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1.
Physical arguments suggest the spiral arms may be manifestations of the galaxy not being in dynamical equilibrium — in the sense that the kinetic energy of tis stars and gas is less relative to its binding energy than that dictated by the virial theorem. Without constant cooling of the galactic disk (i.e., a progressive increase in the binding energy of the galaxy) such a departure from dynamical equilibrium would be corrected and the spiral arms destroyed in about 109 yr due to an increase in the velocity dispersion of the stars in the disk resulting from their interacting with the spiral arms. The rate of cooling required to maintain the spiral arms, about 6×104 L , may be provided by mass loss from stars in the disk population. The cooling arises from the average scale-heights and velocities of these stars being larger than that of the gas in the disk, so that there is a net loss of kinetic energy and an increase in the binding energy of the galaxy due to the ejected gas settling down to a lower terminal velocity and scale-height in the galactic disk.  相似文献   

2.
We simulated collisions of High Velocity Clouds with the galactic disk with a simple hydrodynamical code. Main aspects of the morphology of nearby (d < 500 pc) cloud complexes, like the Oph, Orion and Taurus-Auriga-Perseus complexes, are reproduced. These aspects include total mass, distance from the galactic plane, orientation of elongated gas structures with respect to the plane, and relative position of clusters of O-B stars with respect to the main concentrations of molecular gas. The space distribution of stars of different ages, usually explained in terms of sequential star formation, is interpreted in a new way in our model.  相似文献   

3.
The spectrum of the peculiar O9 star HD 93521 is studied and compared with those of the standard stars 10 Lac and AE Aur. Several possibilities are examined which might explain the high galactic latitude of this star, corresponding toz>750 pc and its slight helium excess. It is suggested that HD 93521 is a runaway binary system composed of the O9 star plus a neutron star left over from a supernova explosion.  相似文献   

4.
The galactic distribution of pulsars and shell remnants of supernovae (SN) as investigated on the basis of newly-estimated parameters. Special attention was paid to taking into account all possible selection effects and an attempt was made to reveal a statistically-pure ensemble of objects. On the basis of this ensemble we studied the radial andz-distribution of pulsars and supernova remnants (SNR).It is shown that the radial distribution of both objects is considered to have an annular structure with the maximum surface density at a distance of 4.5–5.3 kpc (if the distance of the Sun from the galactic centre is assumed to be equal to 8.5 kpc). The scle-height of the progenitors of SNRs is not more than 110 pc and only 15% of the SNRs, whose progenitors may also be massive runaway stars, are situated at 300 pc. The mean application of the pulsars is not more than 300 pc which agrees with the hypothesis about the genetic connection with type-II SN outbursts at the kinematic aget k5×106 yr and thez-component of spatial velocity beingV z=120 km s–1.The possible precursors of type-I SNRs by the shape of their radial distribution in late spirals and the various model calculations given in the literature, are also discussed.  相似文献   

5.
The density distributions of the two main components in interstellar hydrogen are calculated using 21 cm line data from the Berkeley Survey and the Pulkovo Survey. The narrow, dense component (state I of neutral hydrogen) has a Gaussianz-distribution with a scale-height of 50 pc in the local zones (the galactic disk). For the wide, tenuous component (hydrogen in state II) we postulate a distribution valid in the zones where such a material predominates (70 pc?z? 350 pc the galactic stratum) i.e., $$n_H \left( z \right) = n_H \left( 0 \right)exp \left( { - \left( {z/300{\text{ }}pc} \right)^{3/2} } \right).$$ Similar components are found in the dust distribution and in the available stellar data reaching sufficiently highz-altitudes. The scale-heights depend on the stellar type: the stratum in M III stars is considerably wider than in A stars (500–700 pc against 300 pc). The gas to dust ratio is approximately the same in both components: 0.66 atom cm?3 mag?1 kpc in the galactic plane. A third state of the gas is postulated associating it the observed free electron stratum at a scale-height of 660 pc (hydrogen fully ionized at high temperatures). The ratio between the observed dispersions in neutral hydrogen (thermal width plus turbulence) and the total dispersions corresponding to the real inner energies in the medium is obtained by a comparison with the dispersion distribution σ(z) of the different stellar types associated with the disk and the stratum $$\sigma ^2 \left( {total} \right) = \sigma ^2 \left( {21{\text{ cm line}}} \right) \cdot {\text{ }}Q^2 ,$$ from which we graphically obtainedQ 2=2.9 ± 0.3, although that number could be lower in the densest parts of the spiral arms. Its dependence on magnetic field and cosmic rays is analysed, indicating equipartition of the different energy components in the interstellar medium and consistency with the observed values of the magnetic field: i.e., fluctuations with an average of ～ 3 μG (associated with the disk) in a homogeneous background of ～ 1 μG (associated with the stratum). A minimum and maximumK z-force are obtained assuming extreme conditions for the total density distribution (gas plus stars). TheK z-force obtained from the interstellar gas in its different states using approximations of the Boltzmann equation is a reasonable intermediate case between maximum and minimumK z. The mass density obtained in the galactic plane is 0.20±0.05M ⊙ pc?3, and the results indicate that the galactic disk is somewhat narrower and denser than has usually been believed. The effects of wave-like distributions of matter in thez-coordinate are analysed in relation with theK z-force, and comparisons with theoretical results are performed. A qualitative model for the galactic field of force is postulated together with a classification of the different zones of the Galaxy according to their observed ranges in velocity dispersions and the behaviour of the potential well at differentz-altitudes. The disk containing at least two-thirds of the total mass atz<100 pc, the stratum containing one-third or less of the total mass atz≤600–800 pc, and the halo at higherz-altitudes with a small fraction of such a mass which is difficult to evaluate.  相似文献   

