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1.
A theoretical basis for modifying Newtonian dynamics on a galactic scale can be obtained by postulating that cosmic rays interact with graviton exchanges between distant masses. This assumes that these charged particles move under the influence of local electromagnetic fields rather than the weak gravitational fields of distant matter. It leads to an enhancement of graviton exchanges between distant masses via an additional gravitational force term inversely proportional to distance. At planetary and local interstellar distances this predicts an extremely small additional gravitational force, but it can become significant on a galactic scale. The model is used here to predict rotational velocities in a wide range of galaxies including the Milky Way, Andromeda (M31) and some galaxies in the THINGS study. Results are obtained assuming a galactic cosmic ray density consistent with observations in the solar system. This approach is compared with the dark matter hypothesis and with Modified Newtonian Dynamics (MOND), the two primary postulates used to explain the constant rotational velocities observed in most galaxies.  相似文献   

2.
本文对16个高红移类星体的L_α森林吸收线密度N(z_(abs))统计分析的结果,表明它明显地依赖于类星体自身的发射红移z_(em)。这不仅表现在z(em)越大的类星体其全部L_α吸收线的平均数密度N(z_(abs))也越大;更重要的是,对于相同的吸收红移值z_(abs),而言,N(z_(abs))在统计意义上明显地随着类星体z_(em)的增大而增大。另一方面,本文也在“吸收体源自类星体抛射”的框架下作了统计,结果仍表明z_(em)对L_α森林吸收线密度有显著影响,但抛射速度却对被抛射体的数目无显著影响。最后,对所得的结果以及可能影响N(z_(abs))的若干因素作了讨论。  相似文献   

3.
The derivation of dynamic spectra of high energy electrons in flares from high resolution hard X-ray observations is considered. It is shown that the Bethe-Heitler formula for the electronproton bremsstrahlung cross-section over the 20–100 keV range of energies admits of a general analytic solution for the electron spectrum in terms of the X-ray spectrum, in a form convenient for computation. The bearing of this analysis on different models of flare conditions is considered. In examining the hypothesis that the X-rays are produced in regions of high ambient density, the duration of the burst being governed by modulation of the electron source rather than by the decay of trapped electrons injected impulsively, it is emphasised that the energy spectrum of the electrons at their source is different from their effective spectrum in the X-ray emitting region. This spectrum, at the source, is found to be much steeper than that in the X-ray region which means that the entire energy of the flare could reside in the injected electrons.  相似文献   

4.
UBV photometry of the peculiar star FK Comae, obtained during the period January–June 1983, is presented. The amplitude of the photometric variation has raised with respect to the previous observations performed in 1981 and 1982, attaining about 0.18 mag in theV filter. Colour curves indicate that the star is redder at minimum light; this fact is consistent with both the models presented to explain the properties of FK Comae. A Fourier analysis of the light curves available in the literature has been performed; the phases of minimum and maximum light turn out to be noticeably stable in time. This fact is difficult to be reconciled with the hypothesis of dark spots that are observed to migrate in other active stars. Rather, it could be explained by the model of Walter and Basri (1982a, b), implying an extremely evolved Algol-type system accreting mass on its primary component.  相似文献   

5.
We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). Since at high redshift ( z > 5), low-mass stars cannot be dominant sources for dust grains, SNe II and PISNe, whose progenitors are massive stars with short lifetimes, should govern the dust production. Here, we theoretically investigate the extinction curves of dust produced by SNe II and PISNe, taking into account reverse shock destruction induced by collision with ambient interstellar medium. We find that the extinction curve is sensitive to the ambient gas density around a SN, since the efficiency of reverse shock destruction strongly depends on it. The destruction is particularly efficient for small-sized grains, leading to a flat extinction curve in the optical and ultraviolet wavelengths. Such a large ambient density as   n H≳ 1 cm−3  produces too flat an extinction curve to be consistent with the observed extinction curve for SDSS J1048+4637 at z = 6.2. Although the extinction curve is highly sensitive to the ambient density, the hypothesis that the dust is predominantly formed by SNe at z ∼ 6 is still allowed by the current observational constraints. For further quantification, the ambient density should be obtained by some other methods. Finally, we also discuss the importance of our results for observations of high- z galaxies, stressing a possibility of flat extinction curves.  相似文献   

