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1.
The focussing of gravitational radiation by the interior and exterior gravitational field of a Newtonian gravitational lens is considered. A graphical method for determining the caustic structure of a Newtonian gravitational lens is presented and the caustic structure of a solar type gravitational lens is discussed. Estimates of the amplitude magnification in the caustic region indicate that waves with frequencies less than a critical cutoff frequency ω c are not amplified significantly. For a lens of massM this cutoff frequency is ω c ≈(10-1πM)-1; for the Sun ω c ≈104s-1. Work supported in part by National Science Foundation Grant PHY78-05368.  相似文献   

2.
A. H. Sadoyan 《Astrophysics》2006,49(2):211-217
This article discusses the gravitational radiation of rotating and oscillating stellar configurations with an incompressible fluid equation of state. The method used here makes it possible to determine the frequencies and amplitudes of the gravitational waves for arbitrary values of the central densities. At the densities corresponding to neutron stars, the major parameters of the gravitational radiation are consistent with previous results from more realistic models. Depending on the central density, stellar configurations with an incompressible fluid can emit gravitational waves over a wide range of frequencies, from 10−2 to 104 Hz. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 243–250 (May 2006).  相似文献   

3.
The evolution of the spectrum of SN1987a is traced from 1987 February 26 to March 31. Based on the low-resolution spectroscopic data we identify the lines of H, He I, Na I, Fe II, Sc II, Ca II which are known to be present in Type II Supernovae, and also present evidence for the existence of lines of Mg I, CaI, O I, and N I. We discuss the evolution of the Hα profile, and draw attention to its complex structure around March 30. Close to the rest wavelength of Ha a double-peaked structure appeared in the profile with a peak-to-peak separation of ∼ 1400 km s−1, suggestive of an expanding shell or disc of gas. Using the available broadband photometric information, we also trace the evolution of the photosphere of SN1987a assuming that it radiates like a supergiant.  相似文献   

4.
We consider the evolution of a neutron star binary system under the effect of two factors: gravitational radiation and mass transfer between the components. Gravitational radiation is specified under the justified assumption of a circular orbit and point masses and in the approximation of a weak gravitational field at nonrelativistic velocities of the binary components. During the first evolutionary phase determined only by gravitational radiation, the neutron stars approach each other according to a simple analytical solution. The second evolutionary phase begins at the time of Roche-lobe filling by the low-mass component, when the second factor, mass transfer as a result of mass loss by the latter, also begins to affect the evolution. Under the simplest assumptions of conservative mass transfer and exact equality between the Roche-lobe radius and the radius of the low-mass neutron star, it is still possible to extend the analytical solution of the problem of evolution to its second phase. We present this complete solution at both phases and, in particular, give theoretical light curves of gravitational radiation that depend only on two dimensionless parameters (m t and δ 0). Based on the solution found, we analyze the theoretical gravitational signals from SN 1987A; this analysis includes the hypothesis about the rotational explosion mechanism for collapsing supernovae.  相似文献   

5.
We examine the possible emission of gravitational waves from white dwarfs undergoing self-similar oscillations driven by the energy released during relaxation of their differential rotation. Two distributions of the initial angular momentum are considered. It is assumed that 1% of the energy dissipated by a rotating white dwarf is converted into the energy of self-similar oscillations and, therefore, into gravitational radiation. The relative amplitude of the gravitational radiation from an isolated white dwarf at a distance of 50 pc is found to be less than 10−27. The emission from the galactic population of white dwarfs may create a background which overlaps the random cosmological background of gravitational radiation for the improved decihertz detectors currently being proposed. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 231–242 (May 2006).  相似文献   

6.
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   

7.
Most current supernova theories state that this phenomenon lasts a few seconds and ends with a bigfinal explosion.However, these theories do not take into account several experimental results obtained with neutrino and gravitational wave detectors during the explosion of SN1987A, the only supernova observed in a nearby galaxy in modern age. According to these experimental results the phenomenon is much more complex that envisaged by current theories, and has a duration of several hours. Indeed, SN1987A exploded on February 23, 1987, and two neutrino bursts, separated by 4.7 hours were detected: the first one at 2h 52m UT and the second one at 7h 35m UT. Furthermore, correlations between the neutrino and two gravitational wave detectors, ignored by most of the scientific community, were observed during the longer collapse time. Since the current standard theories, based on some rough simplifications, are a clear example of an Aristotelian attitude, still present in our days, we believe that a more Galilean attitude is necessary, being the only correct way for the progress of science.  相似文献   

