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1.
A broad sample of computed realistic equations of state of superdense matter with a quark phase transition is used to construct a series of models of neutron stars with a strange quark core. The integral characteristics of the stellar configurations are obtained: gravitational mass, rest mass, radius, relativistic moment of inertia, and red shift from the star's surface, as well as the mass and radius of the quark core within the allowable range of values for the central pressure. The parameters of some of the characteristic configurations of the calculated series are also given and these are studied in detail. It is found that a new additional region of stability for neutron stars with strange quark cores may exist for some models of the equation of state. 相似文献
2.
We investigate the influence of the following parameters on the crust properties of strange stars: the strange quark mass
(m
s), the strong coupling constant (αc) and the vacuum energy density (B). It is found that the mass density at the crust base of strange stars cannot reach the neutron drip density. For a conventional
parameter set of m
s=200 MeV, B
1/4 = 145 MeV and αc = 0.3, the maximum density at the crust base of a typical strange star is only 5.5 × 1010 gcm-3, and correspondingly the maximum crust mass is 1.4 ×10-6 M⊙. Subsequently, we present the thermal structure and the cooling behavior of strange stars with crusts of different thickness,
and under different diquark pairing gaps. Our work might provide important clues for distinguishing strange stars from neutron
stars. 相似文献
3.
Equilibrium models of differentially rotating nascent neutron stars are constructed, which represent the result of the accretion-induced collapse of rapidly rotating white dwarfs. The models are built in a two-step procedure: (1) a rapidly rotating pre-collapse white dwarf model is constructed; (2) a stationary axisymmetric neutron star having the same total mass and angular momentum distribution as the white dwarf is constructed. The resulting collapsed objects consist of a high-density central core of size roughly 20 km, surrounded by a massive accretion torus extending over 1000 km from the rotation axis. The ratio of the rotational kinetic energy to the gravitational potential energy of these neutron stars ranges from 0.13 to 0.26, suggesting that some of these objects may have a non-axisymmetric dynamical instability that could emit a significant amount of gravitational radiation. 相似文献
4.
Models of strange quark stars with a crust consisting of atomic nuclei and degenerate electrons, maintained by an electrostatic
barrier at the surface of the strange quark matter, are investigated for a realistic range of parameters of the MIT bag model.
The density at which neutrons escape from nuclei, ρ = ρdrip, is taken as the maximum possible boundary density of the crust. Series of strange stars are calculated as a function of
central density. Configurations with masses of 1.44 and 1.77 M{ie330-1} and a gravitational redshift Zs = 0.23, corresponding to the best-known observational data, are investigated. The presence of a crust results in the existence
of a minimum mass for strange stars, and also helps to explain the glitch phenomenon of pulsars within the framework of the
existence of strange quark matter.
Translated from Astrofizika, Vol. 42, No. 3, pp. 439–448, July–September, 1999. 相似文献
5.
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
6.
《天文和天体物理学研究(英文版)》2015,(6)
Using a realistic equation of state(EOS) of strange quark matter, namely,the modified bag model, and considering the constraints on the parameters of EOS by the observational mass limit of neutron stars, we investigate the r-mode instability window of strange stars, and find the same result as in the brief study of Haskell,Degenaar and Ho in 2012 that these instability windows are not consistent with the spin frequency and temperature observations of neutron stars in low mass X-ray binaries. 相似文献
7.
We consider a simple qualitative model to estimate the time-scale forneutronstrange matter decay in dense stellar environments. It is argued that a large mismatch between the former and the microscopic weak interaction time-scale suggests that a dual population of both types of compact objects is unlikely. Assuming the correctness of the strange matter hypothesis all of them should be strange stars. If one instead postulates accretion as the decisive feature for the conversion, a consideration of neutron stars structure indicates a fairly narrow range for the onset of the critical density before the corresponding Chandrasekhar mass is achieved. 相似文献
8.
9.
This is a study of the stability of strange dwarfs, superdense stars with a small self-confining core (M
core
< 0.02 M⊙) containing strange quark matter and an extended crust consisting of atomic nuclei and degenerate electron gas. The mass
and radius of these stars are of the same orders as those of ordinary white dwarfs. It is shown that any study of their stability
must examine the dependence of the mass on two variables, which can, for convenience, be taken to be the rest mass (total
baryon mass) of the quark core and the energy density ρ
tr
of the crust at the surface of the quark core. The range of variation of these quantities over which strange dwarfs are stable
is determined. This region is referred to as the stability valley for strange dwarfs. The mass and radius from theoretical
models of strange dworfs are compared with observational data obtained through the HIPPARCOS program and the most probable
candidate strange dwarfs are identified. 相似文献
10.
