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1.
We present the results of simulations of Type Ia and II supernovae explosions taking into account the rotation of the initial configuration. The main idea is development of a large-scale convective instability which affects strongly the geometry of the explosion. For Type Ia supernova a jet-like structure of the ejecta was obtained. An important point here is the possibility of continuing consecutive flares, produced when the fresh thermonuclear fuel is ignited in the central part of the star. This fuel is moved to the center by convective fluxes from the outer stellar layers. For Type II supernova a large-scale convection results in a non-equilibrium neutronization of the matter. Large bubbles, moving to the surface, contain high-energy neutrinos from the central region of the proto-neutron stellar core. The following ejection of these neutrinos to the stellar envelope gives enough energy support to the bounce shock, which finally destroys the envelope producing a non-spherical explosion. 相似文献
2.
Neutrino transfer via convective flow to the surface of a proto-neutron star is numerically simulated. The evolution of the neutrino distribution in a heated region rising from the center of the proto-neutron star to its surface is simulated using a kinetic equation with a Uehling-Uhlenbeck collision integral in a uniform, isotropic approximation. The composition of the matter in the region under consideration changes due to the “burning” of electrons and protons by beta processes. The simulation results enable the estimation of the characteristic time required for the rising medium to become optically thin to neutrinos and the characteristic spectrum of the neutrinos that are emitted. 相似文献
3.
Two types of supernovae are considered: thermonuclear supernovae, whose explosions are due to thermonuclear energy, and core-collapse supernovae, whose explosions are due to the gravitational energy of collapsing stars released in the form of neutrinos. Numerical models of supernovae are discussed. Themain problem in devising supernova explosion mechanisms is producing the energy required to disperse the envelope. In theoretical models, it is necessary to solve multi-dimensional problems involving complex physics (3D gas dynamics, neutrino transport, large-scale convective instability, and other important physical processes). In recent years, the development of large-scale convection during supernova explosions has been reconsidered. Self-consistent problems problems in three-dimensional, gas-dynamical instability have been considered. Two-dimensional gas-dynamical calculations taking into account neutrino absorption in the envelope have been performed. The spherically symmetric collapse and neutrino transport were calculated including all reactions, leading to a new understanding of possible paths for the development of supernova theory. The main emphasis is placed on the neutrino transport and the basis for promising multidimensional models taking into account large-scale convective instability. 相似文献
4.
The roles of neutrinos and convective instability in collapsing supernovae are considered. Spherically symmetrical computations of the collapse using the Boltzmann equation for the neutrinos lead to the formation of the condition of convective instability, \({\left( {\frac{{\partial P}}{{\partial s}}} \right)_{\rho {Y_l}}}\frac{{ds}}{{dr}} + {\left( {\frac{{\partial P}}{{\partial {Y_L}}}} \right)_{\rho s}}\frac{{d{Y_L}}}{{dr}}\) < 0, in a narrow region of matter accretion above the neutrinosphere. If instability arises in this region, the three-dimensional solution will represent a correction to the spherically symmetrical solution for the gravitational collapse. The mean neutrino energies change only negligibly in the narrow region of accretion. Nuclear statistical equilibrium is usually assumed in the hot proto-neutron stellar core, to simplify the computations of the collapse. Neutronization with the participation of free neutrons is most efficient. However, the decay of nuclei into nucleons is hindered during the collapse, because the density grows too rapidly compared to the growth in the temperature, and an appreciable fraction of the energy is carried away by neutrinos. The entropy of the matter per nucleon is modest at the stellar center. All the energy is in degenerate electrons during the collapse. If the large energy of these degenerate electrons is taken into account, neutrons are efficiently formed, even in cool matter with reduced Ye (the difference between the numbers of electrons and positrons per nucleon). This process brings about an increase in the optical depth to neutrinos, the appearance of free neutrons, and an increase in the entropy per nucleon at the center. The convectively unstable region at the center increases. The development of large-scale convection is illustrated using a multi-dimensional gas-dynamical model for the evolution of a stationary, unstable state (without taking into account neutrino transport). The time for the development of convective instability (several milliseconds) does not exceed the time for the existence of the unstable region at the center (10ms). The realization of this type of instability is fundamentally different from a spherically symmetrical model. The flux of neutrinos changes and the mean energy of the neutrinos is increased, which has important implications for the detection of neutrinos from supernovae. For these same reasons, the energy absorped in the supernova envelope also changes in the transition to such a multi-dimensional model. 相似文献
5.
