共查询到20条相似文献，搜索用时 93 毫秒
1.
相对于核物质和奇异夸克物质, 仅由两味夸克构成的轻夸克物质(即ud夸克物质)有可能更稳定. 而对于由这三类物质构成的典型物质集团, 研究发现如果ud夸克物质具有较大的对称能, 那么其物质团会在特定大小(重子数$A\approx1000$)时最稳定. 在这种情况下, 就可能存在由ud夸克物质团和电子构成的致密矮星, 即ud夸克矮星. 通过进一步研究这类ud夸克矮星的结构可知: 相较于传统的由原子核和电子构成的白矮星, ud夸克矮星通常具有较小的半径, 而被正常物质覆盖的ud夸克矮星的半径则在它们之间, 这与最近观测到的质量和半径都异常小的白矮星相符. 相似文献
2.
Corrado Massa 《Astrophysics and Space Science》2000,271(4):365-369
The idea that pieces of cosmic strings born in the very early universe became the celestial bodies we now observe suggests
a link between the proton lifetime and the Cavendish constant G. A varying G might cause a quick proton decay in hot matter and/or in degenerate matter.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Neil Trentham Ole Möller Enrico Ramirez-Ruiz 《Monthly notices of the Royal Astronomical Society》2001,322(3):658-668
There are a number of theoretical and observational hints that large numbers of low-mass galaxies composed entirely of dark matter exist in the field. The theoretical considerations follow from the prediction of cold dark matter theory that there exist many low-mass galaxies for every massive one. The observational considerations follow from the observed paucity of these low-mass galaxies in the field but not in dense clusters of galaxies; this suggests that the lack of small galaxies in the field is due to the inhibition of star formation in the galaxies as opposed to the fact that their small dark matter haloes do not exist. In this work we outline the likely properties of low-mass dark galaxies, and describe observational strategies for finding them, and where in the sky to search. The results are presented as a function of the global properties of dark matter, in particular the presence or absence of a substantial baryonic dark matter component. If the dark matter is purely cold and has a Navarro, Frenk & White density profile, directly detecting dark galaxies will only be feasible with present technology if the galaxy has a maximum velocity dispersion in excess of 70 km s−1 , in which case the dark galaxies could strongly lens background objects. This is much higher than the maximum velocity dispersions in most dwarf galaxies. If the dark matter in galaxy haloes has a baryonic component close to the cosmic ratio, the possibility of directly detecting dark galaxies is much more realistic; the optimal method of detection will depend on the nature of the dark matter. A number of more indirect methods are also discussed. 相似文献
4.
Dragan Slavkov Hajdukovic 《Astrophysics and Space Science》2010,330(2):207-209
We argue that the so-called “Pioneer Anomaly” is related to the quantum vacuum fluctuations. Our approach is based on the hypothesis of the gravitational repulsion between matter and antimatter, what allows considering, the virtual particle–antiparticle pairs in the physical vacuum, as gravitational dipoles. Our simplified calculations indicate that the anomalous deceleration of the Pioneer spacecrafts could be a consequence of the vacuum polarization in the gravitational field of the Sun. At the large distances, the vacuum polarization by baryonic matter could mimic dark matter what opens possibility that dark matter do not exist, as advocated by the Modified Newtonian Dynamics (MOND). 相似文献
5.
We compare the structure and substructure of dark matter halos in model universes dominated by collisional, strongly self-interacting dark matter (SIDM) and collisionless, weakly interacting dark matter (CDM). While SIDM virialized halos are more nearly spherical than CDM halos, they can be rotationally flattened by as much as 20% in their inner regions. Substructure halos suffer ram-pressure truncation and drag, which are more rapid and severe than their gravitational counterparts tidal stripping and dynamical friction. Lensing constraints on the size of galactic halos in clusters are a factor of 2 smaller than predicted by gravitational stripping, and the recent detection of tidal streams of stars escaping from the satellite galaxy Carina suggests that its tidal radius is close to its optical radius of a few hundred parsecs-an order of magnitude smaller than predicted by CDM models but consistent with SIDM models. The orbits of SIDM satellites suffer significant velocity bias, sigmaSIDM&solm0;sigmaCDM=0.85, and are more circular than CDM satellites, betaSIDM approximately 0.5, in agreement with the inferred orbits of the Galaxy's satellites. In the limit of a short mean free path, SIDM halos have singular isothermal density profiles; thus, in its simplest incarnation SIDM, is inconsistent with galactic rotation curves. 相似文献
6.
