共查询到20条相似文献，搜索用时 93 毫秒
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中子星可以通过重子物质和暗物质的相互作用吸积暗物质,且在一定条件下, 中子星吸积的暗物质粒子可以引发自引力塌缩形成小型黑洞, 生成的黑洞可能会进一步吞噬中子星.依据文献已有模型, 基于以上物理过程给出了在暗物质粒子不同质量下对暗物质粒子--中子的散射截面的限制.使用弱相互作用大质量粒子(Weakly Interacting Massive Particle, WIMP)模型, 并考虑暗物质粒子是玻色子的情形, 讨论了暗物质粒子有无自相互作用以及有无湮灭等条件下对限制暗物质参数的影响.既考虑了已发现的两个中子星系统来给出对暗物质参数空间的限制,也考虑了两个可能存在的年老中子星来预测未来观测可能对暗物质参数空间的限制.对于考虑玻色--爱因斯坦凝聚(Bose-Einstein Condensate, BEC)的玻色子暗物质, 在无自相互作用或有弱自相互作用, 无湮灭或有很小湮灭截面的条件下,中子星给出的间接观测对暗物质粒子-中子散射截面的限制的强度比XENON1T直接探测实验来得更强.未来, 如果在银心附近能观测到年老中子星, 其观测结果可以提升模型给出的对暗物质粒子--中子散射截面的限制, 从而帮助人们进一步理解暗物质. 相似文献
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《天文学进展》2016,(3)
带有暗能量、具有标度不变的绝热原初扰动功率谱的冷暗物质宇宙学模型被视为标准冷暗物质宇宙学模型(ΛCDM模型)。弱相互作用重粒子(WIMPs)成为暗物质的强劲候选者。很多标准模型的扩展模型可以很自然地构造出弱相互作用的大质量粒子。暗物质剩余丰度的标准计算表明,WIMP粒子自然满足?_(DM)h~2≈0.11的天文观测。WIMP粒子的质量较大,运动速度相对缓慢,容易聚集成团,基于WIMPs暗物质模型的数值模拟结果符合对宇宙大尺度结构的观测结果。就实验而言,目前关于暗物质的加速器或非加速器的直接/间接探测,很多都是针对WIMP粒子设计的。因此,基于WIMPs的冷暗物质模型受到了广泛重视。但ΛCDM宇宙学模型描述Mpc以下的小尺度结构时,遇到了比较严重的问题。为了缓解小尺度上出现的问题,提出不同的暗物质模型,但目前并没有确切证据足以排除冷暗物质模型。介绍了基于WIMPs的暗物质模型的研究进展,如WIMPs奇迹、数值模拟、小尺度问题、直接/间接探测,并分析了关于暗物质"冷"、"热"、"温"的区分依据,以及阐述了该领域未来的研究方向。 相似文献
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武向平 《中国天文和天体物理学报》1992,(3)
具有光度函数谱指数陡于-2的背景光源(如类星体、seyfert星系核等)将会由于宇宙中的致密天体引力透镜效应的增亮而优先进入观测样本。而目前观测中并未明显展示出这一特征,从而暗示:宇宙中能引起类星体透镜增亮效应的天体(M>0.01M)其密度是很低的,达些致密天体不足以构成暗物质的主要候选者而使宇宙封闭。 相似文献
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一百年莉 一百年以前,我们对天文学的认识完全不能和今天相比。当时人们并不知道宇宙大爆炸、宇宙膨胀,也不知道宇宙的年龄、宇宙的尺度。正如宇宙微波背景辐射那样,当时人们对于宇宙膨胀和暗能量这些概念是完全想象不到的。我们对银河系外的星系知之甚少,对星系团和暗物质则完全不了解。而对于活动星系核、黑洞和喷流（图1）,我们也是一无所知。我们甚至都还没观测到中性氢或巨分子云（图2）。 相似文献
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神秘而不可见的物质维系着宇宙,使我们生存的世界免于分崩离析,但它们到底是什么？
宇宙并不遵循“所见即所得”的原则。事实上,我们所看到的物质——恒星、气体和尘埃——仅仅占据了宇宙物质质量的10％左右。这些可见的普通物质由质子、中子和电子组成。科学家们把它们称为“重子物质”,因为质子和中子在亚原子粒子中被称为“重子”。宇宙物质的其余90％则是“暗物质”,它们包围着宇宙中的每一个星系。 相似文献
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暗物质既是宇宙必需的组成部分,更是一个依然扑朔迷离的难题。根据对宇宙大爆炸余辉——微波背景辐射——的研究,你、我、每一件日常用品、行星、恒星、星云和星系等,我们周围可见的所有物质仅占据宇宙质量能量的4.9%。与之形成对比的是,暗物质占据了宇宙的26.8%,是普通物质的5倍多,但它们的本质至今不明。 相似文献
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Catherine Vlahakis Stephen Eales Loretta Dunne 《Monthly notices of the Royal Astronomical Society》2007,379(3):1042-1048
We use the results of the SCUBA Local Universe Galaxy Survey, a submillimetre (submm) survey of galaxies in the nearby Universe, to investigate the relationship between the far-infrared (FIR)–submm and radio emission of galaxies at both low and high redshift. At low redshift we show that the correlation between radio and FIR emission is much stronger than the correlation between radio and submm emission, which is evidence that massive stars are the source of both the FIR and radio emission. At high redshift we show that the submm sources detected by SCUBA are brighter sources of radio emission than are predicted from the properties of galaxies in the local Universe. We discuss possible reasons for the cosmic evolution of the relationship between radio and FIR emission. 相似文献
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A special class of type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical
evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion
of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies. 相似文献
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Eline Tolstoy 《Astrophysics and Space Science》1999,265(1-4):199-206