Strange stars are compact objects similar to neutron stars composed of strange matter. This paper investigates the observational effects of the strong interaction between quarks. We believe: 1) that the conversion of a neutron star to a strange star is a large “period glitch” which is determined by the strong interaction; 2) that the strong interaction results in effective damping of oscillation of hot strange stars, which could be a new mechanism of driving supernova explosions; 3) that the strong interaction increases the difference in rotation between strange and neutron stars under high temperatures, making the minimum period for strange stars lower than that for neutron stars. 相似文献
11.
We study universality in gravitational waves emitted from non-rotating neutron stars characterized by different equations of state (EOSs). We find that the quasi-normal mode frequencies of such waves, including the w -modes and the f -mode, display similar universal scaling behaviours that hold for most EOSs. Such behaviours are shown to stem from the mathematical structure of the axial and the polar gravitational wave equations, and the fact that the mass distribution function can be approximated by a cubic–quintic polynomial in the radius. As a benchmark for other realistic neutron stars, a simple model of neutron stars is adopted here to reproduce the pulsation frequencies and the generic scaling behaviours mentioned above with good accuracy. 相似文献
12.
A. I. Chugunov 《Monthly notices of the Royal Astronomical Society》2006,371(1):363-368
We study acoustic oscillations (eigenfrequencies, velocity distributions, damping times) of normal crusts of strange stars. These oscillations are very specific because of huge density jump at the interface between the normal crust and the strange matter core. The oscillation problem is shown to be self-similar. For a low (but non-zero) multipolarity l , the fundamental mode (without radial nodes) has a frequency of ∼300 Hz and mostly horizontal oscillation velocity; other pressure modes have frequencies ≳20 kHz and almost radial oscillation velocities. The latter modes are similar to radial oscillations (having approximately the same frequencies and radial velocity profiles). The oscillation spectrum of strange stars with crust differs from the spectrum of neutron stars. If detected, acoustic oscillations would allow one to discriminate between strange stars with crust and neutron stars and constrain the mass and radius of the star. 相似文献
13.
The energetics involved in the formation of neutron stars in close binaries as a result of supernova explosions are considered. The gravitational binding energy of the neutron star must find proper outlets. The mass ejection and cosmic ray particles can carry away only a small fraction (up to a few per cent) of this energy. Most of the binding energy goes into rotational kinetic energy, gravitational radiation and neutrino emissions. A scenario is considered in which most of the gravitational binding energy goes into rotational kinetic energy and is, ultimately, radiated away as gravitational waves. 相似文献
14.
Matthew R. Edwards 《Astrophysics and Space Science》2012,339(1):13-17
Due to the Hubble redshift, photon energy, chiefly in the form of CMBR photons, is currently disappearing from the universe
at the rate of nearly 1055 erg s−1. An ongoing problem in cosmology concerns the fate of this energy. In one interpretation it is irretrievably lost, i.e., energy is not conserved on the cosmic scale. Here we consider a different possibility which retains universal energy conservation.
Treating gravitational potential energy conventionally as ‘negative’, it has earlier been proposed that the Hubble shift flips
positive energy (photons) to negative energy (gravitons) and vice versa. The lost photon energy would thus be directed towards gravitation, making gravitational energy wells more negative. Conversely, within astrophysical bodies, the flipping of gravitons
to photons would give rise to a ‘Hubble luminosity’ of magnitude −UH
0, where U is the internal gravitational potential energy of the object. Preliminary evidence of such an energy release is presented
in bodies ranging from planets, white dwarfs and neutron stars to supermassive black holes and the visible universe. 相似文献
15.