6.
The chemical evolution of the Galaxy with a pulsating active nucleus is investigated. The surface densities of gas, stellar remnants, stars and chemical species such as helium and heavy elements inZ6 are calculated as functions of the position in the Galaxy and of the evolutional time of the Galaxy. According to this model, the entire luminosity of the galactic disk becomes almost constant at some 2×109 yr after the galactic formation, but the nuclear bulge, whose dimensions gradually diminishes, becomes more and more luminous with time. On the other hand, the abundance depletion of helium and heavy elements appears in the inner region of the disk after some 6×109 yr of the galactic formation. It also becomes clear that the activity for the nucleosynthesis in the nucleus is limited only in the early history of the Galaxy and has been reduced rapidly with time. Using this model, we can account for the observed phenomena such as the smooth dependence of the elemental abundance in the halo population on the distance from the galactic center, the high abundance of heavy elements in quasar spectra and etc.  相似文献   

7.
The characteristics of gravitational bursts from active galactic nuclei, and globular clusters are obtained for three astrophysical situations:(i) scattering of stars by massive black holes residued at the centers of galaxies and globular clusters; (ii) the close encounters of stars in the nuclear regions of these objects; (iii) scattering of stars by black holes of stellar mass containing in the stellar population of galactic nuclei and clusters. The most effective source of gravitational bursts appears to be a scattering of stars by the massive central black holes which produces the bursts with dimensionless amplitudeh10–19–10–21 and frequencies from 10–1 to 10–5 Hz. The characteristics obtained correspond to the possiblities of a future gravitational-wave experiment with use of laser Doppler tracking of interplanetary spacecrafts.  相似文献   

8.
The central energy source of quasars and active galactic nuclei cannot be resolved by observation. When such a compact source is affected by gravitational micro-lensing (lensing of stars in a distant galaxy), brightness changes of the order of magnitudes may occur. Since it is an eclipse-like effect, it gives the possibility of calculating the one-dimensional source profile from the lightcurve. We present the method and the results of its application on simulated lightcurves. It should be possible to obtain information on the structure of the source on a scale smaller than 10–3 pc. The micro gravitational lens effect gives, therefore, the only known possibility of observing directly the central energy source of quasars and active galactic nuclei.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

9.
We have obtained new estimates of the Sun’s distance from the symmetry plane Z ⊙ and the vertical disk scale height h using currently available data on stellar OB associations, Wolf–Rayet stars, HII regions, and Cepheids. Based on individual determinations, we have calculated the mean Z ⊙ = ?16 ± 2 pc. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h = 40.2 ± 2.1 pc from OB associations, h = 47.8 ± 3.9 pc from Wolf–Rayet stars, h = 48.4 ± 2.5 pc from HII regions, and h = 66.2 ± 1.6 pc from Cepheids. We have estimated the surface, Σ = 6 kpc?2, and volume, D(Z ⊙) = 50.6 kpc?3, densities from a sample of OB associations. We have found that there could be ～5000 OB associations in the Galaxy.  相似文献   

