共查询到20条相似文献，搜索用时 78 毫秒
1.
A. V. Tutukov 《Astronomy Reports》2005,49(1):13-23
The formation and evolution of supermassive (102?1010 M ⊙) black holes (SMBHs) in the dense cores of globular clusters and galaxies is investigated. The raw material for the construction of the SMBHs is stellar black holes produced during the evolution of massive (25?150M ⊙) stars. The first SMBHs, with masses of ～1000M ⊙, arise in the centers of the densest and most massive globular clusters. Current scenarios for the formation of SMBHs in the cores of globular clusters are analyzed. The dynamical deceleration of the most massive and slowly moving stellar-mass (< 100M ⊙) black holes, accompanied by the radiation of gravitational waves in late stages, is a probable scenario for the formation of SMBHs in the most massive and densest globular clusters. The dynamical friction of the most massive globular clusters close to the dense cores of their galaxies, with the formation of close binary black holes due to the radiation of gravitational waves, leads to the formation of SMBHs with masses ? 103 M ⊙ in these regions. The stars of these galaxies form galactic bulges, providing a possible explanation for the correlation between the masses of the bulge and of the central SMBHs. The deceleration of the most massive galaxies in the central regions of the most massive and dense clusters of galaxies could lead to the appearance of the most massive (to 1010 M ⊙) SMBHs in the cores of cD galaxies. A side product of this cascade scenario for the formation of massive galaxies with SMBHs in their cores is the appearance of stars with high spatial velocities (> 300 km/s). The velocities of neutron stars and stellar-mass black holes can reach ～105 km/s. 相似文献
2.
Acceleration of spatial motions of stars by close-binary supermassive black holes in galactic nuclei
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
3.
Mikhailov A. G. Piotrovich M. Yu. Buliga S. D. Natsvlishvili T. M. Gnedin Yu. N. 《Astronomy Reports》2019,63(6):433-444
Astronomy Reports - Hybrid models for the generation of relativistic jets are used to place constraints on the spins of supermassive black holes (SMBHs) in active galactic nuclei at redshifts z... 相似文献
4.
The paper presents a catalog of supermassive black holes (SMBHs) sharpened for interferometric observations at millimeter and submillimeter wavelengths, based on open sources. The catalog includes the object’s name, coordinates, angular size, and mass, the angular size of the gravitational radius of the SMBH, and the integrated radio flux associated with the radiosource concluding the SMBH at 20?900 GHz, planned for the Event Horizon Telescope, the future space mission Millimetron, and others. The catalog is intended for use during planning of interferometric observations of SMBH shadows.
相似文献5.
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
6.
The dynamical capture of a binary system consisting of a supermassive black hole (SMBH) and an ordinary star in the gravitational field of a central (more massive) SMBH is considered in the three-body problem in the framework of a modified Hills scenario. The results of numerical simulations predict the existence of objects whose spatial speeds are comparable to the speed of light. The conditions for and constraints imposed on the ejection speeds realized in a classical scenario and the modified Hills scenario are analyzed. The star is modeled using an N-body approach, making it possible to treat it as a structured object, enabling estimation of the probability that the object survives when it is ejected with relativistic speed as a function of the mass of the star, the masses of both SMBHs, and the pericenter distance. It is possible that the modern kinematic classification for stars with anomalously high spatial velocities will be augmented with a new class—stars with relativistic speeds. 相似文献
7.
A model of a star consisting of vacuum-like matter is constructed in the framework of general relativity. Its stability and other physical properties are analyzed. This stellar model is compared with cosmological models consisting of the same vacuum-likematter with a pressure equal to the energy density but with the opposite sign.
相似文献8.
9.
The results of long-term spectral monitoring of the Herbig Be star IL Cep A are presented. A smooth variation in the parameters of the Нα and Нβ line emission component has been discovered. The helium absorption lines He I λ4922 and 5876 Å show seasonal changes, however, these changes do not correlate with changes in hydrogen emission. The radial velocities of the narrow lines D Na I and DIB λ5780, 5796 Å correspond to that of the interstellar medium. The hydrogen emission lines are apparently formed in a triple system, including a close pair of B stars and a remote low-mass K–A component. The orbital elements of this system were calculated using an approximate spectral binary model, where a close pair of massive B stars was considered as one massive component. The rationale for this approach for determining the elements of the orbit is given. The orbital period P = 3550 ± 28 days is determined and some other parameters of the orbit are estimated. 相似文献
10.
Effects due to the interaction of the steam from the inner Lagrangian point with the accretion disk in a cataclysmic variable star are considered. The results of three-dimensional gas-dynamical numerical simulations confirm that the disk thickness in the vicinity of the interaction with the stream is minimum when the component-mass ratio is 0.6. As a consequence, some of the matter from the stream does not collide with the outer edge of the accretion disk, and continues its motion unperturbed toward the accretor. This part of the stream subsequent interacts (collides) with a thickening of the accretion disk due to the presence of a precessional wave in the disk, leading to the appearance of an additional zone of heating at the disk surface. This additional zone of enhanced luminosity (hot spot) is a direct observational manifestation of the precessional wave in the accretion disk. 相似文献
11.