8.
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9.
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical constraints for the total supernova (SN) explosion energy E sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s SN is a type Ia SN we determine for any given explosion energy E sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π 0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc.  相似文献   

10.
Self-consistent system of spinor, scalar and BI gravitational fields in presence of magneto-fluid and Λ term is considered. Assuming that the expansion of the BI universe is proportional to the σ1 component of the shear tensor, exact solutions for the metric functions, as well as for scalar and spinor fields are obtained. For a non-positive Λ, the initially anisotropic space–time becomes isotropic one in the process of expansion; whereas for Λ > 0, an oscillatory mode of expansion of the BI model occurs. PACS numbers: 03.65.Pm and 04.20.Ha  相似文献   

11.
The masses and the evolutionary states of the progenitors of core-collapse supernovae are not well constrained by direct observations. Stellar evolution theory generally predicts that massive stars with initial masses less than about 30M⊙ should undergo core-collapse when they are cool M-type supergiants. However the only two detections of a SN progenitor before explosion are SN1987A and SN1993J, and neither of these was an M-type supergiant. Attempting to identify the progenitors of supernovae is a difficult task, as precisely predicting the time of explosion of a massive star is impossible for obvious reasons. There are several different types of supernovae which have different spectral and photometric evolution, and how exactly these are related to the evolutionary states of the progenitor stars is not currently known. I will describe a novel project which may allow the direct identification of core-collapse supernovae progenitors on pre-explosion images of resolved, nearby galaxies. This project is now possible with the excellent image archives maintained by several facilities and will be enhanced by the new initiatives to create Virtual Observatories, the earliest of which (astrovirtel) is already producing results. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

12.
Modern ground-based gravitational-wave antennas designed to detect bursts of gravitational radiation from astrophysical catastrophes are described. Basic antenna characteristics, peculiarities of the noise background in antennas from various sources, and methods of their suppression are presented. The contribution from cosmic rays to the background is estimated. New programs of searching for low-frequency gravitational waves and potentialities for increasing the sensitivity of antennas of new types are briefly described.  相似文献   

13.
A new paradigm in cosmology is presented: A geometrical phase transition from the Minkowski space to an anti-deSitter space at its maximum of extension instead of a big bang with inflation. This scenario implies an open universe with a negative cosmological constant which replaces completely the cold dark matter in galaxy clusters. Baryonic matter and radiation are created from the gravitational field over a very long period of about 30 billion years. The contracting universe runs then after a further period of 13 billion years through a minimum with T max ≃ 1.8 × 1012 K and a particle density n max ≃ 5 × 1038 cm-3 due to Hagedorn’s theory of a hadron gas. After the run through the minimum the universe expands like a big bang universe and reaches due to the negative cosmological constant after 44 billion years its maximal extension. Then it contracts again, and so on: An open ever-oscillating universe.  相似文献   

14.
The properties of the neutrino burst generated by massive 1.5–2M collapsing stellar iron-oxygen cores are discussed. Special attention is given to the neutrino heat conductivity theory which allows us to calculate the transport of neutrinos through the collapsing stellar core up to the formation and during the first seconds of cooling of a hot hydrostatic neutron star. The theoretical predictions seem to be in good agreement with both the KAMIOKANDE II and IMB data on the neutrino burst detected from SN 1987A. The most reliable constraint on the neutrino rest mass is shown to bem v <20–30eV, while the safest upper limit on the neutrino magnetic moment, µ v < 10–11 Bohr magnetons, results rather from the cooling of white dwarfs than from the SN 1987A neutrino data.Presented to the 13th International Conference Neutrino-88, Boston, U.S.A., 5–11 June, 1988.  相似文献   

15.
The gravitational radiation of n = 1 polytropes undergoing quasiradial pulsations is examined. The intensity of the gravitational radiation and the gravitational wave amplitudes are calculated for polytropic models of white dwarfs and neutron stars when the energy of rotation of the object serves as the source of the radiated energy. Calculations of h0 show that objects with a polytropic equation of state can describe the expected gravitational radiation from white dwarfs and neutron stars. The gravitational radiation of polytropic models of galactic nuclei and quasars is also examined. These objects can create a high enough background of gravitational radiation at frequencies of 10-8–10-11 Hz for gravitational wave detectors operating in this frequency range. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 603–612 (November 2005).  相似文献   

