共查询到20条相似文献，搜索用时 125 毫秒
1.
D. K. Nadyozhin 《Astrophysics and Space Science》1977,51(2):283-301
The collapse of iron-oxygen stars with masses of 2M
has been calculated. The commencement of the collapse is due to dissociation of iron-group nuclei into free nucleons. After a while, the collapse proceeds in consequence of intensive energy losses due to neutrino volume radiation. At an intermediate stage of the collapse, the core — opaque with respect to neutrino radiation (neutrino core) — is formed inside the collapsing star. Both the gradual increase of the mass of the neutrino core and the partial absorption of neutrinos radiated from the surface of the neutrino core by the stellar envelope (deposition) were taken into account in our calculations. The kinetics of oxygen burning in the outer layers of the envelope was also allowed for. Neither the deposition, nor the oxygen burning, result in ejection of stellar envelopes. 相似文献
2.
Physical conditions prevalent in a degenerate carbon plasma lead to the enhancement of the carbon-carbon thermonuclear reaction rates. Nuclear energy generation rate in the carbon core is thereby augmented. The possible dissipation of energy due to pair-annihilation neutrinos, plasma neutrinos and neutrino bremsstrahlung are considered. Neutral current contribution to these weak processes are also taken into account. It is suggested that the enhanced nuclear gene-ration rate in the evolved core might halt the core collapse for a time, thus necessitating a reassessment of the phenomenon of core collapse as a precursor of carbon detonation supernova events. 相似文献
3.
Solution to steady-state, bigroup neutrino transport with isoenergetic and neutrino-electron scattering have been obtained for idealized conditions representative of the outer core or envelope of a star whose inner core is undergoing gravitational collapse. The solutions are presented in a form suitable for comparison with other numerical schemes. The incident neutrino distribution was chosen to be nonequilibrium, and the solutions clearly show the tendency of the neutrinos to equilibrate via neutrino-electron scattering as they propagate through the material. Care is taken to compare solutions obtained by two completely different techniques to ensure that the solutions presented here are accurate and error free. The solutions are compared with those obtained by a simple diffusion scheme, and by a flux limited diffusion scheme. The solutions given by the latter agree well with the solutions derived here, except when the neutrino angular distribution becomes oblate. 相似文献
4.
The effects of neutrino mass and oscillations are investigated in the calculations of energy losses of solar neutrinos. In these calculations, we take into account the full energy dependence of the stopping power of matter for neutrinos. The case of Majorana neutrinos are also investigated. It is found that the total losses of energy of solar neutrinos are too small to account for the solar neutrino problem. 相似文献
5.
D. K. Nadyozhin 《Astrophysics and Space Science》1980,69(1):115-125
A stellar core becomes somewhat less massive due to neutrinos radiated away during its collapse in a neutron star or a black hole. The paper deals with the hydrodynamic motion of stellar envelope induced by such a mass loss. Depending on the structure of the outer stellar layers, the motion results either in ejection of an envelope with mass and energy proper for Nova outbursts; or nearly instantaneous excitation of strong pulsations of the star; or lastly in a slow slipping away of the whole stellar envelope. These phenomena are of importance when more powerful events, like supernova outbursts presumably associated with gravitational collapse, are absent. Such secondary indications of gravitational collapse are of special interest, since they may be a single observable manifestation (besides neutrinos and gravitational waves) of massive black hole formation. 相似文献
6.
Based on the magnetorotational model of a supernova explosion with core collapse, we investigate the significant processes of neutrino heating of the supernova shock. These processes should be taken into account in self-consistent modeling, since the neutrino heating mechanism is capable of increasing the explosion efficiency. We show that, even in the presence of a strong magnetic field (B ～ 1015 G) in the shock formation region, the heating rate is determined with good accuracy by the absorption and emission of neutrinos in direct URCA processes. Moreover, the influence on them of a magnetic field is reduced to insignificant corrections. 相似文献
7.
M. A. Rudzsky 《Astrophysics and Space Science》1990,165(1):65-81
Quantum kinetic equations for the distribution function of massive Dirac neutrinos have been obtained. They describe neutrino spin- and type-oscillations in a medium. The processes of elastic and inelastic scattering of neutrinos with medium components as well as -processes have been taken into account. Applications of developed equations for stellar collapse are discussed. 相似文献
8.
