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1.
Visible-range absorption bands at 600–750 nm were recently detected on two Edgeworth-Kuiper Belt (EKB) objects (Boehnhardt et al., 2002). Most probably the spectral features may be attributed to hydrated silicates originated in the bodies. We consider possibilities for silicate dressing and silicate aqueous alteration within them. According to present models of the protoplanetary disk, the temperatures and pressures at the EKB distances (30–50 AU) at the time of formation of the EKB objects (106 to 108 yr) were very low (15–30 K and 10-9–10-10 bar). At these thermodynamic conditions all volatiles excluding hydrogen, helium and neon were in the solid state. An initial mass fraction of silicates (silicates/(ices + dust)) in EKB parent bodies may be estimated as 0.15–0.30. Decay of the short-lived 26Al in the bodies at the early stage of their evolution and their mutual collisions (at velocities ≥1.5 km s-1) at the subsequent stage were probably two main sources of their heating, sufficient for melting of water ice. Because of the former process, large EKB bodies (R ≥ 100 km) could contain a large amount of liquid water in their interiors for the period of a few 106 yr. Freezing of the internal ocean might have begun at ≈ 5 × 106 yr after formation of the solar nebula (and CAIs). As a result, aqueous alteration of silicates in the bodies could occur. A probable mechanism of silicate dressing was sedimentation of silicates with refractory organics, resulting in accumulation of large silicate-rich cores. Crushing and removing icy covers under collisions and exposing EKB bodies' interiors with increased silicate content could facilitate detection of phyllosilicate spectral features. 相似文献
2.
Near the inner edge of the Edgeworth-Kuiper Belt (EKB) are Pluto and Charon, which are known to have N2- and H2O-dominated surface ices, respectively. Such non-polar and polar ices, and perhaps mixtures of them, also may be present on other trans-Neptunian objects. Pluto, Charon, and all EKB objects reside in a weak, but constant UV-photon and energetic ion radiation environment that drives chemical reactions in their surface ices. Effects of photon and ion processing include changes in ice composition, volatility, spectra, and albedo, and these have been studied in a number of laboratories. This paper focuses on ice processing by ion irradiation and is aimed at understanding the volatiles, ions, and residues that may exist on outer solar system objects. We summarize radiation chemical products of N2-rich and H2O-rich ices containing CO or CH4, including possible volatiles such as alcohols, acids, and bases. Less-volatile products that could accumulate on EKB objects are observed to form in the laboratory from acid-base reactions, reactions promoted by warming, or reactions due to radiation processing of a relatively pure ice (e.g., CO → C3O2). New IR spectra are reported for the 1–5 mu;m region, along with band strengths for the stronger features of carbon suboxide, carbonic acid, the ammonium and cyanate ions, polyoxymethylene, and ethylene glycol. These six materials are possible contributors to EKB surfaces, and will be of interest to observers and future missions. 相似文献
3.
We study the effects of a Mars-like planetoid with a semimajor axis at about ∼60 AU orbiting embedded in the primordial Edgeworth-Kuiper belt (EKB). The origin of such an object can be explained in the framework of our current understanding of the origin of the outer Solar System, and a scenario for the orbital transport mechanism to its present location is given. The existence of such an object would produce a gap in the EKB distribution with an edge at about 50 AU, which seems to be in agreement with the most recent observations. No object at low eccentricity with semimajor axis beyond 50 AU has been detected so far, even though the present observing capabilities would allow an eventual detection (B. Gladman et al. 1998, Astron. J.116, 2042-2054; D. Jewitt et al. 1998, Astron. J.115, 2125-2135; E. I. Chiang and M. E. Brown 1999, Astron. J.118, 1411-1422; R. L. Allen et al. 2000, Astrophys. J.549, 241-244; C. A. Trujillo et al. 2001, Astron. J.122, 457-473; B. Gladman et al. 2001, Astron. J.122, 1051-1066; C. A. Trujillo and M. E. Brown 2001, Astrophys. J.554, 95-98). Finally, ranges for the magnitude and proper motion of the proposed object are given. 相似文献
4.
