I find that the maximum possiblemore » rate of neutron-star formation in the Galaxy which is consistent with energy conservation is one every 21 years, and the probable rate is roughly one every 48 years.« less

Types I and II supernovae and the neutrino mechanism of thermonuclear explosion of degenerate carbon-oxygen stellar cores

The present work studies the hydrodynamic process of thermonuclear explosion of hydrostatic equilibrium, degenerate carbon-oxygen cores withMC=1.40M⊙ with different values of central densityϱc within the interval 2 × 109 <ϱc < 3 × 1010 g cm−3. The initial temperature distribution has been determined by the preceding thermal stage of explosion. The calculations successively include the kinetics of thermonuclear burning, the kinetics of β-processes, and neutrino energy losses. By considering the neutrino mechanism of heating and carbon ignition we obtained in our numerical hydrodynamic calculations two characteristic versions of the development of an explosion: (a) at 2 × 109 <ϱc < 9 × 109 g cm−3 there is disruption of the whole star with either complete or partial burning of the carbon and a 1050–1051 erg kinetic energy; and (b) at 9 × 109 <ϱc < 3 × 1010 g cm−3 the stellar core collapses into a neutron star with partial outburst of the outer envelope with a smaller kinetic energy of 1049–1050 erg. The paper proposes and details a hypothesis (the scenario of supernovae and the formation of neutron stars) on the first version of explosion, corresponding to SNII, and on the second, supplemented by some mechanism of slow energy release into the envelope expelled from the newly formed neutron star, corresponding to SNI. On the basis of the proposed hypothesis a satisfactory agreement with the observed masses and energies of the supernovae envelope, their light curves and spectra, as well as with the data on their chemical composition has been obtained. For this agreement we must assume that type I pre-supernovae are almost bare compact carbon-oxygen stellar cores, and that type II presupernovae are red supergiants. It is most probable that the evolution of type I pre-supernovae occurs in close binaries while the evolution of type II pre-supernovae seems to be very similar to the evolution of a single star.

Neutron star formation by collapse of white dwarfs

Mass-accreting carbon-oxygen white dwarfs become thermally and dynamically unstable when they reach high enough central densities. Carbon ignition at the star's center likely propagates subsonically and, in the case of an initially solid core, leads to collapse if the rate of increase of the core's mass is sufficiently fast. Recent results indicate, however, that solidification of the core induces carbon-oxygen separation. The central regions are then made of pure oxygen while carbon is rejected to lower-density layers. Carbon ignition happens only after neutronization of the central (oxygen) regions. Collapse to a neutron star is then independent from the rate of mass increase and the only possible restrictions are set by the behaviour of the outer, accreted layers. X-ray sources, pulsars and Type I supernovae are likely outcomes of this process.

Physics of Neutron Stars

Since the first identification of neutron stars, in pulsars, a decade ago, theoretical and observational knowledge of these unusual objects has grown at a rapid rate. In this article we describe developments that have taken place since our 1975 review article on neutron stars (Baym & Pethick 1975, referred to hereafter as BP), as well as review several of their more astrophysical aspects not discussed there. The most striking observational fact about neutron stars is their existence: at present 321 pulsars, which are generally accepted to be rapidly rotating neutron stars, have been observed in our galaxy (Manchester et al. 1978, Taylor & Manchester 1977, Manchester & Taylor 1977, Smith 1976). In addition, most of the 16 pulsating compact X-ray sources so far discovered are likely to be accreting neutron stars in close binaries (for a review see Lamb 1977). The association of the Crab and Vela pulsars with supernova remnants provides evidence for the formation of neutron stars in supernovae, a picture supported to a limited extent by comparison of pulsar populations and lifetimes with estimated supernova rates (reviewed in Manchester & Taylor 1977). Optical and X-ray observations of binary X-ray sources provide the possibility of determining the masses of the neutron stars in these objects