J. Marvin Herndon 《Earth, Moon, and Planets》2006,99(1-4):53-89
Only three processes, operant during the formation of the Solar System, are responsible for the diversity of matter in the
Solar System and are directly responsible for planetary internal-structures, including planetocentric nuclear fission reactors,
and for dynamical processes, including and especially, geodynamics. These processes are: (i) Low-pressure, low-temperature
condensation from solar matter in the remote reaches of the Solar System or in the interstellar medium; (ii) High-pressure,
high-temperature condensation from solar matter associated with planetary-formation by raining out from the interiors of giant-gaseous
protoplanets, and; (iii) Stripping of the primordial volatile components from the inner portion of the Solar System by super-intense
solar wind associated with T-Tauri phase mass-ejections, presumably during the thermonuclear ignition of the Sun. As described
herein, these processes lead logically, in a causally related manner, to a coherent vision of planetary formation with profound
implications including, but not limited to, (a) Earth formation as a giant gaseous Jupiter-like planet with vast amounts of
stored energy of protoplanetary compression in its rock-plus-alloy kernel; (b) Removal of approximately 300 Earth-masses of
primordial volatile gases from the Earth, which began Earth’s decompression process, making available the stored energy of
protoplanetary compression for driving geodynamic processes, which I have described by the new whole-Earth decompression dynamics
and which is responsible for emplacing heat at the mantle-crust-interface at the base of the crust through the process I have
described, called mantle decompression thermal-tsunami; and, (c) Uranium accumulations at the planetary centers capable of
self-sustained nuclear fission chain reactions. 相似文献
7.
Dieter Lorenz-Petzold 《Astrophysics and Space Science》1984,98(2):281-286
Exact solutions of the Brans-Dicke field equations of Bianchi types-II, VIII, and IX are derived. The solutions represent locally rotationally symmetric universes with stiff matter content. 相似文献
8.
We present analytic solutions of the Einstein-Maxwell equations for cosmological models of LRS Bianchi type-II, VIII, and IX. The solutions represent anisotropic universes with source-free electromagnetic fields and perfect fluids matter satisfying the equation of state that is a function of the cosmic-time. Some physical properties of the models have been discussed. 相似文献
9.
Starting from the standard Newtonian theory, we derive in the propagation equation of perturbations an effectively Yukawalike potential invoked by several authors as an alternative to dark matter. This approach provides with a simple explanation of the segregation observed for dynamically ‘hot’ systems in the plane defined by their effective parameters. 相似文献
10.
Arch systems lying above quiescent prominences in the solar corona have long drawn the attention of eclipse observers, and such formations have been investigated since the end of the last century. Almost every eclipse photograph shows one or more arches, and in most cases the arch system is accompanied by a quiescent prominence below it and a helmet streamer above it. Also, in some cases there is a dark cavity between the arch system and the prominence.On large-scale photographs obtained at the November 12, 1966 eclipse, detailed photometry has been carried out on a formation in the corona composed of a helmet streamer straddling two multiple-arch systems each with a dark cavity and a quiescent prominence. The excess of electrons in the arches and the deficiency in the cavities are evaluated. We find that the formation of a prominence requires much more material than available in the cavity before depletion. Consequently the condensation theory of coronal matter into prominences seems to have difficulties explaining the necessary amount of matter in the cases where coronal arches - delineating magnetic field lines above the cavity - may exclude inflow of material from the corona. We comment on the low velocity of solar wind in the helmet streamer.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
11.
C. Sivaram 《Astrophysics and Space Science》1994,219(1):135-141
A possible connection between MOND (Modification of Newtonian Dynamics) proposed as an alternative hypothesis to dark matter in galaxies and clusters and a residual cosmological constant term dominating cosmological dynamics in a = 1 universe is explored. 相似文献
12.
We present warm dark matter (WDM) as a possible solution to the missing satellites and angular momentum problem in galaxy
formation and introduce improved initial conditions for numerical simulations of WDM models, which avoid the formation of
unphysical haloes found in earlier simulations. There is a hint, that because of that the mass function of satellite haloes
has been overestimated so far, pointing to higher values for the WDM particle mass.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
G. Venturi 《Astroparticle Physics》1993,1(4):417-428
The matter-gravity system is examined in a path integral approach for the case of conformal matter coupled to a Friedman-Robertson-Walker space time. In particular the case of gravitational potentials of interest in cosmology for which the universe tunnels from a small radius is examined. It is observed that in the presence of such gravitational horizons the universe evolves in a complex time and it is shown how a classical time and temperature emerge. Correspondingly, one will have compensating quantum and thermal fluctuations for the matter and gravity system and it is noted that the unstable mode of gravity corresponding to the universe tunneling into existence will be compensated by an analogous mode for matter corresponding to its creation. This last point is examined in a simple De Sitter model with conformal matter and a relation is found between the cosmological constant, the number of matter fields and the self coupling of matter responsable for its instability. 相似文献
14.