6.
The most recently celebrated cosmological implications of the cosmic microwave background studies with WMAP (2006), though fascinating by themselves, do, however, create some extremely hard conceptual challenges for the present‐day cosmology. These recent extremely refined WMAP observations seem to reflect a universe which was extremely homogeneous at the recombination age and thus is obviously causally closed at the time of the cosmic recombination era. From the very tiny fluctuations apparent at this early epoch the presently observable nonlinear cosmic density structures can, however, only have grown up, if in addition to a mysteriously high percentage of dark matter an even higher percentage of dark energy is admitted as drivers of the cosmic evolution. The required dark energy density, on the other hand, is nevertheless 120 orders of magnitude smaller then the theoretically calculated value. These are outstanding problems of present day cosmology onto which we are looking here under new auspices. We shall investigate in the following, up to what degree a universe simply abolishes all these outstanding problems in case it reveals itself as an universe of constant total energy. As we shall show basic questions like: How could the gigantic mass of the universe of about 1080 proton masses at all become created? – Why is the presently recognized and obviously indispensable cosmic vacuum energy density so terribly much smaller than is expected from quantum theoretical considerations, but nevertheless terribly important for the cosmic evolution? – Why is the universe within its world horizon a causally closed system? –, can perhaps simply be answered, when the assumption is made that the universe has a constant total energy with the consequence that the total mass density of the universe (matter and vacuum) scales with . Such a scaling of matter and vacuum energy abolishes the horizon problem, and the cosmic vacuum energy density can easily be reconciled with its theoretical expectation values. In this model the mass of the universe increases linearly with the world extension Ru and can grow up from a Planck mass as a vacuum fluctuation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

7.
The hypothesis that damped Lyα systems (DLAs) are large galactic discs (Milky Way sized) is tested by confronting predictions of models of the formation and evolution of (large) disc galaxies with observations, in particular the zinc abundance distribution with neutral hydrogen column density found for DLAs. A pronounced mismatch is found, strongly hinting that the majority of DLAs may not be large galactic discs. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
By measuring the decaying shape of the scatter-broadened pulse from the bright distant pulsar PSR J1644−4559, we probe waves scattered at relatively high angles by very small spatial scales in the interstellar plasma, which allows us to test for a wavenumber cutoff in the plasma density spectrum. Under the hypothesis that the density spectrum is due to plasma turbulence, we can thus investigate the (inner) scale at which the turbulence is dissipated. We report observations carried out with the Parkes radio telescope at 660 MHz from which we find strong evidence for an inner scale in the range 70–100 km, assuming an isotropic Kolmogorov spectrum. By identifying the inner scale with the ion inertial scale, we can also estimate the mean electron density of the scattering region to be 5–10 cm−3. This is comparable with the electron density of H  ii region G339.1−0.4, which lies in front of the pulsar, and so confirms that this region dominates the scattering. We conclude that the plasma inside the region is characterized by fully developed turbulence with an outer scale in the range 1–20 pc and an inner scale of 70–100 km. The shape of the rising edge of the pulse constrains the distribution of the strongly scattering plasma to be spread over about 20 per cent of the 4.6 kpc path from the pulsar, but with similarly high electron densities in two or more thin layers, their thicknesses can only be 10–20 pc.  相似文献   

9.
Young T Tauri stars exhibit strong solar-type magnetic activity, with extremely high temperature coronae and energetic flares. In a few systems discovered with Chandra and XMM-Newton there is also evidence for X-ray emission produced by shocks associated with magnetically channeled accretion. A recent 489 ksec Chandra HETG/ACIS-S observation of the classical T Tauri star TW Hydrae has provided a wealth of spectroscopic diagnostics not available in lower signal-to-noise ratio observations. Using line ratios for electron temperature, electron density, and column density we have found that the shock produced by the accelerating material in the accretion stream behaves as predicted by standard theory. However, the properties of the post-shock plasma differ substantially from the predictions of standard 1D shock models (Brickhouse et al. in Astrophys. J. 710:1835, 2010). The accretion process apparently heats the stellar atmosphere up to soft X-ray emitting temperatures, providing hot ions to populate the magnetic corona, in loops, stellar wind, and/or jets. This gas is highly turbulent, as evidenced by non-thermal line broadening. The observed properties of the accretion-fed corona should constrain theoretical models of an accretion-driven dynamo.  相似文献   