Collapse of White Dwarfs in Close Binary Systems

The presence of neutron stars in close binary systems, shown by the pulsating X-ray sources, poses the problem of their origin. In the case of the low-mass (M1 + M2 ≤ 5 M⊙) X-ray binaries, the neutron star might have originated from a massive white dwarf, driven over the Chandrasekhar limit by mass transfer (Schatzman 1974). A similar scenario had been put forward by Whelan and Iben (1973) for type I supernovae. To solve the problem of the very low eccentricities observed for the orbits, and to facilitate keeping the system bound after neutron star formation, Canal and Schatzman (1976) suggested a non explosive collapse of the white dwarf to a neutron star. The occurence of this kind of collapse depended on the possibility of avoiding thermonuclear ignition by means of neutronization. Since there is a density interval where the electron captures on carbon go faster than the pycnonuclear reactions, just above the critical density for the beginning of the collapse, there seemed also to be a chance of escape from thermonuclear runaway. A closer examination of this picture leads, however, to significant changes.

Parity nonconservation and stellar collapse

ACCORDING to the current theory, the evolution of sufficiently massive stars leads eventually to gravitational instability and collapse. After thermonuclear burning has stopped, dense stellar cores become unstable and collapse to form neutron stars (pulsars) or black holes. In both cases energy of the order of 0.1 Mc2 is released, mostly in the form of neutrinos and gravitational waves. As the radius of the core decreases, its magnetic field grows (magnetic flux is conserved) and can reach huge values of order 1012–1013 G. Even greater azimuthal fields (∼3 × 1015 G) can be generated by differential rotation of the core1. It will be shown here that neutrino emission in the collapse is asymmetric, as a result of parity nonconservation in weak interactions. Neutrinos and antineutrinos are emitted preferentially in the direction parallel to the local magnetic field of the collapsing core.

Rotating neutron stars in general relativity - Exact solutions for the case of slow rotation

Two new solutions to Einstein's field equations are presented which are valid for the case of slow rotation. These new solutions represent uniformly rotating spheres which may be of use as neutron star and pulsar models. One solution is a family of fluid spheres which have vanishing pressure at the surface. It is not necessary to introduce a discontinuous region over which the pressure is brought to zero as is the case with solutions based on the polytropic equation of state of Misner and Zapolsky. The second solutions depicts a uniformly rotatin sphere composed of solid matter of constant density. This solution represents the most compact mass undergoing slow rotation possible within the framework of general relativity. Any pulsar safisfying the conditions of slow rotation and requiring parameters based on a more compact object must of necessity be a black hole. The matching of these solutions to form neutron stars with both solid and fluid components is considered.

The rate of formation of neutron stars in the Galaxy estimated from stellar statistics

Stellar statistics and stellar evolution models can be used to estimate the rate of formation of neutron stars in the Galaxy. A recent analysis by Hills suggests that the mean interval between neutron-star births is greater than 27 years. This is incompatible with estimates based on pulsar statistics. However, a closer examination of the stellar data shows that Hill's result is incorrect. A mean interval between neutron-star births as short as 4 years is consistent with (though certainly not required by) stellar evolution theory.

Why do collapsed stars rotate so slowly

view Abstract Citations (17) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Why do collapsed stars rotate so slowly? Brecher, K. ; Chanmugam, G. Abstract The case of the puzzingly slow rotation of neutron stars and white dwarfs is examined. Continuing mass loss during formation can rapidly stop the rotation of white dwarfs which have magnetic-field strengths of at least 1 million gauss, for mass-loss rates consistent with current theories. If mass loss can occur during formation of neutron stars, magnetic braking may be significant in slowing their rotation as well. The observed slow rotation of the 'nonmagnetic' white dwarfs, however, remains a mystery. Publication: The Astrophysical Journal Pub Date: May 1978 DOI: 10.1086/156101 Bibcode: 1978ApJ...221..969B Keywords: Gravitational Collapse; Neutron Stars; Stellar Mass Ejection; Stellar Rotation; White Dwarf Stars; Magnetic Stars; Pulsars; Stellar Evolution; Astrophysics; Neutron Stars:Rotation; Rotation:White Dwarfs full text sources ADS |

