共查询到20条相似文献，搜索用时 31 毫秒
1.
Maxim Yu.Khlopov 《中国天文和天体物理学报》2010,10(6)
Primordial black holes (PBHs) are a profound signature of primordial cos-mological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to re-strict a wide range of particle physics models, predicting an enhancement of the ul-traviolet part of the spectrum of density perturbations, early dust-like stages, first or-der phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflation-ary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds. 相似文献
2.
Yan Gong Xin Wang Zheng Zheng Xue-Lei Chen National Astronomical Observatories Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China Institute for Advanced Study Einstein Drive Princeton NJ USA Center of High Energy Physics Peking University Beijing China Kavli Institute for Theoretical Physics China CAS Beijing 《中国天文和天体物理学报》2010,10(2)
The primordial non-Gaussianity (PNG) in the matter density perturbation is a very powerful probe of the physics of the very early Universe. The local PNG can induce a distinct scale-dependent bias on the large scale structure distribution of galaxies and quasars, which could be used for constraining it. We study the detection limits of PNG from the surveys of the LAMOST telescope. The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and the quasar survey of dif- ferent magnitude limits... 相似文献
3.
《New Astronomy Reviews》2002,46(11):709-723
The dark age of the Universe is generally pointed out as the period between the recombination epoch (z∼1000) and the horizon of current observations (z∼5–6). The arrow of time in the cosmic history describes the progression from simplicity to complexity, because the present Universe is clumpy and complicated unlike the homogeneous early Universe. Thus it is crucial to know the nature of the constituents, in order to understand the conditions of the formation of the first bound objects. In this paper we analyse the chemical history of this dark age through the creation of the primordial nuclei to the formation of the first atoms and molecules. Then we will describe the consequences of the molecular formation on the birth of the proto-objects. In this context we will mention the important works of Dennis W. Sciama who influenced a large number of theorists—cosmologists and astronomers—on this new field of research dedicated to primordial molecules. 相似文献
4.
Shiv K. Sethi Kandaswamy Subramanian 《Monthly notices of the Royal Astronomical Society》2005,356(2):778-788
We explore the ways in which primordial magnetic fields influence the thermal and ionization history of the post-recombination Universe. After recombination, the Universe becomes mostly neutral, resulting also in a sharp drop in the radiative viscosity. Primordial magnetic fields can then dissipate their energy into the intergalactic medium via ambipolar diffusion and, for small enough scales, by generating decaying magnetohydrodynamics turbulence. These processes can significantly modify the thermal and ionization history of the post-recombination Universe. We show that the dissipation effects of magnetic fields, which redshifts to a present value B 0 = 3 × 10−9 G smoothed on the magnetic Jeans scale and below, can give rise to Thomson scattering optical depths τ≳ 0.1 , although not in the range of redshifts needed to explain the recent Wilkinson Microwave Anisotropy Probe ( WMAP ) polarization observations. We also study the possibility that primordial fields could induce the formation of subgalactic structures for z ≳ 15 . We show that early structure formation induced by nanoGauss magnetic fields is potentially capable of producing the early reionization implied by the WMAP data. Future cosmic microwave background observations will be very useful to probe the modified ionization histories produced by primordial magnetic field evolution and constrain their strength. 相似文献
5.
We consider the possibility of low-mass primordial black holes being formed in terms of the inflationary theory of the early Universe. We found a condition on the reheating temperature under which the relic remnants of primordial black holes had been formed by now. These relic remnants may account for a part of the dark matter in our Universe. 相似文献
6.
Hiroyuki Tashiro Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2006,368(2):965-970
Early reionization of the intergalactic medium (IGM), which is favoured from the WMAP temperature–polarization cross-correlations, contests the validity of the standard scenario of structure formation in the cold dark matter (CDM) cosmogony. It is difficult to achieve early enough star formation without rather extreme assumptions such as a very high escape fraction of ionizing photons from protogalaxies or a top-heavy initial mass function (IMF). Here, we propose an alternative scenario that additional fluctuations on small scales induced by primordial magnetic fields trigger early structure formation. We found that ionizing photons from Population III stars formed in dark haloes can easily reionize the Universe by z ≃ 15 if the strength of primordial magnetic fields is between 0.7 and 1.5 × 10−9 G . 相似文献
7.