10.
Recently, it has been shown that the cataclysmic variable EI UMa should be attributed to intermediate polars on the basis of its X-ray spectrum. However, no short-period oscillations with a high degree of coherence typical of intermediate polars could be detected in this star. Therefore, it was suggested to call it a “hidden” intermediate polar. Using a multichannel photometer and a 70-cm telescope, we performed observations of EI UMa for 60 h. Analysis of the observations has clearly revealed a brightness oscillation with a period of 769.63±0.10 s and a mean semiamplitude of 0· m 008 completely coherent during one month of our observations that was detectable during each of the 13 observing nights. On the basis of this detection, EI UMa should be considered a classical intermediate polar rather than a hidden one. In addition, we have managed to detect the orbital variability of EI UMa for the first time. The orbital light curve is extremely interesting, showing evidence of partial eclipses of the accretion flow.  相似文献   

11.
The tidal theory of the evolution of the lunar orbit has remained inconsistent with the observational values of the apparent secular accelerations of the Sun and Moon since it was first developed by Jeffreys in 1920. Allowance for a changing moment of inertia of the Earth enables the discrepancy to be completely removed if a decrease is occurring at a rate of just about the amount already required by the phase-change theory of the nature of the terrestrial core. The agreement of the resulting theory with the latest determinations of the lunar acceleration increases confidence in the phase-change hypothesis. On the other hand the theory renders it most unlikely that a changing constant of gravitation will prove necessary to account for the observations. On the present theory of itself the Moon would have been extremely close to the Earth only about 109 yr ago which suggests that some additional process may at times have influenced the lunar orbit.  相似文献   

12.
Confronted with microwave background observations by WMAP and with consternating supernova locations in the magnitude–redshift diagram modern cosmology feels enforced to call for cosmic vacuum energy as a necessary cosmological ingredient. Most often this vacuum energy is associated with Einstein’s cosmological constant Λ or with so-called “dark energy”. A positive value of Λ describes an inflationary action on cosmic dynamics which in view of recent cosmological data appears as an absolute need. In this article, however, we question the hypothesis of a constant vacuum energy density since not justifiable on physical grounds. Instead we show that gravitational binding energy of cosmic matter, connected with ongoing structure formation during cosmic expansion, acts similar to vacuum energy, since it reduces the effective gravitating proper mass density. Thus one may be encouraged to believe that actions of cosmic vacuum energy and gravitational binding energy concerning their cosmological effects are closely related to each other, perhaps in some respects even have identical phenomenologies.  相似文献   

13.
NGC 3741: the dark halo profile from the most extended rotation curve   总被引：1，自引：0，他引：1  
We present new H  i observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended H  i disc, which allows us to trace the rotation curve out to unprecedented distances in terms of the optical disc: we reach 42 B -band exponential scalelengths or about 7 kpc. The H  i disc is strongly warped, but the warp is very symmetric. The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. In order to account for the observed features in the data cube, radial motions of the order of 5–13 km s−1 are needed. They are consistent with an inner bar of several hundreds of pc and accretion of material in the outer regions.
The observed rotation curve was decomposed into its stellar, gaseous and dark components. The Burkert dark halo (with a central constant density core) provides very good fits. The dark halo density distribution predicted by the Λ cold dark matter (CDM) theory fails to fit the data, unless NGC 3741 is a 2.5σ exception to the predicted relation between concentration parameter and virial mass and at the same time a high value of the virial mass (though poorly constrained) of  1011 M⊙  . Noticeably, modified Newtonian dynamics (MOND) seems to be consistent with the observed rotation curve. Scaling up the contribution of the gaseous disc also gives a good fit.  相似文献   

14.
The time structure and intensity of OSO-6 observations of EUV bursts were studied in relation to the corresponding 10–1030 Å enhancements deduced from SFD data. Impulsive EUV emissions from lines normally emitted from either the chromosphere or from the chromosphere-corona transition region rise simultaneously with the 10–1030 Å flash, to within the time resolution of the OSO-6 observations. Mg × 625 Å also showed concurrent impulsive emissions and a close intensity relation to the 10–1030 Å enhancement. The observational results are consistent with the hypothesis that most of the EUV radiation is being produced thermally in a region of chromospheric density, which is being heated by collisional losses of nonthermal electrons.  相似文献   

