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1.
Clovis Jacinto de Matos 《Astrophysics and Space Science》2012,337(1):353-354
The phenomenological nature of a new gravitational type interaction between two different bodies derived from Verlinde’s entropic
approach to gravitation in combination with Sorkin’s definition of Universe’s quantum information content, is investigated.
Assuming that the energy stored in this entropic gravitational field is dissipated under the form of gravitational waves and
that the Heisenberg principle holds for this system, one calculates a possible value for an absolute minimum time scale in
nature
t = \frac1516 \fracL1/2(h/2p) Gc4 ~ 9.27×10-105\tau=\frac{15}{16} \frac{\Lambda^{1/2}\hbar G}{c^{4}}\sim9.27\times10^{-105} seconds, which is much smaller than the Planck time t
P
=(ħG/c
5)1/2∼5.38×10−44 seconds. This appears together with an absolute possible maximum value for Newtonian gravitational forces generated by matter
Fg=\frac3230\fracc7L (h/2p) G2 ~ 3.84×10165F_{g}=\frac{32}{30}\frac{c^{7}}{\Lambda \hbar G^{2}}\sim 3.84\times 10^{165} Newtons, which is much higher than the gravitational field between two Planck masses separated by the Planck length F
gP
=c
4/G∼1.21×1044 Newtons. 相似文献
2.
Xian-Feng Zhao 《Astrophysics and Space Science》2011,332(1):139-144
The effect of the Σ-meson well depth on the gravitational redshift is examined within the framework of relativistic mean field
theory for the baryon octet system. It is found that, for a stable neutron star, the gravitational redshift increases with
the central energy density increase or with the mass increase but decreases as the radius increases. Considering a change
of US(N)U_{\Sigma}^{(N)} from −30 MeV to 30 MeV, for a stable neutron star the gravitational redshift near to the maximum mass increases. In addition,
it is also found that the growth of the US(N)U_{\Sigma}^{(N)} makes the gravitational redshift as a function of M
max /R increase, the higher the US(N)U_{\Sigma}^{(N)} the less the change in the gravitational redshift. 相似文献
3.
Xian-Feng Zhao 《Journal of Astrophysics and Astronomy》2011,32(3):391-399
The influence of the potential well depth US(N)U_{\Sigma}^{(N)} of Σ in nuclear matter on the surface gravitational red-shift of a proto neutron star is examined within the framework of
the relativistic mean field theory for the baryon octet system. It is found that as US(N)U_{\Sigma}^{(N)} increases from −35 MeV to +35 MeV, the surface gravitational red-shift increases and the influence of the negative US(N)U_{\Sigma}^{(N)} on the surface gravitational red-shift is larger than that of the positive ones. Furthermore, the M
max/R and the surface gravitational red-shift corresponding to the maximum mass all increase as the US(N)U_{\Sigma}^{(N)} increases, M
max and R being the maximum mass of the proto neutron star and the corresponding radius respectively. 相似文献
4.
Markus Ackermann 《Astrophysics and Space Science》2007,309(1-4):421-427
The AMANDA-II telescope, operated by the IceCube collaboration, is currently the world’s most sensitive telescope to fluxes
of neutrinos from individual sources. A data sample of 4282 neutrino induced events collected in 1001 days of detector livetime
during the years 2000–2004 have now been analyzed looking for a neutrino signal from point-like sources. A sensitivity to
fluxes of
of d
Φ/dE=1.0×10−10(E/TeV)−2 TeV−1 cm−2s−1 was reached in the energy range between 1.7 TeV and 2.4 PeV. So far no statistically significant localized excess of events
over the background of atmospheric neutrinos has been found, which would be ascribed to a neutrino source. However, the flux
upper limits derived from the non-observation of a signal are comparable to observed fluxes of high energy gamma rays from
blazars and within the range of current models for neutrino emission from selected sources. Possible constraints on these
models are discussed.
相似文献
5.
In this paper we first emphasize why it is important to know the successive zonal harmonics of the Sun's figure with high
accuracy: mainly fundamental astrometry, helioseismology, planetary motions and relativistic effects. Then we briefly comment
why the Sun appears oblate, going back to primitive definitions in order to underline some discrepancies in theories and to
emphasize again the relevant hypotheses. We propose a new theoretical approach entirely based on an expansion in terms of
Legendre's functions, including the differential rotation of the Sun at the surface. This permits linking the two first spherical
harmonic coefficients (J
2 and J
4) with the geometric parameters that can be measured on the Sun (equatorial and polar radii). We emphasize the difficulties
in inferring gravitational oblateness from visual measurements of the geometric oblateness, and more generally a dynamical
flattening. Results are given for different observed rotational laws. It is shown that the surface oblateness is surely upper
bounded by 11 milliarcsecond. As a consequence of the observed surface and sub-surface differential rotation laws, we deduce
a measure of the two first gravitational harmonics, the quadrupole and the octopole moment of the Sun: J
2=−(6.13±2.52)×10−7 if all observed data are taken into account, and respectively, J
2=−(6.84±3.75)×10−7 if only sunspot data are considered, and J
2=−(3.49±1.86)×10−7 in the case of helioseismic data alone. The value deduced from all available data for the octopole is: J
4=(2.8±2.1)×10−12. These values are compared to some others found in the literature.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005238718479 相似文献
6.
