The evolution of stars paired with supermassive black holes     

A. V. Tutukov  A. V. Fedorova 《Astronomy Reports》2017,61(8):663-677

A star located in the close vicinity of a supermassive black hole (SMBH) in a galactic nucleus or a globular-cluster core could form a close binary with the SMBH, with the star possibly filling its Roche lobe. The evolution of such binary systems is studied assuming that the SMBH mainly accretes matter from the companion star and that the presence of gas in the vicinity of the SMBH does not appreciably influence variations in the star’s orbit. The evolution of the star–SMBH system is mainly determined by the same processes as those determining the evolution of ordinary binaries. The main differences are that the star is subject to an incident flux of hard radiation arising during the accretion of matter by the SMBH, and, in detached systems, the SMBH captures virtually all the wind emitted by its stellar companion, which appreciably influences the evolution of the major axis of the orbit. Moreover, the exchange between the orbital angular momentum and the angular momentum of the overflowing matter may not be entirely standard in such systems. The computations assume that there will be no such exchange of angular momentum if the characteristic timescale for mass transfer is shorter than the thermal time scale of the star. The absorption of external radiation in the stellar envelope was computed using the same formalism applied when computing the opacity of the stellar matter. The numerical simulations show that, with the adopted assumptions, three types of evolution are possible for such a binary system, depending on the masses and the initial separation of the SMBH and star. Type I evolution leads to the complete destruction of the star. Only this type of evolution is realized for low-mass main-sequence (MS) stars, even those with large initial separations from their SMBHs. Massive MS stars will also be destroyed if the initial separation is sufficiently small. However, two other types of evolution are possible for massive stars, with a determining role in the time variations of the parameters of the star–SMBH system being played by the possible growth of the massive star into a red giant during the time it is located in the close vicinity of the SMBH. Type II evolution can be realized for massive MS stars that are initially farther from the SMBH than in the case of disruption. In this case, the massive star fills its Roche lobe during its expansion, but is not fully destroyed; the star retreats inside its Roche lobe after a period of intense mass loss. This type of evolution is characterized by an increase in the orbital period of the system with time. As a result, the remnant of the star (its former core) is preserved as a white dwarf, and can end up at a fairly large distance from the SMBH. Type III evolution can be realized formassiveMSstars that are initially located still farther from their SMBHs, and also for massive stars that are already evolved at the initial time. In these cases, the star moves away from the SMBH without filling its Roche lobe, due to its intense stellar wind. The remnants of such stars can also end up at a fairly large distances from their SMBHs.  相似文献   

Transformation of the quality of overland runoff in the influence zone of a metallurgic complex     

E. V. Fedorova 《Water Resources》2008,35(5):583-590

The transformation of water chemical composition at different stages of overland runoff formation in the influence zone of a metallurgic complex is considered. The dynamics of concentrations of basic ions and microelements in different categories of overland water at various distances from the source of emissions is shown. The amounts of metals carried out by spring flood runoff into water bodies as a consequence of the air-born anthropogenic pollution of watersheds are calculated.  相似文献   

Acceleration of spatial motions of stars by close-binary supermassive black holes in galactic nuclei     

A. V. Tutukov  A. V. Fedorova 《Astronomy Reports》2005,49(9):678-692

The conditions for the acceleration of the spatial motions of stars by close-binary supermassive black holes (SMBHs) in galactic nuclei are analyzed in order to derive the velocity distribution for stars ejected from galaxies by such black holes. A close binary system consisting of two SMBHs in circular orbits was subject to a spherically symmetrical “barrage” of solar-mass stars with various initial velocities. The SMBHs were treated as point objects with Newtonian gravitational fields. Models with binary component-mass ratios of 1, 0.1, 0.01, and 0.001 were studied. The results demonstrate the possibility of accelerating neutron stars, stellar-mass black holes, and degenerate dwarfs to velocities comparable to the relative orbital velocities of the binary-SMBH components. In the stage when the binary components are merging due to the action of gravitational-wave radiation, this velocity can approach the speed of light. The most massive binary black-holes (M ? 10⁹M_⊙) can also accelerate main-sequence stars with solar or subsolar masses to such velocities.  相似文献   