16.
Three decades have passed since the supernova SN 1987A was observed in the Large Magellanic Cloud, inside which the product is most likely a neutron star (NS) formed in the core collapse explosion.Although lots of observations with sensitive radio telescopes have taken place, astronomers have not yet detected any evidence for a radio pulsar around the remnant of 1987A. To investigate pulsars inside the SN remnants, we calculate the cut-off oscillation frequency of the plasma around the presumed NS inside SN1987A, as shown to be about 33 GHz at present (2018 CE), which is much higher than the favorite “searching window” (e.g. L-band ∼ 1.4 GHz) of radio pulsar surveys that have been commonly exploited by astronomers. Since radio waves with frequencies lower than the plasma cut-off frequency cannot penetrate the SN remnant media, we suggest that astronomers use higher frequency bands to search for a pulsar in SN 1987A.Furthermore, with the expansion of SN remnant media, we find that the plasma cut-off frequency can decay to the L-band (1.4 GHz) in the future. The strategy of finding a pulsar of SN 1987A is that either the high frequency bands of radio telescopes, or the high energy detections at Gamma-ray and X-ray bands by space satellites are applied.  相似文献   

17.
It is shown that in the most general version of the bimetric scalar-tensor theory of gravitation, a spherically symmetric vacuum gravitational field is static if the gravitational scalar does not depend on time. This result is generalized to certain cases in which a source is present, including an electromagnetic field. Both branches of solutions with a variable and a constant scalar field are considered. Translated from Astrofizika, Vol. 40, No. 2, pp. 281–290, April–June, 1997.  相似文献   

18.
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   

19.
Arrival-time analysis for a millisecond pulsar   总被引：1，自引：0，他引：1  
Arrival times from a fast, quiet pulsar can be used to obtain accurate determinations of pulsar parameters. In the case of the millisecond pulsar, PSR 1937 + 214, the remarkably small rms residual to the timing fit indicates that precise measurements of position, proper motion and perhaps even trigonometric parallax will be possible (Backer 1984). The variances in these parameters, however, will depend strongly on the nature of the underlying noise spectrum. We demonstrate that for very red spectrai.e. those dominated by low-frequency noise, the uncertainties can be larger than the present estimates (based on a white-noise model) and can even grow with the observation period. The possibility of improved parameter estimation through prewhitening’ the data and the application of these results to other pulsar observations are briefly discussed. The post-fit rms residual of PSR 1937 + 214 may be used to limit the energy density of a gravitational radiation background at periods of a few months to years. However, fitting the pulsar position and pulse-emission times filters out significant amounts of residual power, especially for observation periods of less than three years. Consequently the present upper bound on the energy density of gravitational waves Ωg <3 × 10-4 R Μs 2 , though already more stringent than any other available, is not as restrictive as had been previously estimated. The present limit is insufficient to exclude scenarios which use primordial cosmic strings for galaxy formation, but should improve rapidly with time. On leave from Raman Research Institute, Bangalore 560080, India.  相似文献   

20.
Supernova Remnants (SNRs) are the most likely sources of the galactic cosmic rays up to energies of about 1015 eV/nuc. The large scale shock waves of SNRs are almost ideal sites to accelerate particles up to these highly non-thermal energies by a first order Fermi mechanism which operates through scattering of the particles at magnetic irregularities. In order to get an estimate on the total amount of the explosion energy E SNconverted into high energy particles the evolution of a SNR has to be followed up to the final merging with the interstellar medium. This can only be done by numerical simulations since the non-linear modifications of the shock wave due to particle acceleration as well as radiative cooling processes at later SNR stages have to be considered in such investigations. Based on a large sample of numerical evolution calculations performed for different ambient densities n ext, SN explosion energies, magnetic fields etc. we discuss the final ‘yields’ of cosmic rays at the final SNR stage where the Mach number of the shock waves drops below 2. At these times the cosmic rays start to diffuse out of the remnant. In the range of external densities of10-2 ≤ n ext/[cm-3] ≤ 30 we find a the total acceleration efficiency of about 0.15 E SN with an increase up to 0.24 E SN at maximum for an external density of n ext = 10 cm-3. Since for the larger ambient densities radiative cooling can reduce significantly the total thermal energy content of the remnant dissipation of Alfvén waves can provide an important heating mechanism for the gas at these later stages. From the collisions of the cosmic rays with the thermal plasma neutral pions are generated which decay subsequently into observable γ-rays above 100 MeV. Hence, we calculate these γ-ray luminosities of SNRs and compare them with current upper limits of ground based γ-raytelescopes. The development of dense shells due to cooling of the thermal plasma increases the γ-ray luminosities and e.g. an external density of n ext = 10 cm-3 with E SN = 1051 erg can lead to a γ-ray flux above 10-6 ph cm-2 s-1 for a remnant located at a distance of 1 kpc. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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