What can we learn from the somewhat arduous study of old stellar populations in nearby galaxies? Unless the nearby universe is subtly anomalous, it should contain a relatively normal selection of galaxies whose histories are representative of field galaxies in general throughout the Universe. We can therefore take advantage of our ability to resolve local galaxies into individual stars to directly, and accurately, measure star formation histories. The star formation histories are determined from numerical models, based on stellar evolution tracks, of colour-magnitude diagrams. The most accurate information on star formation rates extending back to the earliest epoches can be obtained from the structure of the main sequence. However, the oldest main sequence turnoffs are very faint, and it is often necessary to use the brighter, more evolved, populations to infer the star formation history at older times. A complete star formation history can be compared with the spectroscopic properties of galaxies seen over a large range of lookback times in redshift surveys. There is considerable evidence that the faint blue galaxies seen in large numbers in cosmological surveys are the progenitors of the late-type irregular galaxies seen in copious numbers in the Local Group, and beyond. We consider how the `Madau-diagram', the star formation history of the Universe, would look if the Local Group were to be considered representative of the Universe as a whole. 相似文献
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Radhakhrishna Somanah Soonil D.D.V. Rughooputh Harry C.S. Rughooputh 《Astrophysics and Space Science》2002,282(1):161-169
Recognition/Classification of galaxies is an important issue in the large-scale study of the Universe; it is not a simple
task. According to estimates computed from the Hubble Deep Field (HDF), astronomers predict that the universe may potentially
contain over 100 billion galaxies. Several techniques have been reported for the classification of galaxies. Parallel developments
in the field of neural networks have come to a stage that they can participate well in the recognition of objects. Recently,
the Pulse-Coupled Neural Network (PCNN) has been shown to be useful for image pre-processing. In this paper, we present a
novel way to identify optical galaxies by presenting the images of the galaxies to a hierarchical neural network involving
two PCNNs. The image is presented to the network to generate binary barcodes (one per iteration) of the galaxies; the barcodes
are unique to the input galactic image. In the current study, we exploit this property to identify optical galaxies by comparing
the signatures (binary barcode) from a corresponding database.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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A. M. Swinbank R. G. Bower Graham P. Smith Ian Smail J.-P. Kneib R. S. Ellis D. P. Stark A. J. Bunker 《Monthly notices of the Royal Astronomical Society》2006,368(4):1631-1645
We exploit the gravitational potential of massive cluster lenses to probe the emission-line properties of six z = 1 galaxies which appear as highly magnified luminous arcs. Using the Gemini Multi-Object Spectrograph (GMOS) integral field spectrograph together with detailed cluster lens models, we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to ∼0.5 kpc (unlensed) at z = 1 . Four of the galaxies have stable disc-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I -band Tully–Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B band, the observations suggest 0.5 ± 0.3 mag of brightening, consistent with increased star-formation activity at z = 1 . However, the galaxies with stable disc kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counterparts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high-redshift Universe than that possible with conventional surveys. 相似文献
