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1.
A method for detecting voids in the galaxy distribution is presented. Using this method, we have identified 732 voids with a radius of the seed sphere R seed > 4.0h ?1 Mpc in a volume-limited sample of galaxies from the southern part of the 2dFGRS survey. 110 voids with R seed > 9.0h ?1 Mpc have a positive significance. The mean volume of such voids is ～19 × 103 h ?3 Mpc3. Voids with R seed > 9.0h ?1 Mpc occupy 55% of the sample volume. We construct a dependence of the volumes of all the identified voids on their ranks and determine parameters of the galaxy distribution. The dependence of the volume of voids on their rank is consistent with a fractal model (Zipf’s power law) of the galaxy distribution with a fractal dimension D ≈ 2.1 (given the uncertainty in determining the dimension using our method and the results of a correlation analysis) up to scales of ～25h ?1 Mpc with the subsequent transition to homogeneity. The directions of the greatest elongations of voids and their ellipticities (oblateness) are determined from the parameters of equivalent ellipsoids. The directions of the greatest void elongations have an enhanced concentration to the directions perpendicular to the line of sight.  相似文献   

2.
We present the results of the search for spherical volumes containing no galaxies with luminosities brighter than the Magellanic Clouds in the Local Supercluster and its vicinity. Within a distance of 40 Mpc from us, 89 cosmic voids were discovered with the diameters of 24 to 12 Mpc, containing no galaxies with absolute magnitudes brighter than M K < ?18.4. A list of these voids and the sky distribution maps are given. It was found that 93% of spherical voids overlap, forming three more extended percolated voids (hypervoids). The largest of them, HV1, has 56 initial spherical cells and extends in a horseshoe shape, enveloping the Local Volume and the Virgo cluster. The Local Void (Tully, 1988) in the Hercules-Aquila region is the closest part of the HV1. Another hypervoid, HV2, contains 22 spherical voids in the Eridanus constellation, and the third compact hypervoid (HV3) comprises 6 spherical cells in the Bootes. The total volume of these voids incorporates about 30% of the Local Universe. Among 2906 dwarf galaxies excluded from the original sample (n = 10502) in the search for spherical volumes, only 68 are located in the voids we have discovered. They are characterized by late morphological types (85% are Ir, Im, BCD, Sm), absolute magnitudes MB ranging from ?13.0 to ?16.7, moderate star formation rates (log SSFR ～ ?10 M ⊙ yr?1 L ?1 ⊙ ) and gas reserves per luminosity unit twice to three times larger than in the other dwarf galaxies located in normal environments. The dwarf population of the voids shows a certain tendency to sit shallow near the surfaces of cosmic voids.  相似文献   

3.
Using the method of searching for arbitrary shaped voids in the distribution of volume-limited samples of galaxies from the DR5 SDSS survey, we have identified voids and investigated their characteristics and the change in these characteristics with decreasing M lim (from ?19.7 to ?21.2, H 0 = 100 km s?1 Mpc?1)—the upper limit on the absolute magnitude of the galaxies involved in the construction of voids. The total volume of the 50 largest voids increases with decreasing M lim with a break near M* = ?20.44—the characteristic value of the luminosity function for SDSS galaxies. The mean overdensity in voids increases with decreasing M lim also with a weak break near M*. The exponent of the dependence of the volume of a void on its rank increases significantly with decreasing M lim starting from M lim ～ ?20.4 in the characteristic range of volumes, which reflects the tendency for greater clustering of brighter galaxies. The averaged profile of the galaxy overdensity in voids has a similar pattern almost at all M lim. The galaxies mostly tend to gravitate toward the void boundaries and to avoid the central void regions; the overdensity profile is flat in the intermediate range of distances from the void boundaries. The axial ratios of the ellipsoids equivalent to the voids are, on average, retained with changing M lim and correspond to elongated and nonoblate void shapes, but some of the voids can change their shape significantly. The directions of the greatest void elongations change chaotically and are distributed randomly at a given M lim. The void centers show correlations reflecting the correlations of the galaxy distribution on scales (35–70)h ?1 Mpc. The galaxy distribution in the identified voids is nonrandom—groups and filaments can be identified. We have compared the properties of the galaxies in voids (in our case, the voids are determined by the galaxies with absolute magnitudes M abs < M lim = ?20.44, except for the isolated galaxies) and galaxies in structures identified using the minimum spanning tree. A bimodal color distribution of the galaxies in voids has been obtained. A noticeable difference is observed in the mean color indices and star formation rates per unit stellar mass of the galaxies in dense regions (structures)—as expected, the galaxies in voids are, on average, bluer and have higher log (SFR/M star). These tendencies become stronger toward the central void regions.  相似文献   