P. N. Okeke 《Astrophysics and Space Science》1980,71(2):371-375
We calculate the number of positrons emitted per second from the evaporating primordial black hole (PBH) in the various mass ranges. We estimate the number of those positrons from PBH which may likely annihilate within the Galaxy to give rise to the 0.511 MeV line radiation and those which may be degraded or leak out of the Galaxy. We then show that the PBH positrons are likely to be not only the primary source of low energy positrons but also high energy positrons which are energetic enough to leak out of the Galaxy. 相似文献
8.
Cosimo Bambi Douglas Spolyar Alexander D. Dolgov Katherine Freese Marta Volonteri 《Monthly notices of the Royal Astronomical Society》2009,399(3):1347-1356
If the cosmological dark matter has a component made of small primordial black holes (BHs), they may have a significant impact on the physics of the first stars and on the subsequent formation of massive BHs. Primordial BHs would be adiabatically contracted into these stars and then would sink to the stellar centre by dynamical friction, creating a larger BH which may quickly swallow the whole star. If these primordial BHs are heavier than ∼1022 g , the first stars would likely live only for a very short time and would not contribute much to the reionization of the Universe. They would instead become 10–103 M⊙ BHs which (depending on subsequent accretion) could serve as seeds for the super-massive BHs seen at high redshifts as well as those inside galaxies today. 相似文献
9.
David M. Coward Ronald R. Burman David G. Blair 《Monthly notices of the Royal Astronomical Society》2001,324(4):1015-1022
We investigate the stochastic gravitational wave background that results from neutron star birth throughout the Universe. The neutron star birth rate, as a function of redshift, is calculated using an observation-based model for the evolving star formation rate, together with an estimate of the rate of core-collapse supernovae in the nearby Universe and an estimate of the neutron star/black hole branching ratio. Using three sample waveforms, based on numerical models of stellar core collapse by Zwerger & Müller, the spectral flux density, spectral strain, spectral energy density and duty cycle of the background have been computed. Our results show, contrary to recent claims, that the spectrum of the stochastic background clearly reflects the different physics in the core-collapse models. For a star formation model that is corrected for dust extinction, the neutron star formation rate throughout the Universe is high enough to result in a nearly continuous background of gravitational waves, with spectral features that can be related to emission mechanisms. 相似文献
10.
Formation of black holes may be constrained by intrinsic parameters characterizing them such as electric charge. Here we discuss the effects of a relatively minute excess of charge on extremal black hole formation and the horizon. We extend the implications of this argument to the formation of primordial black holes (PBH) in the early universe which gives a possible reason for the lack of detection of Hawking radiation. These charge limits also apply to dark matter (DM) particles that may form PHBs in the early universe. The constraint thus obtained on the electric charge of DM particles could also account for the required magnitude of the repulsive dark energy (DE) currently causing an accelerated universe which provides a possible unified picture of DM and DE. 相似文献
11.
The “Spektr-UF” project (“World Space Observatory-Ultraviolet” (WSO-UV)) will be the largest space observatory for observations in the UV band. In this paper we briefly outline the key science issues that the WSO-UV will address during its lifetime with the help of its instrumentation: spectrographs and a field camera unit. Of special interest are early Universe physics (reionization and search for baryonic matter), star formation, chemical evolution of galaxies, astrophysical accretion processes, stellar atmosphere physics, and planetary atmosphere studies. 相似文献
12.
《New Astronomy》2020
Three decades ago an expression for the maximum acceleration of elementary particles was derived using quantum theory. There is no experimental confirmation of this so far. In this paper we study the phenomenon of acceleration of elementary particles by the surface gravity of primordial black holes (PBH) formed in the early universe and the associated Hawking-Unruh effect. From a heuristic theory we find that every elementary particle can be associated with a PBH of unique mass and Hawking temperature. This implies a unique Hawking-Unruh acceleration for each elementary particle. The inferred values of maximum acceleration from our theory range from 6.24 × 1033 m/s2 for top quarks to 1.85 × 1028 m/s2 for electrons. These values can be considered to be the maximum acceleration given by the general expression of elementary particles of given rest mass (m) due to the force of gravity. Elementary particles with the maximum Compton wavelength ( m) and an inferred mass of 0.0185 eV (possibly neutrinos) are found to be associated with a PBH whose Hawking temperature is identical to the cosmic microwave background temperature of the present Universe. 相似文献
13.