The evolutionary status of ultraluminous X-ray sources     

A. V. Tutukov  A. V. Fedorova 《Astronomy Reports》2004,48(7):534-549

We analyze models for quasi-stationary, ultraluminous X-ray sources (ULXs) with luminosities 10³⁸–10⁴⁰ erg/s exceeding the Eddington limit for a ～1.4M_⊙ neutron star. With the exception of relatively rare stationary ULXs that are associated with supernova remnants or background quasars, most ULXs are close binary systems containing a massive stellar black hole (BH) that accretes matter donated by a stellar companion. To explain the observed luminosities of ～10⁴⁰ erg/s, the mass of the BH must be ～40M_⊙ if the accreted matter is helium and ～60M_⊙ if the accreted matter has the solar chemical composition. We consider donors in the form of main-sequence stars, red giants, red supergiants, degenerate helium dwarfs, heavy disks that are the remnants of disrupted degenerate dwarfs, helium nondegenerate stars, and Wolf-Rayet stars. The most common ULXs in galaxies with active star formation are BHs with Roche-lobe-filling main-sequence companions with masses ～7M_⊙ or close Wolf-Rayet companions, which support the required mass-exchange rate via their strong stellar winds. The most probable candidate ULXs in old galaxies are BHs surrounded by massive disks and close binaries containing a BH and degenerate helium-dwarf, red-giant, or red-supergiant donor.  相似文献   

Formation of ring structures in galactic disks during close passages of galaxies     

A. V. Tutukov  A. V. Fedorova 《Astronomy Reports》2016,60(1):116-128

The formation of ring structures in galactic disks is investigated. It is shown that, in addition to the known mechanism of forming rings in “head-on” collisions between galaxies, ring structures can be formed during close passages of galaxies if the perturbing galaxy moves in a plane close to the equatorial plane of the perturbed disk galaxy, opposite to the direction of rotation of the disk. Numerical simulations of the formation of structures in the disk of a massive galaxy undergoing a passage with another galaxy are considered. The results of these cmputations show the formation of pronounced ring structures in the galactic disk when the initial inclination of the trajectory of the perturbing galaxy to the equatorial plane of the perturbed galaxy is no more than ~25°. However, the probability of close passages of galaxies with these parameters is small, as is the probability of head-on collisions. The characteristic time scale for the existence of pronounced rings is of order the dynamical time scale at the edge of the galaxy, 200–300 million years, close to the corresponding time for head-on collisions. The evolution of the rings has the same character in both cases: they gradually expand and move toward the periphery of the galaxy. The results of these simulations can also be applied to a close passage of one star by another star with a protoplanetary disk. According to the computation results, the characteristic time scale for the existence of pronounced rings in such a protoplanetary disk depends mainly on the size of the disk; this time scale can reach several tens of thousands of years for a disk radius of about 1000 AU. The formation of ring structures in such a disk could influence the formation and evolution of planetesimals, and possibly the character of the formation of planets and the distribution of their orbital semi-major axes.  相似文献   

Study of the anomalous magnetic field structure in the Ural region using parallel algorithms     

P. S. Martyshko  N. V. Fedorova  D. V. Gemaidinov 《Doklady Earth Sciences》2012,446(1):1102-1104

The anomalous structure in the magnetic field of the Ural Region has been studied in the segment bounded by 52°?C64° N and 54°?C66° E. Analytical apparatus for upward continuation of airborne magnetic data to different heights was applied. To recalculate magnetic field, parallel algorithms and software for multiprocessor computers were used. Maps of magnetic anomalies for different ranges of wave lengths showing the distribution of magnetization in the layers of the Earth??s crust were built.  相似文献   

A layer of ozone detected in the nightside upper atmosphere of Venus     

F. Montmessin  J.-L. Bertaux  F. Lefèvre  E. Marcq  D. Belyaev  J.-C. Gérard  O. Korablev  A. Fedorova  V. Sarago  A.C. Vandaele 《Icarus》2011,216(1):82-85

To date, ozone has only been identified in the atmospheres of Earth and Mars. This study reports the first detection of ozone in the atmosphere of Venus by the SPICAV ultraviolet instrument onboard the Venus Express spacecraft. Venusian ozone is characterized by a vertically confined and horizontally variable layer residing in the thermosphere at a mean altitude of 100 km, with local concentrations of the order of 10⁷–10⁸ molecules cm⁻³. The observed ozone concentrations are consistent with values expected for a chlorine-catalyzed destruction scheme, indicating that the key chemical reactions operating in Earth’s upper stratosphere may also operate on Venus.  相似文献   