10.
An attempt is made to present all the relevant observations of our galactic centre and to explain them by means of a working scheme that involves a minimum number ofad hoc assumptions.In this scheme, the central engine is Sgr A*, a supermassive star of some 103 M and surface temperature 3.6×104 K in Keplerian rotation, fuelled by the strongly magnetized disk. It drives both a non-thermal (pair-plasma) wind and a thermal wind. Interactions with the central star cluster and with the circumnuclear disk give rise to the thermal vortex Sgr A West and to the non-thermal spill-over bubble Sgr A East. The relativistic pair plasma escapes supersonically through the galactic chimney into the galactic twin jets, as in Seyfert galaxies.  相似文献   

11.
It is found from analysis of the position angles of the plane of polarization of about 3000 stars (¦b¦ 5° andP 0.5%) that the angle between the magnetic field and the equatorial plane of the galaxy is approximately 0–5°. The distance within which the local magnetic fields of the galaxy have a greater effect on the position angles of the plane of polarization than the galactic magnetic field is estimated to be about 500 pc. The effect of the galactic magnetic field becomes dominant for distancesr 1000 pc.Translated fromAstrofizika, Vol. 39, No. 4, pp. 553–559, November, 1996.  相似文献   

12.
Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA v=0 . m 38 up to 500 pc.  相似文献   

13.
The magnetic fields observed in the galactic disc are generated by the differential rotation and the helical turbulent motions of interstellar gas. On the scalesl=2k –1 which lie in the intervall 0<l<l e (l 0100 pc is the energy-range scale of the galactic turbulence), the spectral density of the kinetic energy of turbulence (k –5/3) exceeds the magnetic energy spectral density (k –1). The equipartition between magnetic and kinetic energies is reached atl=l e 6 pc in the intercloud medium and is maintained down to the scalel=l d 0.03 pc. In dense interstellar cloudsl e is determined by the individual cloud size andl d 0.1 pc.The internal turbulent velocities in Hi clouds (cloud size is assumed to be 10 pc) lie in the range from 1.8 to 5.6km s–1, fitting well within the observed range of internal rms velocities. Dissipation of the interstellar MHD turbulence leads to creation of temperature fluctuations with amplitudes of 150 K and 65 K in dense clouds and intercloud medium, respectively. The small-scale fluctuations observed in the interstellar medium may arise from such perturbations due to the thermal instability, for instance. Dissipation of the MHD turbulence energy provides nearly half of the energy supply needed to maintain the thermal balance of the interstellar medium.  相似文献   

14.
This paper reviews and analyses various observational data about the local interstellar medium (LISM)-a volume with a radius of about 200 pc near the Sun. There are collected radio, IR, optical, UV, and X-ray observations of the ISM and data on the Sco-Cen association. All available information confirms Weaver's (1979) conclusions that the Sun is located near an edge of a giant cavern with a radius of about 180 pc and the cavern center coincides with the Sco-Cen associated center. The outer rim of the cavern is observed as numerous, very longHi flaments, filaments of the interstellar polarization, and soft X-rays radiated by coronal gas with a temperature of about 106K. Close environment (from 10–4 to 2–5 pc) of the Sun is filled by warm (about 104 K)Hi with the number density 0.1–0.2 cm–3, which is a corona of the local cloud of the ISM. The central part of the cloud is observed to the galactical center direction at a distance of 10–20 pc as Sancini and van Woerden's (1970)Hi filament. The cloud blown round by stellar winds has a horseshoe-like shape, bordering the Sun. Tinbergen's (1982) patch of polarization is observational evidence of the shape.Several arguments are given to show that the bright spots of soft X-rays (130–284 eV) near the galactic poles are produced by an interaction of stellar winds with outer edge of the local cloud near the ends of the patch of polarization. Lyman continuum radiation from Sco-Cen stars was shown to be probably the main source of ionization of extendedHii regions of low density in the LISM. Various data evidence that the North Polar Spur is a SNR in the local cavern with the age of about 105 years. Interaction of the local cavern with an interstellar absorption-free tunnel stretched for more than 1 kpc along the galactical longitudel=240° is discussed. In conclusion several actual problems of investigation of the LISM were formulated.  相似文献   