4.
The results of JHKLM photometry for Nova Delphini 2013 obtained in the first sixty days after its outburst are analyzed. Analysis of the energy distribution in a wide spectral range (0.36–5 µm) has shown that the source mimics the emission of normal supergiants of spectral types B5 and A0 for two dates near its optical brightness maximum, August 15.94 UT and August 16.86 UT, respectively. The distance to the nova has been estimated to be D ≈ 3 kpc. For these dates, the following parameters have been estimated: the source’s bolometric fluxes ～9 × 10?7 and ～7.2 × 10?7 erg s?1 cm?2, luminosities L ≈ 2.5 × 105 L ⊙ and ≈2 × 105 L ⊙, and radii R ≈ 6.3 × 1012 and ≈1.2 × 1013 cm. The nova’s expansion velocity near its optical brightness maximum was ～700 km s?1. An infrared (IR) excess associated with the formation of a dust shell is shown to have appeared in the energy distribution one month after the optical brightness maximum. The parameters of the dust component have been estimated for two dates of observations, JD2456557.28 (September 21, 2013) and JD2456577.18 (October 11, 2013). For these dates, the dust shell parameters have been estimated: the color temperatures ≈1500 and ≈1200 K, radii ≈6.5 × 1013 and 1.7 × 1014 cm, luminosities ～4 × 103 L ⊙ and ～1.1 × 104 L ⊙, and the dust mass ～1.6 × 1024 and ～1025 g. The total mass of the material ejected in twenty days (gas + dust) could reach ～1.1 × 10?6 M ⊙. The rate of dust supply to the nova shell was ～8 × 10?8 M ⊙ yr?1. The expansion velocity of the dust shell was about 600 km s?1.  相似文献   

5.
W. Macy 《Icarus》1980,41(1):153-158
Matching computed spectra for the ν4 band of methane, the ν9 band of ethane, and the R branch of the ν5 band of acetylene to observed spectra for Neptune suggests mixing ratios of CH4/H2 ～ 10?3?10?2, C2H6/H2 ～ 10?6, and C2H2/H2 ～ 10?8 in the stratosphere.  相似文献   

6.
In this paper, we modify our previous research carefully, and derive a new expression of electron energy density in superhigh magnetic fields. Based on our improved model, we re-compute the electron capture rates and the magnetic fields’ evolutionary timescales t of magnetars. According to the calculated results, the superhigh magnetic fields may evolve on timescales ～(106?107) yrs for common magnetars, and the maximum timescale of the field decay, t≈2.9507×106 yrs, corresponding to an initial internal magnetic field B 0=3.0×1015 G and an initial inner temperature T 0=2.6×108 K. Motivated by the results of the neutron star-supernova remnant (SNR) association of Zhang and Xie (2011), we calculate the maximum B 0 of magnetar progenitors, B max～(2.0×1014?2.93×1015) G when T 0=2.6×108 K. When T 0～2.75×108?1.75×108 K, the maximum B 0 will also be in the range of ～1014?1015 G, not exceeding the upper limit of magnetic field of a magnetar under our magnetar model. We also investigate the relationship between the spin-down ages of magnetars and the ages of their SNRs, and explain why all AXPs associated with SNRs look older than their real ages, whereas all SGRs associated with SNRs appear younger than they are.  相似文献   

7.
A model is presented for the photochemistry of PH3 in the upper troposphere and lower stratosphere of Saturn that includes the effects of coupling with NH3 and hydrocarbon photochemistry, specifically the C2H2 catalyzed photodissociation of CH4. PH3 is rapidly depleted with altitude (scale height ～35 km) in the upper troposphere when K～104cm2sec?1; an upper limit for K at the tropopause is estimated at ～105cm2sec?1. If there is no gas phase P2H4 because of sublimation, P2 and P4 formation is unlikely unless the rate of the spin-forbidden recombination reaction PH + H2 + M → PH3 + M is exceedingly slow. An upper limit P4 column density of ～2×1015cm?2 is estimated in the limit of no recombination. If sublimation does not remove all gas phase P2H4, P2 and P4 may be produced in potentially larger quantities, although they would be restricted almost entirely to the lowest levels of our model, where T?100°K. Potentially observable amounts of the organophosphorus compounds CH3P2H2 and HCP are predicted, with column densities of >1017 cm?2 and production rates of ～2×108cm?2sec?1. The possible importance of electronically excited states of PHx and additional PH3/hydrocarbon photochemical coupling paths are also considered.  相似文献   