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K. -H. Schmidt 《Astrophysics and Space Science》1975,34(1):23-31
The existence of intergalactic dust has been proved by the following observational facts: the decrease of the numbers of distant galaxies and clusters of galaxies behind the central regions of near clusters of galaxies; the different distributions of RR Lyrae stars and galaxies near ι Microscopii (Hoffmeister's cloud); the dependence of colour excesses of galaxies on supergalactic coordinates as well as on the surface density of bright galaxies; the colour index vs redshift correlation of quasistellar objects. The densities of intergalactic dust are estimated to be between 5×10?30 g cm?3 (near the centers of clusters of galaxies) and 2×10?34 g cm?3 (in general intergalactic space). The grains may be formed either in the early phases of the Universe (25相似文献
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L. Zaninetti 《Journal of Astrophysics and Astronomy》2012,33(4):399-416
The cosmological principle in its various versions states that: (i) the galaxy does not occupy a particular position, (ii) the Universe is homogeneous and isotropic. This statement does not agree with the recent astronomical observations in the range z lower than 0.05 which are in agreement with a cellular structure of the Universe. Here we present a local analysis of the inhomogeneity of the Universe. When z is greater than 0.05 our analysis cannot be applied because the astronomical sample of galaxies here processed is not complete. The two tools of the Poisson Voronoi Tessellation (PVT) and the luminosity function for galaxies allow building a new version of the local cosmological principle. 相似文献
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We have investigated the apparent variation of the surface brightness distribution of disc galaxies with distance within three different samples 1) a diameter limited sample of ESO catalogue galaxies in the direction of the cluster A3574 in Centaurus, 2) all ESO catalogue disc galaxies with redshifts, and 3) a sample of fainter galaxies from our surveys of the Fornax Cluster area. In each case we find, as predicted for a sample dominated by surface brightness selection effects, that the distribution narrows with distance. Both high and low surface brightness galaxies are underrepresented in galaxy catalogues. Not because they are rare, but because the volume over which they are sampled is considerably smaller than that of their normal surface brightness counterparts. The question of how many galaxies there are in the Universe remains un-answered. In addition, since selection is byapparent surface brightness, the most distant sample (where cosmological dimming becomes important) contains galaxies of higher intrinsic surface brightness than do the nearby samples, again confirming a previous theoretical prediction. The galaxies we observe in the distant Universe are very different to those we observe close by because of observational selection. 相似文献
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金属丰度是表征星系特征的重要参量,对于理解星系的形成与演化具有重要意义。随着观测设备的不断完善与发展,已经获得越来越多的星系(包括近邻星系、中等红移及高红移星系)金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用。有多种方法可以用来估计星系的金属丰度(主要是星际介质中气相的O丰度),介绍和评述了估计星系的O丰度的多种方法,包括电子温度的方法、R23方法以及其他一些“强线”比值的方法,并给出了相应的解析公式,同时介绍了电离星云的物理本质及由光致电离模型估计星系金属丰度的方法,还给出了估计星系的C和N元素丰度的方法。 相似文献