Most of the energy released in the gravitational collapse of the cores of massive stars is carried away by neutrinos. Neutrinos play a pivotal role in explaining core-collapse supernovae. In this work the multidimensional gas dynamics is used with neutrino transport in the flux-limited diffusion approximation to study the role of multi-dimensional effects. The possibility of large-scale convection is discussed, which is interesting both for explaining SNII and for setting up observations to register possible high-energy (?10 MeV) neutrinos from the supernova. In compare with the previous work describing a new multidimensional gas dynamics method with neutrino transport we investigate the role of the rotation in the convection. 相似文献
6.
Most of the energy released in the gravitational collapse of the cores of massive stars is carried away by neutrinos. Neutrinos play a pivotal role in explaining core-collape supernovae. Currently, mathematical models of the gravitational collapse are based on multi-dimensional gas dynamics and thermonuclear reactions, while neutrino transport is considered in a simplified way. Multidimensional gas dynamics is used with neutrino transport in the flux-limited diffusion approximation to study the role of multi-dimensional effects. The possibility of large-scale convection is discussed, which is interesting both for explaining SN II and for setting up observations to register possible high-energy (?10MeV) neutrinos from the supernova. A new multi-dimensional, multi-temperature gas dynamics method with neutrino transport is presented. 相似文献
7.
8.
The aim of this study is to investigate the accretion of matter onto a compact gravitating remnant (neutron star) in the central region of the expanding shell of a Type II supernova. Computations of an explosion with the energetics of a Type II supernova have been performed to derive the structure of matter in the vicinity of the neutron star. The energy of the expanding shell and the parameters of the presupernova correspond to the known values for SN 1987A. This accretion leads to the formation of a layer of fairly dense and hot gas at the surface of the compact remnant, providing the conditions for nucleosynthesis reactions. Thus, one result of the study is to demonstrate the importance of the r and rbc processes, or explosive nucleosynthesis, in the compact envelope of a neutron star. A second result is the production of emission lines from unstable elements formed in the central part of the neutron-star envelope.
相似文献9.
We have computed the ejection of a massive envelope by a star during a type II supernova explosion in the presence of a compact
remnant (a neutron star or black hole). This problem is of interest because of the possible presence of a compact remnant
following the SN 1987A explosion. The computations demonstrate that a fairly large amount of matter is left in the neighborhood
of the compact gravitating body. We present computations of the accretion rate onto the surface of the compact remnant. The
estimated luminosity exceeds that observed for SN 1987A in various frequency ranges by several orders of magnitude. 相似文献
10.
We list and analyze the main currently known mechanisms for accelerating the space motions of stars. A high space velocity
of a star can be a consequence of its formation in the early stages of the evolution of a massive galaxy, when it was spheroidal
and non-stationary, so that stars were born with velocities close to the escape velocity for the galaxy. Another possibility
is that the star arrived from another galaxy with a velocity that is high for our Galaxy. The decay of unstable close multiple
stars or supernova explosions in close binaries can also provide velocities of up to several hundreds of km/s to main-sequence
stars and velocities of up to ∼1000 km/s to degenerate stars, neutron stars, and stellar-mass black holes. The merger of components
of a binary system containing two neutron stars or a neutron star and a black hole due to gravitational-wave radiation can
accelerate the nascent black hole to a velocity∼1000 km/s. Hypervelocity relativistic stars can be born due to asymmetric
neutrino ejection during a supernova explosion. Stars can be efficiently accelerated by single and binary supermassive black
holes (with masses from several millions to several billions of solar masses) in the nuclei of galaxies. Thanks to their gravitational
field and fast orbital motion (in the case of binary objects), supermassive black holes are able to accelerate even main-sequence
stars to relativistic velocities. 相似文献
11.