8.
V.S. Safronov  E.L. Ruskol 《Icarus》1982,49(2):284-296
A two-stage growth of the giant planets, Jupiter and Saturn, is considered, which is different from the model of contraction of large gaseous protoplanets. In the first stage, within a time of ～3 × 107 years in Jupiter's zone and ～2 × 108 years in Saturn's zone, a nucleus forms from condensed (solid) material having the mass, ～1028 g, necessary for the beginning of acceleration. The second stage may gravitating body, and a relatively slow accretion begins until the mass of the planet reaches ～10 m⊕. Then a rapid accretion begins with the critical radius less than the radius of the Hill lobe, so that the classical formulae for the rate of accretion may be applied. At a mass m > m1 ≈ 50 m⊕ accretion proceeds slower than it would according to these formulae. When the planet sweeps out all the gas from its nearest zone of feeding (m = m2 ≈ 130 m⊕), the width of the exhausted zone being ～built13 of the whole zone of the planet) growth is provided the slow diffusion of gas from the rest of the zone (time scale increases to 105?106 years and more). The process is terminated by the dissipation of the remnants of gas. In Saturn's zone m1 > m2 ≈ 30 m⊕. The initial mass of the gas in Jupiter's zone is estimated. Before the beginning of the rapid accretion about 90% of the gas should have been lost from the solar system, and in the planet's zone less than two Jupiter masses remain. The highest temperature of Jupiter's surface, ≈5000°K, is reached at the stage of rapid accretion, m < 100 m⊕, when the luminosity of the planet reaches 3 × 10?3 L⊙. This favors an effective heating of the inner parts of the accretionary disk and the dissipation of gas from the disk. The accretion of Saturn produced a temperature rise up to 2000?2400° K (at m ≈ 20?25 m⊕) and a luminosity up to 10?4 L⊙.  相似文献   

9.
We have studied the fine structure of the active H2O supermaser emission region in Orion KL with an angular resolution of 0.1 mas. We found central features suggestive of a bipolar outflow, bullets, and an envelope which correspond to the earliest stage of low-mass star formation. The ejector is a bright compact source ≤0.05 AU in size with a brightness temperature T b ?1017 K. The highly collimated bipolar outflow ～30 has a velocity v ej ?10 km s?1, a rotation period of ～0.5 yr, a precession period of ～10 yr, and a precession angle of ～33°. Precession gives rise to a jet in the shape of a conical helix. The envelope amplifies the radio emission from the components by about three orders of magnitude at a velocity v=7.65 km s?1.  相似文献   

10.
We investigate the relation between the optical (g-band) and X-ray (0.5–10 keV) luminosities of accreting nonmagnetic white dwarfs. According to the present-day counts of the populations of star systems in our Galaxy, these systems have the highest space density among the close binary systems with white dwarfs. We show that the dependence of the optical luminosity of accreting white dwarfs on their X-ray luminosity forms a fairly narrow one-parameter curve. The typical half-width of this curve does not exceed 0.2–0.3 dex in optical and X-ray luminosities, which is essentially consistent with the amplitude of the aperiodic flux variability for these objects. At X-ray luminosities L x ～ 1032 erg s?1 or lower, the optical g-band luminosity of the accretion flow is shown to be related to its X-ray luminosity by a factor ～2–3. At even lower X-ray luminosities (L x ? 1030 erg s?1), the contribution from the photosphere of the white dwarf begins to dominate in the optical spectrum of the binary system and its optical brightness does not drop below M g ～ 13–14. Using the latter fact, we show that in current and planned X-ray sky surveys, the family of accreting nonmagnetic white dwarfs can be completely identified to the distance determined by the sensitivity of an optical sky survey in this region. For the Sloan Digital Sky Survey (SDSS) with a limiting sensitivity m g ～ 22.5, this distance is ～400–600 pc.  相似文献   