V. I. Dokuchaev 《Astronomy Letters》2002,28(8):522-526
We discuss the possible observational manifestation of the formation of massive black holes in galactic nuclei in the form of an intense high-energy neutrino flux. A short-lived (≤10 yr) hidden neutrino source results from the natural dynamicalal evolution of a central star cluster in the galactic nucleus before its gravitational collapse. The central star cluster at the final evolutionary stage consists of degenerate compact stars (neutron stars and stellar-mass black holes) and is embedded in a massive gaseous envelope produced by destructive collisions of normal stars. Multiple fireballs from frequent collisions of neutron stars give rise to a tenuous quasi-stationary cavity in the central part of the massive envelope. The cavity is filled with shock waves on which an effective cosmic-ray acceleration takes place. Allthe accelerated particles, except the secondary high-energy neutrinos, are absorbed in the dense envelope. The neutrino signal that carries information on the dynamicals of the collapsing galactic nucleus can be recorded by a neutrino detector with an effective area S∼1 km2. 相似文献
9.
The equations of neutrino hydrodynamics are derived in two different approximations taking into consideration the neutrino scattering from stellar material. In a thermal-conductivity approximation which holds good when neutrino optical depth with respect to absorption exceeds 1, the neutrino scattering is taken into account, analogously with photon radiative conductivity, by introducing the transport cross-section in the neutrino mean free path. In a practically important case when the neutrino optical thickness with respect to scattering is high enough, whereas that concerning absorption is sufficiently low, another approximation of Comptonized neutrinos is valid. In this case, the neutrino and antineutrino chemical potentials are independent of each other. They have to be calculated from equations of continuity established for neutrino and antineutrino alongside with the diffusion equation expressing the law of lepton-charge conservation. The equations of neutrino hydrodynamics are written out both with and without inclusion of muon neutrinos and antineutrinos.The equations obtained are established to deal properly with neutrino diffusion inside collapsing stars. 相似文献
10.
We have ascertained an important role of rotation effects in a collapsing stellar core using a quasi-one-dimensional hydrodynamic
model with a rigorous allowance for the neutrino energy losses including the neutrino opacity stage. However, the neutrino
scattering processes are not considered in the neutrino emission kinetics as secondary compared to the absorption processes.
The quasi-one-dimensional approximation (with averaging of the expression for the centrifugal force over the polar angle)
allows numerical calculations to be performed relatively easily up to the formation of a hydrostatically equilibrium neutron
star after a very long stage of collapsar cooling by neutrino emission (about 2 s). We present detailed results of our numerical
solution, including the neutrino spectra, with electron neutrinos making a dominant contribution to them and the contribution
from electron antineutrinos being smaller by an order of magnitude. In the model under consideration, we solve the equation
of matter neutronization kinetics by taking into account the main process of nuclear reactions on free nucleons, although
the contribution from iron and helium nuclei is included in the equation of state. 相似文献
11.
We present numerical simulations of the axisymmetric accretion of a massive magnetized plasma torus on a rotating black hole. We use a realistic equation of state, which takes into account neutrino cooling and energy loss due to nucleus dissociations. The calculation are performed in the ideal relativistic MHD approximation using an upwind conservative scheme that is based on a linear Riemann solver and the constrained transport method to evolve the magnetic field. The gravitational attraction of the black hole is introduced via the Kerr metric in the Kerr–Schild coordinates. We simulate various magnetic field configurations and torus models, both optically thick and thin for neutrinos.We have found an effect of alternation of the magnetic field orientation in the ultrarelativistic jet formed as a result of the collapse. The calculations show evidence for heating of the wind surrounding the collapsar by the shock waves generated at the jet–wind border. It is shown that the neutrino cooling does not significantly change either the structure of the accretion flow or the total energy release of the system. The angular momentum of the accreting matter defines the time scale of the accretion. Due to the absence of the magnetic dynamo in our calculations, the initial strength and topology of the magnetic field determines the magnetization of the black hole, jet formation properties and the total energy yield. We estimate the total energy of accretion which transformed to jets as 1.3 × 1052 ergs which was sufficient to explain hypernova explosions like GRB 980425 or GRB 030329. 相似文献
12.
A quasi-one-dimensional hydrodynamic model for the collapse of a rotating iron stellar core is used to determine the neutrino
spectra in the limiting case of total transparency to neutrino emission (without any deposition effect). The derived spectra
allow the previously constructed spectra used to theoretically estimate the number of events in the LSD underground neutrino
detector from SN 1987A to be refined. At typical iron stellar core parameters, including those that characterize the core
rotation specified in the initial conditions of the model, this number has turned out to be 1.6, which is close in order of
magnitude to its experimental value of 5. Here, we compare in detail these results by assuming that the transparency of the
collapsing iron core itself could be attributable to the development of its three-dimensional dynamical instability—the subject
of future theoretical studies. The physical formulation of the problem coincides closely with the collapse model proposed
in our previous paper, where the above number of events turned out to be 0.5. We have confirmed the previously published results
with regard to the neutrino spectra, including the significant superiority of electron neutrinos over electron antineutrinos
in them. The hydrostatically equilibrium configuration (a rotating collapsar) obtained in our model calculation is discussed
in comparison with self-similar solutions that are close in physical formulation of the problem. This result seems a nontrivial
consequence of the included rotation effects that hinder nonstop collapse established in the mentioned self-similar solutions. 相似文献
13.