E. M. Trunkovskii 《Astronomy Reports》2018,62(7):469-473
The results of photoelectric observation of the occultation of the visual binary star SAO 79361 = ADS 6038 by the Moon during the total lunar eclipse of January 9, 1982 are presented. The upper limit of the angular diameter of the brighter component A is estimated to be dul ? 0.0011″ based on direct measurements, which is in agreement with indirect estimates. Accurate estimates for the magnitude difference between components A and B, their angular separation, p ? 3.2″, and the inclination of the Moon’s edge’s at the point of occultation to the mean lunar horizon, θ ? +25°, are obtained. The time of the geometrical occultation of the center of the stellar disk of component A is determined with an accuracy of 1 ms. The results obtained for this star are unique among observations worldwide. 相似文献
12.
The photometric variability of the uniqueMdwarf flare star GJ 1243 (KIC 9726699) is investigated using the most complete set of observationalmaterial obtained with the Kepler Space Telescope. The analysis is based on 49 487 individual brightness measurements obtained during an interval of 1460 days (nearly four years). The periodicity of the brightness variations with the period Pphot = 0.59261 ± 0.00060d is confirmed. The temperature inhomogeneities on the stellar surface reconstructed from the light curve are used to drive maps of these surface-temperature inhomogeneities (of the filling factor f). The resulting maps are used to determine the positions of active regions. Analysis of the surface-temperature maps for GJ 1243 led to the conclusion that the positions of spots on the stellar surface displayed appreciable evolution during the analyzed time interval. The maximum value for the lower limit on the differentialrotation parameter ΔΩ is 0.0022 rad/day. This more accurate estimate of ΔΩ is lower than the values presented earlier by Davenport et al. [1] (0.0058 and 0.0036 rad/day), due to the more accurate account of variations in the positions of the most active longitude in the current study. However, the differentialrotation estimate obtained in [1] using a method based on fitting the evolution of spots using twodimensional Gaussian functions essentially coincides with the new estimate presented here. The fractional area of the total spotted surface S of the star during the observing interval considered varied from 7 to 2%. The amplitude of the brightness variability of the star slowly decreased, varying in the range 1.6?0.5%. Overall, the position of GJ 1243 in spottedness–age, spottedness–rotation period, and spottedness–Rossby number diagrams agrees very well with the general character of the dependences displayed in earlier studies of M dwarfs. 相似文献
13.
Abstract The Panther Tongue of the Star Point Formation in central Utah contains a variety of transgressive lag deposits that, when mapped regionally, show a sensitive dependence upon pre‐existing topography of the palaeoshoreline. The Panther Tongue consists of a coarsening‐upward sandstone wedge that prograded into the Western Interior Seaway during Late Cretaceous (Santonian) time. High‐resolution sequence stratigraphic analysis revealed that this member was deposited during the long‐distance (>50 km) regression and transgression of a delta into shallow‐marine environments, containing basal highstand, forced regression, lowstand and transgressive systems tracts. Based on grain size, clast composition, lateral extent and stratigraphic position, the coarse sandstones on top of the Panther Tongue were classified into four types: (1) simple; (2) dispersed; (3) oxidized; and (4) local lags. The simple lag is composed of dark grey coarse sandstone with oyster fragments and shark teeth. This lag is typically extensively bioturbated and massive. Laminated and cross‐bedded units are also common. This type of coarse sandstone is interpreted as a typical transgressive lag. The dispersed lag differs in that it contains abundant mud and commonly occurs as multiple beds in thick intervals of muddy sandstone. Mixing of bay/estuarine and shallow ‐ marine mud with simple lag sand may be responsible for deposition of this type of coarse sandstone. The oxidized lag is distinctive in its reddish colour with extensive bioturbation and is commonly overlain by a simple lag. The local lag is composed of thin‐bedded, dark grey, coarse sandstone, occurring locally between the mouth bar and distributary channel. The variation in types, grain size and bed thickness of the coarse‐grained lags was mainly controlled by antecedent topography as suggested by immediately underlying lithofacies. Relatively thick (≈30 cm) simple lags are present on top of mouth‐bar sandstones, whereas dispersed lags are common on top of the distributary channel sandstone and in bay/estuarine and shallow‐marine mudstones. Erosion of topographic highs (mouth bar) resulted in relatively thick accumulation of simple lags. In topographic low areas such as distributary channel, estuary, bay and shallow‐marine environments, fine‐grained muddy sands that were eroded from the nearby topographic highs were redeposited. Intermittent storm waves transported coarse sands both landward and seaward, forming a dispersed lag. The net effect was reworking of local topographic relief during overall transgression, forming an apparently planar transgressive surface of erosion. 相似文献
14.