We present a kinetic model of a disk of solid particles, orbiting a primary and experiencing inelastic collisions. In distinction to other collisional models that use a 2D (mass-semimajor axis) binning and perform a separate analysis of the velocity (eccentricity, inclination) evolution, we choose mass and orbital elements as independent variables of a phase space. The distribution function in this space contains full information on the combined mass, spatial, and velocity distributions of particles. A general kinetic equation for the distribution function is derived, valid for any set of orbital elements and for any collisional outcome, specified by a single kernel function. The first implementation of the model utilizes a 3D phase space (mass-semimajor axis-eccentricity) and involves averages over the inclination and all angular elements. We assume collisions to be destructive, simulate them with available material- and size-dependent scaling laws, and include collisional damping. A closed set of kinetic equations for a mass-semimajor axis-eccentricity distribution is written and transformation rules to usual mass and spatial distributions of the disk material are obtained. The kinetic “core” of our approach is generic. It is possible to add inclination as an additional phase space variable, to include cratering collisions and agglomeration, dynamical friction and viscous stirring, gravity of large perturbers, drag forces, and other effects into the model. As a specific application, we address the collisional evolution of the classical population in the Edgeworth-Kuiper belt (EKB). We run the model for different initial disk's masses and radial profiles and different impact strengths of objects. Our results for the size distribution, collisional timescales, and mass loss are in agreement with previous studies. In particular, collisional evolution is found to be most substantial in the inner part of the EKB, where the separation size between the survivors over EKB's age and fragments of earlier collisions lies between a few and several tens of km. The size distribution in the EKB is not a single Dohnanyi-type power law, reflecting the size dependence of the critical specific energy in both strength and gravity regimes. The net mass loss rate of an evolved disk is nearly constant and is dominated by disruption of larger objects. Finally, assuming an initially uniform distribution of orbital eccentricities, we show that an evolved disk contains more objects in orbits with intermediate eccentricities than in nearly circular or more eccentric orbits. This property holds for objects of any size and is explained in terms of collisional probabilities. The effect should modulate the eccentricity distribution shaped by dynamical mechanisms, such as resonances and truncation of perihelia by Neptune. 相似文献
5.
The effects that a hypothetical trans-Plutonian planet would produce on theorbital distribution of the Classical Edgeworth-Kuiper-Belt, has beensurveyed for different physical and orbital parameters of the hypotheticalbody in Melita et al. (2003a). The best fits were obtained by a moderatelyeccentric and inclined Earth-sized object with a semimajor axis of ～ 70AU. However the history of some objects in the `Extended Scattered disk’still represent a puzzle. One possibility is that they can be `extracted’from the Scattered disk by the planetoid. In this work we confirm that such anhypothesis would not explain the present orbit of 2000 CR105, given theconditions for a gap as observed to be formed in the Classical EKB. 相似文献
6.
J. E. Horvath 《Astrophysics and Space Science》2007,307(4):419-422
We address in this work the general features of a possible compact stars composed by elementary fermions beyond the quark
level. The locus of these hypothetic objects in the mass-radius plane is constructed for the maximum mass (minimum radius) of the sequence
of models in terms of a compositeness scale only, and in fact this approach applies for any composite model postulating fermions
at or beyond the preon level. We point out a constraint on the preon mass arising from the applicability of the General Relativity
structure equations, leading to the questioning of the hypothesis of light preons if the preon scale is high, provided classical
compact objects are enforced. Some remarks on the existence of superdense stars of astrophysical and primordial origin are
made and discussed.
相似文献
7.
C. Fedeli L. Moscardini S. Matarrese 《Monthly notices of the Royal Astronomical Society》2009,397(2):1125-1137
We predict the biasing and clustering properties of galaxy clusters that are expected to be observed in the catalogues produced by two forthcoming X-ray and Sunyaev–Zel'dovich effect surveys. We study a set of flat cosmological models where the primordial density probability distribution shows deviations from Gaussianity in agreement with current observational bounds form the background radiation. We consider both local and equilateral shapes for the primordial bispectrum in non-Gaussian models. The two catalogues investigated are those produced by the e ROSITA wide survey and from a survey based on South Pole Telescope observations. It turns out that both the bias and observed power spectrum of galaxy clusters are severely affected in non-Gaussian models with local shape of the primordial bispectrum, especially at large scales. On the other hand, models with equilateral shape of the primordial bispectrum show only a mild effect at all scales, that is difficult to be detected with clustering observations. Between the two catalogues, the one performing better is the e ROSITA one, since it contains only the largest masses that are more sensitive to primordial non-Gaussianity. 相似文献
8.