15.
We investigate the viability of the Galactic corona model of -ray bursts by calculating the spatial distribution of neutron stars born with high velocities in the Galactic disk, and comparing the resulting brightness and angular distribution with the BATSE data. We find that the Galactic corona model can reproduce the BATSE peak flux and angular distribution data for neutron star kick velocities 800 km s–1, source turn-on ages 10 Myrs, and sampling depths 100 kpc d max 400 kpc.  相似文献   

16.
The difference of spatial distributions between the O-type stars, supernovae and red giant stars found by Riekeet al. (1980) in the nuclear region of M82 can be interpreted if the star formation has been triggered by shock waves expanding from the nucleus with velocities of 100 km s–1 at 300 pc from the centre and if the explosions have recurrently occurred with time interval of about 2×106 yr. The recurrent formation of such giant compressed gas layer makes the formation rate of massive stars efficient.  相似文献   

17.
We investigate the dynamics and evolution of coalescing neutron stars. The three-dimensional Newtonian equations of hydrodynamics are integrated by the Piecewise Parabolic Method on an equidistant Cartesian grid. The code is purely Newtonian, but does include the emission of gravitational waves and their back-reaction. The properties of neutron star matter are described by the equation of state of Lattimer and Swesty (1991). Energy loss by all types of neutrinos and changes of the electron fraction due to the emission of electron neutrinos and antineutrinos are taken into account by an elaborate neutrino leakage scheme. We simulate the coalescence of two identical, cool neutron stars with a baryonic mass of 1.6M and a radius of 15 km and with an initial center-to-center distance of 42 km. The initial distributions of density and electron concentration are given from a model of a cold neutron star in hydrostatic equilibrium. We investigate three cases which differ by the initial velocity distribution in the neutron stars. The orbit decays due to gravitational-wave emission and after one revolution the stars are so close that dynamical instability sets in. Within 1 ms the neutron stars merge into a rapidly spinning (P 1 ms), high-density body ( 1014 g/cm3) with a surrounding thick disk of material with densities 1010 – 1012 g/cm3 and orbital velocities of 0.3-0.5 c. The peak emission of gravitational waves has a maximum luminosity of a few times 1055 erg/s and is reached for about 1 ms. The amplitudes of the gravitational waves are close to 3 10–23 at a distance of 1 Gpc and the typical frequency is near the dynamical value of the orbital motion of the merging neutron stars of 2 KHz. In a post-processing step, the rate of neutrino-antineutrino annihilation is calculated from the neutrino luminosities generated during the hydrodynamical simulations. We find the integral annihilation rate to be a few 1050 erg/s during the phase of strongest neutrino emission, which is too small to generate the observed bursts considering the fact that the merged object of about 3M will most likely collapse to a black hole within milliseconds.  相似文献   

18.
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   

19.
Rotating white dwarfs undergoing quasi-radial oscillations can emit gravitational radiation in a frequency range from 0.1-0.3 Hz. Assuming that the energy source for the gravitational radiation comes from the oblateness of the white dwarf induced by the rotation, the strain amplitude is found to be 10-25 for a white dwarf at 50 pc. We had calculated thermal energy losses through a magneto-hydrodynamic mechanism and found it smaller than estimated before. The galactic population of these sources is estimated to be 107 and may produce a confusion-limited foreground for proposed advanced detectors in the frequency band between space-based and ground-based interferometers. Nearby oscillating white dwarfs may provide a clear enough signal to investigate white dwarf interiors through gravitational wave astroseismology.  相似文献   

20.
At present, it is widely believed that anomalous X-ray pulsars (AXPs), soft gamma-ray repeaters (SGRs), rotational radio transients (RRATs), compact central objects (CCOs) in supernova remnants, and X-ray dim isolated neutron stars (XDINSs) belong to different classes of anomalous objects in which the central bodies are isolated neutron stars. Previously, we have shown that AXPs and SGRs can be described in terms of the drift model for parameters of the central neutron star typical of radio pulsars (rotation periods P ～ 0.1–1 s and surface magnetic fields B ～ 1011–1013 G). Here, we show that some of the peculiarities of the sources under consideration can be explained by their geometry (in particular, by the angle β between the rotation axis and the magnetic moment). If β ? 10° (an aligned rotator), the drift waves in the outer layers of the neutron star magnetosphere can account for the observed periodicity in the radiation. For large β (a nearly orthogonal rotator), the observed modulation of the radiation and its short bursts can be explained by mass accretion from the ambient medium (e.g., a relic disk).  相似文献   

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