The influence of dynamical friction on peculiar velocities in a two-component medium is considered. One of the components is assumed to consist of heavy particles with small gravitational interactions and the other is assumed uniform and its particles of much less weight. Here the solutions for the stationary as well as for the cosmologically expanding medium are obtained. These solutions illustrate the possibility for clusters of galaxies to have super-low velocities. It is emphasized that the presence of two components leads to the formation of individual strings and general string structure in one of the component. A string-like structure of the Universe becomes inevitable in the case when an initial perturbations spectrum has a specific scale, and falls down abruptly for larger and smaller distances. Such a picture of the formation of large-scale structure of the Universe is similar to the formation of particle tracks in the Wilson chamber, where tracks are the observational clusters of galaxies, and ‘particles’ are invisible perturbations in the second (neutrino?) component. 相似文献
14.
在精确宇宙学的时代, 多信使、高精度、小尺度的宇宙学观测在帮助人们从更加深刻的层面理解宇宙极早期的同时, 也给基于线性近似和微扰展开宇宙学扰动理论带来了新的挑战. 近年来, 对原初引力波和原初黑洞的搜寻使得研究人员们对早期宇宙在小尺度上的非线性非微扰过程产生了浓厚的研究兴趣. 综述了在宇宙学小尺度上关于原初黑洞产生以及引力波研究取得的诸多进展, 重点关注了使用Mathieu方程的共振效应来研究小尺度功率谱放大以及诱导产生可观测的原初引力波的方法. 此外, 还尝试探讨了非高斯尾巴对原初黑洞形成的影响. 发现Mathieu方程所具备的共振效应可以提供一种有效的方法来刻画原初宇宙中小尺度的非微扰动力学过程, 从而能够更好地理解原初黑洞的形成以及相关的引力波产生机制. 同时, 非微扰的非高斯性在原初黑洞形成中可能会产生不可忽视的影响. 相似文献
15.
16.
Just forty years ago, Hawking wrote his famous paper on primordial black holes (PBH). There have been since innumerable discussions on the consequences of the existence of such exotic objects and ramifications of their properties. Here we suggest that PBH’s in an ever expanding universe (as implied by dark energy domination, especially of a cosmological constant) could be the ultimate repository for long lived living systems. PBH’s having solar surface temperatures would last 1032 years as a steady power source and should be considered in any discussion on exobiological life. 相似文献
17.
From the assumption of a universal upper limit for the temperature of about 1012 K which is suggested by the experiences of high energy physics, it follows taking additionally into account the strong interaction between hadrons explicitly that in the earliest stage of the Universe the numbers of nucleon number by a factor of about 107. Accordingly the 3K background radiation, is generated for the most part by annihilation of nearly all primordial heavy particles. 相似文献
18.
C. Sivaram 《Astrophysics and Space Science》1982,88(2):507-510
It is pointed out that the gross parameters characterizing the Universe such as the overall size and mass can be arrived at from microphysical considerations involving the fundamental interactions of elementary particle physics. Interesting relations for the Hubble radius and closure density are obtained in terms of the coupling constants underlying these interactions. 相似文献
19.
The maximal entropy and the final parameters of the expansive-creative evolution phase of the ultrastable Universe can be determined from model properties of the expansive nondecelerative Universe.The possibility of existence of primordial black holes with temperature of the Universe follows from the initial entropy of the Universe. This fact throws new light on the problem of dark matter. 相似文献
20.
It is shown that certain anomalies connected with the primordial abundances of light nuclei may be resolved if it is assumed that the Universe oscillates between phases of finite densities. Since general relativity does not produce bouncing models of the Universe, such models are obtained through the introduction of a negative energy scalar field of zero rest mass. It is shown that all the relevant parameters of the dynamics of the model and the nucleosynthesis in it are determined by observations and that a self-consistent picture emerges. The model is capable of admitting more than three neutrino flavours without an embarrassingly high primordial helium content. It is also shown that the calculations could be adapted to described production of light nuclei in compact massive bouncing objects. 相似文献