The formation of a neutrino pulse emitted during the relativistic collapse of a spherical supermassive star is considered. The free collapse of a body with uniform density in the absence of rotation and with the free escape of the emitted neutrinos can be solved analytically by quadrature. The light curve of the collapsing star and the spectrum of the emitted neutrinos at various times are calculated. 相似文献
12.
The formation of neutron stars in the closest binary systems (P orb<12 h) gives the young neutron star/pulsar a high rotational velocity and energy. The presence of a magnetic field of 3×1011–3×1013 G, as is observed for radio pulsars, enables the neutron star to transfer ～1051 erg of its rotational energy to the envelope over a time scale of less than an hour, leading to a magnetorotational supernova explosion. Estimates indicate that about 30% of all type-Ib,c supernovae may be the products of magnetorotational explosions. Young pulsars produced by such supernovae should exhibit comparatively slow rotation (P rot>0.01 s), since a large fraction of their rotational angular momentum is lost during the explosion. The magnetorotational mechanism for the ejection of the envelope is also reflected by the shape of the envelope. It is possible that the Crab radio pulsar is an example of a product of a magnetorotational supernova. A possible scenario for the formation of the close binary radio pulsar discovered recently by Lyne et al. is considered. 相似文献
13.
The influence of dark gravitating matter on the present-day Sun and its evolution is studied. Numerical simulations show that substantial departures of the main model parameters (luminosity, effective temperature, neutrino flux, and age) from the modern solar parameters would occur if the relative mass of dark matter exceeded 2–5% of the solar gravitational mass. The flux of solar neutrinos is relatively insensitive to the presence of uniformly distributed dark matter. However, a strong concentration of dark matter toward the center of the Sun would increase the neutrino flux beyond the observational limits. 相似文献
14.
We use a two-phase model for the structure of the circumstellar nebulae of hot stars to analyze the radiative cooling of a dense, compact cloud behind the shock produced by the compression of the cloud by hot gas from the stellar wind, taking into account ionization and heating by radiation from the central star. We can distinguish three stages of the evolution of the cloud during its compression. In the first stage, relevant for the entire cloud before compression and the gas ahead of the shock front, the state of the gas is determined purely by ionization by the stellar radiation. The next stage is characterized by the simultaneous action of two gas excitation mechanisms—photoionization by the stellar radiation and shock heating. In this stage, the gas intensively radiates thermal energy received at the shock front. After radiative cooling, in the final stage, ionization and heating of the gas are again determined mainly by the star. To compute the spectrum of the cloud radiation, we solved for the propagation of a plane-parallel, homogeneous flux through the shock front in the radiation field of the hot star. The computations show that a combination of two excitation mechanisms considerably enriches the theoretical spectrum. The relative intensities of emission lines of a single cloud may resemble either those for an HII region or of a supernova remnant. 相似文献
15.
We apply a population synthesis technique to study the formation and evolution of low-mass X-ray binaries with black holes, observed as X-ray novae, from hierarchical triple systems. A scenario is suggested in which an inner close binary system evolves into an X-ray system with a large mass ratio. The high rate of accretion onto the neutron star leads to a common envelope stage, which may result in the formation of a Thorne-Zytkow (TZ) object. During its evolution, the envelope of the TZ object expands, encompassing the third star. The recurrent common-envelope stage decreases the size of the orbit of the third star, leading to the formation of a lowmass X-ray nova with a black hole. The dynamical stability of triple systems automatically ensures that only lowmass X-ray novae form. We also consider the possible formation of an X-ray nova from a binary in the case of asymmetrical core collapse during a supernova explosion. 相似文献
16.