From 2000 to 2010, monitoring of radio emission from the Crab pulsar at Xinjiang Observatory detected a total of nine glitches. The occurrence of glitches appears to be a random process as described by previous researches. A persistent change in pulse frequency and pulse frequency derivative after each glitch was found. There is no obvious correlation between glitch sizes and the time since last glitch. For these glitches Δν p and D[(n)\dot]p\Delta\dot{\nu}_{p} span two orders of magnitude. The pulsar suffered the largest frequency jump ever seen on MJD 53067.1. The size of the glitch is ∼6.8×10−6 Hz, ∼3.5 times that of the glitch occurred in 1989 glitch, with a very large permanent changes in frequency and pulse frequency derivative and followed by a decay with time constant ∼21 days. The braking index presents significant changes. We attribute this variation to a varying particle wind strength which may be caused by glitch activities. We discuss the properties of detected glitches in Crab pulsar and compare them with glitches in the Vela pulsar. 相似文献
7.
More than 635 thousand positional observations of planets and spacecraft of various types (mostly radiotechnical ones, 1961–2010)
were used to estimate possible changes in the gravitational constant, Sun’s mass, and semi-major axes of planetary orbits,
as well as the associated value of the astronomical unit. The observations were analyzed based on the EPM2010 ephemerides
constructed at the Institute of Applied Astronomy (Russian Academy of Sciences) in a post-Newtonian approximation as a result
of simultanious numerical integration of the equations of motion of nine major planets, the Sun, the Moon, asteroids, and
trans-Neptunian objects. The heliocentric gravitational constant GM
⊙ was found to vary with a rate of (GṀ
⊙/GM
⊙ = (−5.0 ± 4.1)) × 10−14 per year (at the 3σ level). The positive secular changes in the semimajor axes ȧ
i
/a
i
were found for Mercury, Venus, Mars, Jupiter, and Saturn provided by high-precision observations. These changes also correspond
to the decrease in the heliocentric gravitational constant. The changing of GM
⊙, itself is probably caused by the loss of the mass M
⊙ of the Sun due to its radiation and solar wind; these effects are partly compensated by the material falling onto the Sun.
Allowing for the maximum bounds on the possible change in the Sun’s mass M
⊙, it has been found from the change obtained in GM
⊙ that the annual change Ġ/G of the gravitational constant G falls within the interval −4.2 × 10−14 < ȧ/G < +7.5 × 10−14 with a 95% probability. The astronomical unit (AU) is connected by its definition only with the heliocentric gravitational
constant. The decrease of GM
⊙ obtained in this paper should correspond to a secular decrease in the AU. It is shown, however, that the modern level of
accuracy does not allow us to determine a change in the AU. The attained posibility of determining changes in GM
⊙ using high-accuracy observations encourages us to have a relation between GM
⊙ and the AU fixed for a certain moment in time, since it is inconvenient to have a time-dependent length for the AU. 相似文献
8.
We present multi-colour CCD observations of the low-temperature contact binaries, V453 Mon and V523 Cas. Their light curves
are modelled to determine a new set of stellar and orbital parameters. Analysis of mid-eclipse times yields a new linear ephemeris
for both systems. A period decrease (dP/dt=2.3×10−7 days/yr) in V453 Mon is discovered. V523 Cas, however, is detected to show a period increase (dP/dt=9.8×10−8 days/yr) because of the mass transfer of a rate of 1.1×10−7 M⊙ yr−1, from a less massive donor. Using these findings we can determine the physical parameters of the components of V523 Cas to
be M
1=0.76 (3)M
⊙, M
2=0.39 (2)M
⊙, R
1=0.74 (2)R
⊙, R
2=0.55 (2)R
⊙, L
1=0.19 (3)L
⊙, L
2=0.14 (3)L
⊙, and the distance of system as 46(9) pc. 相似文献
9.
The ionizing star BD+60°2522 is known as the central star of Bubble Nebulae NGC 7635—wind-blown bubble created by the interaction
of the stellar wind of BD+60°2522 (O6.5 IIIef, V=8.7 mag, mass loss rate 10−5.76
M
⊙/year) with the ambient interstellar medium. From the evolutionary calculations for the star with mass loss and overshooting,
we find that the initial mass of the star is 60M
⊙, its present age is 2.5×106 years, and the present mass is 45M
⊙. 相似文献
10.