I present here a brief overview of the effects caused by parity violating cosmological sources (such as magnetic or kinetic helicity) on the CMB fluctuations. I discuss also primordial helicity induced relic gravitational waves. All these effects can serve as cosmological tests for primordial helicity detection. 相似文献
9.
D. Dwivedee B. Nayak M. Jamil L. P. Singh R. Myrzakulov 《Journal of Astrophysics and Astronomy》2014,35(1):97-106
In this work, we study the evolution of primordial black holes within the context of loop quantum cosmology. First we calculate the scale factor and energy density of the Universe for different cosmic era and then taking these as inputs, we study evolution of primordial black holes. From our estimation it is found that accretion of radiation does not affect evolution of primordial black holes in loop quantum cosmology. We also conclude that due to slow variation of scale factor, the upper bound on initial mass fraction of presently evaporating PBHs are much greater in loop quantum cosmology than the standard case. 相似文献
10.
11.
V. N. Lukash E. V. Mikheeva V. Müller A. M. Malinovsky 《Monthly notices of the Royal Astronomical Society》2000,317(4):795-800
We propose a -inflation model that explains a significant part of the COBE signal by primordial cosmic gravitational waves. The primordial density perturbations fulfil both the constraints of large-scale microwave background and galaxy cluster normalization. The model is tested against the galaxy cluster power spectrum and the high-multipole angular cosmic microwave background anisotropy. 相似文献
12.
We consider the possibility of low-mass primordial black holes being formed in terms of the inflationary theory of the early Universe. We found a condition on the reheating temperature under which the relic remnants of primordial black holes had been formed by now. These relic remnants may account for a part of the dark matter in our Universe. 相似文献
13.
Licia Verde Raul Jimenez Marc Kamionkowski Sabino Matarrese 《Monthly notices of the Royal Astronomical Society》2001,325(1):412-418
We investigate the relative sensitivities of several tests for deviations from Gaussianity in the primordial distribution of density perturbations. We consider models for non-Gaussianity that mimic that which comes from inflation as well as that which comes from topological defects. The tests we consider involve the cosmic microwave background (CMB), large-scale structure, high-redshift galaxies, and the abundances and properties of clusters. We find that the CMB is superior at finding non-Gaussianity in the primordial gravitational potential (as inflation would produce), while observations of high-redshift galaxies are much better suited to find non-Gaussianity that resembles that expected from topological defects. We derive a simple expression that relates the abundance of high-redshift objects in non-Gaussian models to the primordial skewness. 相似文献
14.
Primordial helium abundance in the universe was determined based on spectral observations of low-metallicity blue compact dwarf galaxies. The intensities of the observed emission lines were corrected for several mechanisms, including stellar absorption and collisional excitation of the helium and hydrogen emission spectra. Parameters that were necessary for correcting the deviations of the emission lines?? intensities from their recombination values were determined using the Monte Carlo method. The obtained value of primordial helium of 0.2557 ± 0.0014 is higher by 3% than the value obtained from the analysis of the microwave background radiation fluctuations under the assumption of the standard model of primordial nucleosynthesis. This points to the existence of new types of neutrino in the primordial nucleosynthesis epoch, in addition to the three known ones. 相似文献
15.