We have studied the brightness and color variations of the symbiotic nova HM Sge based on longterm UBVRJHKLM photometry of the star and data on its energy distribution in the middle infrared (7.7–22.7 µm) obtained with the low-resolution spectrometers of the IRAS satellite and ISO orbital observatory. We have also calculated models for the steady-state, spherically symmetrical, extended dust envelope of the star for two extreme heating cases: heating only by radiation from the cool component of the system and by the combined radiation from both components. Model fitting to the IRAS and ISO data indicates that models with a single, central Mira-type source are more appropriate. This indicates that the radiation of the hot component is largely processed by the surrounding gas, and does not substantially affect the infrared spectrum of the symbiotic nova directly. The mean spectral energy distribution based on 1983 IRAS data differs appreciably from the ISO spectrum obtained on October 1, 1996. The observed evolution of the envelope spectrum probably reflects an increase of the density and decrease of the temperature of the dust grains near the inner boundary of the envelope, related to a decrease of the luminosity and increase of the temperature of the hot component. We estimate the total mass-loss rate, velocity of gas expansion at the outer envelope boundary, and upper limit for the mass of the central source of radiation. 相似文献
17.
A. V. Tutukov 《Astronomy Reports》2005,49(12):993-1000
We consider the evolution of close binaries in which the initial secondary component is a nondegenerate helium star with mass MHe = 0.4–60 M⊙, while the initially more massive primary has evolved into a black hole, neutron star, or degenerate dwarf. The neutron star is assumed to originate as a result of the evolution of a helium star with a mass of 2.5 M⊙ ≤ MHe ≤ 10 M⊙ after the explosion of a type Ib,c supernova. If the axial rotation of the helium star before the explosion is rigid-body and synchronized with the orbital rotation, for Porb ≤ 0.16 day, the rotational energy of the young neutron star will exceed the energy of an ordinary supernova. If the magnetic field of the neutron star is sufficiently strong, the necessary conditions for a magnetic-rotational supernova are provided. The initial rotational period of a young neutron star originating in a system with an orbital period shorter than ～50 days is shorter than ～4 s, which, according to observations, is required for the appearance of a radio pulsar. A helium star whose mass exceeds ～10 M⊙ in a close binary with an orbital period shorter than one day and with the axial rotation of the helium presupernova synchronous with the orbital rotation evolves into a Kerr black hole, whose formation is likely to be accompanied by a gamma-ray burst with a duration longer than two seconds. In particular, we consider close binaries in which the second supernova results in the formation of a neutron star that remains in the binary. The theoretical distribution of orbital periods and eccentricities for such systems is consistent with that observed for radio pulsars in the Galactic disk in binaries with compact components and orbital eccentricities exceeding ～0.09, providing an explanation for the observed correlation between the orbital eccentricities and orbital periods for these systems. 相似文献
18.
E. I. Staritsin 《Astronomy Reports》2017,61(5):450-460
Partial mixing of material in the radiative envelopes and convective cores of rotating main sequence stars with masses of 8 and 16 M ⊙ is considered as a function of the inital angular momentum of the stars. Losses of rotational kinetic energy to the generation of shear turbulence in the radiative envelope and the subsequent mixing of material in the envelope are taken into account. With an initial equatorial rotational velocity of 100 km/s, partial mixing develops in the upper part of the layer with variable chemical composition and the lower part of the chemically homogeneous radiative envelope. When the initial equatorial rotational velocity is 150–250 km/s, the joint action of shear turbulence and semi-convection leads to partial mixing in the radiative envelope and central parts of the star. The surface abundance of helium is enhanced, with this effect increasing with the angular momentum of the star. With an initial equatorial rotational velocity of 250 km/s, the ratio of the surface abundances of helium and hydrogen grows by ~30% and ~70% toward the end of the main-sequence evolution of an 8 M ⊙ and 16 M ⊙ star, respectively. The transformation of rotational kinetic energy into the energy of partial mixing increases with the angular momentum of the star, but does not exceed ~2%?3% in the cases considered. 相似文献
19.