Libby D. Tunney Patrick J. A. Hill Christopher D. K. Herd Robert W. Hilts 《Meteoritics & planetary science》2023,58(2):207-217
Organic matter in astromaterials can provide important information for understanding the chemistry of our solar system and the prebiotic conditions of the early Earth. However, once astromaterials reach the Earth's surface, they can be readily contaminated through contact with the Earth's surface as well as during processing and curation. Here, we investigate how typical handling and curation materials interact with meteorite specimens by documenting hydrophobic organic compound contamination in the laboratory environment and on materials that might be used for their collection and storage. We use gas chromatography–mass spectrometry analysis of soluble organic compounds in dichloromethane extracts of these materials to gain insights into what materials and methods are best for the collection and curation of astromaterials. Our results have implications for how extraterrestrial samples—especially those containing significant intrinsic organic matter—are handled and curated to preserve them in their most pristine states. Following recommendations of other researchers in the area of returned sample curation, we advocate for a thorough investigation into the materials used in handling and curation of meteorites to create a contamination baseline to inform soluble organic analyses on astromaterials and enable the discrimination of terrestrial and extraterrestrial compounds. 相似文献
15.
Based on maps of the extragalactic radio sources Cyg A, Her A, Cen A, 3C 277.3 and others, arguments are given that the twin-jets
from the respective active galactic nucleus ram their channels repeatedly through thin, massive shells. The jets are thereby
temporarily choked and blow radio bubbles. Warm shell matter in the cocoon shows up radio-dark through electron-scattering. 相似文献
16.
The conversion from neutron stars with different equation of states (EOSs) for neutron matter into strange stars with different EOSs for strange quark matter has been studied in a general relativistic numerical calculation in this paper. For hot neutron stars, their conversion may lead to great variations in their rotation periods, of which the magnitude would be greatly dependent upon the EOS for neutron matter, and of which the timescale would be greatly determined by the EOS for strange matter. This phenomenon appears as giant glitches, which might provide a probe of EOSs for both neutron matter and strange matter. But for cold neutron stars, their conversion may result in a population of gamma-ray bursts. 相似文献
17.
This paper has been devoted to a basic molecular studies of polyatomics. A critical analysis of the 70 available references in literature has been made to select 37 polyatomic molecules, molecular ions, and radicals containing six, seven, eight, nine, ten, eleven, twelve, and thirteen atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the spectral region, transition levels, astrophysical objects where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, interstellar cloud, molecular cloud, interstellar space, Galaxy, etc.). Two-hundred fourteen new polyatomic molecules (containing 6, 7, 8, 9, and 10 atoms) of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper II. 相似文献
18.
E. Pignatelli E. M. Corsini J. C. Vega Beltrán C. Scarlata A. Pizzella J. G. Funes S. J. W. W. Zeilinger J. E. Beckman F. Bertola 《Monthly notices of the Royal Astronomical Society》2001,323(1):188-210
We present V -band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, 3898 and 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allows us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects.
NGC 772 and 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (| r |≲8 arcsec) of NGC 3898, where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter. 相似文献
NGC 772 and 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (| r |≲8 arcsec) of NGC 3898, where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter. 相似文献
19.
Organic matter from comet 81P/Wild 2, IDPs,and carbonaceous meteorites; similarities and differences
S. Wirick G. J. Flynn L. P. Keller K. Nakamura‐Messenger C. Peltzer C. Jacobsen S. Sandford M. Zolensky 《Meteoritics & planetary science》2009,44(10):1611-1626
Abstract— During preliminary examination of 81P/Wild 2 particles collected by the NASA Stardust spacecraft, we analyzed seven, sulfur embedded and ultramicrotomed particles extracted from five different tracks. Sections were analyzed using a scanning transmission X‐ray microscope (SXTM) and carbon X‐ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty‐four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty‐four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites. 相似文献
20.
Gravitational lensing allows us to probe the structure of matter on a broad range of astronomical scales, and as light from a distant source traverses an intervening galaxy, compact matter such as planets, stars, and black holes act as individual lenses. The magnification from such microlensing results in rapid brightness fluctuations which reveal not only the properties of the lensing masses, but also the surface brightness distribution in the source. However, while the combination of deflections due to individual stars is linear, the resulting magnifications are highly non-linear, leading to significant computational challenges which currently limit the range of problems which can be tackled. This paper presents a new and novel implementation of a numerical approach to gravitational microlensing, increasing the scale of the problems that can be tackled by more than two orders of magnitude, opening up a new regime of astrophysically interesting problems. 相似文献