15.
Anomalous X‐ray Pulsars and Soft Gamma‐ray Repeaters are believed to be magnetars: isolated neutron stars powered by the decay of extremely high magnetic fields. We review some of the main results obtained with XMM‐Newton and discuss the prospects for future observations of this small but extremely interesting class of objects. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

16.
The hypothesis of an extended red emission (ERE) in diffuse Galactic light (DGL) has been put forward in 1998 by Gordon, Witt & Friedmann who found that scattered starlight was not enough to explain the amount of DGL in the R band, in some high Galactic latitude directions. This paper re-investigates, for high Galactic latitudes, the brightnesses and colours of DGL, integrated star and galaxy light (ISGL), and of the total extrasolar light (ISGL+DGL) measured by Pioneer. Under the traditional assumption that DGL is forward scattering of background starlight by interstellar dust on the line of sight, ISGL and Pioneer have very close colours, as it is found by Gordon, Witt & Friedmann. Pioneer observations at high |b| thus accept an alternative and simple interpretation, with no involvement of ERE in DGL.  相似文献   

17.
The solution of the hydrogenic Schrödinger equation are given with two boundary conditions imposed on the wave function, for distances of the order of magnitude of one hundred times the Bohr radius from the central nucleus. Thus the shifts and splitting of the H-H26 lines are given which arise from the non-vacant environment. The Inglis-Teller limit is revised since from the shifts it follows that it gives a correct charged particle density only in the case of extremely high electron and ion densities. The gas density is derived from the number of the visible Balmer lines, and usually the widths and the contours but not the coalescence include information on the charged particle density.  相似文献   

18.
One of the largest rotation curve data bases of spiral galaxies currently available is that provided by Persic& Salucci (1995; hereafter, PS) which has been derived by them from unreduced rotation curve data of 965 southern sky spirals obtained by Mathewson, Ford& Buchhorn (1992; hereafter, MFB). Of the original sample of 965 galaxies, the observations on 900 were considered by PS to be good enough for rotation curve studies, and the present analysis concerns itself with these 900 rotation curves. The analysis is performed within the context of the hypothesis that velocity fields within spiral discs can be described by generalized power-laws. Rotation curve data was found to impose an extremely strong and detailed correlation between the free parameters of the power-law model, and this correlation accounts for virtually all the variation in the pivotal diagram. In the process, the analysis reveals completely unexpected structure which indicates that rotation curves can be partitioned into well-defined discrete subclasses.  相似文献   

19.
The hypothesis that large-scale shocks accompanying spiral density waves are the main sources of cosmic-ray electrons for whole galactic disks has been tested utilizing results of 10.7 GHz observations of spiral galaxies. It is suggested that the 10.7 GHz emission of galactic disks is largely controlled by star-forming processes, and that large-scale shocks apparently play a minor role.  相似文献   

20.
For the November 5, 1980 flare it is investigated how the plasma in a large flaring loop responds to the injection of energetic electrons. Observations are compared with the results of a one-dimensional numerical simulation. For the simulation it is assumed that at the time the injection is started, the plasma is in an equilibrium state with a constant pressure along the loop and conductive heating compensated by radiative losses. Especially important for the evolution of the impulsively heated plasma is the penetration depth of the fast electrons compared to the depth of the transition layer. Both parameters are known from the observations. The injected energy is 2.6 × 1011 ergs cm ?2 in 30 s (as derived from the hard X-ray observations) and computations show that the high temperature plasma of the loop responds to it with upward motions of about 50 km s?1, i.e. with velocities much smaller than the ion sound speed (≈ 500km s?1). The heating of the plasma due to the absorption of beam energy can be understood using a constant density approximation. After the heating phase the plasma returns in about 5 min to its initial state by conductive cooling. The downward conducted energy is radiated away in the transition zone. The numerical simulation shows that impulsive heating by non-thermal electrons only does not explain the observed large increase in the density of the loop during the flare. It is therefore required that continuous energy and/or mass input occur after the impulsive phase.  相似文献   

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