We present the results of long-term (1978–1998) infrared and optical observations of the unique symbiotic system CH Cygni. The system’s IR brightness and color variations are generally consistent with a model in which the source is surrounded by a dust envelope with variable optical depth. There was evidence for a hot source in the CH Cyg system during the entire period from 1978 to 1998, with the exception of several hundred days in 1987–1989. Over the observation period, there was tendency for the system to gradually redden at 0.36–5 µm, accompanied by a brightness decrease at 0.36–2.2µm and a brightness increase at 3.5 and 5 µm. The “activation” of the cool sources in 1986–1989 nearly coincided with the disappearance of radiation from the hot source. The dust envelope of CH Cyg is not spherically symmetrical, and its optical depth along the line of sight is substantially lower than its emission coefficient, the mean values being τex(L)～0.06 and τem(L)～0.16. We confirm the presence of a 1800-to 2000-day period in both the optical and IR, both accounting for, and not accounting for, a linear trend. The spectral type of the cool star varied between M5III and M7III. The spectral type was M5III during the phase of maximum activity of the system’s hot source, while the spectral type was M7III when the star’s optical radiation was almost completely absent. The luminosity of the cool giant varied from (6300–9100)L ⊙; its radius varied by approximately 30%. The ratio of the luminosities of the dust envelope and the cool giant varied from 0.08 to 0.5; i.e., up to 50% of the cool star’s radiation could be absorbed in the envelope. The temperature of dust particles in the emitting envelope varied from 550 to 750 K; the radius of the envelope varied by more than a factor of 2. The expansion of the emitting dust envelope observed in 1979–1988 accelerated: its initial velocity (in 1979) was ～8 km/s, while the maximum velocity (in 1987–1989) was ～180 km/s. Beginning in 1988, the radiation radius of the dust envelope began to decrease, first at ～45 km/s and then (in 1996–1998) at ～3 km/s. From 1979 until 1996, the mass of the emitting dust envelope increased by approximately a factor of 27 (the masses in 1979 and 1988 were ～1.4×10?7 M ⊙ and ～3.8×10?6 M ⊙, respectively), after which (by 1999) it decreased by nearly a factor of 7. The mass-loss rate of the cool star increased in 1979–1989, reaching ～3.5×10?6 ～3.5×10?6 M ⊙/yr in 1988. Subsequently (up to the summer of 1999), the envelope itself began to lose mass at a rate exceeding that of the cool star. The largest input of matter to the envelope occurred after the phase of optical activity in 1978–1985. If the envelope’s gas-to-dust ratio is ～100, the mass of matter ejected in 1988 was ～4×10?4 M ⊙. 相似文献
20.
V. Bychkov M. V. Popov A. M. Oparin L. Stenflo V. M. Chechetkin 《Astronomy Reports》2006,50(4):298-311
We consider the motion of a bubble in a central acceleration field created by gravity or a centrifugal force. In the former case, the bubble moves outwards from and, in the latter, towards the center. We have calculated the characteristic time needed for a bubble to leave or reach the center. The solution obtained provides insight into the processes of thermonuclear supernovae and combustion; in other words, into the interaction between a flame and a turbulent vortex. In the case of combustion, a light bubble of burnt material propagates towards the axis of a strong turbulent vortex faster than it drifts in the direction of rotation of the vortex. It is expected that the development of bubbles should prevent the formation of “pockets” at the flame front, similar to those predicted by a simplified model of turbulent combustion in a constant density flux. In the case of a thermonuclear supernova in a deflagration burning regime, it is shown that light products of burning rise from the center of the white dwarf substantially more rapidly than the thermonuclear flame front propagates. As a result, a flame cannot completely burn the central part of the star, and instead is pushed to the outer layers of the white dwarf. The effect of bubble motion (large-scale convection) makes spherically symmetric models for thermonuclear supernovae unrealistic, which is of prime importance for the supernova spectrum and energy. The motion of bubbles is even faster in the case of a rotating white dwarf; under certain conditions, the centrifugal force may dominate over the gravitational force. To test this theory, we have carried out numerical simulations of supernovae explosions for various sizes of the burned region in the core of the presupernova. We have derived a relation between the rate of large-scale convection and the size of the burned region, which is specified by the rate of the deflagration in the thermonuclear burning. 相似文献