V. M. Chechetkin S. S. Gershtein V. S. Imshennik L. N. Ivanova M. Yu. Khlopov 《Astrophysics and Space Science》1980,67(1):61-97
The present work studies the hydrodynamic process of thermonuclear explosion of hydrostatic equilibrium, degenerate carbon-oxygen
cores withM
C=1.40M
⊙ with different values of central densityϱ
c
within the interval 2 × 109 <ϱ
c
< 3 × 1010 g cm−3. The initial temperature distribution has been determined by the preceding thermal stage of explosion. The calculations successively
include the kinetics of thermonuclear burning, the kinetics of β-processes, and neutrino energy losses. By considering the
neutrino mechanism of heating and carbon ignition we obtained in our numerical hydrodynamic calculations two characteristic
versions of the development of an explosion: (a) at 2 × 109 <ϱ
c
< 9 × 109 g cm−3 there is disruption of the whole star with either complete or partial burning of the carbon and a 1050–1051 erg kinetic energy; and (b) at 9 × 109 <ϱ
c
< 3 × 1010 g cm−3 the stellar core collapses into a neutron star with partial outburst of the outer envelope with a smaller kinetic energy
of 1049–1050 erg. The paper proposes and details a hypothesis (the scenario of supernovae and the formation of neutron stars) on the first
version of explosion, corresponding to SNII, and on the second, supplemented by some mechanism of slow energy release into
the envelope expelled from the newly formed neutron star, corresponding to SNI. On the basis of the proposed hypothesis a
satisfactory agreement with the observed masses and energies of the supernovae envelope, their light curves and spectra, as
well as with the data on their chemical composition has been obtained. For this agreement we must assume that type I pre-supernovae
are almost bare compact carbon-oxygen stellar cores, and that type II presupernovae are red supergiants. It is most probable
that the evolution of type I pre-supernovae occurs in close binaries while the evolution of type II pre-supernovae seems to
be very similar to the evolution of a single star. 相似文献
11.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes,
proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to
the Galactic center R
0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
For R
0 = 8 kpc, we have found the circular velocity of the Sun to be V
0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to
the local standard of rest and the component (V
⊙)LSR depend significantly on the Sun’s phase in the spiral wave. 相似文献
12.
In the present article, a family of static spherical symmetric well behaved interior solutions is derived by considering the
metric potential g
44=B(1−Cr
2)−n
for the various values of n, such that (1+n)/(1−n) is positive integer. The solutions so obtained are utilised to construct the heavenly bodies’ like quasi-black holes such
as white dwarfs, neutron stars, quarks etc., by taking the surface density 2×1014 gm/cm3. The red shifts at the centre and on the surface are also computed for the different star models. Moreover the adiabatic
index is calculated in each case. In this process the authors come across the quarks star only. Least and maximum mass are
fond to be 3.4348M
Θ and 4.410454M
Θ along with the radii 21.0932 km and 23.7245 km respectively. 相似文献
13.
The results of two color photometry of active close binary CN And are presented and analyzed. The light curves of the system
are obviously asymmetric, with the primary maximum brighter than the secondary maximum, which is known as the O’Conell effect.
The most plausible explanation of the asymmetry is expected to be due to spot activity of the primary component. For the determination
of physical and geometrical parameters, the most new version of W-D code was used, but the presence of asymmetry prevented
the convergence of the method when the whole light curves were used. The solutions were obtained by applying mode 3 of W-D
code to the first half of the light curves, assuming synchronous rotation and zero eccentricity. Absolute parameters of the
system were obtained from combining the photometric solution with spectroscopic data obtained from radial velocity curve analysis.
The results indicate the poor thermal contact of the components and transit primary minimum. Finally the O-C diagram was analyzed.
It was found that the orbital period of the system is changing with a rate ofd P/dt = − 2.2(6) × 10−10 which corresponds to mass transfer from more massive component to less massive with the rate ofd M/dt ∼4.82 × 10−8
M
sun/year. 相似文献
14.
A closed form solution to the minimum DVtot2{\Delta V_{\rm tot}^2} Lambert problem between two assigned positions in two distinct orbits is presented. Motivation comes from the need of computing
optimal orbit transfer matrices to solve re-configuration problems of satellite constellations and the complexity associated
in facing these problems with the minimization of DVtot{\Delta V_{\rm tot}}. Extensive numerical tests show that the difference in fuel consumption between the solutions obtained by minimizing DVtot2{\Delta V_{\rm tot}^2} and DVtot{\Delta V_{\rm tot}} does not exceed 17%. The DVtot2{\Delta V_{\rm tot}^2} solution can be adopted as starting point to find the minimum DVtot{\Delta V_{\rm tot}}. The solving equation for minimum DVtot2{\Delta V_{\rm tot}^2} Lambert problem is a quartic polynomial in term of the angular momentum modulus of the optimal transfer orbit. The root selection
is discussed and the singular case, occurring when the initial and final radii are parallel, is analytically solved. A numerical
example for the general case (orbit transfer “pork-chop” between two non-coplanar elliptical orbits) and two examples for
the singular case (Hohmann and GTO transfers) are provided. 相似文献
15.
Stochastic temperatures and turbulence are characterized by average velocities u
th
and < u
turb
> ≡ u
0 and fluctuations u¢th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl¢D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <Hλ>. Usually, only the average velocities u
th
and u
0 are taken into account in photospheric models and these yield the Doppler width DlD(0) \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl¢D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < αλ > is larger than the usual αλ, which depends only on the average velocities u
th
and u
0. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical
effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the
average level of fluctuations in the Doppler width, h =
á | Dl¢D |
ñ