11.
Expected characteristics of RR Lyrae stars as a function of the evolutive parameters are reported. Results from both evolutionary and pulsational investigations are collected in a suitable form, to show the general constraints to any interpretative analysis of the observations. It is shown that the spread in luminosity among the RR Lyrae stars results a function of the original chemical composition. On this basis a set of independent indications is found, suggesting that the globular cluster ω Cen is more He-rich than M 3; agreement with the whole observational frame is attained ifY ωCen～0.35,Z ωCen～5×10?4 andY M3～0.25,Z M3～10?3. No mass loss is needed to account for the RR Lyrae stars observed in ω Cen. The results are discussed, and it is shown that M 13-type clusters can be just characterized by a larger value ofZ in comparison with ω Cen. It is suggested that variations in the original helium content of the order of ΔY～0.1 and a correlationZ=Z(t) can account for some well-observed galactic globular clusters, without allowing for mass loss in the redder HB stars belonging to each cluster.  相似文献   

12.
We present results of the dual-frequency radio sounding of the Venusian ionosphere carried out by the Venera 9 and 10 satellites in 1975. Thirteen height profiles of electron density for different solar zenith angles varying from 10 to 87° have been obtained by analyzing the refraction bending of radiorays in the sounded ionssphere. The main maximum of electron density at a height of 140–150 km depends on the solar zenith angle and is 1.4 to 5 × 105 cm?3. The lower maximum is determined definitely to be at ～130 km high. In the main and lower maxima the electron density variations with solar zenith angle are in good agreement with the Chapman layer theory. For the first time it is found that the height of the upper boundary for the daytime ionosphere (hi) depends regularly on the solar zenith angle. At Z⊙ < 60°, hi does not exceed 300 km while at Z⊙ > 60°, it increases with Z⊙ and comes up to ～ 600 km at Z⊙ ～ 80°.  相似文献   

13.
Results of the scattered solar radiation spectrum measurements made deep in the Venus atmosphere by the Venera 11 and 12 descent probes are presented. The instrument had two channels: spectrometric (to measure downward radiation in the range 0.45 < γ < 1.17 μm) and photometric (four filters and circular angle scanning in an almost vertical plane). Spectra and angular scans were made in the height range from 63 km above the planet surface. The integral flux of solar radiation is 90 ± 12 W m?2 measured on the surface at the subsolar point. The mean value of surface absorbed radiation flux per planetary unit area is 17.5 ± 2.3 W m?2. For Venera 11 and 12 landing sites the atmospheric absorbed radiation flux is ～15 W m?2 for H >; 43 km and ～45 W m?2 for H < 48 km in the range 0.45 to 1.55 μm. At the landing sites of the two probes the investigated portion of the cloud layer has almost the same structure: it consists of three parts with boundaries between them at about 51 and 57 km. The base of clouds is near 48 km above the surface. The optical depth of the cloud layer (below 63 km) in the range 0.5 to 1 μm does not depend on the wavelength and is ～29 and ～38 for the Venera 11 and 12 landing sites, respectively. The single-scattering albedo, ω0, in the clouds is very close to 1 outside the absorption bands. Below 58 km the parameter (1 ? ω0) is <10?3 for 0.49 and 0.7 μm. The parameter (1 ? ω0) obviously increases above 60 km. Below 48 km some aerosol is present. The optical depth here is a strong function of wavelength. It varies from 1.5 to 3 at λ = 0.49 μm and from 0.13 to 0.4 at 1.0 μm. The mean size of particles below the cloud deck is about 0.1 μm. Below 35 km true absorption was found at λ < 0.55 μm with the (1 ? ω0) maximum at H ≈ 15 km. The wavelength and height dependence of the absorption coefficient are compatible with the assumption that sulfur with a mixing ratio ～2 × 10?8 normalized to S2 molecules is the absorber. The upper limits of the mixing ratio for Cl2, Br2, and NO2 are 4 × 10?8, 2 × 10?11, and 4 × 10?10, respectively. The CO2 and H2O bands are confidently identified in the observed spectra. The mean value of the H2O mixing ratio is 3 × 10?5 < FH2O < 10?4 in the undercloud atmosphere. The H2O mixing ratio evidently varies with height. The most probable profile is characterized by a gradual increase from FH2O = 2 × 10?5 near the surface to a 10 to 20 times higher value in the clouds.  相似文献   