Jinho Kim Hee Il Kim Hyung Mok Lee 《Monthly notices of the Royal Astronomical Society》2009,399(1):229-238
We obtain equilibrium solutions for rotating compact stars, including special relativistic effects. The gravity is assumed to be Newtonian, but we use the active mass density, which takes into account all energies such as the motion of the fluid, internal energy and pressure energy in addition to the rest-mass energy, in computing the gravitational potential using Poisson's equation. Such a treatment could be applicable to neutron stars with relativistic motions or a relativistic equation of state. We applied Hachisu's self-consistent field (SCF) method to find spheroidal as well as toroidal sequences of equilibrium solutions. Our solutions show better agreement with general relativistic solutions than the Newtonian relativistic hydrodynamic approach, which does not take into account the active mass. Physical quantities such as the peak density and equatorial radii in our solutions agree with the general relativistic ones to within 5 per cent. Therefore our approach can be used as a simple alternative to the fully relativistic one when a large number of model calculations is necessary, as it requires much fewer computational resources. 相似文献
16.
We analyze the structure of a nuclear deflagration front in the crust of accreting neutron stars. Models of quasi-stationary deflagration fronts are calculated and subsequently evolved in time and space in order to check their stability. Unlike white dwarfs, where the velocity of aninwards propagating combustion front is governed mainly by energy losses to the gravitational field, the structure of a deflagration front in neutron stars is determined essentially by the heat fluxes into the stellar core. 相似文献
17.
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
18.
Chris Vuille 《Astrophysics and Space Science》1996,245(1):151-155
Intermediate-range gravitational forces have been predicted by certain grand unified theories. If such forces exist, they would naturally affect the structure of neutron stars. Here, a simple rotating neutron star model is constructed which, under fairly mild assumptions, can be integrated exactly for the pressure. According to this model, the effect on neutron star masses by intermediate range forces is negligible, except when the range approaches the radius of the star and the coupling constant is close to the usual gravitation constant. In addition, extremely short range forces can be shown to have negligible effect, even when the coupling constant is many orders of magnitude greater thanG. Thus, there appears to be little hope of using neutron star mass measurements to test such grand unified theories. 相似文献
19.
极端质量比旋进系统是空间引力波探测器最重要的波源之一。对引力波的探测需要高精度波形模版。当前主流的极端质量比旋进系统引力波计算模型中,人们一般将小质量天体当作试验粒子进行计算,而忽略了其结构及自身引力对背景引力场的影响。利用Mathisson-Papapetrou-Dixon方程研究延展体在弯曲时空中的运动,以及小天体自旋和质量多极矩对引力波信号识别产生的影响。结果表明,质量比在10?6-10?4范围的旋进系统,其自旋达到很大时,自旋对延展体的轨道运动有不可忽略的影响;在质量比10?4-10?2区间内,需要考虑中心黑洞潮汐作用导致的白矮星形变;在质量比大于10?4,且白矮星自旋很大时,其自旋产生的形变会对小天体轨道运动产生不可忽略的影响。大质量黑洞潮汐作用导致的恒星级黑洞或中子星产生的形变可以忽略,中子星和黑洞的自旋会对轨道运动产生不可忽略的影响,而自旋产生的四极矩对轨道运动不产生影响。 相似文献
20.
Massive stars are of interest as progenitors of supernovae, i.e. neutron stars and black holes, which can be sources of gravitational waves. Recent population synthesis models can predict neutron star and gravitational wave observations but deal with a fixed supernova rate or an assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernova progenitors, i.e. with O‐ and early B‐type stars, and also all supergiants within 3 kpc. We restrict our sample to those massive stars detected both in 2MASS and observed by Hipparcos, i.e. only those stars with parallax and precise photometry. To determine the luminosities we calculated the extinctions from published multi‐colour photometry, spectral types, luminosity class, all corrected for multiplicity and recently revised Hipparcos distances. We use luminosities and temperatures to estimate the masses and ages of these stars using different models from different authors. Having estimated the luminosities of all our stars within 3 kpc, in particular for all O‐ and early B‐type stars, we have determined the median and mean luminosities for all spectral types for luminosity classes I, III, and V. Our luminosity values for supergiants deviate from earlier results: Previous work generally overestimates distances and luminosities compared to our data, this is likely due to Hipparcos parallaxes (generally more accurate and larger than previous ground‐based data) and the fact that many massive stars have recently been resolved into multiples of lower masses and luminosities. From luminosities and effective temperatures we derived masses and ages using mass tracks and isochrones from different authors. From masses and ages we estimated lifetimes and derived a lower limit for the supernova rate of ≈20 events/Myr averaged over the next 10 Myr within 600 pc from the sun. These data are then used to search for areas in the sky with higher likelihood for a supernova or gravitational wave event (like OB associations) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献