Tim Adams Melvyn B. Davies Richard F. Jameson Aylwyn Scally 《Monthly notices of the Royal Astronomical Society》2002,333(3):547-560
We present the results of multiple simulations of open clusters, modelling the dynamics of a population of brown dwarf members. We consider the effects of a large range of primordial binary populations, including the possibilities of having brown dwarf members contained within a binary system. We also examine the effects of various cluster diameters and masses. Our examination of a population of wide binary systems containing brown dwarfs, reveals evidence for exchange reactions whereby the brown dwarf is ejected from the system and replaced by a heavier main-sequence star. We find that there exists the possibility of hiding a large fraction of the brown dwarfs contained within the primordial binary population. We conclude that it is probable that the majority of brown dwarfs are contained within primordial binary systems which then hides a large proportion of them from detection. 相似文献
16.
Cosmic structure formation is thought to occur as a bottom-up scenario, i.e. the lightest objects would have formed first. It has been suggested that the earliest structures to form could have been primordial planets. Here we propose the possibility of formation of primordial planets at high redshifts composed predominantly of dark matter (DM) particles, with planetary masses ranging from Neptune mass to asteroid mass. Most of these primordial DM planets could be free floating without being attached to a host star and a substantial fraction could be present in the halo contributing to the DM. Here we suggest that the flux of DM particles could be significantly reduced as substantial number of DM particles are now trapped in such objects, perhaps accounting for the negative results seen so far in the ongoing DM detection experiments.
相似文献17.
R. Cayrel 《Journal of Astrophysics and Astronomy》1987,8(2):153-159
A new interpretation is given to the low metallicity peak of the bimodal metallicity histogram of galactic globular clusters.
It is proposed that these globular clusters are primordial,i.e., formed out of big-bang matter. Their nonvanishing metallicity is attributed to pollution by supermassive stars like R 136a.
The first stellar generation is formed out of the ‘dirty’ primordial matter. 相似文献
18.
H. Meusinger 《Astrophysics and Space Science》1992,188(1):19-39
The abundance evolution of oxygen in the local galactic disk is discussed. The age-metallicity relation of nearby stars is confronted with predictions from simple evolution models where infall of primordial gas and outflow of disk gas and dust are allowed. Gas infall and expulsion of dust grains have considerable effects on the age-metallicity relation. Dust outflow may be important in order to solve the discrepancy between the observed rate of infall of primordial gas and rates predicted by simple evolution models. 相似文献
19.
We study the effects of possible deviations of fundamental physical constants on the yields of light nuclides, 2D, 3He, 4He, 7Li, and others during primordial nucleosynthesis. The deviations of fundamental constants from their current values are considered in the low-energy approximation of string theories; the latter predict the existence of a scalar field, which, apart from the tensor gravitational field, determines the space geometry. A two-parameter (η, δ) model is constructed for primordial nucleosynthesis: η = n B /n γ is the baryon-to-photon density ratio, and Ω is the relative deviation of fundamental physical constants at the epoch of primordial nucleosynthesis from their current values. A dependence of η on the deviation of coupling constants Ω has been derived on condition that the primordial helium abundance is Y p = f(η, δ) = const, where const corresponds to experimental values. We thus showed that the relative baryonic density (and hence ΩB could vary over a much wider range than allowed by the standard nucleosynthesis model. Considering this result, we discuss the recently found mismatch between ΩB obtained from an analysis of CMBR anisotropy and from the standard primordial nucleosynthesis model. 相似文献
20.
The clustering of fine particles by mutual thermal collisions is investigated experimentally. Fine particles are prepared in an argon gas atmosphere by the gas evaporation technique. Mass distributions of clusters of the particles are obtained from micrographs of specimen grids placed at different heights above the evaporating source. The cluster growth is clearly seen in the change of mass distribution with height. A comparison of the experimental results with a theoretical model indicates that the cluster of fine particles does not grow in the spherical manner usually assumed, but in a planar manner. As an important consequence of the conclusion to the primordial solar nebula, the sedimentation time of the grains sinking towards the equatorial plane of the solar disk becomes longer than the value previously adopted because of the large ratio of surface to volume of a planar cluster. This longer time should alter the scenario of the evolution of the solar system after sedimentation.Invited contribution to the Proceedings of a Workshop onThermodynamics and Kinetics of Dust Formation in the Space medium held at the Lunar and Planetary Institute, Houston, 6–8 September, 1978. 相似文献