14.
We present the results of measurements of the total X-ray flux from the Andromeda galaxy (M31) in the 3-100 keV band based on data from the RXTE/PCA, INTEGRAL/ISGRI, and SWIFT/BAT space experiments. We show that the total emission from the galaxy has a multicomponent spectrum whose main characteristics are specified by binaries emitting in the optically thick and optically thin regimes. The galaxy’s luminosity at energies 20–100 keV gives about 6% of its total luminosity in the 3–100 keV band. The emissivity of the stellar population in M31 is L 2–20 keV ～ 1.1 × 1029 erg s?1 M ⊙ ?1 in the 2–20 keV band and L 20–100 keV ～ 8 × 1027 erg s?1 M ⊙ ?1 in the 20–100 keV band. Since low-mass X-ray binaries at high luminosities pass into a soft state with a small fraction of hard X-ray emission, the detection of individual hard X-ray sources in M31 requires a sensitivity that is tens of times better (up to 10?13 erg s?1 cm?2) than is needed to detect the total hard X-ray emission from the entire galaxy. Allowance for the contribution from the hard spectral component of the galaxy changes the galaxy’s effective Compton temperature approximately by a factor of 2, from ～1.1 to ～2.1 keV.  相似文献   

15.
Two quasars SDSS J010013.02+280225.8 and J030642.51+185315.8 with redshifts z = 6.30 and z = 5.363 were recently discovered. Their apparent magnitudes in the standard cosmological model give the luminosities of Lbol ～ 4.3 × 1014L⊙ and Lbol ～ 3.4 × 1014L⊙. In the framework of modern concepts it is accepted that the energy release of quasars is provided by the accretion onto black holes with masses of 1.24 ± 0.19 × 1010M⊙ and 1.07 ± 0.27 × 1010M⊙. As within the standard cosmological model the ages of these objects are about one billion years, this creates serious difficulties for the scenario of formation of such objects. Here we interpret the ultra-high luminosities of quasars as the effect of lensing of their radiation by the foreground globular clusters or dwarf galaxies.  相似文献   

16.
Exploratory models of the collapse of spherical self-gravitating clouds are studied in relation to the problem of the formation of first generation star-systems. The masses which were considered are in the range of 83 to 5.2×1010 M ⊙. For simplicity, the assumed composition includes hydrogen only, which could be in the form of H, H2, H+ or H?. Since the physical conditions that might have prevailed in a primeval nebula are not well known, rather simple initial conditions were chosen: The gas starts from rest and has initially a uniform temperature. We consider the case of rather cool (T 0～100 K) neutral clouds with different initial ionization degrees. Some of the initial density-distributions here considered are uniform while others are decreasing from the center outwards. The assumed initial values for the densities are ～10?24 g cm?3, except for one of the models, for which it is ～10?26 g cm?3. Several atomic processes within the gas, including physical-chemical reactions and the evaluation of radiative emission coefficients are considered. A system of differential equations is set up in order to evaluate the concentrationsn H,n H 2,n H +,n H ? andn e as a function of time. The treatment makes possible the study of the cooling and heating properties of the gas. Furthermore, the dynamical, thermal and chemical evolution of the cloud can be followed during the collapse. The computations apply only to the optically thin stages. The models show the importance of a correct evaluation of the chemical reactions and dissipative mechanisms, which cannot be ignored in a realistic treatment of the collapse of self-gravitating clouds. The influence of the initial conditions on the dynamical and thermal properties during evolution are also analysed.  相似文献   

