1,721,010 research outputs found
Dark energy or local acceleration?
No full textWe find that an observer with a suitable acceleration relative to the frame comoving with the cosmic fluid, in the context of the FRW decelerating universe, measures the same cosmological redshift as in the ΛCDM model. The estimated value of this acceleration is β ≃ 1.4 × 10−9 m/s2. We discuss two different scenarios, a motion with constant acceleration and a helical motion (although other alternatives are also likely), and we show that the final value of the peculiar velocity is sensitive to the type of the peculiar motion
Underlining some aspects of the equivalence principle
No full textWe want to shed light on some discussed aspects of the principle of equivalence. We consider two different phases in the evolution of the principle. We pay attention to the fact that some textbooks do not dwell on the mathematical meaning of 'locally flat spacetime', which can confuse students and, occasionally, can also lead to misinterpretations. For example, the non-eliminability of tidal forces, not even locally, may suggest that the equivalence principle is wrong. By contrast, we want to show that this is in perfect agreement with the Einstein geometrical interpretation of spacetime. Finally, in order to check the approximations used in the Gedankenexperiment of an elevator, we estimate explicitly the magnitude of the deflection of light and the effects of tidal forces in a 'real lift'
Some remarks about the effects of acceleration on time dilation in experiments with a Mössbauer source
No full textWe suggest an alternative interpretation of the experimental results obtained studying the circular accelerated motion of a rotor that plays the role of an absorber of photons emitted by a Mössbauer source. A spectral shift was discovered and interpreted in the light of a generalized relativistic theory with maximal acceleration. Alternatively we propose that the shift could be explained by a time-dependent Doppler effect in standard relativity
Little Perturbations Grow up...Without Dark Matter
No full textOne of the main problems of Cosmology is to conciliate the initial homogeneity and isotropy of the Universe with the subsequent formation of galaxies. In order to find a solution, the Cosmic Microwave Radiation was deeply investigated and a very small anisotropy was finally detected and indicated as the cause of the structure formation. In the standard cosmological theory it is often demonstrated that the linear perturbations do not evolve in a way able to explain the large scale structure of the today observed Universe. In our paper we want to give a simple counterexample showing that it would be possible the formation of a clustered structure in the Universe without the help of the existence of Dark Matter. © 2011 Springer Science+Business Media, LLC
A A Hertzsprung-Russell-like diagram for galaxies: the M_BH versus M_G sigma^2 relation
No full textWe show that the relation between the mass of supermassive black holes located in the center of the host galaxies and the kinetic energy of random motions of the corresponding bulges is a useful tool to study the evolution of galaxies. In the form log_10(M_∙ )=b+m log_10(M_Gσ^2/c^2), the best-fitting results for a sample of 64 galaxies of various morphological types are the slope m = 0.80 ± 0.03 and the normalization b = 4.53 ± 0.13. We note that, in analogy with the Hertzsprung-Russell diagram for stars, each morphological type of galaxy generally occupies a different area in the M <SUB>∙</SUB>-(M <SUB>G</SUB>σ<SUP>2</SUP>)/c <SUP>2</SUP> plane. In particular, we find elliptical galaxies in the upper part of the line of best fit, the lenticular galaxies in the middle part, and the late-type galaxies in the lower part, the mass of the central black hole giving an estimate of the age, whereas the kinetic energy of the stellar bulges is directly connected with the temperature of each galactic system. Finally, the values of the linear correlation coefficient, the intrinsic scatter, and the χ<SUP>2</SUP> obtained by using the M <SUB>∙</SUB>-M <SUB>G</SUB>σ<SUP>2</SUP> relation are better than the corresponding ones obtained from the M <SUB>∙</SUB>-σ or the M <SUB>∙</SUB>-M <SUB>G</SUB> relation
A fundamental equation for supermassive black holes
No full textWe developed a theoretical model that is able to give a common origin to the correlations between the mass Mââ¬Â¢ of supermassive black holes and the mass, velocity dispersion, kinetic energy and momentum parameter of the corresponding host galaxies. Our model is essentially based on the transformation of the angular momentum of the interstellar material, which falls into the black hole, into the angular momentum of the radiation emitted in this process. In this framework, we predict the existence of a relation of the form Mââ¬Â¢ âË ReÃÆ3, which is confirmed by the experimental data and can be the starting point to understand the other popular scaling laws too
The scaling relation between the mass of supermassive black holes and the kinetic energy of random motions of the host galaxies
No full textContext. Thanks to the improved angular resolution of modern telescopes and kinematic models, the existence of supermassive black holes (SMBHs) in the inner part of galaxies, regardless their morphology and nuclear activity, has been established on quite solid grounds. A possible correlation between the mass of SMBHs (M<SUB>∙</SUB>) and the evolutionary state of their host galaxies is expected and is currently under a heated debate. <BR /> Aims: Based on the recent 2D decomposition of 3.6 μm Spitzer/IRAC images of local late- and early-type galaxies with M<SUB>∙</SUB> measurements, we investigated various scaling laws, studying what is the best predictor of the mass of the central black holes, that is the one with the lowest value of intrinsic scatter. In particular, we focused on the M<SUB>∙</SUB> - M<SUB>G</SUB>σ<SUP>2</SUP> law, that is the relation between the mass of SMBHs and the kinetic energy of random motions of the corresponding host galaxies, M<SUB>G</SUB> is the mass and σ the velocity dispersion of the host galaxy (bulge). <BR /> Methods: In order to find the best fit for each of the scaling laws examined, we performed a least-squares regression of M<SUB>∙</SUB> on x for the considered sample of galaxies, x being a whatever known parameter of the galaxy bulge. For this purpose, we made use of both the linear regression LINMIX_ERR and FITEXY methods. <BR /> Results: Our analysis shows that M<SUB>∙</SUB> - M<SUB>G</SUB>σ<SUP>2</SUP> law fits the examined experimental data successfully as much as the other known scaling laws (all correlations have similar intrinsic scatters within the errors) and shows a value of χ<SUP>2</SUP> (estimated by FITEXY) better than the others, a result which is consistent with previous determinations at shorter wavelengths. This means that a combination of σ and M<SUB>G</SUB> (or R<SUB>e</SUB>) could be necessary to drive the correlations between M<SUB>∙</SUB> and other bulge properties. This issue has been investigated by a careful, although not fully conclusive, analysis of the residuals of the various relations. <BR /> Conclusions: In order to avoid rushed conclusions on galaxy activity and evolution, the indirect inferring of the masses of the supermassive black holes from the kinetic energy of random motions via the M<SUB>∙</SUB> - M<SUB>G</SUB>σ<SUP>2</SUP> relation should be considered, especially when applied to higher redshift galaxies (z > 0.01). This statement is suggested by a reanalysis of Sloan Digital Sky Survey (SDSS) data used to study the black hole growth in the nearby Universe. By adopting the M<SUB>∙</SUB> - M<SUB>G</SUB>σ<SUP>2</SUP> relation instead of the M<SUB>∙</SUB> - σ relation, a radio-quiet/radio-loud dichotomy appears in the SMBH mass distribution of the corresponding SDSS early-type AGN galaxies
- …