The characteristics of the gravitational collapse of a supernova and the fluxes of active and sterile neutrinos produced during the formation of its protoneutron core have been calculated numerically. The relative yields of active and sterile neutrinos in corematter with different degrees of neutronization have been calculated for various input parameters and various initial conditions. A significant increase in the fraction of sterile neutrinos produced in superdense core matter at the resonant degree of neutronization has been confirmed. The contributions of sterile neutrinos to the collapse dynamics and the total flux of neutrinos produced during collapse have been shown to be relatively small. The total luminosity of sterile neutrinos is considerably lower than the luminosity of electron neutrinos, but their spectrum is considerably harder at high energies. 相似文献
14.
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)). 相似文献
15.
16.
Masaaki Kondo 《Earth, Moon, and Planets》1978,19(2):245-252
The spherical collapse of a protostar with one solar mass is calculated from a gravitationally unstable initial stage, by solving the equations of hydrodynamics and pherical radiative transfer. The temperature dependence of the dust opacity is taken into account in contrast to the earlier calculations with temperature independent opacities. It is shown that the opaque core is equivalent to the adiabatic core in the purely adiabatic case. The blanketing effect of dust grains strengthens the shock of the opaque core and may result in raising the central entropy of protostars.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 7, 1978. 相似文献
17.
The effects of uncertainties in determining the loss of neutrinos and the generation of entropy during the collapse of a stellar core are studied using a simple spherically-symmetric homologous collapse model with an improved treatment for the excited nuclei. It is found that the neutrino loss and entropy generation are not altogether insensitive to most variations of the assumptions regarding the input physics, collapse rate and initial conditions and in particular the need to determine accurately beta capture rates in stellar collapse is pointed out. 相似文献
18.
《天文和天体物理学研究(英文版)》2017,(9)
The neutrino burst detected during supernova SN 1987A is explained in a strangeon star model, in which it is proposed that a pulsar-like compact object is composed of strangeons(strangeon:an abbreviation for "strange nucleon"). A nascent strangeon star's initial internal energy is calculated,with the inclusion of pion excitation(energy around 10~(53) erg, comparable to the gravitational binding energy of a collapsed core). A liquid-solid phase transition at temperature ~ 1-2MeV may occur only a few tens of seconds after core collapse, and the thermal evolution of a strangeon star is then modeled.It is found that the neutrino burst observed from SN 1987A can be reproduced in such a cooling model. 相似文献
19.
H. J. Haubold 《Astronomische Nachrichten》1981,302(5):223-226
According to the suggestion of T. J. Mazurek (1979) neutrino oscillations occuring during the dynamic stellar collapse (M ≥ 10M) could be result in a transfer of leptonic zero-point energy to baryons. Then the adiabatic index increases above γ ≥ 4/3, and such an increase is necessary to reverse the collapse. From the theory of neutrino oscillations of B. Pontekorvo (1967) we derive the oszillation length L of neutrinos in vacuum and the characteristic oscillation lengh L* of neutrinos taking into consideration the refraction index ne of neutron star matter. The comparison of both oscillation lenghts shows that for electron densities, characteristically of neutron star matter, the oscillation lenght L is considerable larger than the oscillation lenght L*. Therefore neutrino oscillations cannot influence the scenario for neutrino emission of the neutron star. 相似文献
20.
A MC approach to simulate up- and down-going neutrino showers including local topographic conditions
The extragalactic flux of protons is predicted to be suppressed above the famous Greisen–Zatsepin–Kuzmin cut-off at about EGZK 50 EeV due to the resonant photo-pion production with the cosmic microwave background. Current cosmic ray data do not give a conclusive confirmation of the GZK cut-off and the quest about the origin and the chemical composition of the highest energy cosmic rays is still open. Amongst other particles neutrinos are expected to add to the composition of the cosmic radiation at highest energies. We present an approach to simulate neutrino induced air showers by a full Monte Carlo simulation chain. Starting with neutrinos at the top of the atmosphere, the performed simulations take into account the details of the neutrino propagation inside the Earth and atmosphere as well as inside the surrounding mountains. The products of the interactions are input for air shower simulations. The mountains are modelled by means of a digital elevation map. To exemplify the potential and features of the developed tools we study the possibility to detect neutrino induced extensive air showers with the fluorescence detector set-up of the Pierre Auger Observatory. Both, down-going neutrinos and up-going neutrinos are simulated and their rates are determined. To evaluate the sensitivity, as a function of the incoming direction, the aperture, the acceptance and the total observable event rates are calculated for the Waxman–Bahcall (WB) bound. 相似文献