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排序方式: 共有379条查询结果,搜索用时 11 毫秒
101.
J. L. Christiansen A. Derekas M. C. B. Ashley J. K. Webb M. G. Hidas D. W. Hamacher L. L. Kiss 《Monthly notices of the Royal Astronomical Society》2007,382(1):239-244
Consider radar ranging of a distant galaxy in a Friedman–Lemaître cosmological model. In this model the comoving coordinate of the galaxy is constant; hence, the equations of null geodesics for photons travelling to the distant galaxy and back imply Here, τe , τr and τo are, respectively, the times of emission, reflection and observation of the reflected photons, and a (τ) is the scalefactor. Since the Universe is expanding, a (τ) is a monotonically increasing function, so the return traveltime, τo −τr , must be greater than the forward traveltime, τr −τe . Clearly, space expands, and on their way back, the photons must travel a longer distance! This paper explains why this argument for the Expansion of Space (EoS) is wrong. We argue that, unlike the expansion of the cosmic substratum, the EoS is unobservable. We therefore propose to apply to it – just like to the ether – Ockham's razor. 相似文献
102.
103.
时间、距离、速度、红移基本物理概念的演变简史 总被引:1,自引:0,他引:1
为了尝试回答“我们能否观测到退行速度超过光速的星系”这一问题,重新考察了在牛顿物理学、狭义相对论、广义相对论和宇宙学中的时伺、距离、速度和红移等概念.揭开了一些错误观念的实质,发现只要摆脱狭义相对论先入为主的束缚,上述问题即可迎刃而解.强调了宇宙学并不是纯粹的广义相对论,而是该理论在服从宇宙学原理的条件下的一个特例,其中一系列基本物理概念都因此得到新的内涵。 相似文献
104.
105.
A. M. Beloborodov 《Monthly notices of the Royal Astronomical Society》1998,297(3):739-746
We calculate the structure of the accretion disc around a rapidly rotating black hole with a super-Eddington accretion rate. The luminosity and height of the disc are reduced by the advection effect. In the case of large viscosity parameter, α>0.03, the accretion flow deviates strongly from thermodynamic equilibrium and overheats in the central region. With increasing accretion rate, the flow temperature steeply increases, reaches maximum, and then falls off. The maximum is achieved in the advection-dominated regime of accretion. The maximum temperature in the disc around a massive black hole of M =108 M⊙ with α=0.3 is of order 3×108 K. The discs with large accretion rates can emit X-rays in quasars as well as in galactic black hole candidates. 相似文献
106.
David Langlois David M. Sedrakian & Brandon Carter 《Monthly notices of the Royal Astronomical Society》1998,297(4):1189-1201
It is shown how to set up a mathematically elegant and fully relativistic superfluid model that can provide a realistic approximation (neglecting small anisotropies due to crust solidity, magnetic fields, etc., but allowing for the regions with vortex pinning) of the global structure of a rotating neutron star, in terms of just two independently moving constituents. One of these represents the differentially rotating neutron superfluid, while the other part represents the combination of all the other ingredients, including the degenerate electrons, the superfluid protons in the core, and the ions in the crust, the electromagnetic interactions of which will tend to keep them locked together in a state of approximately rigid rotation. Order of magnitude estimates are provided for relevant parameters such as the resistive drag coefficient. 相似文献
107.
D. Lorenz-Petzold 《Journal of Astrophysics and Astronomy》1986,7(3):155-170
We present a detailed study of the inhomogeneous Stephani-Krasinski solution with time-dependent curvature index. In general,
the cosmological behaviour of the models depends on six arbitrary functions of time. Such models are termed ‘private universes’
and cannot be in accord with observation in the most general case. Two simple models with changing topology are considered
as illustrating examples. In one of these models the pressure turns out to be negative and hence a violation of the weak energy
condition in the singularity theorems is possible. A brief review of other inhomogeneous cosmologies is included for the sake
of clarity. It is shown that the geodesic equation can be reduced to a complicated differential equation, which depends on
the three arbitrary functions involved. Therefore, it is difficult to obtain explicit formulas for the various observational
relations. 相似文献
108.
109.
110.
G. Srinivasan 《Astronomy and Astrophysics Review》2002,11(1):67-96
Summary. The maximum mass of neutron stars plays an important role in determining the end point of the evolution of massive stars.
As the number of stellar mass black holes in binary x-ray sources grows, and as the mass spectrum of the black holes emerges,
the value of the maximum mass of neutron stars has acquired great significance. Although it is now more than sixty years since
the first attempt by Oppenheimer and Volkoff, no definitive answer can be given. This review will attempt to outline the main
difficulties, both conceptual as well as technical, that stand in the way of a reliable estimate of the maximum mass. We shall
also highlight how laboratory experiments, as well as astronomical observations, may help to clarify the true nature of the
interior of neutron stars.
Received 26 November 2001 / Published online 22 April 2002 相似文献