17.
We have undertaken mapping and spectroscopy of a broad range of type I post-Main-Sequence nebulae in COJ=1→0,J=2→1, andJ=3→2, using the 12 m antenna at Kitt Peak, and the 45 m facility of the Nobeyama Radio Observatory. As a consequence, we find COJ=2→1 emission associated with NGC 3132 and NGC 6445, determine the location of COJ=1→0 emission in the nucleus of NGC 6302, and obtain (for the first time) COJ=3→2 spectroscopy for a substantial cross-section of type I sources. LVG analysis of the results suggests densitiesn(H2) ～ 104 cm?3, and velocity gradients dv/dr ～ 2×102 in both NGC 7027 and CRL 618, commensurate with uniform expansion of a constant velocity outflow, whilst for the case of NGC 2346 these values probably exceedn(H2) ～ 4.0×105 cm?3. dv/dr ～ 2.6×103 km s?1 andT k ～102 K, implying appreciable compression (and shock heating?) of the CO excitation zone. Hi masses extend over a typical range 0.01<M(Hi)/M ⊙<1, whilst corresponding estimates of the progenitor mass imply 0.7<M prog/M ⊙<2.3; values significantly in excess of those pertinent for normal PN, although somewhat at the lower end of the type I mass range. COJ=3→2 profiles for CRL 2688 confirm the presence of an extended plateau with width Δv～85 km s?1, whilst modestJ=3→2 enhancement is also observed for the high-velocity components in NGC 7027. TheJ=3→2 spectrum for NGC 2346 appears to mimic lower-frequency results reasonably closely, confirming the presence of a double-peaked structure towards the core, and predominantly unitary profiles to the north and south, whilst there is also evidence to suggest appreciableJ=3→2 asymmetry in CRL 618 compared to lower-frequency measures. The status of an extended cloud near HB 5 remains uncertain, although this clearly represents a remarkably complex region with velocity span ΔV～50 km s?1. Our presentJ=3→2 results appear to track lower frequency measures extremely closely, implying local densitiesn(H2)>3×103 cm?3—although temperatures close to theV lsr of HB 5 are relatively weak, and of orderT MB (J=3→2)≤0.9 K. Finally, as a result of both this, and previous investigations we find that of type I sources so far observed in CO, some ～42% appear to possess detectable levels of emissionT r * >0.1 K. Similarly, in cross-correlating this data with other results, we note a closely linear relation betweenJ=2→1 antenna temperaturesT MB, and the surface brightness of H2 S(1) quadrupole emissionS(H2)—a trend which appears also to be reflected betweenS(H2) and corresponding parameters for [Oi], [Oii], [Ni], [Nii], and [Sii]. Such relations almost certainly arise from comparable secular variations in line intensities, although the CO, H2, and optical emission components are likely to derive from disparate line excitation zones. As a consequence, it is clear that whilst H2 S(1) emission is probably enhanced as a result of local shock activity, the evidence for post-shock excitation of the CO and optical forbidden lines is at best marginal. Similarly, although it seems likely that CO emission derives from circum-nebular Hi shells with kinetic temperatureT k ～ 30 K or greater, the predominant fraction of low-excitation emission arises from a mix of charge exchange reactions, nebular stratification and, probably most importantly, the influence of UV shadow zones and associated neutral inclusions.  相似文献   

18.
We consider a cosmological model in which part of the Universe, Ωh～10?5, is in the form of primordial black holes with masses of ～ 105 M ⊙. These primordial black holes were the centers for growing protogalaxies, which experienced multiple mergers with ordinary galaxies and with each other. The galaxy formation is accompanied by the merging and growth of central black holes in the galactic nuclei. We show that the recently discovered correlations between central black hole masses and galactic bulge parameters naturally arise in this scenario.  相似文献   

19.
We analyze the statistical properties of normal galaxies to be detected in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configuration and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be ≈10?14 erg s?1 in the 0.5–2 keV band. This will allow ～(1.5–2) × 104 normal galaxies with approximately the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in the survey are located within ～200–400 Mpc. A typical (most probable) galaxy will have a luminosity log L X ～ 40.5–41.0, will be located at a distance of ～70–90 Mpc, and will be either a star-forming galaxy with a star formation rate of ～20M ⊙ yr?1 whose X-ray emission is produced by ultraluminous X-ray sources (ULXs) or an elliptical galaxy with amass log M * ～ 11.3 emitting through to a hot interstellar gas. The galaxies within 35 Mpc will collectively contain ～102 ULXs with luminosities log L X > 40, ～80% of whichwill be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum luminosity of ULXs.  相似文献   

20.
Earlier, under certain simplifying assumptions, on the basis of the General Theory of Relativity, it has been concluded by many authors that when the radius of a gravitationally collapsing spherical object of massM reaches the critical value of the Scharzschild radiusR s=2GM/c 2, then, in a co-moving frame, the object collapses catastrophically to a point. However, in drawing this conclusion due consideration has not been given to the nuclear forces between the nucleons. In particular, the very strong ‘hard-core’ repulsive interaction between the nucleons which has the range ～0.4×10?13 cm has been totally ignored. On taking into account this ‘hard-core’ repulsive interaction, it is found that no spherical object of massM g can collapse to a volume of radius smaller thanR min=(1.68×10?6)M 1/3 cm or to a density larger than ρmax=5.0 × 1016 g cm?3. It has also been pointed out that objects of mass smaller thanM c～1.21×1033 g can not cross the Schwarzschild barrier and gravitationally collapse. The only course left to the objects of mass less thanM cis to reach the equilibrium as either a white dwarf or a neutron star.  相似文献   

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