An upper limit to the rate of formation of neutron stars in the Galaxy

view Abstract Citations (19) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An upper limit to the rate of formation of neutron stars in the Galaxy. Hills, J. G. Abstract Energy conservation and the observed luminosity of the Galaxy place a firm upper limit on the possible rate of formation of neutron stars in the Galaxy. If the entire stellar luminosity of the Galaxy were from neutron-star progenitors, the maximum rate of neutron-star formation would be one every 8 years. As it is, most of the luminosity is from white-dwarf progenitors. Allowing for this indicates a probable upper limit on the rate of neutron-star formation of one every 53 years. Making the maximum possible allowance for the physical uncertainties establishes afirm upper limit of one every 27 years. The most probable rate of neutron-star formation is one every 75-100 years. The fact that these limits are much smaller than the probable rates inferred recently from pulsar statistics may indicate that these pulsar results are subject to systematic errors. Since these limits are comparable to estimates of the rate of formation of gaseous supernova remnants, they do not support the recent suggestion that only a small fraction of supernovae leave long-lived remnants. Subject headings: stars: formation - stars: neutron - stars: stellar statistics Publication: The Astrophysical Journal Pub Date: May 1978 DOI: 10.1086/156102 Bibcode: 1978ApJ...221..973H Keywords: Milky Way Galaxy; Neutron Stars; Stellar Evolution; Pulsars; Statistical Analysis; Stellar Luminosity; Stellar Mass; White Dwarf Stars; Astrophysics; Formation:Neutron Stars full text sources ADS |

X-ray lines and magnetic field of Her X-1

THE report1 of a possible detection of an X-ray emission line with energy about 53 keV from the binary X-ray source Her X-1 created great excitement. Interpreting the line as arising from non-relativistic electron cyclotron emission at the surface of an accreting neutron star member of the binary star system, Trumper et al.1 deduce a neutron star surface magnetic field of 4.6 × 1012 G. If the line is real (of cosmic origin and not due to background effects), significant (not due to a statistical fluctuation) and correctly interpreted as arising from non-relativistic cyclotron emission) it could provide the first direct and quantitative measure of the magnetic field of a neutron star, and be direct support for our ideas on the formation of neutron stars and the role of magnetic fields in the radiation mechanisms of pulsars and binary X-ray sources. Furthermore, it would conclusively rule out the possibility that Her X-1 contains a rotating or pulsating white dwarf (which, for dynamical stability requires B≪G1/2MR−2≃1012G for M≃M⊙ and R=RWD≃ 109 cm).

The neutrino radiation for a hot neutron star formation and the envelope outburst problem

With the equations of neutrino heat conductivity being used, the neutrino light curve is calculated for the spherically symmetrical collapse of an iron-oxygen 2M ⊙ star (Figure 1) up to the formation of a hot hydrostatically equilibrium neutron star. The total energy, radiated in the form of muon and electron neutrinos, is 5.8×1053 erg (0.16Mc 2). The mean neutrino particle energy is ∼12 MeV for all the time the collapse proceeds. The maximum neutrino luminosity value is equal to 3×1053 erg s−1. For a 10M ⊙ star collapse, the luminosity maximum 3×1054 erg s−1 takes place just at the moment of the formation of a black hole inside the collapsing star. The total radiated energy in this case is about 0.08Mc 2. The set of calculations, allowing for the deposition of momentum by means of neutrino-nuclear coherent scattering, brings us to a conclusion that the envelope outburst is only possible if the scattering cross-section is 50 times larger than the value experimentally accepted (inequality 20)).

On the emission of neutrinos and gravitational waves in the formation of neutron stars

The energetics involved in the formation of neutron stars in close binaries as a result of supernova explosions are considered. The gravitational binding energy of the neutron star must find proper outlets. The mass ejection and cosmic ray particles can carry away only a small fraction (up to a few per cent) of this energy. Most of the binding energy goes into rotational kinetic energy, gravitational radiation and neutrino emissions. A scenario is considered in which most of the gravitational binding energy goes into rotational kinetic energy and is, ultimately, radiated away as gravitational waves.