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
15.
通过常规的宝石学测试方法、电子探针分析及紫外-可见光谱分析等测试, 详细研究了3块待测样品的化学成分和物理性质, 并将其与天然刚玉及合成星光刚玉进行了对比研究.3块待测样品的颜色分别为橙红色、褐红色及紫红色, 透明度较高, 其中橙红色的为近透明, 另外2粒为半透明.强光下发现样品的表面有一层云雾状的物质.星光浮于表面, 且较为发散、弯曲.星光相交处可见宝光.显微镜下观察发现, 3块样品的表面均有较多的凹坑, 其中2块近表面可见隐约的丝状包裹体, 但定向性较差; 1块似有熔融的特征.这些特征表明, 这3块样品中包裹体可能是经过高温处理而成, 非合成退火所致.3块样品均可见到较明显的细密的弯曲生长纹, 表明其为焰熔法合成产物.电子探针分析结果显示, 3块样品的致色元素均为铬, 为红宝石; 丝状体为钛酸铝.紫外-可见光谱测试结果表明, 其吸收光谱为铬吸收谱.综合分析所有的特征, 认为这3块样品为焰熔法合成红宝石, 星光的产生是在合成红宝石生成加工后, 通过扩散作用所形成的丝状钛酸铝对光的反射所致. 相似文献
16.
Astronomy Reports - This paper provides an overview of the current state of the stripping model for short gamma-ray bursts. After the historical joint detection of the gravitational wave event... 相似文献
17.
We have derived the fine structure of the region of the H2O supermaserflare in the Orion Nebula at epoch 1985.8. This structure includes a chain of compact components that extends to 25 AU and has a width of 0.4 AU. The velocities of the components vary along the chain. The structure corresponds to an accretion disk separated into protoplanetary rings, viewed edge-on. The velocities of the components correspond to Keplerian motion around an object with a mass of M=0.3±0.2M⊙. The velocity of the central object relative to the Local Standard of Rest is VLSR=4.0±0.7 km/s. The radius of the inner part of the disk is 9±4 AU, while the radius of the outer disk is 35±6 AU. The rotational velocities of the inner and outer rings are 5±1 km/s and 2.5±0.5 km/s, respectively. The emission of the structure is amplified in the ambient medium—an envelope with velocities of 7.6±0.3 km/s. The rate at which the envelope is accreting onto the central object is 3.6±0.7 km/s. The gradient of the infall velocity is 1.1 km/s. 相似文献
18.
Grinin V. P. Barsunova O. Yu. Sergeev S. G. Shugarov S. Yu. Fedorova E. I. 《Astronomy Reports》2021,65(9):864-868
Astronomy Reports - The results of new photometric ( $$VRI$$ ) observations of the young star V719 Per from the IC 348 cluster are presented. Up until 2014, this star demonstrated brightness... 相似文献
19.
V. P. Grinin O. Yu. Barsunova S. G. Sergeev A. A. Arkharov S. Yu. Shugarov A. O. Semenov N. V. Efimova 《Astronomy Reports》2018,62(10):677-688
The results of many-year photometric observations of the weak-line T Tauri star V715 Per in the optical (V RI) and infrared (JHK) photometric bands are presented. The period of the star’s lowamplitude brightness variations in the V RI bands detected earlier, 5.23d, is confirmed. This period persists during the entire 14-year time interval of the observations, but its amplitude varies with time. The same period was found in the variations of JHK infrared fluxes, with the brightness variations in the two ranges being almost synchronous. The most probable origin of these variations is periodic eclipses of the star by its own disk, perturbed by its interaction with the magnetosphere (AA Tau-type variations). In addition to the periodic brightness variations, the star also displayed sporadic Algol-like minima characteristic of UX Ori stars during several years (2005–2011). The amplitude of these variations increasedmonotonically, reaching approximately 1m in the V band by the end of 2010, after which the deep fadings ended. During this entire time interval, the amplitude of the periodic variations was observed to decrease. After 2011, the periodic component began to become stronger again. These changes of the photometric activity of V715 Per can be explained by an increasing rate of gas accretion onto the star, decreasing the radius of warped regions of the disk and leading to accompanying Algol-like fadings. This model assumes a low inclination of the circumstellar disk in V715 Per to the line of sight. 相似文献
20.
The radial profile of the star-formation rate (SFR) in the galaxy NGC 628 is shown to be modulated by a spiral-density wave. The radial profile of the velocity of gas inflow into the spiral arm is similar to the radial distribution of the surface density of the SFR. The position of the corotation resonance is determined along with other parameters of the spiral-density wave via a Fourier analysis of the azimuthal distribution of the observed radial velocities in annular zones of the disk of NGC 628. The radial profile of the surface density of the SFR is determined using the empirical SFR—linear size relation for star-formation complexes (giant HII regions) and measurements of the coordinates, Hα fluxes, and the sizes of HII regions in NGC 628. 相似文献