Close binaries containing Supermassive Black Holes     

A. V. Tutukov  A. V. Fedorova 《Astronomy Reports》2010,54(9):808-822

We consider the evolution of binary systems formed by a Supermassive Black Hole (SMBH) residing in the center of a galaxy or a globular cluster and a star in its immediate vicinity. The star is assumed to fill its Roche lobe, and the SMBH accretes primarily the matter of this star. The evolution of such a system is mainly determined by the same processes as for an ordinary binary. The main differences are that the donor star is irradiated by hard radiation emitted during accretion onto the SMBH; in a detached system, nearly all the donor wind is captured by the black hole, which strongly affects the evolution of the semi-major axis; it is not possible for companions of the most massive SMBHs to fill their Roche lobes, since the corresponding orbital separations are smaller than the radius of the last stable orbit in the gravitational field of the SMBH. Moreover, there may not be efficient exchange between the orbital angular momentum and the angular momentum of the overflowing matter in such systems. Our computations assumed that, if the characteristic timescale for mass transfer is smaller than the thermal timescale of the star, no momentum exchange occurs. Absorption of incident external radiation in the stellar envelope was treated using the same formalism that was used when computing the radiative transfer in the stellar atmosphere. Numerical simulations show that Roche-lobe overflow is possible for a broad range of initial system parameters. The evolution of semi-detached systems containing a star and a SMBH nearly always ends with the dynamical disruption of the star. Stars with masses close to the solar mass are destroyed immediately after they fill their Roche lobes. During the accretion of matter of disrupted stars, the SMBH can achieve quasar luminosities. If the SMBH accretes ambient gas as well as gas stripped from stars, the star is subject to additional radiation in the detached phase of its evolution, strengthening its stellar wind. This leads to an increase of the semi-major axis and subsequent decrease of the probability of Roche-lobe overflow during the subsequent evolution of the system.  相似文献   

Multi-frequency studies of the non-stationary radiation of the blazar 3C 454.3     

A. E. Vol’vach  L. N. Vol’vach  A. M. Kut’kin  M. G. Larionov  M. Villata  K. M. Panteri  A. Lahteenmaki  M. Tornikoski  P. Savolainen  G. Tammi  A. F. Aller  H. D. Aller  S. G. Sergeev  V. T. Doroshenko  Yu. S. Efimov  S. A. Klimanov  S. V. Nazarov  G. V. Borman  A. B. Pushkarev  V. I. Zhdanov  E. V. Fedorova  I. B. Vavilova  N. G. Chesnok 《Astronomy Reports》2011,55(7):608-615

Long-term monitoring data at five radio frequencies from 4.8 to 37 GHz obtained at the Crimean Astrophysical Observatory, Metsahovi Radio Observatory of Aalto University, and the University of Michigan Radio Astronomy Observatory are used to analyze variations of the flux of the Active Galactic Nucleus (AGN) 3C 454.3. The dynamical characteristics of the three latest powerful flares from 2004 to 2010 are analyzed in detail. Observations in the gamma-ray (0.1–300 GeV), X-ray (2–10 kev, 15–50 keV), and optical are also used. Delays in the development of flares at different frequencies are derived. An empirical frequency dependence for the delays of flares from the gamma-ray to the radio is determined, which can be fit using a logarithmic low and remains the same from flare to flare. The physical characteristics of the central region of the AGN 3C 454.3 are used to estimate the size of its Strömgren sphere, taking into account the relevant mechanisms for heating and cooling the medium, as well as the adopted laws for the variation of the density and temperature with distance from the source of ionization. A model for the location of the radiation regions in the jet at various frequency ranges during the development of flares is proposed.  相似文献   

The evolutionary status of the most massive WNh stars in close binary systems. NGC 3603-A1     

A. V. Tutukov  A. V. Fedorova  A. M. Cherepashchuk 《Astronomy Reports》2011,55(3):247-255

The evolution of the components of the unique, massive, close binary system NGC 3603-A1, which consists of stars of spectral types WN6ha and WN6h, is analyzed. The component masses are estimated to be 116 and 89M _⊙, close to the highest measured stellar masses. Numerical modeling of the evolution of the components has been carried out, taking into account mass loss via the stellar winds of the two massive stars. It is shown that the maximum possible initial component masses are close to 140 and 125M _⊙. The components are currently slightly evolved main-sequence stars, with a comparative low degree of helium enrichment at their surfaces. Further evolution of the system will lead to filling of the Roche lobe of the primary and subsequent evolution in a common envelope. This may lead to the merger of the components, with the evolution of the system ending in the formation of a singlemassive black hole after the second supernova explosion. Otherwise, depending on the masses of the resulting black holes, either a binary system of two black holes or two unbound black holes may form, accompanied by gamma-ray bursts.  相似文献